GillesRasigade/pattern

'use strict';

const Command = require('./Command');

/**
 * @class Commands
 * @constructor
 *
 * @param {Object} [context=this] Future commands execution context
 * @param {Constructor} [CommandConstructor=Command] Constructor of the command
 *
 * @description
 *
 * Adding the commands capability to an object allows to access naturaly to the
 * undo, redo pattern.
 *
 * @example
 * const a = {
 *   sum: 0,
 *   incr() {
 *     this.sum++;
 *   },
 *   decr() {
 *     this.sum--;
 *   }
 * };
 *
 * const commands = new pattern.Commands(a);
 *
 * commands.execute('incr', [], 'decr', []);
 * console.log(`a.sum = ${a.sum}`); // a.sum = 1;
 *
 * commands.undo();
 * console.log(`a.sum = ${a.sum}`); // a.sum = 0;
 *
 * commands.redo();
 * console.log(`a.sum = ${a.sum}`); // a.sum = 1;
 */
class Commands {
  constructor(context = this, CommandConstructor = Command) {
    // Store the commands context:
    this.context = context;
    this.Command = CommandConstructor;

    // Initialize the empty history:
    this.history = [];

    // Current history index:
    this.index = -1;
  }

  /**
   * Push the command to the commands history.
   *
   * @param {Command} command - Undoable command
   * @return {Commands} Commands with updated history
   */
  pushHistory(command) {
    // Push the command to the history:
    this.index++;
    this.history = this.history.slice(0, this.index);
    this.history.push({ date: new Date(), command });

    return this;
  }

  /**
   * Execute the given command
   *
   * @example
   * // ...
   * commands.execute('incr', [], 'decr', []);
   *
   * @param {String} execute Method to execute on the given context
   * @param {Array} executeArguments List of arguments to apply on the method
   * @param {String} [undo] Method to apply for undo
   * @param {Array} [executeArguments] List of arguments to apply on the undo method
   */
  execute(execute, executeArguments, undo, undoArguments) {
    // Create the command to be executed:
    const command = new this.Command(this.context, execute, executeArguments, undo, undoArguments);

    const result = command.execute();

    // Push the command to the commands history:
    this.pushHistory(command);

    return result;
  }

  /**
   * Undo the last executed command if possible.
   * @see Command#undo
   */
  undo() {
    let result = null;
    // Get the last command from the history:
    if (this.history[this.index]) {
      const command = this.history[this.index].command;
      result = command.undo();
      this.index = this.index - 1;
    }

    return result;
  }

  /*
   * Redo the last reversed action
   */
  redo() {
    let result = null;
    const index = this.index + 1;
    if (this.history[index]) {
      const command = this.history[index].command;
      result = command.execute();
      this.index = index;
    }

    return result;
  }

  last() {
    if (this.history.length === 0) return null;

    return this.history[this.history.length - 1];
  }
}

module.exports = Commands;