/**
 * Copyright (c) 2013-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule DraftEditorCompositionHandler
 * @format
 * @flow
 */

'use strict';

import type DraftEditor from './DraftEditor.react';

const DraftFeatureFlags = require('./DraftFeatureFlags');
const DraftModifier = require('./DraftModifier');
const EditorState = require('./EditorState');
const Keys = require('fbjs/lib/Keys');

const getEntityKeyForSelection = require('./getEntityKeyForSelection');
const isEventHandled = require('./isEventHandled');
const isSelectionAtLeafStart = require('./isSelectionAtLeafStart');

/**
 * Millisecond delay to allow `compositionstart` to fire again upon
 * `compositionend`.
 *
 * This is used for Korean input to ensure that typing can continue without
 * the editor trying to render too quickly. More specifically, Safari 7.1+
 * triggers `compositionstart` a little slower than Chrome/FF, which
 * leads to composed characters being resolved and re-render occurring
 * sooner than we want.
 */
const RESOLVE_DELAY = 20;

/**
 * A handful of variables used to track the current composition and its
 * resolution status. These exist at the module level because it is not
 * possible to have compositions occurring in multiple editors simultaneously,
 * and it simplifies state management with respect to the DraftEditor component.
 */
let resolved = false;
let stillComposing = false;
let textInputData = '';

var DraftEditorCompositionHandler = {
  onBeforeInput: function (editor: DraftEditor, e: SyntheticInputEvent<>): void {
    textInputData = (textInputData || '') + e.data;
  },

  /**
   * A `compositionstart` event has fired while we're still in composition
   * mode. Continue the current composition session to prevent a re-render.
   */
  onCompositionStart: function (editor: DraftEditor): void {
    stillComposing = true;
  },

  /**
   * Attempt to end the current composition session.
   *
   * Defer handling because browser will still insert the chars into active
   * element after `compositionend`. If a `compositionstart` event fires
   * before `resolveComposition` executes, our composition session will
   * continue.
   *
   * The `resolved` flag is useful because certain IME interfaces fire the
   * `compositionend` event multiple times, thus queueing up multiple attempts
   * at handling the composition. Since handling the same composition event
   * twice could break the DOM, we only use the first event. Example: Arabic
   * Google Input Tools on Windows 8.1 fires `compositionend` three times.
   */
  onCompositionEnd: function (editor: DraftEditor): void {
    resolved = false;
    stillComposing = false;
    setTimeout(() => {
      if (!resolved) {
        DraftEditorCompositionHandler.resolveComposition(editor);
      }
    }, RESOLVE_DELAY);
  },

  /**
   * In Safari, keydown events may fire when committing compositions. If
   * the arrow keys are used to commit, prevent default so that the cursor
   * doesn't move, otherwise it will jump back noticeably on re-render.
   */
  onKeyDown: function (editor: DraftEditor, e: SyntheticKeyboardEvent<>): void {
    if (!stillComposing) {
      // If a keydown event is received after compositionend but before the
      // 20ms timer expires (ex: type option-E then backspace, or type A then
      // backspace in 2-Set Korean), we should immediately resolve the
      // composition and reinterpret the key press in edit mode.
      DraftEditorCompositionHandler.resolveComposition(editor);
      editor._onKeyDown(e);
      return;
    }
    if (e.which === Keys.RIGHT || e.which === Keys.LEFT) {
      e.preventDefault();
    }
  },

  /**
   * Keypress events may fire when committing compositions. In Firefox,
   * pressing RETURN commits the composition and inserts extra newline
   * characters that we do not want. `preventDefault` allows the composition
   * to be committed while preventing the extra characters.
   */
  onKeyPress: function (editor: DraftEditor, e: SyntheticKeyboardEvent<>): void {
    if (e.which === Keys.RETURN) {
      e.preventDefault();
    }
  },

  /**
   * Attempt to insert composed characters into the document.
   *
   * If we are still in a composition session, do nothing. Otherwise, insert
   * the characters into the document and terminate the composition session.
   *
   * If no characters were composed -- for instance, the user
   * deleted all composed characters and committed nothing new --
   * force a re-render. We also re-render when the composition occurs
   * at the beginning of a leaf, to ensure that if the browser has
   * created a new text node for the composition, we will discard it.
   *
   * Resetting innerHTML will move focus to the beginning of the editor,
   * so we update to force it back to the correct place.
   */
  resolveComposition: function (editor: DraftEditor): void {
    if (stillComposing) {
      return;
    }

    resolved = true;
    const composedChars = textInputData;
    textInputData = '';

    const editorState = EditorState.set(editor._latestEditorState, {
      inCompositionMode: false
    });

    const currentStyle = editorState.getCurrentInlineStyle();
    const entityKey = getEntityKeyForSelection(editorState.getCurrentContent(), editorState.getSelection());

    const mustReset = !composedChars || isSelectionAtLeafStart(editorState) || currentStyle.size > 0 || entityKey !== null;

    if (mustReset) {
      editor.restoreEditorDOM();
    }

    editor.exitCurrentMode();

    if (composedChars) {
      if (DraftFeatureFlags.draft_handlebeforeinput_composed_text && editor.props.handleBeforeInput && isEventHandled(editor.props.handleBeforeInput(composedChars, editorState))) {
        return;
      }
      // If characters have been composed, re-rendering with the update
      // is sufficient to reset the editor.
      const contentState = DraftModifier.replaceText(editorState.getCurrentContent(), editorState.getSelection(), composedChars, currentStyle, entityKey);
      editor.update(EditorState.push(editorState, contentState, 'insert-characters'));
      return;
    }

    if (mustReset) {
      editor.update(EditorState.set(editorState, {
        nativelyRenderedContent: null,
        forceSelection: true
      }));
    }
  }
};

module.exports = DraftEditorCompositionHandler;