/**
 * 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 getDraftEditorSelectionWithNodes
 * @format
 * @flow
 */

'use strict';

import type { DOMDerivedSelection } from './DOMDerivedSelection';
import type EditorState from './EditorState';

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

type SelectionPoint = {
  key: string;
  offset: number;
};

/**
 * Convert the current selection range to an anchor/focus pair of offset keys
 * and values that can be interpreted by components.
 */
function getDraftEditorSelectionWithNodes(editorState: EditorState, root: ?HTMLElement, anchorNode: Node, anchorOffset: number, focusNode: Node, focusOffset: number): DOMDerivedSelection {
  var anchorIsTextNode = anchorNode.nodeType === Node.TEXT_NODE;
  var focusIsTextNode = focusNode.nodeType === Node.TEXT_NODE;

  // If the selection range lies only on text nodes, the task is simple.
  // Find the nearest offset-aware elements and use the
  // offset values supplied by the selection range.
  if (anchorIsTextNode && focusIsTextNode) {
    return {
      selectionState: getUpdatedSelectionState(editorState, nullthrows(findAncestorOffsetKey(anchorNode)), anchorOffset, nullthrows(findAncestorOffsetKey(focusNode)), focusOffset),
      needsRecovery: false
    };
  }

  var anchorPoint = null;
  var focusPoint = null;
  var needsRecovery = true;

  // An element is selected. Convert this selection range into leaf offset
  // keys and offset values for consumption at the component level. This
  // is common in Firefox, where select-all and triple click behavior leads
  // to entire elements being selected.
  //
  // Note that we use the `needsRecovery` parameter in the callback here. This
  // is because when certain elements are selected, the behavior for subsequent
  // cursor movement (e.g. via arrow keys) is uncertain and may not match
  // expectations at the component level. For example, if an entire <div> is
  // selected and the user presses the right arrow, Firefox keeps the selection
  // on the <div>. If we allow subsequent keypresses to insert characters
  // natively, they will be inserted into a browser-created text node to the
  // right of that <div>. This is obviously undesirable.
  //
  // With the `needsRecovery` flag, we inform the caller that it is responsible
  // for manually setting the selection state on the rendered document to
  // ensure proper selection state maintenance.

  if (anchorIsTextNode) {
    anchorPoint = {
      key: nullthrows(findAncestorOffsetKey(anchorNode)),
      offset: anchorOffset
    };
    focusPoint = getPointForNonTextNode(root, focusNode, focusOffset);
  } else if (focusIsTextNode) {
    focusPoint = {
      key: nullthrows(findAncestorOffsetKey(focusNode)),
      offset: focusOffset
    };
    anchorPoint = getPointForNonTextNode(root, anchorNode, anchorOffset);
  } else {
    anchorPoint = getPointForNonTextNode(root, anchorNode, anchorOffset);
    focusPoint = getPointForNonTextNode(root, focusNode, focusOffset);

    // If the selection is collapsed on an empty block, don't force recovery.
    // This way, on arrow key selection changes, the browser can move the
    // cursor from a non-zero offset on one block, through empty blocks,
    // to a matching non-zero offset on other text blocks.
    if (anchorNode === focusNode && anchorOffset === focusOffset) {
      needsRecovery = !!anchorNode.firstChild && anchorNode.firstChild.nodeName !== 'BR';
    }
  }

  return {
    selectionState: getUpdatedSelectionState(editorState, anchorPoint.key, anchorPoint.offset, focusPoint.key, focusPoint.offset),
    needsRecovery
  };
}

/**
 * Identify the first leaf descendant for the given node.
 */
function getFirstLeaf(node: any): Node {
  while (node.firstChild && (
  // data-blocks has no offset
  node.firstChild instanceof Element && node.firstChild.getAttribute('data-blocks') === 'true' || getSelectionOffsetKeyForNode(node.firstChild))) {
    node = node.firstChild;
  }
  return node;
}

/**
 * Identify the last leaf descendant for the given node.
 */
function getLastLeaf(node: any): Node {
  while (node.lastChild && (
  // data-blocks has no offset
  node.lastChild instanceof Element && node.lastChild.getAttribute('data-blocks') === 'true' || getSelectionOffsetKeyForNode(node.lastChild))) {
    node = node.lastChild;
  }
  return node;
}

function getPointForNonTextNode(editorRoot: ?HTMLElement, startNode: Node, childOffset: number): SelectionPoint {
  let node = startNode;
  var offsetKey: ?string = findAncestorOffsetKey(node);

  invariant(offsetKey != null || editorRoot && (editorRoot === node || editorRoot.firstChild === node), 'Unknown node in selection range.');

  // If the editorRoot is the selection, step downward into the content
  // wrapper.
  if (editorRoot === node) {
    node = node.firstChild;
    invariant(node instanceof Element && node.getAttribute('data-contents') === 'true', 'Invalid DraftEditorContents structure.');
    if (childOffset > 0) {
      childOffset = node.childNodes.length;
    }
  }

  // If the child offset is zero and we have an offset key, we're done.
  // If there's no offset key because the entire editor is selected,
  // find the leftmost ("first") leaf in the tree and use that as the offset
  // key.
  if (childOffset === 0) {
    var key: ?string = null;
    if (offsetKey != null) {
      key = offsetKey;
    } else {
      var firstLeaf = getFirstLeaf(node);
      key = nullthrows(getSelectionOffsetKeyForNode(firstLeaf));
    }
    return { key, offset: 0 };
  }

  var nodeBeforeCursor = node.childNodes[childOffset - 1];
  var leafKey: ?string = null;
  var textLength: ?number = null;

  if (!getSelectionOffsetKeyForNode(nodeBeforeCursor)) {
    // Our target node may be a leaf or a text node, in which case we're
    // already where we want to be and can just use the child's length as
    // our offset.
    leafKey = nullthrows(offsetKey);
    textLength = getTextContentLength(nodeBeforeCursor);
  } else {
    // Otherwise, we'll look at the child to the left of the cursor and find
    // the last leaf node in its subtree.
    var lastLeaf = getLastLeaf(nodeBeforeCursor);
    leafKey = nullthrows(getSelectionOffsetKeyForNode(lastLeaf));
    textLength = getTextContentLength(lastLeaf);
  }

  return {
    key: leafKey,
    offset: textLength
  };
}

/**
 * Return the length of a node's textContent, regarding single newline
 * characters as zero-length. This allows us to avoid problems with identifying
 * the correct selection offset for empty blocks in IE, in which we
 * render newlines instead of break tags.
 */
function getTextContentLength(node: Node): number {
  var textContent = node.textContent;
  return textContent === '\n' ? 0 : textContent.length;
}

module.exports = getDraftEditorSelectionWithNodes;