Implement history helper and tests - #5508

src/vs/base/common/history.ts

@@ -0,0 +1,70 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import { ArraySet } from 'vs/base/common/set';
+import { INavigator, ArrayNavigator } from 'vs/base/common/iterator';
+
+export class HistoryNavigator<T> implements INavigator<T> {
+
+	private _history: ArraySet<T>;
+	private _limit: number;
+	private _navigator: ArrayNavigator<T>;
+
+	constructor(history: T[] = [], limit: number = 10) {
+		this._history = new ArraySet(history);
+		this._limit = limit;
+		this._onChange();
+	}
+
+	public add(t: T) {
+		this._history.set(t);
+		this._onChange();
+	}
+
+	public next(): T {
+		if (this._navigator.next()) {
+			return this._navigator.current();
+		}
+		this.last();
+		return null;
+	}
+
+	public previous(): T {
+		if (this._navigator.previous()) {
+			return this._navigator.current();
+		}
+		this.first();
+		return null;
+	}
+
+	public current(): T {
+		return this._navigator.current();
+	}
+
+	public parent(): T {
+		return null;
+	}
+
+	public first(): T {
+		return this._navigator.first();
+	}
+
+	public last(): T {
+		return this._navigator.last();
+	}
+
+	private _onChange() {
+		this._reduceToLimit();
+		this._navigator = new ArrayNavigator(this._history.elements);
+		this._navigator.last();
+	}
+
+	private _reduceToLimit() {
+		let data = this._history.elements;
+		if (data.length > this._limit) {
+			this._history = new ArraySet<T>(data.slice(data.length - this._limit));
+		}
+	}
+}

src/vs/base/test/common/history.test.ts

@@ -0,0 +1,114 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+'use strict';
+
+import * as assert from 'assert';
+import {HistoryNavigator} from 'vs/base/common/history';
+
+suite('History Navigator', () => {
+
+	test('create reduces the input to limit', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 2);
+
+		assert.deepEqual(['3', '4'], toArray(testObject));
+	});
+
+	test('create sets the position to last', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		assert.equal('4', testObject.current());
+		assert.equal(null, testObject.next());
+		assert.equal('3', testObject.previous());
+	});
+
+	test('last returns last element', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		testObject.first();
+
+		assert.equal('4', testObject.last());
+	});
+
+	test('first returns first element', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		assert.equal('2', testObject.first());
+	});
+
+	test('next returns next element', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		testObject.first();
+
+		assert.equal('3', testObject.next());
+		assert.equal('4', testObject.next());
+		assert.equal(null, testObject.next());
+	});
+
+	test('previous returns previous element', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		assert.equal('3', testObject.previous());
+		assert.equal('2', testObject.previous());
+		assert.equal(null, testObject.previous());
+	});
+
+	test('next on last element returs null and remains on last', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		testObject.first();
+		testObject.last();
+
+		assert.equal('4', testObject.current());
+		assert.equal(null, testObject.next());
+	});
+
+	test('previous on first element returs null and remains on first', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		testObject.first();
+
+		assert.equal('2', testObject.current());
+		assert.equal(null, testObject.previous());
+	});
+
+	test('add reduces the input to limit', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 2);
+
+		testObject.add('5');
+
+		assert.deepEqual(['4', '5'], toArray(testObject));
+	});
+
+	test('adding existing element changes the position', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 2);
+
+		testObject.add('2');
+
+		assert.deepEqual(['4', '2'], toArray(testObject));
+	});
+
+	test('add resets the navigator to last', function () {
+		let testObject = new HistoryNavigator(['1', '2', '3', '4'], 3);
+
+		testObject.first();
+		testObject.add('5');
+
+		assert.equal('5', testObject.current());
+		assert.equal(null, testObject.next());
+	});
+
+	function toArray(historyNavigator: HistoryNavigator<string>): string[] {
+		let result = [];
+		historyNavigator.first();
+		if (historyNavigator.current()) {
+			do {
+				result.push(historyNavigator.current());
+			} while (historyNavigator.next());
+		}
+		return result;
+	}
+});
+