'use strict';

var clear    = require('es5-ext/array/#/clear')
  , assign   = require('es5-ext/object/assign')
  , callable = require('es5-ext/object/valid-callable')
  , value    = require('es5-ext/object/valid-value')
  , d        = require('d')
  , autoBind = require('d/auto-bind')
  , Symbol   = require('es6-symbol')

  , defineProperty = Object.defineProperty
  , defineProperties = Object.defineProperties
  , Iterator;

module.exports = Iterator = function (list, context) {
	if (!(this instanceof Iterator)) return new Iterator(list, context);
	defineProperties(this, {
		__list__: d('w', value(list)),
		__context__: d('w', context),
		__nextIndex__: d('w', 0)
	});
	if (!context) return;
	callable(context.on);
	context.on('_add', this._onAdd);
	context.on('_delete', this._onDelete);
	context.on('_clear', this._onClear);
};

defineProperties(Iterator.prototype, assign({
	constructor: d(Iterator),
	_next: d(function () {
		var i;
		if (!this.__list__) return;
		if (this.__redo__) {
			i = this.__redo__.shift();
			if (i !== undefined) return i;
		}
		if (this.__nextIndex__ < this.__list__.length) return this.__nextIndex__++;
		this._unBind();
	}),
	next: d(function () { return this._createResult(this._next()); }),
	_createResult: d(function (i) {
		if (i === undefined) return { done: true, value: undefined };
		return { done: false, value: this._resolve(i) };
	}),
	_resolve: d(function (i) { return this.__list__[i]; }),
	_unBind: d(function () {
		this.__list__ = null;
		delete this.__redo__;
		if (!this.__context__) return;
		this.__context__.off('_add', this._onAdd);
		this.__context__.off('_delete', this._onDelete);
		this.__context__.off('_clear', this._onClear);
		this.__context__ = null;
	}),
	toString: d(function () { return '[object Iterator]'; })
}, autoBind({
	_onAdd: d(function (index) {
		if (index >= this.__nextIndex__) return;
		++this.__nextIndex__;
		if (!this.__redo__) {
			defineProperty(this, '__redo__', d('c', [index]));
			return;
		}
		this.__redo__.forEach(function (redo, i) {
			if (redo >= index) this.__redo__[i] = ++redo;
		}, this);
		this.__redo__.push(index);
	}),
	_onDelete: d(function (index) {
		var i;
		if (index >= this.__nextIndex__) return;
		--this.__nextIndex__;
		if (!this.__redo__) return;
		i = this.__redo__.indexOf(index);
		if (i !== -1) this.__redo__.splice(i, 1);
		this.__redo__.forEach(function (redo, i) {
			if (redo > index) this.__redo__[i] = --redo;
		}, this);
	}),
	_onClear: d(function () {
		if (this.__redo__) clear.call(this.__redo__);
		this.__nextIndex__ = 0;
	})
})));

defineProperty(Iterator.prototype, Symbol.iterator, d(function () {
	return this;
}));
defineProperty(Iterator.prototype, Symbol.toStringTag, d('', 'Iterator'));