/**
 * 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 editOnInput
 * @format
 * @flow
 */

'use strict';

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

const DraftFeatureFlags = require('./DraftFeatureFlags');
var DraftModifier = require('./DraftModifier');
var DraftOffsetKey = require('./DraftOffsetKey');
var EditorState = require('./EditorState');
var UserAgent = require('fbjs/lib/UserAgent');

var findAncestorOffsetKey = require('./findAncestorOffsetKey');
var nullthrows = require('fbjs/lib/nullthrows');

var isGecko = UserAgent.isEngine('Gecko');

var DOUBLE_NEWLINE = '\n\n';

/**
 * This function is intended to handle spellcheck and autocorrect changes,
 * which occur in the DOM natively without any opportunity to observe or
 * interpret the changes before they occur.
 *
 * The `input` event fires in contentEditable elements reliably for non-IE
 * browsers, immediately after changes occur to the editor DOM. Since our other
 * handlers override or otherwise handle cover other varieties of text input,
 * the DOM state should match the model in all controlled input cases. Thus,
 * when an `input` change leads to a DOM/model mismatch, the change should be
 * due to a spellcheck change, and we can incorporate it into our model.
 */
function editOnInput(editor: DraftEditor): void {
  if (editor._pendingStateFromBeforeInput !== undefined) {
    editor.update(editor._pendingStateFromBeforeInput);
    editor._pendingStateFromBeforeInput = undefined;
  }

  var domSelection = global.getSelection();

  var { anchorNode, isCollapsed } = domSelection;
  const isNotTextNode = anchorNode.nodeType !== Node.TEXT_NODE;
  const isNotTextOrElementNode = anchorNode.nodeType !== Node.TEXT_NODE && anchorNode.nodeType !== Node.ELEMENT_NODE;

  if (DraftFeatureFlags.draft_killswitch_allow_nontextnodes) {
    if (isNotTextNode) {
      return;
    }
  } else {
    if (isNotTextOrElementNode) {
      // TODO: (t16149272) figure out context for this change
      return;
    }
  }

  if (anchorNode.nodeType === Node.TEXT_NODE && (anchorNode.previousSibling !== null || anchorNode.nextSibling !== null)) {
    // When typing at the beginning of a visual line, Chrome splits the text
    // nodes into two. Why? No one knows. This commit is suspicious:
    // https://chromium.googlesource.com/chromium/src/+/a3b600981286b135632371477f902214c55a1724
    // To work around, we'll merge the sibling text nodes back into this one.
    const span = anchorNode.parentNode;
    anchorNode.nodeValue = span.textContent;
    for (let child = span.firstChild; child !== null; child = child.nextSibling) {
      if (child !== anchorNode) {
        span.removeChild(child);
      }
    }
  }

  var domText = anchorNode.textContent;
  var editorState = editor._latestEditorState;
  var offsetKey = nullthrows(findAncestorOffsetKey(anchorNode));
  var { blockKey, decoratorKey, leafKey } = DraftOffsetKey.decode(offsetKey);

  var { start, end } = editorState.getBlockTree(blockKey).getIn([decoratorKey, 'leaves', leafKey]);

  var content = editorState.getCurrentContent();
  var block = content.getBlockForKey(blockKey);
  var modelText = block.getText().slice(start, end);

  // Special-case soft newlines here. If the DOM text ends in a soft newline,
  // we will have manually inserted an extra soft newline in DraftEditorLeaf.
  // We want to remove this extra newline for the purpose of our comparison
  // of DOM and model text.
  if (domText.endsWith(DOUBLE_NEWLINE)) {
    domText = domText.slice(0, -1);
  }

  // No change -- the DOM is up to date. Nothing to do here.
  if (domText === modelText) {
    // This can be buggy for some Android keyboards because they don't fire
    // standard onkeydown/pressed events and only fired editOnInput
    // so domText is already changed by the browser and ends up being equal
    // to modelText unexpectedly
    return;
  }

  var selection = editorState.getSelection();

  // We'll replace the entire leaf with the text content of the target.
  var targetRange = selection.merge({
    anchorOffset: start,
    focusOffset: end,
    isBackward: false
  });

  const entityKey = block.getEntityAt(start);
  const entity = entityKey && content.getEntity(entityKey);
  const entityType = entity && entity.getMutability();
  const preserveEntity = entityType === 'MUTABLE';

  // Immutable or segmented entities cannot properly be handled by the
  // default browser undo, so we have to use a different change type to
  // force using our internal undo method instead of falling through to the
  // native browser undo.
  const changeType = preserveEntity ? 'spellcheck-change' : 'apply-entity';

  const newContent = DraftModifier.replaceText(content, targetRange, domText, block.getInlineStyleAt(start), preserveEntity ? block.getEntityAt(start) : null);

  var anchorOffset, focusOffset, startOffset, endOffset;

  if (isGecko) {
    // Firefox selection does not change while the context menu is open, so
    // we preserve the anchor and focus values of the DOM selection.
    anchorOffset = domSelection.anchorOffset;
    focusOffset = domSelection.focusOffset;
    startOffset = start + Math.min(anchorOffset, focusOffset);
    endOffset = startOffset + Math.abs(anchorOffset - focusOffset);
    anchorOffset = startOffset;
    focusOffset = endOffset;
  } else {
    // Browsers other than Firefox may adjust DOM selection while the context
    // menu is open, and Safari autocorrect is prone to providing an inaccurate
    // DOM selection. Don't trust it. Instead, use our existing SelectionState
    // and adjust it based on the number of characters changed during the
    // mutation.
    var charDelta = domText.length - modelText.length;
    startOffset = selection.getStartOffset();
    endOffset = selection.getEndOffset();

    anchorOffset = isCollapsed ? endOffset + charDelta : startOffset;
    focusOffset = endOffset + charDelta;
  }

  // Segmented entities are completely or partially removed when their
  // text content changes. For this case we do not want any text to be selected
  // after the change, so we are not merging the selection.
  var contentWithAdjustedDOMSelection = newContent.merge({
    selectionBefore: content.getSelectionAfter(),
    selectionAfter: selection.merge({ anchorOffset, focusOffset })
  });

  editor.update(EditorState.push(editorState, contentWithAdjustedDOMSelection, changeType));
}

module.exports = editOnInput;