Adds an abstract date selection model (#13033)

This PR also includes a single date implementation of the selection model and the range implementation.

Author: roboshoes

src/lib/core/datetime/date-selection.ts

@@ -0,0 +1,156 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {DateAdapter} from '@angular/material/core';
+
+export abstract class MatDateSelection<D> {
+  constructor(protected readonly adapter: DateAdapter<D>) {}
+
+  abstract add(date: D): void;
+  abstract clone(): MatDateSelection<D>;
+  abstract getFirstSelectedDate(): D|null;
+  abstract getLastSelectedDate(): D|null;
+  abstract isComplete(): boolean;
+  abstract isSame(other: MatDateSelection<D>): boolean;
+  abstract isValid(): boolean;
+}
+
+export interface DateRange<D> {
+  start: D | null;
+  end: D | null;
+}
+
+/**
+ * Concrete implementation of a MatDateSelection that holds a single date.
+ */
+export class MatSingleDateSelection<D> extends MatDateSelection<D> {
+  private date: D | null = null;
+
+  constructor(adapter: DateAdapter<D>, date?: D | null) {
+    super(adapter);
+
+    if (date) {
+      this.date = date;
+    }
+  }
+
+  add(date: D) {
+    this.date = date;
+  }
+
+  clone(): MatDateSelection<D> {
+    const copy = new MatSingleDateSelection<D>(this.adapter);
+
+    if (this.date) {
+      copy.add(this.adapter.clone(this.date));
+    }
+
+    return copy as MatDateSelection<D>;
+  }
+
+  getFirstSelectedDate() { return this.date; }
+
+  getLastSelectedDate() { return this.date; }
+
+  isComplete() { return !!this.date; }
+
+  isSame(other: MatDateSelection<D>): boolean {
+    return other instanceof MatSingleDateSelection &&
+        this.adapter.sameDate(other.getFirstSelectedDate(), this.getFirstSelectedDate());
+  }
+
+  isValid(): boolean {
+    return !!(this.date && this.adapter.isValid(this.date));
+  }
+
+  asDate(): D | null {
+    return this.date;
+  }
+}
+
+/**
+ * Concrete implementation of a MatDateSelection that holds a date range, represented by
+ * a start date and an end date.
+ */
+export class MatRangeDateSelection<D> extends MatDateSelection<D> {
+  private start: D | null = null;
+  private end: D | null = null;
+
+  constructor(adapter: DateAdapter<D>, start?: D | null, end?: D | null) {
+    super(adapter);
+
+    if (start) {
+      this.start = start;
+    }
+
+    if (end) {
+      this.end = end;
+    }
+  }
+
+  /**
+   * Adds an additional date to the range. If no date is set thus far, it will set it to the
+   * beginning. If the beginning is set, it will set it to the end.
+   * If add is called on a complete selection, it will empty the selection and set it as the start.
+   */
+  add(date: D): void {
+    if (!this.start) {
+      this.start = date;
+    } else if (!this.end) {
+      this.end = date;
+    } else {
+      this.start = date;
+      this.end = null;
+    }
+  }
+
+
+  clone(): MatDateSelection<D> {
+    const copy = new MatRangeDateSelection<D>(this.adapter);
+
+    if (this.start) {
+      copy.setFirstSelectedDate(this.adapter.clone(this.start));
+    }
+
+    if (this.end) {
+      copy.setLastSelectedDate(this.adapter.clone(this.end));
+    }
+
+    return copy as MatDateSelection<D>;
+  }
+
+  getFirstSelectedDate() { return this.start; }
+
+  getLastSelectedDate() { return this.end; }
+
+  setFirstSelectedDate(value: D | null) { this.start = value; }
+
+  setLastSelectedDate(value: D | null) { this.end = value; }
+
+  isComplete(): boolean {
+    return !!(this.start && this.end);
+  }
+
+  isSame(other: MatDateSelection<D>): boolean {
+    return other instanceof MatRangeDateSelection &&
+        this.adapter.sameDate(this.getFirstSelectedDate(), other.getFirstSelectedDate()) &&
+        this.adapter.sameDate(this.getLastSelectedDate(), other.getLastSelectedDate());
+  }
+
+  isValid(): boolean {
+    return !!(this.start && this.end &&
+        this.adapter.isValid(this.start!) && this.adapter.isValid(this.end!));
+  }
+
+  asRange(): DateRange<D> {
+    return {
+      start: this.start,
+      end: this.end,
+    };
+  }
+}

src/lib/core/datetime/index.ts

@@ -17,6 +17,7 @@ export * from './date-adapter';
 export * from './date-formats';
 export * from './native-date-adapter';
 export * from './native-date-formats';
+export * from './date-selection';
 
 
 @NgModule({