nerdbank-streams/src/Deferred.ts

Multiplexing of streams

/**
 * A TaskCompletionSource-like class that allows promises to be resolved or rejected whenever.
 */
export class Deferred<T> {
	public readonly promise: Promise<T>
	private resolvePromise!: (value: T | PromiseLike<T>) => void
	private rejectPromise!: (reason?: any) => void
	private _isResolved: boolean = false
	private _isRejected: boolean = false
	private _error: any

	constructor(public state?: any) {
		this.promise = new Promise<T>((resolve, reject) => {
			this.resolvePromise = resolve
			this.rejectPromise = reject
		})
	}

	/**
	 * Gets a value indicating whether this promise has been completed.
	 */
	public get isCompleted() {
		return this._isResolved || this._isRejected
	}

	/**
	 * Gets a value indicating whether this promise is resolved.
	 */
	public get isResolved() {
		return this._isResolved
	}

	/**
	 * Gets a value indicating whether this promise is rejected.
	 */
	public get isRejected() {
		return this._isRejected
	}

	/**
	 * Gets the reason for promise rejection, if applicable.
	 */
	public get error() {
		return this._error
	}

	/**
	 * Resolves the promise.
	 * @param value The result of the promise.
	 */
	public resolve(value: T | PromiseLike<T>): boolean {
		if (this.isCompleted) {
			return false
		}

		this.resolvePromise(value)
		this._isResolved = true
		return true
	}

	/**
	 * Rejects the promise.
	 * @param reason The reason for rejecting the promise.
	 */
	public reject(reason?: any): boolean {
		if (this.isCompleted) {
			return false
		}

		this.rejectPromise(reason)
		this._error = reason
		this._isRejected = true
		return true
	}
}