accounts-frontend/packages/app/services/request/PromiseMiddlewareLayer.ts

import { Options } from './request';

type Action = 'catch' | 'then' | 'before';

export interface MiddlewareRequestOptions {
    url: string;
    options: Options;
}

export interface Middleware {
    before?: (options: MiddlewareRequestOptions) => Promise<MiddlewareRequestOptions>;
    then?: (resp: any, options: MiddlewareRequestOptions) => Promise<any>;
    catch?: (resp: any, options: MiddlewareRequestOptions, restart: () => Promise<any>) => Promise<any>;
}

/**
 * A class to handle middleware layer
 */
class PromiseMiddlewareLayer {
    private middlewares: Middleware[] = [];

    /**
     * Adds middleware into layer.
     *
     * `middleware` is an object, that may have multiple keys of type function.
     * Each key is a name of an action that may be passed through the layer. Each
     * function should return a Promise. An action with name catch has a special
     * meaning: it will be invoked as catch callback on Promise (for middlewares,
     * that should handle errors)
     *
     * @param {object} middleware
     */
    add(middleware: Middleware) {
        if (typeof middleware !== 'object') {
            throw new Error('A middleware must be an object');
        }

        if (!this.middlewares.some((mdware) => mdware === middleware)) {
            this.middlewares.push(middleware);
        }
    }

    /**
     * @param {string} action - the name of middleware's hook
     * @param {object} data - the initial data to pass through middlewares chain
     * @param {Function} restart - a function to restart current request (for `catch` hook)
     *
     * @returns {Promise}
     */
    run(
        action: 'before',
        options: MiddlewareRequestOptions,
        arg3?: never,
        arg4?: never,
    ): Promise<MiddlewareRequestOptions>;
    run(action: 'then', resp: any, options: MiddlewareRequestOptions, arg4?: never): Promise<any>;
    run(action: 'catch', resp: any, options: MiddlewareRequestOptions, restart: () => Promise<any>): Promise<any>;
    run(action: Action, data: any, ...rest: any) {
        const promiseMethod = action === 'catch' ? 'catch' : 'then';

        return this.middlewares
            .filter((middleware) => middleware[action])
            .reduce(
                (promise: Promise<any>, middleware) =>
                    invoke(promise, promiseMethod)((resp: any) => invoke(middleware, action)(resp, ...rest)),
                invoke(Promise, action === 'catch' ? 'reject' : 'resolve')(data),
            );
    }
}

function invoke(instance: Record<string, any>, method: string) {
    if (typeof instance[method] !== 'function') {
        throw new Error(`Can not invoke ${method} on ${instance}`);
    }

    return (...args: any) => instance[method](...args);
}

export default PromiseMiddlewareLayer;