feat: add a common class to be used when dealing with selection logic (#2562)

* feat: add a common class to be used when dealing with selection logic

Adds the `MdSelectionModel` class that can be used when dealing with single and multiple selection within a component.

Relates to #2412.

* Refactor and simplify based on the feedback.

* Rename private method.

* Move the clearing logic to _select and shuffle the method order.

* Rename private methods.

src/lib/core/core.ts

@@ -72,6 +72,10 @@ export {
   LIVE_ANNOUNCER_ELEMENT_TOKEN,
   LIVE_ANNOUNCER_PROVIDER,
 } from './a11y/live-announcer';
+
+// Selection
+export * from './selection/selection';
+
 /** @deprecated */
 export {LiveAnnouncer as MdLiveAnnouncer} from './a11y/live-announcer';
 

src/lib/core/selection/selection.spec.ts

@@ -0,0 +1,172 @@
+import {SelectionModel} from './selection';
+
+
+describe('SelectionModel', () => {
+  describe('single selection', () => {
+    let model: SelectionModel<any>;
+
+    beforeEach(() => model = new SelectionModel());
+
+    it('should be able to select a single value', () => {
+      model.select(1);
+
+      expect(model.selected.length).toBe(1);
+      expect(model.isSelected(1)).toBe(true);
+    });
+
+    it('should deselect the previously selected value', () => {
+      model.select(1);
+      model.select(2);
+
+      expect(model.isSelected(1)).toBe(false);
+      expect(model.isSelected(2)).toBe(true);
+    });
+
+    it('should only preselect one value', () => {
+      model = new SelectionModel(false, [1, 2]);
+
+      expect(model.selected.length).toBe(1);
+      expect(model.isSelected(1)).toBe(true);
+      expect(model.isSelected(2)).toBe(false);
+    });
+  });
+
+  describe('multiple selection', () => {
+    let model: SelectionModel<any>;
+
+    beforeEach(() => model = new SelectionModel(true));
+
+    it('should be able to select multiple options at the same time', () => {
+      model.select(1);
+      model.select(2);
+
+      expect(model.selected.length).toBe(2);
+      expect(model.isSelected(1)).toBe(true);
+      expect(model.isSelected(2)).toBe(true);
+    });
+
+    it('should be able to preselect multiple options', () => {
+      model = new SelectionModel(true, [1, 2]);
+
+      expect(model.selected.length).toBe(2);
+      expect(model.isSelected(1)).toBe(true);
+      expect(model.isSelected(2)).toBe(true);
+    });
+  });
+
+  describe('onChange event', () => {
+    it('should return both the added and removed values', () => {
+      let model = new SelectionModel();
+      let spy = jasmine.createSpy('SelectionModel change event');
+
+      model.select(1);
+
+      model.onChange.subscribe(spy);
+
+      model.select(2);
+
+      let event = spy.calls.mostRecent().args[0];
+
+      expect(spy).toHaveBeenCalled();
+      expect(event.removed).toEqual([1]);
+      expect(event.added).toEqual([2]);
+    });
+
+    describe('selection', () => {
+      let model: SelectionModel<any>;
+      let spy: jasmine.Spy;
+
+      beforeEach(() => {
+        model = new SelectionModel(true);
+        spy = jasmine.createSpy('SelectionModel change event');
+
+        model.onChange.subscribe(spy);
+      });
+
+      it('should emit an event when a value is selected', () => {
+        model.select(1);
+
+        let event = spy.calls.mostRecent().args[0];
+
+        expect(spy).toHaveBeenCalled();
+        expect(event.added).toEqual([1]);
+        expect(event.removed).toEqual([]);
+      });
+
+      it('should not emit multiple events for the same value', () => {
+        model.select(1);
+        model.select(1);
+
+        expect(spy).toHaveBeenCalledTimes(1);
+      });
+
+      it('should not emit an event when preselecting values', () => {
+        model = new SelectionModel(false, [1]);
+        spy = jasmine.createSpy('SelectionModel initial change event');
+        model.onChange.subscribe(spy);
+
+        expect(spy).not.toHaveBeenCalled();
+      });
+    });
+
+    describe('deselection', () => {
+      let model: SelectionModel<any>;
+      let spy: jasmine.Spy;
+
+      beforeEach(() => {
+        model = new SelectionModel(true, [1, 2, 3]);
+        spy = jasmine.createSpy('SelectionModel change event');
+
+        model.onChange.subscribe(spy);
+      });
+
+      it('should emit an event when a value is deselected', () => {
+        model.deselect(1);
+
+        let event = spy.calls.mostRecent().args[0];
+
+        expect(spy).toHaveBeenCalled();
+        expect(event.removed).toEqual([1]);
+      });
+
+      it('should not emit an event when a non-selected value is deselected', () => {
+        model.deselect(4);
+        expect(spy).not.toHaveBeenCalled();
+      });
+
+      it('should emit a single event when clearing all of the selected options', () => {
+        model.clear();
+
+        let event = spy.calls.mostRecent().args[0];
+
+        expect(spy).toHaveBeenCalledTimes(1);
+        expect(event.removed).toEqual([1, 2, 3]);
+      });
+
+    });
+  });
+
+  it('should be able to determine whether it is empty', () => {
+    let model = new SelectionModel();
+
+    expect(model.isEmpty()).toBe(true);
+
+    model.select(1);
+
+    expect(model.isEmpty()).toBe(false);
+  });
+
+  it('should be able to clear the selected options', () => {
+    let model = new SelectionModel(true);
+
+    model.select(1);
+    model.select(2);
+
+    expect(model.selected.length).toBe(2);
+
+    model.clear();
+
+    expect(model.selected.length).toBe(0);
+    expect(model.isEmpty()).toBe(true);
+  });
+});

src/lib/core/selection/selection.ts

@@ -0,0 +1,130 @@
+import {Subject} from 'rxjs/Subject';
+
+
+/**
+ * Class to be used to power selecting one or more options from a list.
+ * @docs-private
+ */
+export class SelectionModel<T> {
+  /** Currently-selected values. */
+  private _selection: Set<T> = new Set();
+
+  /** Keeps track of the deselected options that haven't been emitted by the change event. */
+  private _deselectedToEmit: T[] = [];
+
+  /** Keeps track of the selected option that haven't been emitted by the change event. */
+  private _selectedToEmit: T[] = [];
+
+  /** Cache for the array value of the selected items. */
+  private _selected: T[];
+
+  /** Selected value(s). */
+  get selected(): T[] {
+    if (!this._selected) {
+      this._selected = Array.from(this._selection.values());
+    }
+
+    return this._selected;
+  }
+
+  /** Event emitted when the value has changed. */
+  onChange: Subject<SelectionChange<T>> = new Subject();
+
+  constructor(private _isMulti = false, initiallySelectedValues?: T[]) {
+    if (initiallySelectedValues) {
+      if (_isMulti) {
+        initiallySelectedValues.forEach(value => this._markSelected(value));
+      } else {
+        this._markSelected(initiallySelectedValues[0]);
+      }
+
+      // Clear the array in order to avoid firing the change event for preselected values.
+      this._selectedToEmit.length = 0;
+    }
+  }
+
+  /**
+   * Selects a value or an array of values.
+   */
+  select(value: T): void {
+    this._markSelected(value);
+    this._emitChangeEvent();
+  }
+
+  /**
+   * Deselects a value or an array of values.
+   */
+  deselect(value: T): void {
+    this._unmarkSelected(value);
+    this._emitChangeEvent();
+  }
+
+  /**
+   * Clears all of the selected values.
+   */
+  clear(): void {
+    this._unmarkAll();
+    this._emitChangeEvent();
+  }
+
+  /**
+   * Determines whether a value is selected.
+   */
+  isSelected(value: T): boolean {
+    return this._selection.has(value);
+  }
+
+  /**
+   * Determines whether the model has a value.
+   */
+  isEmpty(): boolean {
+    return this._selection.size === 0;
+  }
+
+  /** Emits a change event and clears the records of selected and deselected values. */
+  private _emitChangeEvent() {
+    if (this._selectedToEmit.length || this._deselectedToEmit.length) {
+      let eventData = new SelectionChange(this._selectedToEmit, this._deselectedToEmit);
+
+      this.onChange.next(eventData);
+      this._deselectedToEmit = [];
+      this._selectedToEmit = [];
+      this._selected = null;
+    }
+  }
+
+  /** Selects a value. */
+  private _markSelected(value: T) {
+    if (!this.isSelected(value)) {
+      if (!this._isMulti) {
+        this._unmarkAll();
+      }
+
+      this._selection.add(value);
+      this._selectedToEmit.push(value);
+    }
+  }
+
+   /** Deselects a value. */
+   private _unmarkSelected(value: T) {
+     if (this.isSelected(value)) {
+       this._selection.delete(value);
+       this._deselectedToEmit.push(value);
+     }
+   }
+
+  /** Clears out the selected values. */
+  private _unmarkAll() {
+    if (!this.isEmpty()) {
+      this._selection.forEach(value => this._unmarkSelected(value));
+    }
+  }
+}
+
+/**
+ * Describes an event emitted when the value of a MdSelectionModel has changed.
+ * @docs-private
+ */
+export class SelectionChange<T> {
+  constructor(public added?: T[], public removed?: T[]) { }
+}