From f5560604944b192346945953be5fefc4207421c7 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Tue, 15 Nov 2022 08:06:47 +0100
Subject: [PATCH 01/17] Bump flyway-core from 9.7.0 to 9.8.1 (#689)

Bumps [flyway-core](https://github.com/flyway/flyway) from 9.7.0 to 9.8.1.
- [Release notes](https://github.com/flyway/flyway/releases)
- [Commits](https://github.com/flyway/flyway/compare/flyway-9.7.0...flyway-9.8.1)

---
updated-dependencies:
- dependency-name: org.flywaydb:flyway-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 database/build.gradle | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/database/build.gradle b/database/build.gradle
index 4b7902eced..fdc1e82a7c 100644
--- a/database/build.gradle
+++ b/database/build.gradle
@@ -7,7 +7,7 @@ var sqliteVersion = "3.39.2.0"
 dependencies {
     implementation 'com.google.code.findbugs:jsr305:3.0.2'
     implementation "org.xerial:sqlite-jdbc:${sqliteVersion}"
-    implementation 'org.flywaydb:flyway-core:9.7.0'
+    implementation 'org.flywaydb:flyway-core:9.8.1'
     implementation "org.jooq:jooq:$jooqVersion"
 
     implementation project(':utils')

From a677ba148f6281ca01daf5f45a112b16c0da8c03 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Tue, 15 Nov 2022 08:20:00 +0100
Subject: [PATCH 02/17] Bump mockito-core from 4.8.0 to 4.9.0 (#690)

Bumps [mockito-core](https://github.com/mockito/mockito) from 4.8.0 to 4.9.0.
- [Release notes](https://github.com/mockito/mockito/releases)
- [Commits](https://github.com/mockito/mockito/compare/v4.8.0...v4.9.0)

---
updated-dependencies:
- dependency-name: org.mockito:mockito-core
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 application/build.gradle | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/application/build.gradle b/application/build.gradle
index 1d2426892e..8792486c1d 100644
--- a/application/build.gradle
+++ b/application/build.gradle
@@ -70,7 +70,7 @@ dependencies {
 
     implementation 'com.github.ben-manes.caffeine:caffeine:3.1.1'
 
-    testImplementation 'org.mockito:mockito-core:4.8.0'
+    testImplementation 'org.mockito:mockito-core:4.9.0'
     testImplementation 'org.junit.jupiter:junit-jupiter-api:5.9.0'
     testImplementation 'org.junit.jupiter:junit-jupiter-params:5.9.0'
     testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.9.0'

From 8c29c37c15f8e29df9cda9d5e48c5d921c118157 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Tue, 15 Nov 2022 08:20:30 +0100
Subject: [PATCH 03/17] Bump gradle-plugin-publishing from 9.7.0 to 9.8.1
 (#691)

Bumps gradle-plugin-publishing from 9.7.0 to 9.8.1.

---
updated-dependencies:
- dependency-name: gradle.plugin.org.flywaydb:gradle-plugin-publishing
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 buildSrc/build.gradle | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/buildSrc/build.gradle b/buildSrc/build.gradle
index 30898ce55d..db4883292f 100644
--- a/buildSrc/build.gradle
+++ b/buildSrc/build.gradle
@@ -7,6 +7,6 @@ repositories {
 }
 
 dependencies {
-    implementation "gradle.plugin.org.flywaydb:gradle-plugin-publishing:9.7.0"
+    implementation "gradle.plugin.org.flywaydb:gradle-plugin-publishing:9.8.1"
     implementation 'nu.studer:gradle-jooq-plugin:8.0'
 }

From 48f262cde98d2d6bf649d8cdf022285ef09a19ac Mon Sep 17 00:00:00 2001
From: Daniel Tischner <zabuza.dev@gmail.com>
Date: Tue, 15 Nov 2022 11:31:31 +0100
Subject: [PATCH 04/17] Create devcontainer.json (#692)

---
 .devcontainer/devcontainer.json | 37 +++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 .devcontainer/devcontainer.json

diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
new file mode 100644
index 0000000000..9a08c62340
--- /dev/null
+++ b/.devcontainer/devcontainer.json
@@ -0,0 +1,37 @@
+{
+  "name": "TJ-Bot",
+  "image": "mcr.microsoft.com/devcontainers/universal:2",
+  "hostRequirements": {
+    "cpus": 1,
+    "memory": "1gb",
+    "storage": "2gb"
+  },
+  "features": {
+    "ghcr.io/devcontainers/features/java:1": {
+      "version": "18.0.2.1-tem",
+      "jdkDistro": "tem",
+      "installGradle": true
+    },
+    "ghcr.io/devcontainers-contrib/features/pre-commit:1": {}
+  },
+  "customizations": {
+    "vscode": {
+      "extensions": [
+        "vscjava.vscode-java-pack",
+        "vscjava.vscode-gradle",
+        "alexcvzz.vscode-sqlite",
+        "richardwillis.vscode-spotless-gradle"
+      ],
+      "settings": {
+        "[java]": {
+          "spotlessGradle.format.enable": true,
+          "editor.defaultFormatter": "richardwillis.vscode-spotless-gradle"
+        }
+      }
+    }
+  },
+  "postCreateCommand": {
+    "config": "cp application/config.json.template application/config.json",
+    "gradle": "gradle build"
+  }
+}

From b0d06ecab3da9f7db6974c14400aaf67af099254 Mon Sep 17 00:00:00 2001
From: Daniel Tischner <zabuza.dev@gmail.com>
Date: Tue, 15 Nov 2022 10:35:44 +0100
Subject: [PATCH 05/17] Removed delete button for manual selection (#687)

* also logging who deleted what
---
 .../code/CodeMessageAutoDetection.java        |  2 +-
 .../commands/code/CodeMessageHandler.java     | 35 ++++++++++---------
 .../code/CodeMessageManualDetection.java      |  2 +-
 3 files changed, 21 insertions(+), 18 deletions(-)

diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageAutoDetection.java b/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageAutoDetection.java
index d8adecc0d1..64572420b2 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageAutoDetection.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageAutoDetection.java
@@ -63,7 +63,7 @@ public void onMessageReceived(MessageReceivedEvent event) {
             return;
         }
 
-        codeMessageHandler.addAndHandleCodeMessage(originalMessage);
+        codeMessageHandler.addAndHandleCodeMessage(originalMessage, true);
     }
 
     private boolean isHelpThread(MessageReceivedEvent event) {
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageHandler.java b/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageHandler.java
index a45a5c0f80..341c8ad351 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageHandler.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageHandler.java
@@ -27,20 +27,16 @@
 import javax.annotation.Nullable;
 
 import java.awt.Color;
-import java.util.LinkedHashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.Optional;
+import java.util.*;
 import java.util.function.Function;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
-import java.util.stream.Stream;
 
 /**
  * Handles code in registered messages and offers code actions to the user, such as formatting their
  * code.
  * <p>
- * Messages can be registered by using {@link #addAndHandleCodeMessage(Message)}.
+ * Messages can be registered by using {@link #addAndHandleCodeMessage(Message, boolean)}.
  * <p>
  * Code actions are automatically updated whenever the code in the original message is edited or
  * deleted.
@@ -111,10 +107,12 @@ public void acceptComponentIdGenerator(ComponentIdGenerator generator) {
      * corresponding code-reply to the author.
      *
      * @param originalMessage the code message to add to this handler
+     * @param showDeleteButton whether the code-actions should initially have a delete button or not
      */
-    public void addAndHandleCodeMessage(Message originalMessage) {
+    public void addAndHandleCodeMessage(Message originalMessage, boolean showDeleteButton) {
         // Suggest code actions and remember the message <-> reply
-        MessageCreateData codeReply = createCodeReplyMessage(originalMessage.getIdLong());
+        MessageCreateData codeReply =
+                createCodeReplyMessage(originalMessage.getIdLong(), showDeleteButton);
 
         originalMessage.reply(codeReply)
             .onSuccess(replyMessage -> originalMessageToCodeReply.put(originalMessage.getIdLong(),
@@ -122,22 +120,24 @@ public void addAndHandleCodeMessage(Message originalMessage) {
             .queue();
     }
 
-    private MessageCreateData createCodeReplyMessage(long originalMessageId) {
+    private MessageCreateData createCodeReplyMessage(long originalMessageId,
+            boolean showDeleteButton) {
+        List<Button> codeActionButtons = new ArrayList<>(createButtons(originalMessageId, null));
+        if (showDeleteButton) {
+            codeActionButtons.add(createDeleteButton(originalMessageId));
+        }
+
         return new MessageCreateBuilder().setContent("Detected code, here are some useful tools:")
-            .setActionRow(createButtons(originalMessageId, null))
+            .setActionRow(codeActionButtons)
             .build();
     }
 
     private List<Button> createButtons(long originalMessageId,
             @Nullable CodeAction currentlyActiveAction) {
-        Stream<Button> codeActionButtons = labelToCodeAction.values().stream().map(action -> {
+        return labelToCodeAction.values().stream().map(action -> {
             Button button = createButtonForAction(action, originalMessageId);
             return action == currentlyActiveAction ? button.asDisabled() : button;
-        });
-
-        Stream<Button> otherButtons = Stream.of(createDeleteButton(originalMessageId));
-
-        return Stream.concat(codeActionButtons, otherButtons).toList();
+        }).toList();
     }
 
     private Button createDeleteButton(long originalMessageId) {
@@ -192,6 +192,9 @@ public void onButtonClick(ButtonInteractionEvent event, List<String> args) {
     }
 
     private void deleteCodeReply(ButtonInteractionEvent event, long originalMessageId) {
+        logger.debug("User {} deleted the code-reply from original message {} in channel {}",
+                event.getUser().getId(), originalMessageId, event.getChannel().getName());
+
         originalMessageToCodeReply.invalidate(originalMessageId);
         event.getMessage().delete().queue();
     }
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageManualDetection.java b/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageManualDetection.java
index bd1d770b42..3647002f53 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageManualDetection.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/code/CodeMessageManualDetection.java
@@ -32,6 +32,6 @@ public void onMessageContext(MessageContextInteractionEvent event) {
             .setEphemeral(true)
             .queue();
 
-        codeMessageHandler.addAndHandleCodeMessage(event.getTarget());
+        codeMessageHandler.addAndHandleCodeMessage(event.getTarget(), false);
     }
 }

From f000b62fc28ba92bf130e73e396504ba9a4b9a6b Mon Sep 17 00:00:00 2001
From: Daniel Tischner <zabuza.dev@gmail.com>
Date: Tue, 15 Nov 2022 11:56:41 +0100
Subject: [PATCH 06/17] Update devcontainer.json

---
 .devcontainer/devcontainer.json | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/.devcontainer/devcontainer.json b/.devcontainer/devcontainer.json
index 9a08c62340..8d17ee2cb9 100644
--- a/.devcontainer/devcontainer.json
+++ b/.devcontainer/devcontainer.json
@@ -31,7 +31,6 @@
     }
   },
   "postCreateCommand": {
-    "config": "cp application/config.json.template application/config.json",
-    "gradle": "gradle build"
+    "config": "cp application/config.json.template application/config.json"
   }
 }

From b7e2910945621bd491b24d746487534f19e56410 Mon Sep 17 00:00:00 2001
From: Daniel Tischner <zabuza.dev@gmail.com>
Date: Wed, 16 Nov 2022 10:11:58 +0100
Subject: [PATCH 07/17] Link/Image previews for tags (#616)

* Raw draft of link preview for tags

* add todo

* draft for opengraph preview

* Rebase adjustment

* moved link preview stuff into dedicated classes

* Reworked/Improved link previews

* Bugfix with tag-autocomplete with small amount of tags

* javadoc

* minor naming issue

* logger warnings
---
 application/build.gradle                      |   4 +
 .../tjbot/commands/tags/TagCommand.java       |  96 +++++++--
 .../tjbot/commands/utils/LinkPreview.java     |  73 +++++++
 .../tjbot/commands/utils/LinkPreviews.java    | 201 ++++++++++++++++++
 .../tjbot/commands/utils/StringDistances.java |   2 +-
 5 files changed, 352 insertions(+), 24 deletions(-)
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreview.java
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreviews.java

diff --git a/application/build.gradle b/application/build.gradle
index 8792486c1d..9924efdbb9 100644
--- a/application/build.gradle
+++ b/application/build.gradle
@@ -57,6 +57,8 @@ dependencies {
 
     implementation 'io.mikael:urlbuilder:2.0.9'
 
+    implementation 'org.jsoup:jsoup:1.15.3'
+
     implementation 'org.scilab.forge:jlatexmath:1.0.7'
     implementation 'org.scilab.forge:jlatexmath-font-greek:1.0.7'
     implementation 'org.scilab.forge:jlatexmath-font-cyrillic:1.0.7'
@@ -68,6 +70,8 @@ dependencies {
 
 	implementation 'com.github.freva:ascii-table:1.8.0'
 
+    implementation 'io.github.url-detector:url-detector:0.1.23'
+
     implementation 'com.github.ben-manes.caffeine:caffeine:3.1.1'
 
     testImplementation 'org.mockito:mockito-core:4.9.0'
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/tags/TagCommand.java b/application/src/main/java/org/togetherjava/tjbot/commands/tags/TagCommand.java
index 5818a34afb..679b4101e7 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/tags/TagCommand.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/tags/TagCommand.java
@@ -1,21 +1,29 @@
 package org.togetherjava.tjbot.commands.tags;
 
 import net.dv8tion.jda.api.EmbedBuilder;
+import net.dv8tion.jda.api.entities.Message;
+import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.entities.User;
 import net.dv8tion.jda.api.events.interaction.command.CommandAutoCompleteInteractionEvent;
 import net.dv8tion.jda.api.events.interaction.command.SlashCommandInteractionEvent;
 import net.dv8tion.jda.api.interactions.AutoCompleteQuery;
+import net.dv8tion.jda.api.interactions.InteractionHook;
 import net.dv8tion.jda.api.interactions.commands.Command;
 import net.dv8tion.jda.api.interactions.commands.OptionMapping;
 import net.dv8tion.jda.api.interactions.commands.OptionType;
 import net.dv8tion.jda.api.interactions.commands.build.OptionData;
 import net.dv8tion.jda.api.requests.restaction.interactions.ReplyCallbackAction;
+import net.dv8tion.jda.api.utils.FileUpload;
+import net.dv8tion.jda.api.utils.messages.MessageEditBuilder;
 
 import org.togetherjava.tjbot.commands.CommandVisibility;
 import org.togetherjava.tjbot.commands.SlashCommandAdapter;
+import org.togetherjava.tjbot.commands.utils.LinkPreview;
+import org.togetherjava.tjbot.commands.utils.LinkPreviews;
 import org.togetherjava.tjbot.commands.utils.StringDistances;
 
 import java.time.Instant;
-import java.util.Collection;
+import java.util.*;
 
 /**
  * Implements the {@code /tag} command which lets the bot respond content of a tag that has been
@@ -47,28 +55,6 @@ public TagCommand(TagSystem tagSystem) {
                         "Optionally, the user who you want to reply to", false));
     }
 
-    @Override
-    public void onSlashCommand(SlashCommandInteractionEvent event) {
-        String id = event.getOption(ID_OPTION).getAsString();
-        OptionMapping replyToUserOption = event.getOption(REPLY_TO_USER_OPTION);
-
-        if (tagSystem.handleIsUnknownTag(id, event)) {
-            return;
-        }
-
-        ReplyCallbackAction message = event
-            .replyEmbeds(new EmbedBuilder().setDescription(tagSystem.getTag(id).orElseThrow())
-                .setFooter(event.getUser().getName() + " • used " + event.getCommandString())
-                .setTimestamp(Instant.now())
-                .setColor(TagSystem.AMBIENT_COLOR)
-                .build());
-
-        if (replyToUserOption != null) {
-            message = message.setContent(replyToUserOption.getAsUser().getAsMention());
-        }
-        message.queue();
-    }
-
     @Override
     public void onAutoComplete(CommandAutoCompleteInteractionEvent event) {
         AutoCompleteQuery focusedOption = event.getFocusedOption();
@@ -86,4 +72,68 @@ public void onAutoComplete(CommandAutoCompleteInteractionEvent event) {
 
         event.replyChoices(choices).queue();
     }
+
+    @Override
+    public void onSlashCommand(SlashCommandInteractionEvent event) {
+        String id = event.getOption(ID_OPTION).getAsString();
+        OptionMapping replyToUserOption = event.getOption(REPLY_TO_USER_OPTION);
+
+        if (tagSystem.handleIsUnknownTag(id, event)) {
+            return;
+        }
+
+        String tagContent = tagSystem.getTag(id).orElseThrow();
+        MessageEmbed contentEmbed = new EmbedBuilder().setDescription(tagContent)
+            .setFooter(event.getUser().getName() + " • used " + event.getCommandString())
+            .setTimestamp(Instant.now())
+            .setColor(TagSystem.AMBIENT_COLOR)
+            .build();
+
+        Optional<String> replyToUserMention = Optional.ofNullable(replyToUserOption)
+            .map(OptionMapping::getAsUser)
+            .map(User::getAsMention);
+
+        List<String> links = LinkPreviews.extractLinks(tagContent)
+            .stream()
+            .limit(Message.MAX_EMBED_COUNT - 1L)
+            .toList();
+        if (links.isEmpty()) {
+            // No link previews
+            ReplyCallbackAction message = event.replyEmbeds(contentEmbed);
+            replyToUserMention.ifPresent(message::setContent);
+            message.queue();
+            return;
+        }
+
+        event.deferReply().queue();
+
+        respondWithLinkPreviews(event.getHook(), links, contentEmbed, replyToUserMention);
+    }
+
+    private void respondWithLinkPreviews(InteractionHook eventHook, List<String> links,
+            MessageEmbed contentEmbed, Optional<String> replyToUserMention) {
+        LinkPreviews.createLinkPreviews(links).thenAccept(linkPreviews -> {
+            if (linkPreviews.isEmpty()) {
+                // Did not find any previews
+                MessageEditBuilder message = new MessageEditBuilder().setEmbeds(contentEmbed);
+                replyToUserMention.ifPresent(message::setContent);
+                eventHook.editOriginal(message.build()).queue();
+                return;
+            }
+
+            Collection<MessageEmbed> embeds = new ArrayList<>();
+            embeds.add(contentEmbed);
+            embeds.addAll(linkPreviews.stream().map(LinkPreview::embed).toList());
+
+            List<FileUpload> attachments = linkPreviews.stream()
+                .map(LinkPreview::attachment)
+                .filter(Objects::nonNull)
+                .toList();
+
+            MessageEditBuilder message =
+                    new MessageEditBuilder().setEmbeds(embeds).setFiles(attachments);
+            replyToUserMention.ifPresent(message::setContent);
+            eventHook.editOriginal(message.build()).queue();
+        });
+    }
 }
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreview.java b/application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreview.java
new file mode 100644
index 0000000000..e6a0e66509
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreview.java
@@ -0,0 +1,73 @@
+package org.togetherjava.tjbot.commands.utils;
+
+import net.dv8tion.jda.api.EmbedBuilder;
+import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.utils.FileUpload;
+
+import javax.annotation.Nullable;
+
+import java.io.InputStream;
+
+/**
+ * Preview of a URL for display as embed in Discord.
+ * <p>
+ * If the attachment is not {@code null}, it has to be made available to the message as well, for
+ * example
+ * {@code new MessageCreateBuilder().addEmbeds(linkPreview.embed).addFiles(linkPreview.attachment)}.
+ *
+ * @param attachment the thumbnail image of the link, referenced within the embed, if present
+ * @param embed the embed representing the preview of the link
+ */
+public record LinkPreview(@Nullable FileUpload attachment, MessageEmbed embed) {
+    /**
+     * Creates a new instance of this link preview, but with the given thumbnail.
+     * <p>
+     * Any previous thumbnail is overridden and replaced.
+     *
+     * @param thumbnailName the name of the thumbnail, with extension, e.g. {@code foo.png}
+     * @param thumbnail the thumbnails data as raw data stream
+     * @return this preview, but with a thumbnail
+     */
+    LinkPreview withThumbnail(String thumbnailName, InputStream thumbnail) {
+        return createWithThumbnail(embed, thumbnailName, thumbnail);
+    }
+
+    /**
+     * Creates a link preview that only has a thumbnail and no other text.
+     * 
+     * @param thumbnailName the name of the thumbnail, with extension, e.g. {@code foo.png}
+     * @param thumbnail the thumbnails data as raw data stream
+     * @return the thumbnail as link preview
+     */
+    static LinkPreview ofThumbnail(String thumbnailName, InputStream thumbnail) {
+        return createWithThumbnail(null, thumbnailName, thumbnail);
+    }
+
+    /**
+     * Creates a link preview that consists of the given text.
+     * <p>
+     * Use {@link #withThumbnail(String, InputStream)} to decorate the preview also with a thumbnail
+     * image.
+     *
+     * @param title the title of the preview, if present
+     * @param url the link to the resource this preview represents
+     * @param description the description of the preview, if present
+     * @return the text as link preview
+     */
+    static LinkPreview ofText(@Nullable String title, String url, @Nullable String description) {
+        MessageEmbed embed =
+                new EmbedBuilder().setTitle(title, url).setDescription(description).build();
+
+        return new LinkPreview(null, embed);
+    }
+
+    private static LinkPreview createWithThumbnail(@Nullable MessageEmbed embedToDecorate,
+            String thumbnailName, InputStream thumbnail) {
+        FileUpload attachment = FileUpload.fromData(thumbnail, thumbnailName);
+        MessageEmbed embed =
+                new EmbedBuilder(embedToDecorate).setThumbnail("attachment://" + thumbnailName)
+                    .build();
+
+        return new LinkPreview(attachment, embed);
+    }
+}
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreviews.java b/application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreviews.java
new file mode 100644
index 0000000000..bdbc1e556c
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/utils/LinkPreviews.java
@@ -0,0 +1,201 @@
+package org.togetherjava.tjbot.commands.utils;
+
+import com.linkedin.urls.Url;
+import com.linkedin.urls.detection.UrlDetector;
+import com.linkedin.urls.detection.UrlDetectorOptions;
+import org.jsoup.Jsoup;
+import org.jsoup.nodes.Document;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import javax.annotation.Nullable;
+
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.HttpURLConnection;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.util.Collection;
+import java.util.List;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.function.Predicate;
+import java.util.stream.IntStream;
+
+/**
+ * Provides means to create previews of links. See {@link #extractLinks(String)} and
+ * {@link #createLinkPreviews(List)}.
+ */
+public final class LinkPreviews {
+    private static final Logger logger = LoggerFactory.getLogger(LinkPreviews.class);
+
+    private static final String IMAGE_CONTENT_TYPE_PREFIX = "image";
+    private static final String IMAGE_META_NAME = "image";
+
+    private static final HttpClient CLIENT = HttpClient.newHttpClient();
+
+    private LinkPreviews() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+
+    /**
+     * Extracts all links from the given content.
+     * 
+     * @param content the content to search through
+     * @return a list of all found links, can be empty
+     */
+    public static List<String> extractLinks(String content) {
+        return new UrlDetector(content, UrlDetectorOptions.BRACKET_MATCH).detect()
+            .stream()
+            .map(Url::getFullUrl)
+            .toList();
+    }
+
+    /**
+     * Attempts to create previews of all given links.
+     * <p>
+     * A link preview is a short representation of the links contents, for example a thumbnail with
+     * a description.
+     * <p>
+     * The returned result does not necessarily contain a preview for all given links. Preview
+     * creation can fail for various reasons, failed previews are omitted in the result.
+     *
+     * @param links the links to preview
+     * @return a list of all previews created successfully, can be empty
+     */
+    public static CompletableFuture<List<LinkPreview>> createLinkPreviews(List<String> links) {
+        if (links.isEmpty()) {
+            return CompletableFuture.completedFuture(List.of());
+        }
+
+        List<CompletableFuture<Optional<LinkPreview>>> tasks = IntStream.range(0, links.size())
+            .mapToObj(i -> createLinkPreview(links.get(i), i + ".png"))
+            .toList();
+
+        var allDoneTask = CompletableFuture.allOf(tasks.toArray(CompletableFuture[]::new));
+        return allDoneTask.thenApply(any -> extractResults(tasks));
+    }
+
+    private static <T> List<T> extractResults(
+            Collection<? extends CompletableFuture<Optional<T>>> tasks) {
+        return tasks.stream()
+            .filter(Predicate.not(CompletableFuture::isCompletedExceptionally))
+            .map(CompletableFuture::join)
+            .flatMap(Optional::stream)
+            .toList();
+    }
+
+    private static CompletableFuture<Optional<LinkPreview>> createLinkPreview(String link,
+            String attachmentName) {
+        return readLinkContent(link).thenCompose(maybeContent -> {
+            if (maybeContent.isEmpty()) {
+                return noResult();
+            }
+            HttpContent content = maybeContent.orElseThrow();
+
+            if (content.type.startsWith(IMAGE_CONTENT_TYPE_PREFIX)) {
+                return result(LinkPreview.ofThumbnail(attachmentName, content.dataStream));
+            }
+
+            if (content.type.startsWith("text/html")) {
+                return parseWebsite(link, attachmentName, content.dataStream);
+            }
+            return noResult();
+        });
+    }
+
+    private static CompletableFuture<Optional<HttpContent>> readLinkContent(String link) {
+        URI linkAsUri;
+        try {
+            linkAsUri = URI.create(link);
+        } catch (IllegalArgumentException e) {
+            logger.warn("Attempted to create a preview for {}, but the URL is invalid.", link, e);
+            return noResult();
+        }
+
+        HttpRequest request = HttpRequest.newBuilder(linkAsUri).build();
+        CompletableFuture<HttpResponse<InputStream>> task =
+                CLIENT.sendAsync(request, HttpResponse.BodyHandlers.ofInputStream());
+
+        return task.thenApply(response -> {
+            int statusCode = response.statusCode();
+            if (statusCode < HttpURLConnection.HTTP_OK
+                    || statusCode >= HttpURLConnection.HTTP_MULT_CHOICE) {
+                logger.warn("Attempted to create a preview for {}, but the site returned code {}.",
+                        link, statusCode);
+                return Optional.empty();
+            }
+
+            String contentType = response.headers().firstValue("Content-Type").orElse("");
+            return Optional.of(new HttpContent(contentType, response.body()));
+        });
+    }
+
+    private record HttpContent(String type, InputStream dataStream) {
+    }
+
+    private static CompletableFuture<Optional<LinkPreview>> parseWebsite(String link,
+            String attachmentName, InputStream websiteContent) {
+        Document doc;
+        try {
+            doc = Jsoup.parse(websiteContent, null, link);
+        } catch (IOException e) {
+            logger.warn("Attempted to create a preview for {}, but the content invalid.", link, e);
+            return noResult();
+        }
+
+        String title = parseOpenGraphTwitterMeta(doc, "title", doc.title()).orElse(null);
+        String description =
+                parseOpenGraphTwitterMeta(doc, "description", doc.title()).orElse(null);
+
+        LinkPreview textPreview = LinkPreview.ofText(title, link, description);
+
+        String image = parseOpenGraphMeta(doc, IMAGE_META_NAME).orElse(null);
+        if (image == null) {
+            return result(textPreview);
+        }
+
+        return readLinkContent(image).thenCompose(maybeContent -> {
+            if (maybeContent.isEmpty()) {
+                return result(textPreview);
+            }
+            HttpContent content = maybeContent.orElseThrow();
+
+            if (!content.type.startsWith(IMAGE_CONTENT_TYPE_PREFIX)) {
+                return result(textPreview);
+            }
+
+            return result(textPreview.withThumbnail(attachmentName, content.dataStream));
+        });
+    }
+
+    private static Optional<String> parseOpenGraphTwitterMeta(Document doc, String metaProperty,
+            @Nullable String fallback) {
+        String value = Optional
+            .ofNullable(doc.selectFirst("meta[property=og:%s]".formatted(metaProperty)))
+            .or(() -> Optional
+                .ofNullable(doc.selectFirst("meta[property=twitter:%s".formatted(metaProperty))))
+            .map(element -> element.attr("content"))
+            .orElse(fallback);
+        if (value == null) {
+            return Optional.empty();
+        }
+        return value.isBlank() ? Optional.empty() : Optional.of(value);
+    }
+
+    private static Optional<String> parseOpenGraphMeta(Document doc, String metaProperty) {
+        return Optional.ofNullable(doc.selectFirst("meta[property=og:%s]".formatted(metaProperty)))
+            .map(element -> element.attr("content"))
+            .filter(Predicate.not(String::isBlank));
+    }
+
+    private static <T> CompletableFuture<Optional<T>> noResult() {
+        return CompletableFuture.completedFuture(Optional.empty());
+    }
+
+    private static <T> CompletableFuture<Optional<T>> result(T content) {
+        return CompletableFuture.completedFuture(Optional.of(content));
+    }
+}
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/utils/StringDistances.java b/application/src/main/java/org/togetherjava/tjbot/commands/utils/StringDistances.java
index b3f522bb22..87208e8335 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/utils/StringDistances.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/utils/StringDistances.java
@@ -77,7 +77,7 @@ public static Collection<String> closeMatches(CharSequence prefix,
         bestMatches.addAll(scoredMatches);
 
         return Stream.generate(bestMatches::poll)
-            .limit(limit)
+            .limit(Math.min(limit, bestMatches.size()))
             .takeWhile(matchScore -> isCloseEnough(matchScore, prefix))
             .map(MatchScore::candidate)
             .toList();

From d77cde1966fcfcd9cee6faff669eee09c22f56bb Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Mon, 21 Nov 2022 09:40:25 +0100
Subject: [PATCH 08/17] Bump name.remal.sonarlint from 1.5.0 to 2.0.0 (#695)

* Bump name.remal.sonarlint from 1.5.0 to 2.0.0

Bumps [name.remal.sonarlint](https://github.com/remal-gradle-plugins/sonarlint) from 1.5.0 to 2.0.0.
- [Release notes](https://github.com/remal-gradle-plugins/sonarlint/releases)
- [Commits](https://github.com/remal-gradle-plugins/sonarlint/commits/v2.0.0)

---
updated-dependencies:
- dependency-name: name.remal.sonarlint
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

* Fixed breaking changes and removed obsolete disables

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Zabuzard <zabuza.dev@gmail.com>
---
 build.gradle | 16 ++++++----------
 1 file changed, 6 insertions(+), 10 deletions(-)

diff --git a/build.gradle b/build.gradle
index 09d6f785df..0ebac0bf75 100644
--- a/build.gradle
+++ b/build.gradle
@@ -2,7 +2,7 @@ plugins {
     id 'java'
     id "com.diffplug.spotless" version "6.11.0"
     id "org.sonarqube" version "3.5.0.2730"
-    id "name.remal.sonarlint" version "1.5.0"
+    id "name.remal.sonarlint" version "2.0.0"
 }
 
 group 'org.togetherjava'
@@ -52,15 +52,11 @@ subprojects {
     }
 
     // sonarlint configuration, not to be confused with sonarqube/sonarcloud.
-    sonarlint {
-        excludes {
-            // Disables "Track uses of "TO-DO" tags" rule.
-            message 'java:S1135'
-
-            // Disables "Regular expressions should not overflow the stack" rule.
-            // https://sonarcloud.io/project/issues?id=Together-Java_TJ-Bot&issues=AXvleoajNC7zjjhmSufQ&open=AXvleoajNC7zjjhmSufQ
-            // https://sonarcloud.io/project/issues?id=Together-Java_TJ-Bot&issues=AXvleoX5NC7zjjhmSufP&open=AXvleoX5NC7zjjhmSufP
-            message 'java:S5998'
+    sonarLint {
+        rules {
+            disable(
+                    'java:S1135' // Disables "Track uses of "TO-DO" tags" rule.
+            )
         }
     }
 

From ced7f8f9ad7bfb025573fde2fd231b384f405707 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Wed, 23 Nov 2022 09:25:17 +0100
Subject: [PATCH 09/17] Bump sqlite-jdbc from 3.39.2.0 to 3.40.0.0 (#697)

Bumps [sqlite-jdbc](https://github.com/xerial/sqlite-jdbc) from 3.39.2.0 to 3.40.0.0.
- [Release notes](https://github.com/xerial/sqlite-jdbc/releases)
- [Changelog](https://github.com/xerial/sqlite-jdbc/blob/master/CHANGELOG)
- [Commits](https://github.com/xerial/sqlite-jdbc/compare/3.39.2.0...3.40.0.0)

---
updated-dependencies:
- dependency-name: org.xerial:sqlite-jdbc
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 application/build.gradle | 2 +-
 database/build.gradle    | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/application/build.gradle b/application/build.gradle
index 9924efdbb9..12806c29ca 100644
--- a/application/build.gradle
+++ b/application/build.gradle
@@ -1,6 +1,6 @@
 buildscript {
     dependencies {
-        classpath 'org.xerial:sqlite-jdbc:3.39.2.0'
+        classpath 'org.xerial:sqlite-jdbc:3.40.0.0'
     }
 }
 
diff --git a/database/build.gradle b/database/build.gradle
index fdc1e82a7c..e128ff2679 100644
--- a/database/build.gradle
+++ b/database/build.gradle
@@ -2,7 +2,7 @@ plugins {
     id 'java'
 }
 
-var sqliteVersion = "3.39.2.0"
+var sqliteVersion = "3.40.0.0"
 
 dependencies {
     implementation 'com.google.code.findbugs:jsr305:3.0.2'

From f7eecd7fffbbe9da8bd8d48d0c72ef1a8e675e72 Mon Sep 17 00:00:00 2001
From: Daniel Tischner <zabuza.dev@gmail.com>
Date: Thu, 24 Nov 2022 09:40:45 +0100
Subject: [PATCH 10/17] Added widgetbot to the website (#698)

---
 website/src/main/resources/public/index.html | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/website/src/main/resources/public/index.html b/website/src/main/resources/public/index.html
index 6b10dce33c..dc80abbb13 100644
--- a/website/src/main/resources/public/index.html
+++ b/website/src/main/resources/public/index.html
@@ -79,6 +79,12 @@ <h1><span class="image right"><img style="width: 50%" src="images/logo_frame.png
                 <li>50.000 messages per month</li>
                 <li>monthly giveaways</li>
             </ul>
+            <widgetbot
+                    server="272761734820003841"
+                    channel="272761734820003841"
+                    width="800"
+                    height="400"
+            ></widgetbot>
         </div>
     </section>
 
@@ -274,6 +280,7 @@ <h3>Owners</h3>
 <script src="assets/js/breakpoints.min.js"></script>
 <script src="assets/js/util.js"></script>
 <script src="assets/js/main.js"></script>
+<script src="https://cdn.jsdelivr.net/npm/@widgetbot/html-embed"></script>
 
 </body>
 

From 386d5d6df72f5ada0f3e984d49fdea95b048f33e Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 25 Nov 2022 09:22:29 +0100
Subject: [PATCH 11/17] Bump org.springframework.boot from 2.7.3 to 3.0.0
 (#700)

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 2.7.3 to 3.0.0.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](https://github.com/spring-projects/spring-boot/compare/v2.7.3...v3.0.0)

---
updated-dependencies:
- dependency-name: org.springframework.boot
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 website/build.gradle | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/website/build.gradle b/website/build.gradle
index b42146db15..53b48d433d 100644
--- a/website/build.gradle
+++ b/website/build.gradle
@@ -1,5 +1,5 @@
 plugins {
-    id 'org.springframework.boot' version '2.7.3'
+    id 'org.springframework.boot' version '3.0.0'
     id 'io.spring.dependency-management' version '1.1.0'
     id "com.google.cloud.tools.jib" version "3.3.0"
     id 'java'

From de40bc083a2d70c69815d4f161cfed92e91b0551 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Fri, 25 Nov 2022 09:22:38 +0100
Subject: [PATCH 12/17] Bump com.diffplug.spotless from 6.11.0 to 6.12.0 (#701)

Bumps com.diffplug.spotless from 6.11.0 to 6.12.0.

---
updated-dependencies:
- dependency-name: com.diffplug.spotless
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
---
 build.gradle | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/build.gradle b/build.gradle
index 0ebac0bf75..6132f0e837 100644
--- a/build.gradle
+++ b/build.gradle
@@ -1,6 +1,6 @@
 plugins {
     id 'java'
-    id "com.diffplug.spotless" version "6.11.0"
+    id "com.diffplug.spotless" version "6.12.0"
     id "org.sonarqube" version "3.5.0.2730"
     id "name.remal.sonarlint" version "2.0.0"
 }

From ddbc619237a2bc1a0cf533baaee1d4c196ee3d84 Mon Sep 17 00:00:00 2001
From: Daniel Tischner <zabuza.dev@gmail.com>
Date: Fri, 25 Nov 2022 11:23:43 +0100
Subject: [PATCH 13/17] Create FUNDING.yml

---
 .github/FUNDING.yml | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 .github/FUNDING.yml

diff --git a/.github/FUNDING.yml b/.github/FUNDING.yml
new file mode 100644
index 0000000000..ea6769772e
--- /dev/null
+++ b/.github/FUNDING.yml
@@ -0,0 +1,13 @@
+# These are supported funding model platforms
+
+github: # Replace with up to 4 GitHub Sponsors-enabled usernames e.g., [user1, user2]
+patreon: # Replace with a single Patreon username
+open_collective: together-java
+ko_fi: # Replace with a single Ko-fi username
+tidelift: # Replace with a single Tidelift platform-name/package-name e.g., npm/babel
+community_bridge: # Replace with a single Community Bridge project-name e.g., cloud-foundry
+liberapay: # Replace with a single Liberapay username
+issuehunt: # Replace with a single IssueHunt username
+otechie: # Replace with a single Otechie username
+lfx_crowdfunding: # Replace with a single LFX Crowdfunding project-name e.g., cloud-foundry
+custom: # Replace with up to 4 custom sponsorship URLs e.g., ['link1', 'link2']

From 94ab6713e1803cd5508e0c730900703b751cbd16 Mon Sep 17 00:00:00 2001
From: Mom0aut <30840092+Mom0aut@users.noreply.github.com>
Date: Mon, 28 Nov 2022 09:28:53 +0100
Subject: [PATCH 14/17] files without extenions are blacklisted now (#693)

---
 .../BlacklistedAttachmentListener.java         | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/moderation/attachment/BlacklistedAttachmentListener.java b/application/src/main/java/org/togetherjava/tjbot/commands/moderation/attachment/BlacklistedAttachmentListener.java
index 69a8e6024c..6ec3819d55 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/moderation/attachment/BlacklistedAttachmentListener.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/moderation/attachment/BlacklistedAttachmentListener.java
@@ -15,7 +15,7 @@
 import org.togetherjava.tjbot.config.Config;
 import org.togetherjava.tjbot.moderation.ModAuditLogWriter;
 
-import java.awt.Color;
+import java.awt.*;
 import java.util.List;
 import java.util.Locale;
 import java.util.function.UnaryOperator;
@@ -103,17 +103,21 @@ private MessageCreateData createBaseResponse(String originalMessageContent,
     private List<String> getBlacklistedAttachmentsFromMessage(Message originalMessage) {
         return originalMessage.getAttachments()
             .stream()
-            .filter(attachment -> blacklistedFileExtensions
-                .contains(attachment.getFileExtension().toLowerCase(Locale.US)))
+            .filter(this::containsBlacklistedFileExtensions)
             .map(Message.Attachment::getFileName)
             .toList();
     }
 
     private boolean doesMessageContainBlacklistedContent(Message message) {
-        return message.getAttachments()
-            .stream()
-            .anyMatch(attachment -> blacklistedFileExtensions
-                .contains(attachment.getFileExtension().toLowerCase(Locale.US)));
+        return message.getAttachments().stream().anyMatch(this::containsBlacklistedFileExtensions);
+    }
+
+    private boolean containsBlacklistedFileExtensions(Message.Attachment attachment) {
+        if (attachment.getFileExtension() == null) {
+            return true;
+        }
+        return blacklistedFileExtensions
+            .contains(attachment.getFileExtension().toLowerCase(Locale.US));
     }
 
     private void warnMods(Message sentUserMessage) {

From 0e2d54fa2005f29b4d636d50a01ec3de2184b12f Mon Sep 17 00:00:00 2001
From: Daniel Tischner <zabuza.dev@gmail.com>
Date: Mon, 28 Nov 2022 09:30:38 +0100
Subject: [PATCH 15/17] fixed a small oob bug with extracting code (#696)

* happens in rare conditions when the message is ````` or similar, i.e. more than three backticks
---
 .../org/togetherjava/tjbot/commands/utils/MessageUtils.java   | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java b/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java
index ff670b17f7..e763a48c96 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java
@@ -180,7 +180,8 @@ public static Optional<CodeFence> extractCode(String fullMessage) {
             return Optional.empty();
         }
 
-        int codeFenceEnd = fullMessage.indexOf(CODE_FENCE_SYMBOL, codeFenceStart + 1);
+        int languageStart = codeFenceStart + CODE_FENCE_SYMBOL.length();
+        int codeFenceEnd = fullMessage.indexOf(CODE_FENCE_SYMBOL, languageStart);
         if (codeFenceEnd == -1) {
             return Optional.empty();
         }
@@ -188,7 +189,6 @@ public static Optional<CodeFence> extractCode(String fullMessage) {
         // Language is between ``` and newline, no spaces allowed, like ```java
         // Look for the next newline and then assert no space between
         String language = null;
-        int languageStart = codeFenceStart + CODE_FENCE_SYMBOL.length();
         int languageEnd = fullMessage.indexOf('\n', codeFenceStart);
         if (languageEnd != -1) {
             String languageCandidate = fullMessage.substring(languageStart, languageEnd);

From a7a0944749be3f10ecf6d526f9fed8cc0ceb0eee Mon Sep 17 00:00:00 2001
From: Isvoran Andrei <69761201+isvora@users.noreply.github.com>
Date: Mon, 28 Nov 2022 14:12:13 +0200
Subject: [PATCH 16/17] Ping moderators when /modmail and /report commands are
 used. (#699)

* Ping moderators when /modmail command is used.

* Rename moderator group string to match the style

* Ping moderators when /report command is used.

* Extra space

* Refactor

* Fix CR comments

* Fix CR comments
---
 .../commands/moderation/ReportCommand.java    | 23 ++++++++++++++++---
 .../moderation/modmail/ModMailCommand.java    | 14 +++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/moderation/ReportCommand.java b/application/src/main/java/org/togetherjava/tjbot/commands/moderation/ReportCommand.java
index 005e779587..6127e84f58 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/moderation/ReportCommand.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/moderation/ReportCommand.java
@@ -6,6 +6,7 @@
 import net.dv8tion.jda.api.entities.Guild;
 import net.dv8tion.jda.api.entities.Message;
 import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.entities.Role;
 import net.dv8tion.jda.api.entities.channel.concrete.TextChannel;
 import net.dv8tion.jda.api.events.interaction.ModalInteractionEvent;
 import net.dv8tion.jda.api.events.interaction.command.MessageContextInteractionEvent;
@@ -52,6 +53,7 @@ public final class ReportCommand extends BotCommandAdapter implements MessageCon
     private static final Color AMBIENT_COLOR = Color.BLACK;
     private final Cache<Long, Instant> authorToLastReportInvocation = createCooldownCache();
     private final Predicate<String> modMailChannelNamePredicate;
+    private final Predicate<String> configModGroupPattern;
     private final String configModMailChannelPattern;
 
     /**
@@ -66,6 +68,9 @@ public ReportCommand(Config config) {
                 Pattern.compile(config.getModMailChannelPattern()).asMatchPredicate();
 
         configModMailChannelPattern = config.getModMailChannelPattern();
+
+        configModGroupPattern =
+                Pattern.compile(config.getHeavyModerationRolePattern()).asMatchPredicate();
     }
 
     private Cache<Long, Instant> createCooldownCache() {
@@ -177,9 +182,21 @@ private MessageCreateAction createModMessage(String reportReason,
             .setDescription(reportReason)
             .setColor(AMBIENT_COLOR)
             .build();
-        return modMailAuditLog.sendMessageEmbeds(reportedMessageEmbed, reportReasonEmbed)
-            .addActionRow(DiscordClientAction.Channels.GUILD_CHANNEL_MESSAGE.asLinkButton(
-                    "Go to Message", guild.getId(), reportedMessage.channelID, reportedMessage.id));
+
+        MessageCreateAction message =
+                modMailAuditLog.sendMessageEmbeds(reportedMessageEmbed, reportReasonEmbed)
+                    .addActionRow(DiscordClientAction.Channels.GUILD_CHANNEL_MESSAGE.asLinkButton(
+                            "Go to Message", guild.getId(), reportedMessage.channelID,
+                            reportedMessage.id));
+
+        Optional<Role> moderatorRole = guild.getRoles()
+            .stream()
+            .filter(role -> configModGroupPattern.test(role.getName()))
+            .findFirst();
+
+        moderatorRole.ifPresent(role -> message.setContent(role.getAsMention()));
+
+        return message;
     }
 
     private void sendModMessage(ModalInteractionEvent event, List<String> args,
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/moderation/modmail/ModMailCommand.java b/application/src/main/java/org/togetherjava/tjbot/commands/moderation/modmail/ModMailCommand.java
index 8a83c3badb..0ab3181f7a 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/moderation/modmail/ModMailCommand.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/moderation/modmail/ModMailCommand.java
@@ -5,6 +5,7 @@
 import net.dv8tion.jda.api.EmbedBuilder;
 import net.dv8tion.jda.api.JDA;
 import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.entities.Role;
 import net.dv8tion.jda.api.entities.User;
 import net.dv8tion.jda.api.entities.channel.concrete.TextChannel;
 import net.dv8tion.jda.api.events.interaction.command.SlashCommandInteractionEvent;
@@ -50,6 +51,7 @@ public final class ModMailCommand extends SlashCommandAdapter {
     private static final Color AMBIENT_COLOR = Color.BLACK;
     private final Cache<Long, Instant> authorToLastModMailInvocation = createCooldownCache();
     private final Predicate<String> modMailChannelNamePredicate;
+    private final Predicate<String> configModGroupPattern;
     private final String configModMailChannelPattern;
 
 
@@ -83,6 +85,9 @@ public ModMailCommand(JDA jda, Config config) {
                 Pattern.compile(config.getModMailChannelPattern()).asMatchPredicate();
 
         configModMailChannelPattern = config.getModMailChannelPattern();
+
+        configModGroupPattern =
+                Pattern.compile(config.getHeavyModerationRolePattern()).asMatchPredicate();
     }
 
     private Cache<Long, Instant> createCooldownCache() {
@@ -148,6 +153,15 @@ private MessageCreateAction createModMessage(SlashCommandInteractionEvent event,
             message.addActionRow(DiscordClientAction.General.USER.asLinkButton("Author Profile",
                     String.valueOf(userId)));
         }
+
+        Optional<Role> moderatorRole = event.getGuild()
+            .getRoles()
+            .stream()
+            .filter(role -> configModGroupPattern.test(role.getName()))
+            .findFirst();
+
+        moderatorRole.ifPresent(role -> message.setContent(role.getAsMention()));
+
         return message;
     }
 

From fa434fe92665ab1ac195dcba2a3062384a885ddf Mon Sep 17 00:00:00 2001
From: Nxllpointer <54677650+Nxllpointer@users.noreply.github.com>
Date: Tue, 29 Nov 2022 13:21:02 +0100
Subject: [PATCH 17/17] Bookmark Command (#634)

* Added bookmark command

The bookmark command is a command to add and view bookmarks for help threads. The bookmarks get cleaned after some time if they are not renewed.

* Made bookmarks feature sonarlint compliant

* Removed BookmarksCommand section comments

* Sort bookmarks by latest activity

* Made final embed creations in BookmarksCommand more readable

Created genSimpleEmbed method in BookmarksCommand to make final embed creations more readable

* Revert all changes for rewrite

* Full rewrite of the bookmarks feature

* Added length limit for note option

* Added bookmarks limit to prevent spam

* Created replyEmbedEphemeral method because all messages are ephemeral embeds

* Changed remove-select-menu to display thread name if the thread was found

* Added guild-leave bookmark-removal-scheduling

* Fixed requested changes for version 1 that still applied to the rewrite

* Added missing javadoc dots

* Fixed issue with deleting all bookmarks

* Converted unnecessary multiline Strings to normal Strings

* Split createTinyEmbed into separate methods for every color

* Rename BookmarkPaginatorInteractor to BookmarksPaginatorInteractor

* Add javadoc for BookmarksPaginatorInteractor

* Don't overwrite args in onSelectMenuSelection

* Removed generatePageEmbed overloading for readability

* Renamed highestPageIndex to lastPageIndex in generatePageEmbed

* Removed newline to improve readability in generatePageEmbed

* Removed unnecessary comments in generatePageEmbed

* Renamed uninformative variable from b to bookmark when creating PageEntry

* Added emptiness check to getLastPageIndex to avoid issues in the future

* Fixed ComponentArguments and RemoveComponentArguments having fromStringArgs and toArray in reverse order

* Improved the list subcommand description

* Renamed LEAVE_REMOVAL_DELAY to LEAVE_BOOKMARKS_REMOVAL_DELAY

* Changed requestListPagination and requestRemovePagination to use Objects#requireNonNull instead of a manual null check

* Renamed SCHEDULED_REMOVAL_AT to DELETE_AT

* Improve naming about deleting old bookmarks of users that left the guild

* Improve naming of MAX_BOOKMARK_COUNT_USER to MAX_BOOKMARK_COUNT_PER_USER

* Improve naming of LEAVE_BOOKMARKS_REMOVAL_DELAY to REMOVE_BOOKMARKS_AFTER_LEAVE_DELAY

* Changed constants to be package private instead of public

* Improve speed by using a Set for bookmarksToRemoveChannelIDs

* Improved fetching the result of selectCount

* Improved speed of checking if a user already bookmarked a channel

* Created helper method for createXxxEmbed methods

* Improved javadoc @param descriptions

* Renamed replyEmbedEphemeral to sendResponse for improved readability

* Delayed fetching of the users bookmark count to avoid unnecessary database reads

* Removed subtracting 1 from WARN/MAX_BOOKMARK_COUNT_TOTAL to improve readability

One bookmark more or less will not make a difference

* Fix naming convention violation of delete_at to deleteAt

* Improved bookmark limit warning and error log messages

* Made error messages more friendly

* Improved command descriptions

* Changed to correct way of formatting log arguments

* Revert "Improved fetching the result of selectCount"

This reverts commit e3b08804610bd51a8c75c6b8bbb1c8bde62f403d.

* Actually improved fetching the result of selectCount

* Improved BookmarksSystem constructor javadoc

* Improved the remove subcommand description

* Added the users bookmarks limit to the BOOKMARK_LIMIT_USER_EMBED failure embed

* Renamed ADD_OPTION_NOTE to ADD_BOOKMARK_NOTE_OPTION

* Fixed onSelectMenuSelection not ensuring the page index

* Improved BookmarksPaginatorInteractor javadoc

* Added BookmarksCommand javadoc

* Moved into proper package

* overall flow adjustments

* More improvements

* CR Nxllpointer

* Renamings from CR

* BookmarksPaginationHandler -> BookmarksListRemoveHandler
* RequestWithPagination -> Request

* Fixed bookmark limit reached soon log message

* Added command usage javadoc for BookmarksCommand

* Improved BookmarksSystem javadoc

* Spotless after resolving conflicts

Co-authored-by: Nxllpointer <Nxllpointer@users.noreply.github.com>
Co-authored-by: Zabuzard <zabuza.dev@gmail.com>
---
 .../togetherjava/tjbot/commands/Features.java |   5 +
 .../commands/bookmarks/BookmarksCommand.java  | 185 ++++++++++
 .../bookmarks/BookmarksListRemoveHandler.java | 332 ++++++++++++++++++
 .../commands/bookmarks/BookmarksSystem.java   | 145 ++++++++
 .../LeftoverBookmarksCleanupRoutine.java      |  35 ++
 .../bookmarks/LeftoverBookmarksListener.java  |  40 +++
 .../commands/bookmarks/package-info.java      |  12 +
 .../tjbot/commands/utils/MessageUtils.java    |  13 +
 .../db/V12__Add_Bookmarks_System.sql          |  10 +
 9 files changed, 777 insertions(+)
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksCommand.java
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksListRemoveHandler.java
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksSystem.java
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksCleanupRoutine.java
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksListener.java
 create mode 100644 application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/package-info.java
 create mode 100644 application/src/main/resources/db/V12__Add_Bookmarks_System.sql

diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/Features.java b/application/src/main/java/org/togetherjava/tjbot/commands/Features.java
index 76cdd928b7..d839a05a14 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/Features.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/Features.java
@@ -6,6 +6,7 @@
 import org.togetherjava.tjbot.commands.basic.RoleSelectCommand;
 import org.togetherjava.tjbot.commands.basic.SuggestionsUpDownVoter;
 import org.togetherjava.tjbot.commands.basic.VcActivityCommand;
+import org.togetherjava.tjbot.commands.bookmarks.*;
 import org.togetherjava.tjbot.commands.code.CodeMessageAutoDetection;
 import org.togetherjava.tjbot.commands.code.CodeMessageHandler;
 import org.togetherjava.tjbot.commands.code.CodeMessageManualDetection;
@@ -67,6 +68,7 @@ private Features() {
      */
     public static Collection<Feature> createFeatures(JDA jda, Database database, Config config) {
         TagSystem tagSystem = new TagSystem(database);
+        BookmarksSystem bookmarksSystem = new BookmarksSystem(config, database);
         ModerationActionsStore actionsStore = new ModerationActionsStore(database);
         ModAuditLogWriter modAuditLogWriter = new ModAuditLogWriter(config);
         ScamHistoryStore scamHistoryStore = new ScamHistoryStore(database);
@@ -90,6 +92,7 @@ public static Collection<Feature> createFeatures(JDA jda, Database database, Con
         features
             .add(new AutoPruneHelperRoutine(config, helpSystemHelper, modAuditLogWriter, database));
         features.add(new HelpThreadAutoArchiver(helpSystemHelper));
+        features.add(new LeftoverBookmarksCleanupRoutine(bookmarksSystem));
 
         // Message receivers
         features.add(new TopHelpersMessageListener(database, config));
@@ -107,6 +110,7 @@ public static Collection<Feature> createFeatures(JDA jda, Database database, Con
         features.add(new RejoinModerationRoleListener(actionsStore, config));
         features.add(new OnGuildLeaveCloseThreadListener(database));
         features.add(new UserBannedDeleteRecentThreadsListener(database));
+        features.add(new LeftoverBookmarksListener(bookmarksSystem));
 
         // Message context commands
 
@@ -139,6 +143,7 @@ public static Collection<Feature> createFeatures(JDA jda, Database database, Con
         features.add(new ModMailCommand(jda, config));
         features.add(new HelpThreadCommand(config, helpSystemHelper));
         features.add(new ReportCommand(config));
+        features.add(new BookmarksCommand(bookmarksSystem));
 
         // Mixtures
         features.add(new HelpThreadOverviewUpdater(config, helpSystemHelper));
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksCommand.java b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksCommand.java
new file mode 100644
index 0000000000..16dbbe34f8
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksCommand.java
@@ -0,0 +1,185 @@
+package org.togetherjava.tjbot.commands.bookmarks;
+
+import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.entities.channel.unions.MessageChannelUnion;
+import net.dv8tion.jda.api.events.interaction.command.SlashCommandInteractionEvent;
+import net.dv8tion.jda.api.events.interaction.component.ButtonInteractionEvent;
+import net.dv8tion.jda.api.events.interaction.component.SelectMenuInteractionEvent;
+import net.dv8tion.jda.api.interactions.commands.OptionMapping;
+import net.dv8tion.jda.api.interactions.commands.OptionType;
+import net.dv8tion.jda.api.interactions.commands.build.OptionData;
+import net.dv8tion.jda.api.interactions.commands.build.SubcommandData;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.togetherjava.tjbot.commands.CommandVisibility;
+import org.togetherjava.tjbot.commands.SlashCommandAdapter;
+
+import java.util.List;
+import java.util.Objects;
+
+/**
+ * The bookmarks command is used for managing and viewing bookmarks. A bookmark is a link to a help
+ * thread that can have a note so you can easily remember why you bookmarked a help thread. Writing
+ * to the database and showing the list/remove messages is not done by this class, that is handled
+ * by the {@link BookmarksSystem}. This class only checks if you are able to add a bookmark in the
+ * current channel and tells the {@link BookmarksSystem} to do the rest.
+ * <p>
+ * Usage:
+ * 
+ * <pre>
+ * /bookmarks add [note]
+ * /bookmarks list
+ * /bookmarks remove
+ * </pre>
+ */
+public final class BookmarksCommand extends SlashCommandAdapter {
+
+    private static final Logger logger = LoggerFactory.getLogger(BookmarksCommand.class);
+
+    public static final String COMMAND_NAME = "bookmarks";
+    public static final String SUBCOMMAND_ADD = "add";
+    public static final String SUBCOMMAND_LIST = "list";
+    public static final String SUBCOMMAND_REMOVE = "remove";
+    public static final String ADD_BOOKMARK_NOTE_OPTION = "note";
+
+    private static final MessageEmbed NOT_A_HELP_THREAD_EMBED =
+            BookmarksSystem.createFailureEmbed("You can only bookmark help threads.");
+
+    private static final MessageEmbed ALREADY_BOOKMARKED_EMBED =
+            BookmarksSystem.createFailureEmbed("You have already bookmarked this channel.");
+
+    private static final MessageEmbed BOOKMARK_ADDED_EMBED =
+            BookmarksSystem.createSuccessEmbed("Your bookmark was added.");
+
+    private static final MessageEmbed BOOKMARK_LIMIT_USER_EMBED = BookmarksSystem
+        .createFailureEmbed(
+                "You have exceeded your bookmarks limit of `%d`. Please delete some of your other bookmarks."
+                    .formatted(BookmarksSystem.MAX_BOOKMARK_COUNT_PER_USER));
+
+    private static final MessageEmbed BOOKMARK_LIMIT_TOTAL_EMBED = BookmarksSystem
+        .createWarningEmbed(
+                """
+                        You cannot add a bookmark right now because the total amount of bookmarks has exceeded its limit.
+                        Please wait a bit until some of them have been deleted or contact a moderator.
+                        Sorry for the inconvenience.
+                        """);
+
+    private final BookmarksSystem bookmarksSystem;
+    private final BookmarksListRemoveHandler listRemoveHandler;
+
+    /**
+     * Creates a new instance and registers every sub command.
+     *
+     * @param bookmarksSystem The {@link BookmarksSystem} to request pagination and manage bookmarks
+     */
+    public BookmarksCommand(BookmarksSystem bookmarksSystem) {
+        super(COMMAND_NAME, "Bookmark help threads so that you can easily look them up again",
+                CommandVisibility.GLOBAL);
+        this.bookmarksSystem = bookmarksSystem;
+        listRemoveHandler =
+                new BookmarksListRemoveHandler(bookmarksSystem, this::generateComponentId);
+
+        OptionData addNoteOption = new OptionData(OptionType.STRING, ADD_BOOKMARK_NOTE_OPTION,
+                "Your personal comment on this bookmark")
+                    .setMaxLength(BookmarksSystem.MAX_NOTE_LENGTH)
+                    .setRequired(false);
+
+        SubcommandData addSubCommand = new SubcommandData(SUBCOMMAND_ADD,
+                "Bookmark this help thread, so that you can easily look it up again")
+                    .addOptions(addNoteOption);
+
+        SubcommandData listSubCommand =
+                new SubcommandData(SUBCOMMAND_LIST, "List all of your bookmarks");
+
+        SubcommandData removeSubCommand =
+                new SubcommandData(SUBCOMMAND_REMOVE, "Remove some of your bookmarks");
+
+        getData().addSubcommands(addSubCommand, listSubCommand, removeSubCommand);
+    }
+
+    @Override
+    public void onSlashCommand(SlashCommandInteractionEvent event) {
+        String subCommandName = Objects.requireNonNull(event.getSubcommandName());
+
+        switch (subCommandName) {
+            case SUBCOMMAND_ADD -> addBookmark(event);
+            case SUBCOMMAND_LIST -> listRemoveHandler.handleListRequest(event);
+            case SUBCOMMAND_REMOVE -> listRemoveHandler.handleRemoveRequest(event);
+            default -> throw new IllegalArgumentException("Unknown subcommand");
+        }
+    }
+
+    @Override
+    public void onButtonClick(ButtonInteractionEvent event, List<String> args) {
+        listRemoveHandler.onButtonClick(event, args);
+    }
+
+    @Override
+    public void onSelectMenuSelection(SelectMenuInteractionEvent event, List<String> args) {
+        listRemoveHandler.onSelectMenuSelection(event, args);
+    }
+
+    private void addBookmark(SlashCommandInteractionEvent event) {
+        long userID = event.getUser().getIdLong();
+        long channelID = event.getChannel().getIdLong();
+        String note = event.getOption(ADD_BOOKMARK_NOTE_OPTION, OptionMapping::getAsString);
+
+        if (!handleCanAddBookmark(event)) {
+            return;
+        }
+
+        bookmarksSystem.addBookmark(userID, channelID, note);
+
+        sendResponse(event, BOOKMARK_ADDED_EMBED);
+    }
+
+    private boolean handleCanAddBookmark(SlashCommandInteractionEvent event) {
+        MessageChannelUnion channel = event.getChannel();
+        long channelID = channel.getIdLong();
+        long userID = event.getUser().getIdLong();
+
+        if (!bookmarksSystem.isHelpThread(channel)) {
+            sendResponse(event, NOT_A_HELP_THREAD_EMBED);
+            return false;
+        }
+
+        if (bookmarksSystem.didUserBookmarkChannel(userID, channelID)) {
+            sendResponse(event, ALREADY_BOOKMARKED_EMBED);
+            return false;
+        }
+
+        long bookmarkCountTotal = bookmarksSystem.getTotalBookmarkCount();
+        if (bookmarkCountTotal == BookmarksSystem.WARN_BOOKMARK_COUNT_TOTAL) {
+            logger.warn("""
+                    The bookmark limit will be reached soon (`{}/{}` bookmarks)!
+                    If the limit is reached no new bookmarks can be added!
+                    Please delete some bookmarks!
+                    """, BookmarksSystem.WARN_BOOKMARK_COUNT_TOTAL,
+                    BookmarksSystem.MAX_BOOKMARK_COUNT_TOTAL);
+        }
+        if (bookmarkCountTotal == BookmarksSystem.MAX_BOOKMARK_COUNT_TOTAL) {
+            logger.error("""
+                    The bookmark limit of `{}` has been reached!
+                    No new bookmarks can be added anymore!
+                    Please delete some bookmarks!
+                    """, BookmarksSystem.MAX_BOOKMARK_COUNT_TOTAL);
+        }
+        if (bookmarkCountTotal > BookmarksSystem.MAX_BOOKMARK_COUNT_TOTAL) {
+            sendResponse(event, BOOKMARK_LIMIT_TOTAL_EMBED);
+            return false;
+        }
+
+        long bookmarkCountUser = bookmarksSystem.getUserBookmarkCount(userID);
+        if (bookmarkCountUser >= BookmarksSystem.MAX_BOOKMARK_COUNT_PER_USER) {
+            sendResponse(event, BOOKMARK_LIMIT_USER_EMBED);
+            return false;
+        }
+
+        return true;
+    }
+
+    private void sendResponse(SlashCommandInteractionEvent event, MessageEmbed embed) {
+        event.replyEmbeds(embed).setEphemeral(true).queue();
+    }
+}
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksListRemoveHandler.java b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksListRemoveHandler.java
new file mode 100644
index 0000000000..e3ea0e4b2e
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksListRemoveHandler.java
@@ -0,0 +1,332 @@
+package org.togetherjava.tjbot.commands.bookmarks;
+
+import net.dv8tion.jda.api.EmbedBuilder;
+import net.dv8tion.jda.api.JDA;
+import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.entities.channel.concrete.ThreadChannel;
+import net.dv8tion.jda.api.entities.emoji.Emoji;
+import net.dv8tion.jda.api.events.interaction.command.GenericCommandInteractionEvent;
+import net.dv8tion.jda.api.events.interaction.component.ButtonInteractionEvent;
+import net.dv8tion.jda.api.events.interaction.component.SelectMenuInteractionEvent;
+import net.dv8tion.jda.api.interactions.components.ActionRow;
+import net.dv8tion.jda.api.interactions.components.ComponentInteraction;
+import net.dv8tion.jda.api.interactions.components.LayoutComponent;
+import net.dv8tion.jda.api.interactions.components.buttons.Button;
+import net.dv8tion.jda.api.interactions.components.selections.SelectMenu;
+import net.dv8tion.jda.api.interactions.components.selections.SelectOption;
+
+import org.togetherjava.tjbot.commands.utils.MessageUtils;
+import org.togetherjava.tjbot.db.generated.tables.records.BookmarksRecord;
+
+import java.awt.Color;
+import java.util.*;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.function.UnaryOperator;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+final class BookmarksListRemoveHandler {
+
+    private static final int ENTRIES_PER_PAGE = 10;
+    private static final Emoji BUTTON_PREV_EMOJI = Emoji.fromUnicode("⬅");
+    private static final String BUTTON_PREV_NAME = "button-previous";
+    private static final Emoji BUTTON_NEXT_EMOJI = Emoji.fromUnicode("➡");
+    private static final String BUTTON_NEXT_NAME = "button-next";
+    private static final String BUTTON_REMOVE_LABEL = "Delete selected bookmarks";
+    private static final String BUTTON_REMOVE_NAME = "button-remove";
+    private static final String SELECT_MENU_REMOVE_NAME = "select-menu-remove";
+
+    private static final MessageEmbed NO_BOOKMARKS_EMBED =
+            BookmarksSystem.createFailureEmbed("You don't have any bookmarks yet.");
+
+    private final BookmarksSystem bookmarksSystem;
+    private final Function<String[], String> generateComponentId;
+
+    BookmarksListRemoveHandler(BookmarksSystem bookmarksSystem,
+            Function<String[], String> generateComponentId) {
+        this.bookmarksSystem = bookmarksSystem;
+        this.generateComponentId = generateComponentId;
+    }
+
+    void handleListRequest(GenericCommandInteractionEvent event) {
+        handlePaginatedRequest(event, RequestType.LIST);
+    }
+
+    void handleRemoveRequest(GenericCommandInteractionEvent event) {
+        handlePaginatedRequest(event, RequestType.REMOVE);
+    }
+
+    private void handlePaginatedRequest(GenericCommandInteractionEvent event,
+            RequestType requestType) {
+        JDA jda = event.getJDA();
+        long userID = event.getUser().getIdLong();
+
+        List<BookmarksRecord> bookmarks = bookmarksSystem.getUsersBookmarks(userID);
+        if (bookmarks.isEmpty()) {
+            event.replyEmbeds(NO_BOOKMARKS_EMBED).setEphemeral(true).queue();
+            return;
+        }
+
+        MessageEmbed pageEmbed = generatePageEmbed(bookmarks, requestType, 0);
+
+        Collection<LayoutComponent> components = new ArrayList<>();
+        components.add(generateNavigationComponent(requestType, 0));
+
+        if (requestType == RequestType.REMOVE) {
+            components
+                .addAll(generateRemoveComponents(jda, bookmarks, RequestType.REMOVE, 0, Set.of()));
+        }
+
+        event.replyEmbeds(pageEmbed).setComponents(components).setEphemeral(true).queue();
+    }
+
+    private static MessageEmbed generatePageEmbed(List<BookmarksRecord> bookmarks,
+            RequestType requestType, int currentPageIndex) {
+        int lastPageIndex = getLastPageIndex(bookmarks);
+
+        String title;
+        Color color;
+        switch (requestType) {
+            case LIST -> {
+                title = "Bookmarks List";
+                color = BookmarksSystem.COLOR_SUCCESS;
+            }
+            case REMOVE -> {
+                title = "Remove Bookmarks";
+                color = BookmarksSystem.COLOR_WARNING;
+            }
+            default -> throw new IllegalArgumentException("Unknown request type: " + requestType);
+        }
+
+        StringJoiner descriptionJoiner = new StringJoiner("\n\n");
+
+        getPageEntries(bookmarks, currentPageIndex).forEach(pageEntry -> {
+            int bookmarkNumber = pageEntry.bookmarkNumber;
+            long channelID = pageEntry.bookmark.getChannelId();
+            String note = pageEntry.bookmark.getNote();
+
+            StringJoiner entryJoiner = new StringJoiner("\n");
+
+            entryJoiner.add(
+                    "**%d.** %s".formatted(bookmarkNumber, MessageUtils.mentionChannel(channelID)));
+            if (note != null && requestType != RequestType.REMOVE) {
+                entryJoiner.add("*%s*".formatted(note));
+            }
+
+            descriptionJoiner.add(entryJoiner.toString());
+        });
+
+        String description = descriptionJoiner.toString();
+        String footer = "Page %d/%d".formatted(currentPageIndex + 1, lastPageIndex + 1);
+
+        return new EmbedBuilder().setTitle(title)
+            .setDescription(description)
+            .setFooter(footer)
+            .setColor(color)
+            .build();
+    }
+
+    void onButtonClick(ButtonInteractionEvent event, List<String> args) {
+        Request request = Request.fromArgs(args);
+        long userID = event.getUser().getIdLong();
+
+        List<BookmarksRecord> bookmarks = bookmarksSystem.getUsersBookmarks(userID);
+
+        int nextPageIndex = switch (request.componentName) {
+            case BUTTON_PREV_NAME -> clampPageIndex(bookmarks, request.pageToDisplayIndex - 1);
+            case BUTTON_NEXT_NAME -> clampPageIndex(bookmarks, request.pageToDisplayIndex + 1);
+            case BUTTON_REMOVE_NAME -> {
+                removeSelectedBookmarks(bookmarks, event, request);
+                yield clampPageIndex(bookmarks, request.pageToDisplayIndex);
+            }
+            default -> throw new IllegalArgumentException("Unknown button: " + request.componentName);
+        };
+
+        updatePagination(event, request.atPage(nextPageIndex), bookmarks);
+    }
+
+    private void removeSelectedBookmarks(List<BookmarksRecord> bookmarks,
+            ComponentInteraction event, Request request) {
+        long userID = event.getUser().getIdLong();
+
+        Predicate<BookmarksRecord> isBookmarkSelectedForRemoval =
+                bookmark -> request.bookmarkIdsToRemove.contains(bookmark.getChannelId());
+
+        bookmarks.removeIf(isBookmarkSelectedForRemoval);
+        bookmarksSystem.removeBookmarks(userID, request.bookmarkIdsToRemove);
+    }
+
+    void onSelectMenuSelection(SelectMenuInteractionEvent event, List<String> args) {
+        Request request = Request.fromArgs(args);
+
+        if (request.type != RequestType.REMOVE) {
+            throw new IllegalArgumentException(
+                    "Only remove requests must have a menu, but got " + request.type);
+        }
+        if (!request.componentName.equals(SELECT_MENU_REMOVE_NAME)) {
+            throw new IllegalArgumentException(
+                    "There should only be a single menu, but got " + request.componentName);
+        }
+
+        Set<Long> selectedBookmarkIdsToRemove = event.getSelectedOptions()
+            .stream()
+            .map(SelectOption::getValue)
+            .map(Long::parseLong)
+            .collect(Collectors.toSet());
+        request = request.withSelectedBookmarksToRemove(selectedBookmarkIdsToRemove);
+
+        List<BookmarksRecord> bookmarks =
+                bookmarksSystem.getUsersBookmarks(event.getUser().getIdLong());
+        int updatedPageIndex = clampPageIndex(bookmarks, request.pageToDisplayIndex);
+
+        updatePagination(event, request.atPage(updatedPageIndex), bookmarks);
+    }
+
+    private void updatePagination(ComponentInteraction event, Request request,
+            List<BookmarksRecord> bookmarks) {
+        if (bookmarks.isEmpty()) {
+            event.editMessageEmbeds(NO_BOOKMARKS_EMBED).setComponents().queue();
+            return;
+        }
+
+        MessageEmbed pageEmbed =
+                generatePageEmbed(bookmarks, request.type, request.pageToDisplayIndex);
+
+        Collection<LayoutComponent> components = new ArrayList<>();
+        components.add(generateNavigationComponent(request.type, request.pageToDisplayIndex));
+        if (request.type == RequestType.REMOVE) {
+            components.addAll(generateRemoveComponents(event.getJDA(), bookmarks, request.type,
+                    request.pageToDisplayIndex, request.bookmarkIdsToRemove));
+        }
+
+        event.editMessageEmbeds(pageEmbed).setComponents(components).queue();
+    }
+
+    private LayoutComponent generateNavigationComponent(RequestType requestType,
+            int pageToDisplayIndex) {
+        UnaryOperator<String> generateNavigationComponentId = name -> {
+            Request request = new Request(requestType, name, pageToDisplayIndex, Set.of());
+
+            return generateComponentId.apply(request.toArray());
+        };
+
+        String buttonPrevId = generateNavigationComponentId.apply(BUTTON_PREV_NAME);
+        Button buttonPrev = Button.primary(buttonPrevId, BUTTON_PREV_EMOJI);
+
+        String buttonNextId = generateNavigationComponentId.apply(BUTTON_NEXT_NAME);
+        Button buttonNext = Button.primary(buttonNextId, BUTTON_NEXT_EMOJI);
+
+        return ActionRow.of(buttonPrev, buttonNext);
+    }
+
+    private List<LayoutComponent> generateRemoveComponents(JDA jda,
+            List<? extends BookmarksRecord> bookmarks, RequestType requestType,
+            int pageToDisplayIndex, Set<Long> bookmarksToRemoveChannelIDs) {
+        List<PageEntry> pageEntries = getPageEntries(bookmarks, pageToDisplayIndex);
+
+        UnaryOperator<String> generateRemoveComponentId = name -> {
+            Request request =
+                    new Request(requestType, name, pageToDisplayIndex, bookmarksToRemoveChannelIDs);
+
+            return generateComponentId.apply(request.toArray());
+        };
+
+        List<SelectOption> selectMenuRemoveOptions = pageEntries.stream().map(pageEntry -> {
+            ThreadChannel channel = jda.getThreadChannelById(pageEntry.bookmark.getChannelId());
+            String channelIDString = String.valueOf(pageEntry.bookmark.getChannelId());
+            int bookmarkNumber = pageEntry.bookmarkNumber;
+
+            String label = channel != null ? "%d. %s".formatted(bookmarkNumber, channel.getName())
+                    : "Delete bookmark %d".formatted(bookmarkNumber);
+
+            return SelectOption.of(label, channelIDString);
+        }).toList();
+
+        String selectMenuRemoveId = generateRemoveComponentId.apply(SELECT_MENU_REMOVE_NAME);
+        SelectMenu selectMenuRemove = SelectMenu.create(selectMenuRemoveId)
+            .setPlaceholder("Select bookmarks to delete")
+            .addOptions(selectMenuRemoveOptions)
+            .setDefaultValues(bookmarksToRemoveChannelIDs.stream().map(String::valueOf).toList())
+            .setRequiredRange(0, selectMenuRemoveOptions.size())
+            .build();
+
+        String buttonRemoveId = generateRemoveComponentId.apply(BUTTON_REMOVE_NAME);
+        Button buttonRemove = Button.danger(buttonRemoveId, BUTTON_REMOVE_LABEL)
+            .withDisabled(bookmarksToRemoveChannelIDs.isEmpty());
+
+        return List.of(ActionRow.of(selectMenuRemove), ActionRow.of(buttonRemove));
+    }
+
+    private static List<PageEntry> getPageEntries(List<? extends BookmarksRecord> bookmarks,
+            int pageIndex) {
+        int indexStart = pageIndex * ENTRIES_PER_PAGE;
+        int indexEndMax = bookmarks.size();
+        int indexEnd = Math.min(indexStart + ENTRIES_PER_PAGE, indexEndMax);
+
+        return bookmarks.subList(indexStart, indexEnd)
+            .stream()
+            .map(bookmark -> new PageEntry(bookmarks.indexOf(bookmark) + 1, bookmark))
+            .toList();
+    }
+
+    private static int getLastPageIndex(List<BookmarksRecord> bookmarks) {
+        if (bookmarks.isEmpty()) {
+            return 0;
+        }
+
+        return getPageOfBookmark(bookmarks.size() - 1);
+    }
+
+    private static int getPageOfBookmark(int bookmarkIndex) {
+        return Math.floorDiv(bookmarkIndex, ENTRIES_PER_PAGE);
+    }
+
+    private static int clampPageIndex(List<BookmarksRecord> bookmarks, int pageIndex) {
+        int maxPageIndex = getLastPageIndex(bookmarks);
+
+        return Math.min(Math.max(0, pageIndex), maxPageIndex);
+    }
+
+    private enum RequestType {
+        LIST,
+        REMOVE
+    }
+
+    private record PageEntry(int bookmarkNumber, BookmarksRecord bookmark) {
+    }
+
+    private record Request(RequestType type, String componentName, int pageToDisplayIndex,
+            Set<Long> bookmarkIdsToRemove) {
+        Request atPage(int pageIndex) {
+            return new Request(type, componentName, pageIndex, bookmarkIdsToRemove);
+        }
+
+        Request withSelectedBookmarksToRemove(Set<Long> selectedBookmarkIdsToRemove) {
+            return new Request(type, componentName, pageToDisplayIndex,
+                    selectedBookmarkIdsToRemove);
+        }
+
+        static Request fromArgs(List<String> args) {
+            RequestType requestType = RequestType.valueOf(args.get(0));
+            String componentName = args.get(1);
+            int currentPageIndex = Integer.parseInt(args.get(2));
+
+            Set<Long> bookmarkIdsToRemove = Set.of();
+            if (args.size() > 3) {
+                bookmarkIdsToRemove =
+                        args.stream().skip(3).map(Long::parseLong).collect(Collectors.toSet());
+            }
+
+            return new Request(requestType, componentName, currentPageIndex, bookmarkIdsToRemove);
+        }
+
+        String[] toArray() {
+            Stream<String> primaryArgs =
+                    Stream.of(type.name(), componentName, Integer.toString(pageToDisplayIndex));
+            Stream<String> secondaryArgs = bookmarkIdsToRemove.stream().map(String::valueOf);
+
+            return Stream.concat(primaryArgs, secondaryArgs).toArray(String[]::new);
+        }
+    }
+}
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksSystem.java b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksSystem.java
new file mode 100644
index 0000000000..4c2348f928
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/BookmarksSystem.java
@@ -0,0 +1,145 @@
+package org.togetherjava.tjbot.commands.bookmarks;
+
+import net.dv8tion.jda.api.EmbedBuilder;
+import net.dv8tion.jda.api.entities.MessageEmbed;
+import net.dv8tion.jda.api.entities.channel.ChannelType;
+import net.dv8tion.jda.api.entities.channel.concrete.ThreadChannel;
+import net.dv8tion.jda.api.entities.channel.unions.MessageChannelUnion;
+
+import org.togetherjava.tjbot.config.Config;
+import org.togetherjava.tjbot.db.Database;
+import org.togetherjava.tjbot.db.generated.tables.records.BookmarksRecord;
+
+import javax.annotation.Nullable;
+
+import java.awt.Color;
+import java.time.Duration;
+import java.time.Instant;
+import java.util.List;
+import java.util.Set;
+import java.util.function.Predicate;
+import java.util.regex.Pattern;
+
+import static org.togetherjava.tjbot.db.generated.tables.Bookmarks.BOOKMARKS;
+
+/**
+ * Maintains all bookmarks for all users and provides methods to create, query and remove them. Used
+ * by the other bookmarks classes.
+ */
+public final class BookmarksSystem {
+
+    static final int MAX_BOOKMARK_COUNT_TOTAL = 1_000_000;
+    static final int WARN_BOOKMARK_COUNT_TOTAL = 900_000;
+    static final int MAX_BOOKMARK_COUNT_PER_USER = 500;
+    static final int MAX_NOTE_LENGTH = 150;
+    private static final Duration REMOVE_BOOKMARKS_AFTER_LEAVE_DELAY = Duration.ofDays(7);
+
+    static final Color COLOR_SUCCESS = new Color(166, 218, 149);
+    static final Color COLOR_WARNING = new Color(245, 169, 127);
+    static final Color COLOR_FAILURE = new Color(238, 153, 160);
+
+    private final Database database;
+    private final Predicate<String> isOverviewChannelName;
+
+    /**
+     * Creates a new instance of the bookmarks system.
+     *
+     * @param config The {@link Config} to get the overview channel pattern
+     * @param database The {@link Database} to store and retrieve bookmarks
+     */
+    public BookmarksSystem(Config config, Database database) {
+        this.database = database;
+
+        isOverviewChannelName = Pattern.compile(config.getHelpSystem().getOverviewChannelPattern())
+            .asMatchPredicate();
+    }
+
+    boolean isHelpThread(MessageChannelUnion channel) {
+        if (channel.getType() != ChannelType.GUILD_PUBLIC_THREAD) {
+            return false;
+        }
+
+        ThreadChannel threadChannel = channel.asThreadChannel();
+        String parentChannelName = threadChannel.getParentMessageChannel().getName();
+
+        return isOverviewChannelName.test(parentChannelName);
+    }
+
+    boolean didUserBookmarkChannel(long userID, long channelID) {
+        return database.read(context -> context.selectFrom(BOOKMARKS)
+            .where(BOOKMARKS.AUTHOR_ID.eq(userID), BOOKMARKS.CHANNEL_ID.eq(channelID))
+            .limit(1)
+            .fetchOne() != null);
+    }
+
+    void addBookmark(long authorID, long channelID, @Nullable String note) {
+        database.write(context -> context.newRecord(BOOKMARKS)
+            .setAuthorId(authorID)
+            .setChannelId(channelID)
+            .setCreatedAt(Instant.now())
+            .setNote(note)
+            .setDeleteAt(null)
+            .insert());
+    }
+
+    List<BookmarksRecord> getUsersBookmarks(long authorID) {
+        return database.read(context -> context.selectFrom(BOOKMARKS)
+            .where(BOOKMARKS.AUTHOR_ID.eq(authorID))
+            .orderBy(BOOKMARKS.CREATED_AT.desc())
+            .fetch());
+    }
+
+    void removeBookmarks(long authorID, Set<Long> channelIDs) {
+        database.write(context -> context.deleteFrom(BOOKMARKS)
+            .where(BOOKMARKS.AUTHOR_ID.eq(authorID), BOOKMARKS.CHANNEL_ID.in(channelIDs))
+            .execute());
+    }
+
+    int getTotalBookmarkCount() {
+        return database.read(context -> context.fetchCount(BOOKMARKS));
+    }
+
+    int getUserBookmarkCount(long authorID) {
+        return database
+            .read(context -> context.fetchCount(BOOKMARKS, BOOKMARKS.AUTHOR_ID.eq(authorID)));
+    }
+
+    void startDeletionPeriodForUser(long authorID) {
+        Instant deleteAt = Instant.now().plus(REMOVE_BOOKMARKS_AFTER_LEAVE_DELAY);
+
+        database.write(context -> context.update(BOOKMARKS)
+            .set(BOOKMARKS.DELETE_AT, deleteAt)
+            .where(BOOKMARKS.AUTHOR_ID.eq(authorID))
+            .execute());
+    }
+
+    void cancelDeletionPeriodForUser(long authorID) {
+        database.write(context -> context.update(BOOKMARKS)
+            .setNull(BOOKMARKS.DELETE_AT)
+            .where(BOOKMARKS.AUTHOR_ID.eq(authorID))
+            .execute());
+    }
+
+    void deleteLeftoverBookmarks() {
+        database.write(context -> context.deleteFrom(BOOKMARKS)
+            .where(BOOKMARKS.DELETE_AT.isNotNull(), BOOKMARKS.DELETE_AT.lessThan(Instant.now()))
+            .execute());
+    }
+
+    private static MessageEmbed createColoredEmbed(String content, Color color) {
+        return new EmbedBuilder().setDescription(content).setColor(color).build();
+    }
+
+    static MessageEmbed createSuccessEmbed(String content) {
+        return createColoredEmbed(content, COLOR_SUCCESS);
+    }
+
+    static MessageEmbed createWarningEmbed(String content) {
+        return createColoredEmbed(content, COLOR_WARNING);
+    }
+
+    static MessageEmbed createFailureEmbed(String content) {
+        return createColoredEmbed(content, COLOR_FAILURE);
+    }
+
+}
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksCleanupRoutine.java b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksCleanupRoutine.java
new file mode 100644
index 0000000000..a680d84240
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksCleanupRoutine.java
@@ -0,0 +1,35 @@
+package org.togetherjava.tjbot.commands.bookmarks;
+
+import net.dv8tion.jda.api.JDA;
+
+import org.togetherjava.tjbot.commands.Routine;
+
+import java.util.concurrent.TimeUnit;
+
+/**
+ * Tells the bookmarks system to delete the old bookmarks of users that left the guild
+ */
+public final class LeftoverBookmarksCleanupRoutine implements Routine {
+
+    private final BookmarksSystem bookmarksSystem;
+
+    /**
+     * Creates a new instance.
+     *
+     * @param bookmarksSystem The {@link BookmarksSystem} to delete leftover bookmarks
+     */
+    public LeftoverBookmarksCleanupRoutine(BookmarksSystem bookmarksSystem) {
+        this.bookmarksSystem = bookmarksSystem;
+    }
+
+    @Override
+    public Schedule createSchedule() {
+        return new Schedule(ScheduleMode.FIXED_RATE, 0, 6, TimeUnit.HOURS);
+    }
+
+    @Override
+    public void runRoutine(JDA jda) {
+        bookmarksSystem.deleteLeftoverBookmarks();
+    }
+
+}
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksListener.java b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksListener.java
new file mode 100644
index 0000000000..b18f7ecb70
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/LeftoverBookmarksListener.java
@@ -0,0 +1,40 @@
+package org.togetherjava.tjbot.commands.bookmarks;
+
+import net.dv8tion.jda.api.events.guild.member.GuildMemberJoinEvent;
+import net.dv8tion.jda.api.events.guild.member.GuildMemberRemoveEvent;
+import net.dv8tion.jda.api.hooks.ListenerAdapter;
+import org.jetbrains.annotations.NotNull;
+
+import org.togetherjava.tjbot.commands.EventReceiver;
+
+/**
+ * Initiates the bookmarks deletion period for a user when leaving the guild. When the user rejoins
+ * the guild the deletion period will be canceled
+ */
+public final class LeftoverBookmarksListener extends ListenerAdapter implements EventReceiver {
+
+    private final BookmarksSystem bookmarksSystem;
+
+    /**
+     * Creates a new instance.
+     *
+     * @param bookmarksSystem The {@link BookmarksSystem} to start or cancel the deletion period
+     */
+    public LeftoverBookmarksListener(BookmarksSystem bookmarksSystem) {
+        this.bookmarksSystem = bookmarksSystem;
+    }
+
+    @Override
+    public void onGuildMemberRemove(@NotNull GuildMemberRemoveEvent event) {
+        long userID = event.getUser().getIdLong();
+
+        bookmarksSystem.startDeletionPeriodForUser(userID);
+    }
+
+    @Override
+    public void onGuildMemberJoin(@NotNull GuildMemberJoinEvent event) {
+        long userID = event.getUser().getIdLong();
+
+        bookmarksSystem.cancelDeletionPeriodForUser(userID);
+    }
+}
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/package-info.java b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/package-info.java
new file mode 100644
index 0000000000..8327cf37ab
--- /dev/null
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/bookmarks/package-info.java
@@ -0,0 +1,12 @@
+/**
+ * This package offers all functionality for maintaining bookmarks. For example commands that let
+ * users bookmark a help thread, such as
+ * {@link org.togetherjava.tjbot.commands.bookmarks.BookmarksCommand}.
+ */
+@MethodsReturnNonnullByDefault
+@ParametersAreNonnullByDefault
+package org.togetherjava.tjbot.commands.bookmarks;
+
+import org.togetherjava.tjbot.annotations.MethodsReturnNonnullByDefault;
+
+import javax.annotation.ParametersAreNonnullByDefault;
diff --git a/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java b/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java
index e763a48c96..36939cc097 100644
--- a/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java
+++ b/application/src/main/java/org/togetherjava/tjbot/commands/utils/MessageUtils.java
@@ -122,6 +122,19 @@ private static RestAction<String> mentionSlashCommand(
         });
     }
 
+    /**
+     * Converts the id of a channel to a mentioned channel, which you can directly click on in
+     * Discord.
+     *
+     * @param channelId the id of the channel to mention
+     * @return Formatted string for the mentioned channel
+     */
+    public static String mentionChannel(long channelId) {
+        // NOTE Hardcoded until JDA offers something like User.fromId(id).getAsMention() for
+        // channels as well
+        return "<#%d>".formatted(channelId);
+    }
+
     /**
      * Abbreviates the given text if it is too long.
      * <p>
diff --git a/application/src/main/resources/db/V12__Add_Bookmarks_System.sql b/application/src/main/resources/db/V12__Add_Bookmarks_System.sql
new file mode 100644
index 0000000000..c07a765648
--- /dev/null
+++ b/application/src/main/resources/db/V12__Add_Bookmarks_System.sql
@@ -0,0 +1,10 @@
+CREATE TABLE bookmarks
+(
+    author_id  BIGINT    NOT NULL,
+    channel_id BIGINT    NOT NULL,
+    created_at TIMESTAMP NOT NULL,
+    note       TEXT,
+    delete_at  TIMESTAMP,
+
+    PRIMARY KEY (author_id, channel_id)
+)