/**
 * 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 ReactDOMSelection
 */

"use strict";

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

/**
 * Get the appropriate anchor and focus node/offset pairs for IE.
 *
 * The catch here is that IE's selection API doesn't provide information
 * about whether the selection is forward or backward, so we have to
 * behave as though it's always forward.
 *
 * IE text differs from modern selection in that it behaves as though
 * block elements end with a new line. This means character offsets will
 * differ between the two APIs.
 *
 * @param {DOMElement} node
 * @return {object}
 */
function getIEOffsets(node) {
  var selection = document.selection;
  var selectedRange = selection.createRange();
  var selectedLength = selectedRange.text.length;

  // Duplicate selection so we can move range without breaking user selection.
  var fromStart = selectedRange.duplicate();
  fromStart.moveToElementText(node);
  fromStart.setEndPoint('EndToStart', selectedRange);

  var startOffset = fromStart.text.length;
  var endOffset = startOffset + selectedLength;

  return {
    start: startOffset,
    end: endOffset
  };
}

/**
 * @param {DOMElement} node
 * @return {?object}
 */
function getModernOffsets(node) {
  var selection = window.getSelection();

  if (selection.rangeCount === 0) {
    return null;
  }

  var anchorNode = selection.anchorNode;
  var anchorOffset = selection.anchorOffset;
  var focusNode = selection.focusNode;
  var focusOffset = selection.focusOffset;

  var currentRange = selection.getRangeAt(0);
  var rangeLength = currentRange.toString().length;

  var tempRange = currentRange.cloneRange();
  tempRange.selectNodeContents(node);
  tempRange.setEnd(currentRange.startContainer, currentRange.startOffset);

  var start = tempRange.toString().length;
  var end = start + rangeLength;

  // Detect whether the selection is backward.
  var detectionRange = document.createRange();
  detectionRange.setStart(anchorNode, anchorOffset);
  detectionRange.setEnd(focusNode, focusOffset);
  var isBackward = detectionRange.collapsed;
  detectionRange.detach();

  return {
    start: isBackward ? end : start,
    end: isBackward ? start : end
  };
}

/**
 * @param {DOMElement|DOMTextNode} node
 * @param {object} offsets
 */
function setIEOffsets(node, offsets) {
  var range = document.selection.createRange().duplicate();
  var start, end;

  if (typeof offsets.end === 'undefined') {
    start = offsets.start;
    end = start;
  } else if (offsets.start > offsets.end) {
    start = offsets.end;
    end = offsets.start;
  } else {
    start = offsets.start;
    end = offsets.end;
  }

  range.moveToElementText(node);
  range.moveStart('character', start);
  range.setEndPoint('EndToStart', range);
  range.moveEnd('character', end - start);
  range.select();
}

/**
 * In modern non-IE browsers, we can support both forward and backward
 * selections.
 *
 * Note: IE10+ supports the Selection object, but it does not support
 * the `extend` method, which means that even in modern IE, it's not possible
 * to programatically create a backward selection. Thus, for all IE
 * versions, we use the old IE API to create our selections.
 *
 * @param {DOMElement|DOMTextNode} node
 * @param {object} offsets
 */
function setModernOffsets(node, offsets) {
  var selection = window.getSelection();

  var length = node[getTextContentAccessor()].length;
  var start = Math.min(offsets.start, length);
  var end = typeof offsets.end === 'undefined' ?
    start : Math.min(offsets.end, length);

  var startMarker = getNodeForCharacterOffset(node, start);
  var endMarker = getNodeForCharacterOffset(node, end);

  if (startMarker && endMarker) {
    var range = document.createRange();
    range.setStart(startMarker.node, startMarker.offset);
    selection.removeAllRanges();
    selection.addRange(range);
    selection.extend(endMarker.node, endMarker.offset);
    range.detach();
  }
}

var ReactDOMSelection = {
  /**
   * @param {DOMElement} node
   */
  getOffsets: function(node) {
    var getOffsets = document.selection ? getIEOffsets : getModernOffsets;
    return getOffsets(node);
  },

  /**
   * @param {DOMElement|DOMTextNode} node
   * @param {object} offsets
   */
  setOffsets: function(node, offsets) {
    var setOffsets = document.selection ? setIEOffsets : setModernOffsets;
    setOffsets(node, offsets);
  }
};

module.exports = ReactDOMSelection;
