spaghiajoeojo / express-beans

import { logger } from '@/core';

import {

  isError, Result, wrap,

} from '@/core/errors';

import { Task } from './Task';

const phases = {

  0: 'start',

  1: 'register',

  2: 'routing',

  3: 'init',

  4: 'run',

  5: 'exit',

} as const;

export type ExecutorPhase = typeof phases[keyof typeof phases];

type ExecutorEventMap = {

  [phase in ExecutorPhase]: [Result<void>[]];

} & {

  error: [Error];

};

class ExecutorImpl extends EventEmitter<ExecutorEventMap> {

  public readonly PHASES = phases;

  private tasks: Map<ExecutorPhase, Array<Task>> = new Map();

  private phasePromises: Map<ExecutorPhase, Promise<Result<void>[]>> = new Map();

  private started = false;

  execution: Promise<Result<void>[]> | null = null;

  private taskMap: Map<any, Task> = new Map();

  constructor() {

    super();

  }

  /**

 * Registers a task to be executed in a given phase.

 * @param task {() => Promise<void> | void} function to be executed, can return a Promise or void

 * @param phase {ExecutorPhase} phase in which the task should be executed

 */

  setExecution(phase: ExecutorPhase, taskFn: () => Promise<void> | void, contextKey?: any, order = 0) {

    let phaseTasks = this.tasks.get(phase) ?? [];

    const task = new Task({ task: taskFn, phase, order });

    if (contextKey) {

      this.taskMap.set(contextKey, task);

    }

    phaseTasks.push(task);

    this.tasks.set(phase, phaseTasks);

  }

  getTask(contextKey: any) {

    return this.taskMap.get(contextKey);

  }

  /**

 * Executes all registered tasks in a defined sequence based on phases.

 * Tasks are sorted by their phase index and executed concurrently within each phase.

 * Debug logs are generated for each phase indicating the number of tasks being executed.

 */

  async execute(): Promise<Result<void, Error>[]> {

    this.started = true;

    const phasesToExecute = Object.entries(phases)

      .filter(([, phase]) => phase !== 'exit')

      .map(([idx, phase]) => [Number(idx), phase] as const)

      .sort(([a], [b]) => a - b)

      .map(([, phase]) => phase);

    const results = [];

    for (const phase of phasesToExecute) {

      const result = await this.executePhase(phase);

      results.push(...result);

    }

    return results;

  }

  /**

   * Groups tasks by their execution order

   * @param tasks

   * @returns {{ [order: number]: (() => Promise<void> | void)[] }}}

   */

  private groupByOrder(tasks: Array<Task>): { [order: number]: (() => Promise<void> | void)[] } {

    return tasks.reduce((acc, taskObj) => {

      const { order, task } = taskObj;

      acc[order] = acc[order] ?? [];

      acc[order].push(task);

      return acc;

    }, {} as { [order: number]: (() => Promise<void> | void)[] });

  }

  /**

   * Executes all tasks in a given phase

   * @param phase {ExecutorPhase}

   * @returns {Promise<Result<void>[]>}

   */

  private async executePhase(phase: ExecutorPhase) {

    const tasksToExecute = this.tasks.get(phase) ?? [];

    logger.debug(`Executing phase ${phase} with ${tasksToExecute.length} tasks`);

    const groupedTasks = this.groupByOrder(tasksToExecute);

    const allResults: Result<void>[] = [];

    const sortedGroups = Object.entries(groupedTasks)

      .sort(([a], [b]) => Number(a) - Number(b));

    for (const [, tasks] of sortedGroups) {

      const wrappedTasks = tasks.map((task) => wrap(task));

      const groupResults = await Promise.all(wrappedTasks);

      allResults.push(...groupResults);

    }

    const processedResults = this.processPhaseResults(allResults, phase);

    const phasePromise = Promise.resolve(processedResults);

    this.phasePromises.set(phase, phasePromise);

    const result = await phasePromise;

    this.emit(phase, result);

    return result;

  }

  private processPhaseResults(results: Result<void>[], phase: ExecutorPhase): Result<void>[] {

    return results.map((result, index) => {

      if (isError(result)) {

        logger.error(new Error(`Task ${index} in phase ${phase} failed`, { cause: result.error }));

        this.emit('error', result.error);

      }

      return result;

    });

  }

  private async beforeExit() {

    await this.stopLifecycle();

  }

  private async gracefulShutdown() {

    logger.debug('Graceful shutdown');

    await this.stopLifecycle();

    logger.info('Graceful shutdown completed');

    process.exit(0);

  }

  /**

 * Starts the lifecycle of the ExpressBeans application.

 * If there are tasks to execute, they are executed in the defined sequence.

 * If execution is already in progress, the function does nothing.

 * @returns {void}

 */

  startLifecycle(): void {

    setImmediate(() => {

      if (this.started) {

        return;

      }

      logger.debug('Starting lifecycle');

      process.on('beforeExit', this.beforeExit.bind(this));

      process.on('SIGTERM', this.gracefulShutdown.bind(this));

      process.on('SIGINT', this.gracefulShutdown.bind(this));

      this.execution = this.execute();

    });

  }

  /**

 * Stops the lifecycle of the ExpressBeans application.

 * All tasks are cleared and the lifecycle is stopped.

 * USE ONLY IF YOU KNOW WHAT YOU ARE DOING

 * @returns {Promise<void>}

 */

  async stopLifecycle(): Promise<void> {

    logger.debug('Stopping lifecycle');

    await this.executePhase('exit').then(() => {

      this.phasePromises.clear();

      this.tasks.clear();

      this.started = false;

      this.execution = null;

      this.removeAllListeners();

      logger.debug('Lifecycle stopped');

      process.removeAllListeners();

    });

  }

}

type ExecutorType = typeof ExecutorImpl & ExecutorImpl;

let instance: ExecutorImpl | null = null;

function getInstance() {

  instance ??= new ExecutorImpl();

  return instance as ExecutorType;

}

export const Executor: ExecutorType = getInstance();