/********************************************************************************
 * Copyright (c) 2017-2021 TypeFox and others.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the Eclipse
 * Public License v. 2.0 are satisfied: GNU General Public License, version 2
 * with the GNU Classpath Exception which is available at
 * https://www.gnu.org/software/classpath/license.html.
 *
 * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
 ********************************************************************************/

/**
 * Simple implementation of the deferred pattern.
 * An object that exposes a promise and functions to resolve and reject it.
 */
export class Deferred<T> {
    resolve: (value?: T | PromiseLike<T>) => void;
    reject: (reason?: any) => void;
    readonly promise: Promise<T>;
    private _state: DeferredState = 'unresolved';


    constructor() {
        this.promise = new Promise<T>((resolve, reject) => {
            this.resolve = resolve;
            this.reject = reject;
        });
        this.promise.then(
            res => this._state = 'resolved',
            rej => this._state = 'rejected'
        );
    }

    private set state(state: DeferredState) {
        if (this._state === 'unresolved') {
            this._state = state;
        }
    }

    get state(): DeferredState {
        return this._state;
    }
}

export type DeferredState = 'resolved' | 'rejected' | 'unresolved';