/**
 * Copyright 2013 Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * @providesModule CompositionEventPlugin
 * @typechecks static-only
 */

"use strict";

var EventConstants = require('EventConstants');
var EventPropagators = require('EventPropagators');
var ExecutionEnvironment = require('ExecutionEnvironment');
var ReactInputSelection = require('ReactInputSelection');
var SyntheticCompositionEvent = require('SyntheticCompositionEvent');

var getTextContentAccessor = require('getTextContentAccessor');
var keyOf = require('keyOf');

var END_KEYCODES = [9, 13, 27, 32]; // Tab, Return, Esc, Space
var START_KEYCODE = 229;

var useCompositionEvent = ExecutionEnvironment.canUseDOM &&
  'CompositionEvent' in window;
var topLevelTypes = EventConstants.topLevelTypes;
var currentComposition = null;

// Events and their corresponding property names.
var eventTypes = {
  compositionEnd: {
    phasedRegistrationNames: {
      bubbled: keyOf({onCompositionEnd: null}),
      captured: keyOf({onCompositionEndCapture: null})
    }
  },
  compositionStart: {
    phasedRegistrationNames: {
      bubbled: keyOf({onCompositionStart: null}),
      captured: keyOf({onCompositionStartCapture: null})
    }
  },
  compositionUpdate: {
    phasedRegistrationNames: {
      bubbled: keyOf({onCompositionUpdate: null}),
      captured: keyOf({onCompositionUpdateCapture: null})
    }
  }
};

/**
 * Translate native top level events into event types.
 *
 * @param {string} topLevelType
 * @return {object}
 */
function getCompositionEventType(topLevelType) {
  switch (topLevelType) {
    case topLevelTypes.topCompositionStart:
      return eventTypes.compositionStart;
    case topLevelTypes.topCompositionEnd:
      return eventTypes.compositionEnd;
    case topLevelTypes.topCompositionUpdate:
      return eventTypes.compositionUpdate;
  }
}

/**
 * Does our fallback best-guess model think this event signifies that
 * composition has begun?
 *
 * @param {string} topLevelType
 * @param {object} nativeEvent
 * @return {boolean}
 */
function isFallbackStart(topLevelType, nativeEvent) {
  return (
    topLevelType === topLevelTypes.topKeyDown &&
    nativeEvent.keyCode === START_KEYCODE
  );
}

/**
 * Does our fallback mode think that this event is the end of composition?
 *
 * @param {string} topLevelType
 * @param {object} nativeEvent
 * @return {boolean}
 */
function isFallbackEnd(topLevelType, nativeEvent) {
  switch (topLevelType) {
    case topLevelTypes.topKeyUp:
      // Command keys insert or clear IME input.
      return (END_KEYCODES.indexOf(nativeEvent.keyCode) !== -1);
    case topLevelTypes.topKeyDown:
      // Expect IME keyCode on each keydown. If we get any other
      // code we must have exited earlier.
      return (nativeEvent.keyCode !== START_KEYCODE);
    case topLevelTypes.topKeyPress:
    case topLevelTypes.topMouseDown:
    case topLevelTypes.topBlur:
      // Events are not possible without cancelling IME.
      return true;
    default:
      return false;
  }
}

/**
 * Helper class stores information about selection and document state
 * so we can figure out what changed at a later date.
 *
 * @param {DOMEventTarget} root
 */
function FallbackCompositionState(root) {
  this.root = root;
  this.startSelection = ReactInputSelection.getSelection(root);
  this.startValue = this.getText();
}

/**
 * Get current text of input.
 *
 * @return {string}
 */
FallbackCompositionState.prototype.getText = function() {
  return this.root.value || this.root[getTextContentAccessor()];
};

/**
 * Text that has changed since the start of composition.
 *
 * @return {string}
 */
FallbackCompositionState.prototype.getData = function() {
  var endValue = this.getText();
  var prefixLength = this.startSelection.start;
  var suffixLength = this.startValue.length - this.startSelection.end;

  return endValue.substr(
    prefixLength,
    endValue.length - suffixLength - prefixLength
  );
};

/**
 * This plugin creates `onCompositionStart`, `onCompositionUpdate` and
 * `onCompositionEnd` events on inputs, textareas and contentEditable
 * nodes.
 */
var CompositionEventPlugin = {

  eventTypes: eventTypes,

  /**
   * @param {string} topLevelType Record from `EventConstants`.
   * @param {DOMEventTarget} topLevelTarget The listening component root node.
   * @param {string} topLevelTargetID ID of `topLevelTarget`.
   * @param {object} nativeEvent Native browser event.
   * @return {*} An accumulation of synthetic events.
   * @see {EventPluginHub.extractEvents}
   */
  extractEvents: function(
      topLevelType,
      topLevelTarget,
      topLevelTargetID,
      nativeEvent) {

    var eventType;
    var data;

    if (useCompositionEvent) {
      eventType = getCompositionEventType(topLevelType);
    } else if (!currentComposition) {
      if (isFallbackStart(topLevelType, nativeEvent)) {
        eventType = eventTypes.start;
        currentComposition = new FallbackCompositionState(topLevelTarget);
      }
    } else if (isFallbackEnd(topLevelType, nativeEvent)) {
      eventType = eventTypes.compositionEnd;
      data = currentComposition.getData();
      currentComposition = null;
    }

    if (eventType) {
      var event = SyntheticCompositionEvent.getPooled(
        eventType,
        topLevelTargetID,
        nativeEvent
      );
      if (data) {
        // Inject data generated from fallback path into the synthetic event.
        // This matches the property of native CompositionEventInterface.
        event.data = data;
      }
      EventPropagators.accumulateTwoPhaseDispatches(event);
      return event;
    }
  }
};

module.exports = CompositionEventPlugin;
