import { ListWrapper } from 'angular2/src/facade/collection';
import { getSymbolIterator } from 'angular2/src/facade/lang';
import { EventEmitter } from 'angular2/src/facade/async';
/**
 * An unmodifiable list of items that Angular keeps up to date when the state
 * of the application changes.
 *
 * The type of object that {@link QueryMetadata} and {@link ViewQueryMetadata} provide.
 *
 * Implements an iterable interface, therefore it can be used in both ES6
 * javascript `for (var i of items)` loops as well as in Angular templates with
 * `*ngFor="#i of myList"`.
 *
 * Changes can be observed by subscribing to the changes `Observable`.
 *
 * NOTE: In the future this class will implement an `Observable` interface.
 *
 * ### Example ([live demo](http://plnkr.co/edit/RX8sJnQYl9FWuSCWme5z?p=preview))
 * ```typescript
 * @Component({...})
 * class Container {
 *   constructor(@Query(Item) items: QueryList<Item>) {
 *     items.changes.subscribe(_ => console.log(items.length));
 *   }
 * }
 * ```
 */
export class QueryList {
    constructor() {
        this._results = [];
        this._emitter = new EventEmitter();
    }
    get changes() { return this._emitter; }
    get length() { return this._results.length; }
    get first() { return ListWrapper.first(this._results); }
    get last() { return ListWrapper.last(this._results); }
    /**
     * returns a new array with the passed in function applied to each element.
     */
    map(fn) { return this._results.map(fn); }
    /**
     * returns a filtered array.
     */
    filter(fn) { return this._results.filter(fn); }
    /**
     * returns a reduced value.
     */
    reduce(fn, init) { return this._results.reduce(fn, init); }
    /**
     * converts QueryList into an array
     */
    toArray() { return ListWrapper.clone(this._results); }
    [getSymbolIterator()]() { return this._results[getSymbolIterator()](); }
    toString() { return this._results.toString(); }
    /**
     * @internal
     */
    reset(res) { this._results = res; }
    /** @internal */
    notifyOnChanges() { this._emitter.emit(this); }
}
