var _ = require('../util')
var queue = require('./queue')
var addClass = _.addClass
var removeClass = _.removeClass
var transitionEndEvent = _.transitionEndEvent
var animationEndEvent = _.animationEndEvent
var transDurationProp = _.transitionProp + 'Duration'
var animDurationProp = _.animationProp + 'Duration'
var doc = typeof document === 'undefined' ? null : document

var TYPE_TRANSITION = 1
var TYPE_ANIMATION = 2

/**
 * A Transition object that encapsulates the state and logic
 * of the transition.
 *
 * @param {Element} el
 * @param {String} id
 * @param {Object} hooks
 * @param {Vue} vm
 */

function Transition (el, id, hooks, vm) {
  this.el = el
  this.enterClass = id + '-enter'
  this.leaveClass = id + '-leave'
  this.hooks = hooks
  this.vm = vm
  // async state
  this.pendingCssEvent =
  this.pendingCssCb =
  this.jsCancel =
  this.pendingJsCb =
  this.op =
  this.cb = null
  this.typeCache = {}
  // bind
  var self = this
  ;['enterNextTick', 'enterDone', 'leaveNextTick', 'leaveDone']
    .forEach(function (m) {
      self[m] = _.bind(self[m], self)
    })
}

var p = Transition.prototype

/**
 * Start an entering transition.
 *
 * @param {Function} op - insert/show the element
 * @param {Function} [cb]
 */

p.enter = function (op, cb) {
  this.cancelPending()
  this.callHook('beforeEnter')
  this.cb = cb
  addClass(this.el, this.enterClass)
  op()
  this.callHookWithCb('enter')
  queue.push(this.enterNextTick)
}

/**
 * The "nextTick" phase of an entering transition, which is
 * to be pushed into a queue and executed after a reflow so
 * that removing the class can trigger a CSS transition.
 */

p.enterNextTick = function () {
  var type = this.getCssTransitionType(this.enterClass)
  var enterDone = this.enterDone
  if (type === TYPE_TRANSITION) {
    // trigger transition by removing enter class now
    removeClass(this.el, this.enterClass)
    this.setupCssCb(transitionEndEvent, enterDone)
  } else if (type === TYPE_ANIMATION) {
    this.setupCssCb(animationEndEvent, enterDone)
  } else if (!this.pendingJsCb) {
    enterDone()
  }
}

/**
 * The "cleanup" phase of an entering transition.
 */

p.enterDone = function () {
  this.jsCancel = this.pendingJsCb = null
  removeClass(this.el, this.enterClass)
  this.callHook('afterEnter')
  if (this.cb) this.cb()
}

/**
 * Start a leaving transition.
 *
 * @param {Function} op - remove/hide the element
 * @param {Function} [cb]
 */

p.leave = function (op, cb) {
  this.cancelPending()
  this.callHook('beforeLeave')
  this.op = op
  this.cb = cb
  addClass(this.el, this.leaveClass)
  this.callHookWithCb('leave')
  // only need to do leaveNextTick if there's no explicit
  // js callback
  if (!this.pendingJsCb) {
    queue.push(this.leaveNextTick)
  }
}

/**
 * The "nextTick" phase of a leaving transition.
 */

p.leaveNextTick = function () {
  var type = this.getCssTransitionType(this.leaveClass)
  if (type) {
    var event = type === TYPE_TRANSITION
      ? transitionEndEvent
      : animationEndEvent
    this.setupCssCb(event, this.leaveDone)
  } else {
    this.leaveDone()
  }
}

/**
 * The "cleanup" phase of a leaving transition.
 */

p.leaveDone = function () {
  this.op()
  removeClass(this.el, this.leaveClass)
  this.callHook('afterLeave')
  if (this.cb) this.cb()
}

/**
 * Cancel any pending callbacks from a previously running
 * but not finished transition.
 */

p.cancelPending = function () {
  this.op = this.cb = null
  var hasPending = false
  if (this.pendingCssCb) {
    hasPending = true
    _.off(this.el, this.pendingCssEvent, this.pendingCssCb)
    this.pendingCssEvent = this.pendingCssCb = null
  }
  if (this.pendingJsCb) {
    hasPending = true
    this.pendingJsCb.cancel()
    this.pendingJsCb = null
  }
  if (hasPending) {
    removeClass(this.el, this.enterClass)
    removeClass(this.el, this.leaveClass)
  }
  if (this.jsCancel) {
    this.jsCancel.call(null)
    this.jsCancel = null
  }
}

/**
 * Call a user-provided synchronous hook function.
 *
 * @param {String} type
 */

p.callHook = function (type) {
  if (this.hooks && this.hooks[type]) {
    this.hooks[type].call(this.vm, this.el)
  }
}

/**
 * Call a user-provided, potentially-async hook function.
 * We check for the length of arguments to see if the hook
 * expects a `done` callback. If true, the transition's end
 * will be determined by when the user calls that callback;
 * otherwise, the end is determined by the CSS transition or
 * animation.
 *
 * @param {String} type
 */

p.callHookWithCb = function (type) {
  var hook = this.hooks && this.hooks[type]
  if (hook) {
    if (hook.length > 1) {
      this.pendingJsCb = _.cancellable(this[type + 'Done'])
    }
    this.jsCancel = hook.call(this.vm, this.el, this.pendingJsCb)
  }
}

/**
 * Get an element's transition type based on the
 * calculated styles.
 *
 * @param {String} className
 * @return {Number}
 */

p.getCssTransitionType = function (className) {
  // skip CSS transitions if page is not visible -
  // this solves the issue of transitionend events not
  // firing until the page is visible again.
  // pageVisibility API is supported in IE10+, same as
  // CSS transitions.
  /* istanbul ignore if */
  if (!transitionEndEvent || (doc && doc.hidden)) {
    return
  }
  var type = this.typeCache[className]
  if (type) return type
  var inlineStyles = this.el.style
  var computedStyles = window.getComputedStyle(this.el)
  var transDuration =
    inlineStyles[transDurationProp] ||
    computedStyles[transDurationProp]
  if (transDuration && transDuration !== '0s') {
    type = TYPE_TRANSITION
  } else {
    var animDuration =
      inlineStyles[animDurationProp] ||
      computedStyles[animDurationProp]
    if (animDuration && animDuration !== '0s') {
      type = TYPE_ANIMATION
    }
  }
  if (type) {
    this.typeCache[className] = type
  }
  return type
}

/**
 * Setup a CSS transitionend/animationend callback.
 *
 * @param {String} event
 * @param {Function} cb
 */

p.setupCssCb = function (event, cb) {
  this.pendingCssEvent = event
  var self = this
  var el = this.el
  var onEnd = this.pendingCssCb = function (e) {
    if (e.target === el) {
      _.off(el, event, onEnd)
      self.pendingCssEvent = self.pendingCssCb = null
      if (!self.pendingJsCb && cb) {
        cb()
      }
    }
  }
  _.on(el, event, onEnd)
}

module.exports = Transition