import Vue from '../instance/vue'
import config from '../config'
import {
  extend,
  set,
  isObject,
  isArray,
  isPlainObject,
  hasOwn,
  camelize,
  hyphenate
} from './lang'
import { warn } from './debug'
import { commonTagRE, reservedTagRE } from './component'

/**
 * Option overwriting strategies are functions that handle
 * how to merge a parent option value and a child option
 * value into the final value.
 *
 * All strategy functions follow the same signature:
 *
 * @param {*} parentVal
 * @param {*} childVal
 * @param {Vue} [vm]
 */

var strats = config.optionMergeStrategies = Object.create(null)

/**
 * Helper that recursively merges two data objects together.
 */

function mergeData (to, from) {
  var key, toVal, fromVal
  for (key in from) {
    toVal = to[key]
    fromVal = from[key]
    if (!hasOwn(to, key)) {
      set(to, key, fromVal)
    } else if (isObject(toVal) && isObject(fromVal)) {
      mergeData(toVal, fromVal)
    }
  }
  return to
}

/**
 * Data
 */

strats.data = function (parentVal, childVal, vm) {
  if (!vm) {
    // in a Vue.extend merge, both should be functions
    if (!childVal) {
      return parentVal
    }
    if (typeof childVal !== 'function') {
      process.env.NODE_ENV !== 'production' && warn(
        'The "data" option should be a function ' +
        'that returns a per-instance value in component ' +
        'definitions.',
        vm
      )
      return parentVal
    }
    if (!parentVal) {
      return childVal
    }
    // when parentVal & childVal are both present,
    // we need to return a function that returns the
    // merged result of both functions... no need to
    // check if parentVal is a function here because
    // it has to be a function to pass previous merges.
    return function mergedDataFn () {
      return mergeData(
        childVal.call(this),
        parentVal.call(this)
      )
    }
  } else if (parentVal || childVal) {
    return function mergedInstanceDataFn () {
      // instance merge
      var instanceData = typeof childVal === 'function'
        ? childVal.call(vm)
        : childVal
      var defaultData = typeof parentVal === 'function'
        ? parentVal.call(vm)
        : undefined
      if (instanceData) {
        return mergeData(instanceData, defaultData)
      } else {
        return defaultData
      }
    }
  }
}

/**
 * El
 */

strats.el = function (parentVal, childVal, vm) {
  if (!vm && childVal && typeof childVal !== 'function') {
    process.env.NODE_ENV !== 'production' && warn(
      'The "el" option should be a function ' +
      'that returns a per-instance value in component ' +
      'definitions.',
      vm
    )
    return
  }
  var ret = childVal || parentVal
  // invoke the element factory if this is instance merge
  return vm && typeof ret === 'function'
    ? ret.call(vm)
    : ret
}

/**
 * Hooks and param attributes are merged as arrays.
 */

strats.init =
strats.created =
strats.ready =
strats.attached =
strats.detached =
strats.beforeCompile =
strats.compiled =
strats.beforeDestroy =
strats.destroyed =
strats.activate = function (parentVal, childVal) {
  return childVal
    ? parentVal
      ? parentVal.concat(childVal)
      : isArray(childVal)
        ? childVal
        : [childVal]
    : parentVal
}

/**
 * Assets
 *
 * When a vm is present (instance creation), we need to do
 * a three-way merge between constructor options, instance
 * options and parent options.
 */

function mergeAssets (parentVal, childVal) {
  var res = Object.create(parentVal || null)
  return childVal
    ? extend(res, guardArrayAssets(childVal))
    : res
}

config._assetTypes.forEach(function (type) {
  strats[type + 's'] = mergeAssets
})

/**
 * Events & Watchers.
 *
 * Events & watchers hashes should not overwrite one
 * another, so we merge them as arrays.
 */

strats.watch =
strats.events = function (parentVal, childVal) {
  if (!childVal) return parentVal
  if (!parentVal) return childVal
  var ret = {}
  extend(ret, parentVal)
  for (var key in childVal) {
    var parent = ret[key]
    var child = childVal[key]
    if (parent && !isArray(parent)) {
      parent = [parent]
    }
    ret[key] = parent
      ? parent.concat(child)
      : [child]
  }
  return ret
}

/**
 * Other object hashes.
 */

strats.props =
strats.methods =
strats.computed = function (parentVal, childVal) {
  if (!childVal) return parentVal
  if (!parentVal) return childVal
  var ret = Object.create(null)
  extend(ret, parentVal)
  extend(ret, childVal)
  return ret
}

/**
 * Default strategy.
 */

var defaultStrat = function (parentVal, childVal) {
  return childVal === undefined
    ? parentVal
    : childVal
}

/**
 * Make sure component options get converted to actual
 * constructors.
 *
 * @param {Object} options
 */

function guardComponents (options) {
  if (options.components) {
    var components = options.components =
      guardArrayAssets(options.components)
    var ids = Object.keys(components)
    var def
    if (process.env.NODE_ENV !== 'production') {
      var map = options._componentNameMap = {}
    }
    for (var i = 0, l = ids.length; i < l; i++) {
      var key = ids[i]
      if (commonTagRE.test(key) || reservedTagRE.test(key)) {
        process.env.NODE_ENV !== 'production' && warn(
          'Do not use built-in or reserved HTML elements as component ' +
          'id: ' + key
        )
        continue
      }
      // record a all lowercase <-> kebab-case mapping for
      // possible custom element case error warning
      if (process.env.NODE_ENV !== 'production') {
        map[key.replace(/-/g, '').toLowerCase()] = hyphenate(key)
      }
      def = components[key]
      if (isPlainObject(def)) {
        components[key] = Vue.extend(def)
      }
    }
  }
}

/**
 * Ensure all props option syntax are normalized into the
 * Object-based format.
 *
 * @param {Object} options
 */

function guardProps (options) {
  var props = options.props
  var i, val
  if (isArray(props)) {
    options.props = {}
    i = props.length
    while (i--) {
      val = props[i]
      if (typeof val === 'string') {
        options.props[val] = null
      } else if (val.name) {
        options.props[val.name] = val
      }
    }
  } else if (isPlainObject(props)) {
    var keys = Object.keys(props)
    i = keys.length
    while (i--) {
      val = props[keys[i]]
      if (typeof val === 'function') {
        props[keys[i]] = { type: val }
      }
    }
  }
}

/**
 * Guard an Array-format assets option and converted it
 * into the key-value Object format.
 *
 * @param {Object|Array} assets
 * @return {Object}
 */

function guardArrayAssets (assets) {
  if (isArray(assets)) {
    var res = {}
    var i = assets.length
    var asset
    while (i--) {
      asset = assets[i]
      var id = typeof asset === 'function'
        ? ((asset.options && asset.options.name) || asset.id)
        : (asset.name || asset.id)
      if (!id) {
        process.env.NODE_ENV !== 'production' && warn(
          'Array-syntax assets must provide a "name" or "id" field.'
        )
      } else {
        res[id] = asset
      }
    }
    return res
  }
  return assets
}

/**
 * Merge two option objects into a new one.
 * Core utility used in both instantiation and inheritance.
 *
 * @param {Object} parent
 * @param {Object} child
 * @param {Vue} [vm] - if vm is present, indicates this is
 *                     an instantiation merge.
 */

export function mergeOptions (parent, child, vm) {
  guardComponents(child)
  guardProps(child)
  if (process.env.NODE_ENV !== 'production') {
    if (child.propsData && !vm) {
      warn('propsData can only be used as an instantiation option.')
    }
  }
  var options = {}
  var key
  if (child.extends) {
    parent = typeof child.extends === 'function'
      ? mergeOptions(parent, child.extends.options, vm)
      : mergeOptions(parent, child.extends, vm)
  }
  if (child.mixins) {
    for (var i = 0, l = child.mixins.length; i < l; i++) {
      parent = mergeOptions(parent, child.mixins[i], vm)
    }
  }
  for (key in parent) {
    mergeField(key)
  }
  for (key in child) {
    if (!hasOwn(parent, key)) {
      mergeField(key)
    }
  }
  function mergeField (key) {
    var strat = strats[key] || defaultStrat
    options[key] = strat(parent[key], child[key], vm, key)
  }
  return options
}

/**
 * Resolve an asset.
 * This function is used because child instances need access
 * to assets defined in its ancestor chain.
 *
 * @param {Object} options
 * @param {String} type
 * @param {String} id
 * @param {Boolean} warnMissing
 * @return {Object|Function}
 */

export function resolveAsset (options, type, id, warnMissing) {
  /* istanbul ignore if */
  if (typeof id !== 'string') {
    return
  }
  var assets = options[type]
  var camelizedId
  var res = assets[id] ||
    // camelCase ID
    assets[camelizedId = camelize(id)] ||
    // Pascal Case ID
    assets[camelizedId.charAt(0).toUpperCase() + camelizedId.slice(1)]
  if (process.env.NODE_ENV !== 'production' && warnMissing && !res) {
    warn(
      'Failed to resolve ' + type.slice(0, -1) + ': ' + id,
      options
    )
  }
  return res
}
