import { Disposable, Event, EventEmitter } from "vscode";

export interface PromiseAdapter<T, U> {
	(
		value: T,
		resolve:
			(value: U | PromiseLike<U>) => void,
		reject:
			(reason: any) => void
	): any;
}

const passthrough = (value: any, resolve: (value?: any) => void) => resolve(value);

/**
 * Return a promise that resolves with the next emitted event, or with some future
 * event as decided by an adapter.
 *
 * If specified, the adapter is a function that will be called with
 * `(event, resolve, reject)`. It will be called once per event until it resolves or
 * rejects.
 *
 * The default adapter is the passthrough function `(value, resolve) => resolve(value)`.
 *
 * @param event the event
 * @param adapter controls resolution of the returned promise
 * @returns a promise that resolves or rejects as specified by the adapter
 */
 export function promiseFromEvent<T, U>(event: Event<T>, adapter: PromiseAdapter<T, U> = passthrough): { promise: Promise<U>; cancel: EventEmitter<void> } {
	let subscription: Disposable;
	let cancel = new EventEmitter<void>();
  
	return {
		promise: new Promise<U>((resolve, reject) => {
			cancel.event(_ => reject('Cancelled'));
			subscription = event((value: T) => {
				try {
					Promise.resolve(adapter(value, resolve, reject))
						.catch(reject);
				} catch (error) {
					reject(error);
				}
			});
		}).then(
			(result: U) => {
				subscription.dispose();
				return result;
			},
			error => {
				subscription.dispose();
				throw error;
			}
		),
		cancel
	};
}