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November 18, 2019 15:56
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| import throttle from 'lodash.throttle' | |
| const DEFAULT_HISTORY_CAPACITY = 50 | |
| const DEFAULT_PUSH_THROTTLE_TIMEOUT = 500 | |
| /** | |
| * The object defining the internal state of a History returned by | |
| * `History.getState`. | |
| * | |
| * @template T | |
| * @typedef {object} HistoryState | |
| * @property {number} index The index of the current value. | |
| * @property {T[]} values The values pushed so far. | |
| */ | |
| /** | |
| * The History object itself. | |
| * | |
| * @template T | |
| * @typedef {object} History | |
| * | |
| * @property {function(): HistoryState<T>} getState Get the current state of | |
| * the History. | |
| * | |
| * @property {function(T): void} push Push a value in the History. | |
| * This new value will also become the current one. | |
| * All values that comes after the current index will be lost. | |
| * If the capacity is exceeded the oldest value will be lost. | |
| * | |
| * @property {function(): T} previous Move one value backward and return it. | |
| * If the current value is the first one, this function is a nop. | |
| * | |
| * @property {function(): T} next Move one value forward and return it. | |
| * If the current value is the last one, this function is a nop. | |
| */ | |
| /** | |
| * Create a new History object. | |
| * | |
| * @template T | |
| * @param {T} initialValue The value to use to initialize the History. | |
| * @param {object} options | |
| * | |
| * @param {number} [options.capacity=DEFAULT_HISTORY_CAPACITY] The capacity of | |
| * the History (i.e. the maximum number of values it can keep). | |
| * | |
| * @param {number} [options.pushThrottle=DEFAULT_PUSH_THROTTLE_TIMEOUT] The | |
| * minimum amount of time between to values are pushed. | |
| * The pushed values are throttled to avoid spamming the History. | |
| * | |
| * @returns {History<T>} The History object. | |
| */ | |
| export function createHistory( | |
| initialValue, | |
| { | |
| capacity = DEFAULT_HISTORY_CAPACITY, | |
| pushThrottle = DEFAULT_PUSH_THROTTLE_TIMEOUT, | |
| } = {}, | |
| ) { | |
| let values = [initialValue] | |
| let index = 0 | |
| const push = throttle(value => { | |
| // The previously known futur is now lost. | |
| // We don't keep track of parallel universes. | |
| // GREAT SCOTT! | |
| if (index < values.length - 1) { | |
| values = values.slice(0, index + 1) | |
| } | |
| values = values.concat([value]) | |
| index = index + 1 | |
| if (values.length > capacity) { | |
| values = values.slice(1) | |
| index = index - 1 | |
| } | |
| }, pushThrottle) | |
| function previous() { | |
| // Make sure any previous `push` are ran before. | |
| push.flush() | |
| if (index > 0) { | |
| index = index - 1 | |
| } | |
| return values[index] | |
| } | |
| function next() { | |
| // Make sure any previous `push` are ran before. | |
| push.flush() | |
| if (index < values.length - 1) { | |
| index = index + 1 | |
| } | |
| return values[index] | |
| } | |
| function getState() { | |
| return { index, values } | |
| } | |
| return { push, previous, next, getState } | |
| } | |
| const MAC = | |
| typeof navigator !== `undefined` | |
| ? navigator.appVersion.indexOf('Mac') !== -1 | |
| : true | |
| const SHORTCUT_KEY = MAC ? 'metaKey' : 'ctrlKey' | |
| /** | |
| * Test whether a keyboard event is an undo event. | |
| * | |
| * @param {KeyboardEvent} event | |
| * @returns {boolean} | |
| */ | |
| export function isUndoEvent(event) { | |
| // cmd-z / ctrl-z | |
| return ( | |
| event[SHORTCUT_KEY] && event.key.toLowerCase() === 'z' && !event.shiftKey | |
| ) | |
| } | |
| /** | |
| * Test whether a keyboard event is a redo event. | |
| * | |
| * @param {KeyboardEvent} event | |
| * @returns {boolean} | |
| */ | |
| export function isRedoEvent(event) { | |
| const key = event.key.toLowerCase() | |
| return ( | |
| // cmd-shift-z / ctrl-shift-z | |
| (event[SHORTCUT_KEY] && event.shiftKey && key === 'z') || | |
| // cmd-y / ctrl-y | |
| (event[SHORTCUT_KEY] && key === 'y' && !event.shiftKey) | |
| ) | |
| } |
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