mcs/class/referencesource/System.Xml/System/Xml/XPath/Internal/PrecedingQuery.cs

   1 //------------------------------------------------------------------------------
   2 // <copyright file="precedingquery.cs" company="Microsoft">
   3 //     Copyright (c) Microsoft Corporation.  All rights reserved.
   4 // </copyright>
   5 // <owner current="true" primary="true">Microsoft</owner>
   6 //------------------------------------------------------------------------------
   7
   8 namespace MS.Internal.Xml.XPath {
   9     using System;
  10     using System.Xml;
  11     using System.Xml.XPath;
  12     using System.Diagnostics;
  13     using System.Collections.Generic;
  14     using StackNav = ClonableStack<System.Xml.XPath.XPathNavigator>;
  15
  16     // Algorithm:
  17     // Input assumption: qyInput is in DocOrder.
  18     // Preceding of a sequence of nodes will be preceding of last node in DocOrder in that sequence.
  19     // Because qyInput is in DO last input is last node in DO. -- "last"
  20     // If last node is attribute or namespace move last to it element.
  21     // Push this last node and all its ancestors into the ancestorStk. The root node will be the top-most element on the stack.
  22     // Create descendent iterator from the root. -- "workIterator"
  23     // Advancing workIterator we meet all nodes from the ancestorStk in stack order. Nodes in ancestorStk do no belong to the
  24     // the 'preceding' axis and must be ignored.
  25     // Last node in ancestorStk is a centinel node; when we pop it from ancestorStk, we should stop iterations.
  26
  27     internal sealed class PrecedingQuery : BaseAxisQuery {
  28         private XPathNodeIterator workIterator;
  29         private StackNav ancestorStk;
  30
  31         public PrecedingQuery(Query qyInput, string name, string prefix, XPathNodeType typeTest) : base(qyInput, name, prefix, typeTest) {
  32             ancestorStk = new StackNav();
  33         }
  34         private PrecedingQuery(PrecedingQuery other) : base(other) {
  35             this.workIterator = Clone(other.workIterator);
  36             this.ancestorStk = other.ancestorStk.Clone();
  37         }
  38
  39         public override void Reset() {
  40             workIterator = null;
  41             ancestorStk.Clear();
  42             base.Reset();
  43         }
  44
  45         public override XPathNavigator Advance() {
  46             if (workIterator == null) {
  47                 XPathNavigator last; {
  48                     XPathNavigator input = qyInput.Advance();
  49                     if (input == null) {
  50                         return null;
  51                     }
  52                     last = input.Clone();
  53                     do {
  54                         last.MoveTo(input);
  55                     } while ((input = qyInput.Advance()) != null);
  56
  57                     if (last.NodeType == XPathNodeType.Attribute || last.NodeType == XPathNodeType.Namespace) {
  58                         last.MoveToParent();
  59                     }
  60                 }
  61                 // Fill ancestorStk :
  62                 do {
  63                     ancestorStk.Push(last.Clone());
  64                 } while (last.MoveToParent());
  65                 // Create workIterator :
  66                 // last.MoveToRoot(); We are on root already
  67                 workIterator = last.SelectDescendants(XPathNodeType.All, true);
  68             }
  69
  70             while (workIterator.MoveNext()) {
  71                 currentNode = workIterator.Current;
  72                 if (currentNode.IsSamePosition(ancestorStk.Peek())) {
  73                     ancestorStk.Pop();
  74                     if (ancestorStk.Count == 0) {
  75                         currentNode = null;
  76                         workIterator = null;
  77                         Debug.Assert(qyInput.Advance() == null, "we read all qyInput.Advance() already");
  78                         return null;
  79                     }
  80                     continue;
  81                 }
  82                 if (matches(currentNode)) {
  83                     position++;
  84                     return currentNode;
  85                 }
  86             }
  87             Debug.Fail("Algorithm error: we missed the centinel node");
  88             return null;
  89         }
  90
  91         public override XPathNodeIterator Clone() { return new PrecedingQuery(this); }
  92         public override QueryProps Properties { get { return base.Properties | QueryProps.Reverse; } }
  93     }
  94 }
  95