ebemunk/node-uci

import Promise from 'bluebird'
import debug from 'debug'
import last from 'lodash/last'

import Engine from '../Engine'

const log = debug('uci:EngineChain')

const CHAINABLE = [
  'init',
  'setoption',
  'isready',
  'ucinewgame',
  'quit',
  'position',
  'go',
]

/**
 * EngineChain sets up an api to enable chaining when dealing with {@link Engine}s.
 * ##### chainable methods
 * - init
 * - setoption
 * - isready
 * - ucinewgame
 * - quit
 * - position
 * - go
 *
 * `go` is a special case that ends the chain by calling {@link #EngineChain#exec},
 * and returns the search result.
 * @param {Engine} engine - an {@link Engine} instance
 * @example
 * const engine = new Engine(enginePath)
 * const chain = new EngineChain(engine)
 * // OR: const chain = engine.chain()
 * .init()
 * .setoption('MultiPV', 3)
 * .position('r1bqkbnr/pppp1ppp/2n5/1B2p3/4P3/5N2/PPPP1PPP/RNBQK2R b KQkq - 3 3')
 * .go({depth: 15})
 * .then(result => {
 *   console.log('result', result)
 * })
 */
export default class EngineChain {
  /**
   * Creates a new EngineChain
   * @param {Engine} engine - an instance of {@link Engine}
   * @return {EngineChain} - a new instance
   */
  constructor(engine) {
    if (!engine || !(engine instanceof Engine))
      throw new Error('EngineChain requires a valid Engine.')
    //init
    log('chain init')
    this._engine = engine
    this._queue = []
    //construct chain functions
    CHAINABLE.forEach(funcName => {
      this[funcName] = this.chain(funcName)
    })
  }

  /**
   * Create a new function that puts its invocation to an internal queue.
   * This should not be called unless you're feeling very adventurous.
   * @param {string} funcName - the function to execute on an Engine instance
   * @return {function} - a function that will populate the queue
   * @private
   */
  //returns a function which puts the Engine call and args in the queue
  chain(funcName) {
    const self = this
    return function() {
      this._queue.push([::self._engine[funcName], [...arguments]])
      if (funcName === 'go') {
        return this.exec()
      } else {
        return this
      }
    }
  }

  /**
   * Execute each chained item serially. This ends the chain, and returns the
   * last return value from the {@link Engine}.
   * @return {any} - last return value from the queued {@link Engine} method
   */
  async exec() {
    const results = await Promise.mapSeries(this._queue, ([fn, params]) => {
      return fn(...params)
    })
    this._queue = []
    return last(results)
  }
}