Add Discussions model and api (#279)

* Add Discussions model and API calls.

Author: filippobuletto

src/main/java/org/gitlab4j/api/MergeRequestApi.java

@@ -10,6 +10,7 @@
 
 import org.gitlab4j.api.GitLabApi.ApiVersion;
 import org.gitlab4j.api.models.Commit;
+import org.gitlab4j.api.models.Discussion;
 import org.gitlab4j.api.models.Issue;
 import org.gitlab4j.api.models.MergeRequest;
 import org.gitlab4j.api.models.MergeRequestFilter;
@@ -279,6 +280,44 @@ public Pager<Commit> getCommits(int projectId, int mergeRequestIid, int itemsPer
                 "projects", projectId, "merge_requests", mergeRequestIid, "commits"));
     }
 
+    /**
+     * Get a list of merge request discussions.
+     *
+     * <p>NOTE: GitLab API V4 uses IID (internal ID), V3 uses ID to identify the merge request.</p>
+     *
+     * GET /projects/:id/merge_requests/:merge_request_iid/discussions
+     *
+     * @param projectId the project ID for the merge request
+     * @param mergeRequestIid the internal ID of the merge request
+     * @param page the page to get
+     * @param perPage the number of commits per page
+     * @return a list containing the discussions for the specified merge request
+     * @throws GitLabApiException GitLabApiException if any exception occurs during execution
+     */
+    public List<Discussion> getDiscussions(int projectId, int mergeRequestIid, int page, int perPage) throws GitLabApiException {
+        Form formData = new GitLabApiForm().withParam("owned", false).withParam(PAGE_PARAM,  page).withParam(PER_PAGE_PARAM, perPage);
+        Response response = get(Response.Status.OK, formData.asMap(), "projects", projectId, "merge_requests", mergeRequestIid, "discussions");
+        return (response.readEntity(new GenericType<List<Discussion>>() {}));
+    }
+
+    /**
+     * Get a Pager of merge request discussions.
+     *
+     * <p>NOTE: GitLab API V4 uses IID (internal ID), V3 uses ID to identify the merge request.</p>
+     *
+     * GET /projects/:id/merge_requests/:merge_request_iid/discussions
+     *
+     * @param projectId the project ID for the merge request
+     * @param mergeRequestIid the internal ID of the merge request
+     * @param itemsPerPage the number of Commit instances that will be fetched per page
+     * @return a Pager containing the discussions for the specified merge request
+     * @throws GitLabApiException GitLabApiException if any exception occurs during execution
+     */
+    public Pager<Discussion> getDiscussions(int projectId, int mergeRequestIid, int itemsPerPage) throws GitLabApiException {
+        return (new Pager<Discussion>(this, Discussion.class, itemsPerPage, null,
+              "projects", projectId, "merge_requests", mergeRequestIid, "discussions"));
+    }
+
     /**
      * Creates a merge request and optionally assigns a reviewer to it.
      *

src/main/java/org/gitlab4j/api/models/Discussion.java

@@ -0,0 +1,48 @@
+package org.gitlab4j.api.models;
+
+import java.util.List;
+
+import javax.xml.bind.annotation.XmlAccessType;
+import javax.xml.bind.annotation.XmlAccessorType;
+import javax.xml.bind.annotation.XmlRootElement;
+
+import org.gitlab4j.api.utils.JacksonJson;
+
+@XmlRootElement
+@XmlAccessorType(XmlAccessType.FIELD)
+public class Discussion {
+
+  private String id;
+  private Boolean individualNote;
+  private List<Note> notes;
+
+  public String getId() {
+    return id;
+  }
+
+  public Boolean getIndividualNote() {
+    return individualNote;
+  }
+
+  public List<Note> getNotes() {
+    return notes;
+  }
+
+  public void setId(String id) {
+    this.id = id;
+  }
+
+  public void setIndividualNote(Boolean individualNote) {
+    this.individualNote = individualNote;
+  }
+
+  public void setNotes(List<Note> notes) {
+    this.notes = notes;
+  }
+
+  @Override
+  public String toString() {
+      return (JacksonJson.toJsonString(this));
+  }
+
+}

src/main/java/org/gitlab4j/api/models/Note.java

@@ -59,6 +59,27 @@ public String toString() {
         }
     }
 
+    public static enum Type {
+
+        DISCUSSION_NOTE, DIFF_NOTE;
+        private static JacksonJsonEnumHelper<Type> enumHelper = new JacksonJsonEnumHelper<>(Type.class, true, true);
+
+        @JsonCreator
+        public static Type forValue(String value) {
+            return enumHelper.forValue(value);
+        }
+
+        @JsonValue
+        public String toValue() {
+            return (enumHelper.toString(this));
+        }
+
+        @Override
+        public String toString() {
+            return (enumHelper.toString(this));
+        }
+    }
+
     private String attachment;
     private Author author;
     private String body;
@@ -74,6 +95,10 @@ public String toString() {
     private String title;
     private String updatedAt;
     private Boolean upvote;
+    private Boolean resolved;
+    private Boolean resolvable;
+    private Participant resolvedBy;
+    private Type type;
 
     public String getAttachment() {
         return attachment;
@@ -195,6 +220,38 @@ public void setUpvote(Boolean upvote) {
         this.upvote = upvote;
     }
 
+    public Boolean getResolved() {
+        return resolved;
+    }
+
+    public void setResolved(Boolean resolved) {
+        this.resolved = resolved;
+    }
+
+    public Boolean getResolvable() {
+        return resolvable;
+    }
+
+    public void setResolvable(Boolean resolvable) {
+        this.resolvable = resolvable;
+    }
+
+    public Participant getResolvedBy() {
+        return resolvedBy;
+    }
+
+    public void setResolvedBy(Participant resolvedBy) {
+        this.resolvedBy = resolvedBy;
+    }
+
+    public Type getType() {
+      return type;
+    }
+
+    public void setType(Type type) {
+      this.type = type;
+    }
+
     @Override
     public String toString() {
         return (JacksonJson.toJsonString(this));