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51 lines
1.7 KiB
51 lines
1.7 KiB
/**
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* RecentItems maintains a list of maxCount most recently added items.
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* If an existing item is added, it is moved to the end of the list.
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*
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* @constructor
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* @param {Int} options.maxCount - The maximum number of objects that will be maintained.
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* @param {Function} options.keyFunc - Function that returns a key identifying an item;
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* If an item is added with an existing key, it replaces the previous item in the list but is
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* moved to the end of the list. Defaults to the identity function.
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* @param {Array} options.intialItems - A list of items to populate the list on initialization
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*/
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class RecentItems {
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constructor(options) {
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this._items = new Map();
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this._maxCount = options.maxCount || 0;
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this._keyFunc = options.keyFunc || (item => item);
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if (options.intialItems) this.addItems(options.intialItems);
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}
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addItem(item) {
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// Map maintains entries in the order of insertion, so by deleting and reinserting an entry,
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// we move it to the end of the list.
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this._items.delete(this._keyFunc(item));
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this._items.set(this._keyFunc(item), item);
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// Now that the list is correctly ordered we may need to remove the oldest entry which is
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// the first item.
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if (this._items.size > this._maxCount && this._maxCount !== 0) {
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this._items.delete(this._items.keys().next().value);
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}
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}
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addItems(items) {
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items.forEach(item => {
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this.addItem(item);
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});
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}
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/**
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* Returns a list of the current items in the map. The list is starts with oldest
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* added item and ends with the most recently inserted.
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*
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* @returns {Array} A list of items.
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*/
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listItems() {
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return Array.from(this._items.values());
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}
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}
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module.exports = RecentItems;
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