import {
  isArray,
  isMaybeThenable
} from './utils';
import {
  noop,
  reject,
  fulfill,
  subscribe,
  FULFILLED,
  REJECTED,
  PENDING,
  getThen,
  handleMaybeThenable
} from './-internal';

import then from './then';
import Promise from './promise';
import originalResolve from './promise/resolve';
import originalThen from './then';
import { makePromise, PROMISE_ID } from './-internal';

function validationError() {
  return new Error('Array Methods must be provided an Array');
};

export default class Enumerator {
  constructor(Constructor, input) {
    this._instanceConstructor = Constructor;
    this.promise = new Constructor(noop);

    if (!this.promise[PROMISE_ID]) {
      makePromise(this.promise);
    }

    if (isArray(input)) {
      this.length     = input.length;
      this._remaining = input.length;

      this._result = new Array(this.length);

      if (this.length === 0) {
        fulfill(this.promise, this._result);
      } else {
        this.length = this.length || 0;
        this._enumerate(input);
        if (this._remaining === 0) {
          fulfill(this.promise, this._result);
        }
      }
    } else {
      reject(this.promise, validationError());
    }
  }
  _enumerate(input) {
    for (let i = 0; this._state === PENDING && i < input.length; i++) {
      this._eachEntry(input[i], i);
    }
  }

  _eachEntry(entry, i) {
    let c = this._instanceConstructor;
    let { resolve } = c;

    if (resolve === originalResolve) {
      let then = getThen(entry);

      if (then === originalThen &&
        entry._state !== PENDING) {
        this._settledAt(entry._state, i, entry._result);
      } else if (typeof then !== 'function') {
        this._remaining--;
        this._result[i] = entry;
      } else if (c === Promise) {
        let promise = new c(noop);
        handleMaybeThenable(promise, entry, then);
        this._willSettleAt(promise, i);
      } else {
        this._willSettleAt(new c(resolve => resolve(entry)), i);
      }
    } else {
      this._willSettleAt(resolve(entry), i);
    }
  }

  _settledAt(state, i, value) {
    let { promise } = this;

    if (promise._state === PENDING) {
      this._remaining--;

      if (state === REJECTED) {
        reject(promise, value);
      } else {
        this._result[i] = value;
      }
    }

    if (this._remaining === 0) {
      fulfill(promise, this._result);
    }
  }

  _willSettleAt(promise, i) {
    let enumerator = this;

    subscribe(
      promise, undefined,
      value => enumerator._settledAt(FULFILLED, i, value),
      reason => enumerator._settledAt(REJECTED, i, reason)
    );
  }
};