// Copyright (c) Microsoft Corporation. All rights reserved.
// Licensed under the MIT license. See LICENSE file in the project root for details.

import * as Q from "q";

/**
 * Utilities for working with promises.
 */
export class PromiseUtil {
    public forEach<T>(sourcesMaybePromise: Q.Promise<T[]> | T[], promiseGenerator: (source: T) => Q.Promise<void>): Q.Promise<void> {
        const sourcesPromise = <Q.Promise<T[]>>Q(sourcesMaybePromise);
        return Q(sourcesPromise).then(sources => {
            return Q.all(sources.map(source => {
                return promiseGenerator(source);
            })).then(() => { });
        });
    }

    /**
     * Retries an operation a given number of times. For each retry, a condition is checked.
     * If the condition is not satisfied after the maximum number of retries, and error is thrown.
     * Otherwise, the result of the operation is returned once the condition is satisfied.
     *
     * @param operation - the function to execute.
     * @param condition - the condition to check between iterations.
     * @param maxRetries - the maximum number of retries.
     * @param delay - time between iterations, in milliseconds.
     * @param failure - error description.
     */
    public retryAsync<T>(operation: () => Q.Promise<T>, condition: (result: T) => boolean | Q.Promise<boolean>, maxRetries: number, delay: number, failure: string): Q.Promise<T> {
        return this.retryAsyncIteration(operation, condition, maxRetries, 0, delay, failure);
    }

    public reduce<T>(sources: T[]|Q.Promise<T[]>, generateAsyncOperation: (value: T) => Q.Promise<void>): Q.Promise<void> {
        const promisedSources = <Q.Promise<T[]>>Q(sources);
        return promisedSources.then(resolvedSources => {
            return resolvedSources.reduce((previousReduction: Q.Promise<void>, newSource: T) => {
                return previousReduction.then(() => {
                    return generateAsyncOperation(newSource);
                });
            }, Q<void>(void 0));
        });
    }

    private retryAsyncIteration<T>(operation: () => Q.Promise<T>, condition: (result: T) => boolean | Q.Promise<boolean>, maxRetries: number, iteration: number, delay: number, failure: string): Q.Promise<T> {
        return operation()
            .then(result => {
                return Q(result).then(condition).then((conditionResult => {
                    if (conditionResult) {
                        return result;
                    }

                    if (iteration < maxRetries) {
                        return Q.delay(delay).then(() => this.retryAsyncIteration(operation, condition, maxRetries, iteration + 1, delay, failure));
                    }

                    throw new Error(failure);
                }));
            });
    }
}