Imported Upstream version 4.6.0.125

Former-commit-id: a2155e9bd80020e49e72e86c44da02a8ac0e57a4

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

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+//------------------------------------------------------------------------------
+// <copyright file="precedingquery.cs" company="Microsoft">
+//     Copyright (c) Microsoft Corporation.  All rights reserved.
+// </copyright>                                                                
+// <owner current="true" primary="true">[....]</owner>
+//------------------------------------------------------------------------------
+
+namespace MS.Internal.Xml.XPath {
+    using System;
+    using System.Xml;
+    using System.Xml.XPath;
+    using System.Diagnostics;
+    using System.Collections.Generic;
+    using StackNav = ClonableStack<System.Xml.XPath.XPathNavigator>;
+
+    // Algorithm:
+    // Input assumption: qyInput is in DocOrder.
+    // Preceding of a sequence of nodes will be preceding of last node in DocOrder in that sequence.
+    // Because qyInput is in DO last input is last node in DO. -- "last"
+    // If last node is attribute or namespace move last to it element.
+    // Push this last node and all its ancestors into the ancestorStk. The root node will be the top-most element on the stack.
+    // Create descendent iterator from the root. -- "workIterator"
+    // Advancing workIterator we meet all nodes from the ancestorStk in stack order. Nodes in ancestorStk do no belong to the
+    // the 'preceding' axis and must be ignored.
+    // Last node in ancestorStk is a centinel node; when we pop it from ancestorStk, we should stop iterations.
+
+    internal sealed class PrecedingQuery : BaseAxisQuery {
+        private XPathNodeIterator workIterator;
+        private StackNav ancestorStk;
+
+        public PrecedingQuery(Query qyInput, string name, string prefix, XPathNodeType typeTest) : base(qyInput, name, prefix, typeTest) {
+            ancestorStk = new StackNav();
+        }
+        private PrecedingQuery(PrecedingQuery other) : base(other) {
+            this.workIterator = Clone(other.workIterator);
+            this.ancestorStk = other.ancestorStk.Clone();
+        }
+
+        public override void Reset() {
+            workIterator = null;
+            ancestorStk.Clear();
+            base.Reset();
+        }
+        
+        public override XPathNavigator Advance() {
+            if (workIterator == null) {
+                XPathNavigator last; {
+                    XPathNavigator input = qyInput.Advance();
+                    if (input == null) {
+                        return null;
+                    }
+                    last = input.Clone();
+                    do {
+                        last.MoveTo(input);
+                    } while ((input = qyInput.Advance()) != null);
+
+                    if (last.NodeType == XPathNodeType.Attribute || last.NodeType == XPathNodeType.Namespace) {
+                        last.MoveToParent();
+                    }
+                }
+                // Fill ancestorStk :
+                do {
+                    ancestorStk.Push(last.Clone());
+                } while (last.MoveToParent());
+                // Create workIterator :
+                // last.MoveToRoot(); We are on root already
+                workIterator = last.SelectDescendants(XPathNodeType.All, true);
+            } 
+            
+            while (workIterator.MoveNext()) {
+                currentNode = workIterator.Current;
+                if (currentNode.IsSamePosition(ancestorStk.Peek())) {
+                    ancestorStk.Pop();
+                    if (ancestorStk.Count == 0) {
+                        currentNode = null;
+                        workIterator = null;
+                        Debug.Assert(qyInput.Advance() == null, "we read all qyInput.Advance() already");
+                        return null;
+                    }
+                    continue;
+                }
+                if (matches(currentNode)) {
+                    position++;
+                    return currentNode;
+                }
+            }
+            Debug.Fail("Algorithm error: we missed the centinel node");
+            return null;
+        }
+
+        public override XPathNodeIterator Clone() { return new PrecedingQuery(this); }
+        public override QueryProps Properties { get { return base.Properties | QueryProps.Reverse; } }
+    }
+}
+