promises.ts

/*!
 * Copyright (c) Microsoft Corporation and contributors. All rights reserved.
 * Licensed under the MIT License.
 */

/**
 * A deferred creates a promise and the ability to resolve or reject it
 *
 * @deprecated Moved to the `@fluidframework/core-utils` package.
 * @internal
 */
export class Deferred<T> {
	private readonly p: Promise<T>;
	private res: ((value: T | PromiseLike<T>) => void) | undefined;
	private rej: ((reason?: any) => void) | undefined;
	private completed: boolean = false;

	constructor() {
		this.p = new Promise<T>((resolve, reject) => {
			this.res = resolve;
			this.rej = reject;
		});
	}
	/**
	 * Returns whether the underlying promise has been completed
	 */
	public get isCompleted(): boolean {
		return this.completed;
	}

	/**
	 * Retrieves the underlying promise for the deferred
	 *
	 * @returns the underlying promise
	 */
	public get promise(): Promise<T> {
		return this.p;
	}

	/**
	 * Resolves the promise
	 *
	 * @param value - the value to resolve the promise with
	 */
	public resolve(value: T | PromiseLike<T>): void {
		if (this.res !== undefined) {
			this.completed = true;
			this.res(value);
		}
	}

	/**
	 * Rejects the promise
	 *
	 * @param value - the value to reject the promise with
	 */
	public reject(error: any): void {
		if (this.rej !== undefined) {
			this.completed = true;
			this.rej(error);
		}
	}
}

/**
 * A lazy evaluated promise. The execute function is delayed until
 * the promise is used, e.g. await, then, catch ...
 * The execute function is only called once.
 * All calls are then proxied to the promise returned by the execute method.
 *
 * @deprecated Moved to the `@fluidframework/core-utils` package.
 * @internal
 */
export class LazyPromise<T> implements Promise<T> {
	public get [Symbol.toStringTag](): string {
		return this.getPromise()[Symbol.toStringTag];
	}

	private result: Promise<T> | undefined;

	constructor(private readonly execute: () => Promise<T>) {}

	// eslint-disable-next-line unicorn/no-thenable
	public async then<TResult1 = T, TResult2 = never>(
		// eslint-disable-next-line @rushstack/no-new-null
		onfulfilled?: ((value: T) => TResult1 | PromiseLike<TResult1>) | null | undefined,
		// eslint-disable-next-line @rushstack/no-new-null
		onrejected?: ((reason: any) => TResult2 | PromiseLike<TResult2>) | null | undefined,
	): Promise<TResult1 | TResult2> {
		// eslint-disable-next-line prefer-rest-params
		return this.getPromise().then<TResult1, TResult2>(...arguments);
	}

	public async catch<TResult = never>(
		// eslint-disable-next-line @rushstack/no-new-null
		onrejected?: ((reason: any) => TResult | PromiseLike<TResult>) | null | undefined,
	): Promise<T | TResult> {
		// eslint-disable-next-line prefer-rest-params
		return this.getPromise().catch<TResult>(...arguments);
	}

	// eslint-disable-next-line @rushstack/no-new-null
	public async finally(onfinally?: (() => void) | null | undefined): Promise<T> {
		// eslint-disable-next-line prefer-rest-params
		return this.getPromise().finally(...arguments);
	}

	private async getPromise(): Promise<T> {
		if (this.result === undefined) {
			this.result = this.execute();
		}
		return this.result;
	}
}