// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.

library trydart.selection;

import 'dart:html' show
    CharacterData,
    Element,
    Node,
    NodeFilter,
    Selection,
    Text,
    TreeWalker;

import 'shadow_root.dart' show
    WALKER_NEXT,
    WALKER_RETURN,
    walkNodes;

import 'decoration.dart';

class TrySelection {
  final Node root;
  Node anchorNode;
  int anchorOffset;

  String text;
  int globalOffset = -1;

  TrySelection(this.root, Selection selection)
      : anchorNode = isCollapsed(selection) ? selection.anchorNode : null,
        anchorOffset = isCollapsed(selection) ? selection.anchorOffset : -1;

  TrySelection.empty(this.root)
      : anchorNode = null,
        anchorOffset = -1;

  Text addNodeFromSubstring(int start,
                            int end,
                            List<Node> nodes,
                            [Decoration decoration]) {
    if (start == end) return null;

    Text textNode = new Text(text.substring(start, end));

    if (start <= globalOffset && globalOffset <= end) {
      anchorNode = textNode;
      anchorOffset = globalOffset - start;
    }

    nodes.add(decoration == null ? textNode : decoration.applyTo(textNode));

    return textNode;
  }

  void adjust(Selection selection) {
    if (anchorOffset >= 0) {
      selection.collapse(anchorNode, anchorOffset);
    }
  }

  void updateText(String newText) {
    text = newText;
    globalOffset = computeGlobalOffset(root, anchorNode, anchorOffset);
  }

  TrySelection copyWithRoot(Node root) {
    return new TrySelection.empty(root)
        ..anchorNode = anchorNode
        ..anchorOffset = anchorOffset;
  }

  /// Computes the global offset, that is, the offset from [root].
  static int computeGlobalOffset(Node root, Node anchorNode, int anchorOffset) {
    if (anchorOffset == -1) return -1;

    int offset = 0;
    bool found = false;
    walkNodes(root, (Node node) {
      if (anchorNode == node) {
        offset += anchorOffset;
        found = true;
        return WALKER_RETURN;
      }
      switch (node.nodeType) {
        case Node.CDATA_SECTION_NODE:
        case Node.TEXT_NODE:
          CharacterData text = node;
          offset += text.data.length;
          break;
      }
      return WALKER_NEXT;
    });
    return found ? offset : -1;
  }
}

bool isCollapsed(Selection selection) {
  // Firefox and Chrome don't agree on if the selection is collapsed if there
  // is no node selected.
  return selection.isCollapsed && selection.anchorNode != null;
}