var _ = require('../util')
var isObject = _.isObject
var textParser = require('../parsers/text')
var expParser = require('../parsers/expression')
var templateParser = require('../parsers/template')
var compile = require('../compiler/compile')
var transclude = require('../compiler/transclude')
var mergeOptions = require('../util/merge-option')
var uid = 0

module.exports = {

  /**
   * Setup.
   */

  bind: function () {
    // uid as a cache identifier
    this.id = '__v_repeat_' + (++uid)
    // we need to insert the objToArray converter
    // as the first read filter.
    if (!this.filters) {
      this.filters = {}
    }
    // add the object -> array convert filter
    var objectConverter = _.bind(objToArray, this)
    if (!this.filters.read) {
      this.filters.read = [objectConverter]
    } else {
      this.filters.read.unshift(objectConverter)
    }
    // setup ref node
    this.ref = document.createComment('v-repeat')
    _.replace(this.el, this.ref)
    // check if this is a block repeat
    this.template = this.el.tagName === 'TEMPLATE'
      ? templateParser.parse(this.el, true)
      : this.el
    // check other directives that need to be handled
    // at v-repeat level
    this.checkIf()
    this.checkRef()
    this.checkComponent()
    // check for trackby param
    this.idKey =
      this._checkParam('track-by') ||
      this._checkParam('trackby') // 0.11.0 compat
    // cache for primitive value instances
    this.cache = Object.create(null)
  },

  /**
   * Warn against v-if usage.
   */

  checkIf: function () {
    if (_.attr(this.el, 'if') !== null) {
      _.warn(
        'Don\'t use v-if with v-repeat. ' +
        'Use v-show or the "filterBy" filter instead.'
      )
    }
  },

  /**
   * Check if v-ref/ v-el is also present.
   */

  checkRef: function () {
    var childId = _.attr(this.el, 'ref')
    this.childId = childId
      ? this.vm.$interpolate(childId)
      : null
    var elId = _.attr(this.el, 'el')
    this.elId = elId
      ? this.vm.$interpolate(elId)
      : null
  },

  /**
   * Check the component constructor to use for repeated
   * instances. If static we resolve it now, otherwise it
   * needs to be resolved at build time with actual data.
   */

  checkComponent: function () {
    var id = _.attr(this.el, 'component')
    var options = this.vm.$options
    if (!id) {
      this.Ctor = _.Vue // default constructor
      this.inherit = true // inline repeats should inherit
      // important: transclude with no options, just
      // to ensure block start and block end
      this.template = transclude(this.template)
      this._linker = compile(this.template, options)
    } else {
      var tokens = textParser.parse(id)
      if (!tokens) { // static component
        var Ctor = this.Ctor = options.components[id]
        _.assertAsset(Ctor, 'component', id)
        if (Ctor) {
          // merge an empty object with owner vm as parent
          // so child vms can access parent assets.
          var merged = mergeOptions(
            Ctor.options,
            {},
            { $parent: this.vm }
          )
          this.template = transclude(this.template, merged)
          this._linker = compile(this.template, merged)
        }
      } else {
        // to be resolved later
        var ctorExp = textParser.tokensToExp(tokens)
        this.ctorGetter = expParser.parse(ctorExp).get
      }
    }
  },

  /**
   * Update.
   * This is called whenever the Array mutates.
   *
   * @param {Array} data
   */

  update: function (data) {
    if (typeof data === 'number') {
      data = range(data)
    }
    this.vms = this.diff(data || [], this.vms)
    // update v-ref
    if (this.childId) {
      this.vm.$[this.childId] = this.vms
    }
    if (this.elId) {
      this.vm.$$[this.elId] = this.vms.map(function (vm) {
        return vm.$el
      })
    }
  },

  /**
   * Diff, based on new data and old data, determine the
   * minimum amount of DOM manipulations needed to make the
   * DOM reflect the new data Array.
   *
   * The algorithm diffs the new data Array by storing a
   * hidden reference to an owner vm instance on previously
   * seen data. This allows us to achieve O(n) which is
   * better than a levenshtein distance based algorithm,
   * which is O(m * n).
   *
   * @param {Array} data
   * @param {Array} oldVms
   * @return {Array}
   */

  diff: function (data, oldVms) {
    var idKey = this.idKey
    var converted = this.converted
    var ref = this.ref
    var alias = this.arg
    var init = !oldVms
    var vms = new Array(data.length)
    var obj, raw, vm, i, l
    // First pass, go through the new Array and fill up
    // the new vms array. If a piece of data has a cached
    // instance for it, we reuse it. Otherwise build a new
    // instance.
    for (i = 0, l = data.length; i < l; i++) {
      obj = data[i]
      raw = converted ? obj.value : obj
      vm = !init && this.getVm(raw)
      if (vm) { // reusable instance
        vm._reused = true
        vm.$index = i // update $index
        if (converted) {
          vm.$key = obj.key // update $key
        }
        if (idKey) { // swap track by id data
          if (alias) {
            vm[alias] = raw
          } else {
            vm._setData(raw)
          }
        }
      } else { // new instance
        vm = this.build(obj, i)
        vm._new = true
      }
      vms[i] = vm
      // insert if this is first run
      if (init) {
        vm.$before(ref)
      }
    }
    // if this is the first run, we're done.
    if (init) {
      return vms
    }
    // Second pass, go through the old vm instances and
    // destroy those who are not reused (and remove them
    // from cache)
    for (i = 0, l = oldVms.length; i < l; i++) {
      vm = oldVms[i]
      if (!vm._reused) {
        this.uncacheVm(vm)
        vm.$destroy(true)
      }
    }
    // final pass, move/insert new instances into the
    // right place. We're going in reverse here because
    // insertBefore relies on the next sibling to be
    // resolved.
    var targetNext, currentNext
    i = vms.length
    while (i--) {
      vm = vms[i]
      // this is the vm that we should be in front of
      targetNext = vms[i + 1]
      if (!targetNext) {
        // This is the last item. If it's reused then
        // everything else will eventually be in the right
        // place, so no need to touch it. Otherwise, insert
        // it.
        if (!vm._reused) {
          vm.$before(ref)
        }
      } else {
        if (vm._reused) {
          // this is the vm we are actually in front of
          currentNext = findNextVm(vm, ref)
          // we only need to move if we are not in the right
          // place already.
          if (currentNext !== targetNext) {
            vm.$before(targetNext.$el, null, false)
          }
        } else {
          // new instance, insert to existing next
          vm.$before(targetNext.$el)
        }
      }
      vm._new = false
      vm._reused = false
    }
    return vms
  },

  /**
   * Build a new instance and cache it.
   *
   * @param {Object} data
   * @param {Number} index
   */

  build: function (data, index) {
    var original = data
    var meta = { $index: index }
    if (this.converted) {
      meta.$key = original.key
    }
    var raw = this.converted ? data.value : data
    var alias = this.arg
    var hasAlias = !isObject(raw) || alias
    // wrap the raw data with alias
    data = hasAlias ? {} : raw
    if (alias) {
      data[alias] = raw
    } else if (hasAlias) {
      meta.$value = raw
    }
    // resolve constructor
    var Ctor = this.Ctor || this.resolveCtor(data, meta)
    var vm = this.vm.$addChild({
      el: templateParser.clone(this.template),
      _linker: this._linker,
      _meta: meta,
      data: data,
      inherit: this.inherit
    }, Ctor)
    // cache instance
    this.cacheVm(raw, vm)
    return vm
  },

  /**
   * Resolve a contructor to use for an instance.
   * The tricky part here is that there could be dynamic
   * components depending on instance data.
   *
   * @param {Object} data
   * @param {Object} meta
   * @return {Function}
   */

  resolveCtor: function (data, meta) {
    // create a temporary context object and copy data
    // and meta properties onto it.
    // use _.define to avoid accidentally overwriting scope
    // properties.
    var context = Object.create(this.vm)
    var key
    for (key in data) {
      _.define(context, key, data[key])
    }
    for (key in meta) {
      _.define(context, key, meta[key])
    }
    var id = this.ctorGetter.call(context, context)
    var Ctor = this.vm.$options.components[id]
    _.assertAsset(Ctor, 'component', id)
    return Ctor
  },

  /**
   * Unbind, teardown everything
   */

  unbind: function () {
    if (this.childId) {
      delete this.vm.$[this.childId]
    }
    if (this.vms) {
      var i = this.vms.length
      var vm
      while (i--) {
        vm = this.vms[i]
        this.uncacheVm(vm)
        vm.$destroy()
      }
    }
  },

  /**
   * Cache a vm instance based on its data.
   *
   * If the data is an object, we save the vm's reference on
   * the data object as a hidden property. Otherwise we
   * cache them in an object and for each primitive value
   * there is an array in case there are duplicates.
   *
   * @param {Object} data
   * @param {Vue} vm
   */

  cacheVm: function (data, vm) {
    var idKey = this.idKey
    var cache = this.cache
    var id
    if (idKey) {
      id = data[idKey]
      if (!cache[id]) {
        cache[id] = vm
      } else {
        _.warn('Duplicate ID in v-repeat: ' + id)
      }
    } else if (isObject(data)) {
      id = this.id
      if (data.hasOwnProperty(id)) {
        if (data[id] === null) {
          data[id] = vm
        } else {
          _.warn(
            'Duplicate objects are not supported in v-repeat.'
          )
        }
      } else {
        _.define(data, this.id, vm)
      }
    } else {
      if (!cache[data]) {
        cache[data] = [vm]
      } else {
        cache[data].push(vm)
      }
    }
    vm._raw = data
  },

  /**
   * Try to get a cached instance from a piece of data.
   *
   * @param {Object} data
   * @return {Vue|undefined}
   */

  getVm: function (data) {
    if (this.idKey) {
      return this.cache[data[this.idKey]]
    } else if (isObject(data)) {
      return data[this.id]
    } else {
      var cached = this.cache[data]
      if (cached) {
        var i = 0
        var vm = cached[i]
        // since duplicated vm instances might be a reused
        // one OR a newly created one, we need to return the
        // first instance that is neither of these.
        while (vm && (vm._reused || vm._new)) {
          vm = cached[++i]
        }
        return vm
      }
    }
  },

  /**
   * Delete a cached vm instance.
   *
   * @param {Vue} vm
   */

  uncacheVm: function (vm) {
    var data = vm._raw
    if (this.idKey) {
      this.cache[data[this.idKey]] = null
    } else if (isObject(data)) {
      data[this.id] = null
      vm._raw = null
    } else {
      this.cache[data].pop()
    }
  }

}

/**
 * Helper to find the next element that is an instance
 * root node. This is necessary because a destroyed vm's
 * element could still be lingering in the DOM before its
 * leaving transition finishes, but its __vue__ reference
 * should have been removed so we can skip them.
 *
 * @param {Vue} vm
 * @param {CommentNode} ref
 * @return {Vue}
 */

function findNextVm (vm, ref) {
  var el = (vm._blockEnd || vm.$el).nextSibling
  while (!el.__vue__ && el !== ref) {
    el = el.nextSibling
  }
  return el.__vue__
}

/**
 * Attempt to convert non-Array objects to array.
 * This is the default filter installed to every v-repeat
 * directive.
 *
 * It will be called with **the directive** as `this`
 * context so that we can mark the repeat array as converted
 * from an object.
 *
 * @param {*} obj
 * @return {Array}
 * @private
 */

function objToArray (obj) {
  if (!_.isPlainObject(obj)) {
    return obj
  }
  var keys = Object.keys(obj)
  var i = keys.length
  var res = new Array(i)
  var key
  while (i--) {
    key = keys[i]
    res[i] = {
      key: key,
      value: obj[key]
    }
  }
  // `this` points to the repeat directive instance
  this.converted = true
  return res
}

/**
 * Create a range array from given number.
 *
 * @param {Number} n
 * @return {Array}
 */

function range (n) {
  var i = -1
  var ret = new Array(n)
  while (++i < n) {
    ret[i] = i
  }
  return ret
}