| 1 | // Copyright (c) Jupyter Development Team.
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| 2 | // Distributed under the terms of the Modified BSD License.
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| 3 | /*-----------------------------------------------------------------------------
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| 4 | | Copyright (c) 2014-2017, PhosphorJS Contributors
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| 5 | |
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| 6 | | Distributed under the terms of the BSD 3-Clause License.
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| 7 | |
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| 8 | | The full license is in the file LICENSE, distributed with this software.
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| 9 | |----------------------------------------------------------------------------*/
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| 10 | import { IIterator } from './iter';
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| 11 |
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| 12 | /**
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| 13 | * An object which can produce a reverse iterator over its values.
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| 14 | */
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| 15 | export interface IRetroable<T> {
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| 16 | /**
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| 17 | * Get a reverse iterator over the object's values.
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| 18 | *
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| 19 | * @returns An iterator which yields the object's values in reverse.
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| 20 | */
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| 21 | retro(): IIterator<T>;
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| 22 | }
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| 23 |
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| 24 | /**
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| 25 | * A type alias for a retroable or builtin array-like object.
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| 26 | */
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| 27 | export type RetroableOrArrayLike<T> = IRetroable<T> | ArrayLike<T>;
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| 28 |
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| 29 | /**
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| 30 | * Create an iterator for a retroable object.
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| 31 | *
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| 32 | * @param object - The retroable or array-like object of interest.
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| 33 | *
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| 34 | * @returns An iterator which traverses the object's values in reverse.
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| 35 | *
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| 36 | * #### Example
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| 37 | * ```typescript
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| 38 | * import { retro, toArray } from '@lumino/algorithm';
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| 39 | *
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| 40 | * let data = [1, 2, 3, 4, 5, 6];
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| 41 | *
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| 42 | * let stream = retro(data);
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| 43 | *
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| 44 | * toArray(stream); // [6, 5, 4, 3, 2, 1]
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| 45 | * ```
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| 46 | */
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| 47 | export function retro<T>(object: RetroableOrArrayLike<T>): IIterator<T> {
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| 48 | let it: IIterator<T>;
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| 49 | if (typeof (object as any).retro === 'function') {
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| 50 | it = (object as IRetroable<T>).retro();
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| 51 | } else {
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| 52 | it = new RetroArrayIterator<T>(object as ArrayLike<T>);
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| 53 | }
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| 54 | return it;
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| 55 | }
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| 56 |
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| 57 | /**
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| 58 | * An iterator which traverses an array-like object in reverse.
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| 59 | *
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| 60 | * #### Notes
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| 61 | * This iterator can be used for any builtin JS array-like object.
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| 62 | */
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| 63 | export class RetroArrayIterator<T> implements IIterator<T> {
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| 64 | /**
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| 65 | * Construct a new retro iterator.
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| 66 | *
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| 67 | * @param source - The array-like object of interest.
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| 68 | */
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| 69 | constructor(source: ArrayLike<T>) {
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| 70 | this._source = source;
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| 71 | this._index = source.length - 1;
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| 72 | }
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| 73 |
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| 74 | /**
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| 75 | * Get an iterator over the object's values.
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| 76 | *
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| 77 | * @returns An iterator which yields the object's values.
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| 78 | */
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| 79 | iter(): IIterator<T> {
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| 80 | return this;
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| 81 | }
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| 82 |
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| 83 | /**
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| 84 | * Create an independent clone of the iterator.
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| 85 | *
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| 86 | * @returns A new independent clone of the iterator.
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| 87 | */
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| 88 | clone(): IIterator<T> {
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| 89 | let result = new RetroArrayIterator<T>(this._source);
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| 90 | result._index = this._index;
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| 91 | return result;
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| 92 | }
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| 93 |
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| 94 | /**
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| 95 | * Get the next value from the iterator.
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| 96 | *
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| 97 | * @returns The next value from the iterator, or `undefined`.
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| 98 | */
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| 99 | next(): T | undefined {
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| 100 | if (this._index < 0 || this._index >= this._source.length) {
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| 101 | return undefined;
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| 102 | }
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| 103 | return this._source[this._index--];
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| 104 | }
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| 105 |
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| 106 | private _index: number;
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| 107 | private _source: ArrayLike<T>;
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| 108 | }
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