XPathScanner.cs source code in C# .NET

                        Code:
                         / FX-1434 / FX-1434 / 1.0 / untmp / whidbey / REDBITS / ndp / fx / src / Xml / System / Xml / XPath / Internal / XPathScanner.cs / 1 / XPathScanner.cs
                        
                        
                            //------------------------------------------------------------------------------ 
// 
//     Copyright (c) Microsoft Corporation.  All rights reserved.
// 
// [....] 
//-----------------------------------------------------------------------------
 
namespace MS.Internal.Xml.XPath { 
    using System;
    using System.Xml; 
    using System.Xml.XPath;
    using System.Diagnostics;
    using System.Globalization;
    using System.Text; 
    using System.Collections;
 
    internal sealed class XPathScanner { 
        private string  xpathExpr;
        private int     xpathExprIndex; 
        private LexKind kind;
        private char    currentChar;
        private string  name;
        private string  prefix; 
        private string  stringValue;
        private double  numberValue = double.NaN; 
        private bool    canBeFunction; 
        private XmlCharType xmlCharType = XmlCharType.Instance;
 
        public XPathScanner(string xpathExpr) {
            if (xpathExpr == null) {
                throw XPathException.Create(Res.Xp_ExprExpected, string.Empty);
            } 
            this.xpathExpr = xpathExpr;
 			NextChar(); 
            NextLex(); 
        }
 
        public string SourceText { get { return this.xpathExpr; } }

        private char CurerntChar { get { return currentChar; } }
 
        private bool NextChar() {
            Debug.Assert(0 <= xpathExprIndex && xpathExprIndex <= xpathExpr.Length); 
            if (xpathExprIndex < xpathExpr.Length) { 
				currentChar = xpathExpr[xpathExprIndex ++];
				return true; 
			}
 			else  {
				currentChar = '\0';
                return false; 
            }
        } 
 
        public LexKind Kind { get { return this.kind; } }
 
        public string Name {
            get {
                Debug.Assert(this.kind == LexKind.Name || this.kind == LexKind.Axe);
                Debug.Assert(this.name != null); 
                return this.name;
            } 
        } 

        public string Prefix { 
            get {
                Debug.Assert(this.kind == LexKind.Name);
                Debug.Assert(this.prefix != null);
                return this.prefix; 
            }
        } 
 
        public string StringValue {
            get { 
                Debug.Assert(this.kind == LexKind.String);
                Debug.Assert(this.stringValue != null);
                return this.stringValue;
            } 
        }
 
        public double NumberValue { 
            get {
                Debug.Assert(this.kind == LexKind.Number); 
                Debug.Assert(this.numberValue != double.NaN);
                return this.numberValue;
            }
        } 

        // To parse PathExpr we need a way to distinct name from function. 
        // THis distinction can't be done without context: "or (1 != 0)" this this a function or 'or' in OrExp 
        public bool CanBeFunction {
            get { 
                Debug.Assert(this.kind == LexKind.Name);
                return this.canBeFunction;
            }
        } 

        void SkipSpace() { 
            while (xmlCharType.IsWhiteSpace(this.CurerntChar) && NextChar()) ; 
        }
 
        public bool NextLex() {
            SkipSpace();
            switch (this.CurerntChar) {
            case '\0'  : 
                kind = LexKind.Eof;
                return false; 
            case ',': case '@': case '(': case ')': 
            case '|': case '*': case '[': case ']':
            case '+': case '-': case '=': case '#': 
            case '$':
                kind =  (LexKind) Convert.ToInt32(this.CurerntChar, CultureInfo.InvariantCulture);
                NextChar();
                break; 
            case '<':
                kind = LexKind.Lt; 
                NextChar(); 
                if (this.CurerntChar == '=') {
                    kind = LexKind.Le; 
                    NextChar();
                }
                break;
            case '>': 
                kind = LexKind.Gt;
                NextChar(); 
                if (this.CurerntChar == '=') { 
                    kind = LexKind.Ge;
                    NextChar(); 
                }
                break;
            case '!':
                kind = LexKind.Bang; 
                NextChar();
                if (this.CurerntChar == '=') { 
                    kind = LexKind.Ne; 
                    NextChar();
                } 
                break;
            case '.':
                kind = LexKind.Dot;
                NextChar(); 
                if (this.CurerntChar == '.') {
                    kind = LexKind.DotDot; 
                    NextChar(); 
                }
                else if (xmlCharType.IsDigit(this.CurerntChar)) { 
                    kind = LexKind.Number;
                    numberValue = ScanFraction();
                }
                break; 
            case '/':
                kind = LexKind.Slash; 
                NextChar(); 
                if (this.CurerntChar == '/') {
                    kind = LexKind.SlashSlash; 
                    NextChar();
                }
                break;
            case '"': 
            case '\'':
                this.kind = LexKind.String; 
                this.stringValue = ScanString(); 
                break;
            default: 
                if (xmlCharType.IsDigit(this.CurerntChar)) {
                    kind = LexKind.Number;
                    numberValue = ScanNumber();
                } 
                else if (xmlCharType.IsStartNCNameChar(this.CurerntChar)) {
                    kind = LexKind.Name; 
                    this.name   = ScanName(); 
                    this.prefix = string.Empty;
                    // "foo:bar" is one lexem not three because it doesn't allow spaces in between 
                    // We should distinct it from "foo::" and need process "foo ::" as well
                    if (this.CurerntChar == ':') {
                        NextChar();
                        // can be "foo:bar" or "foo::" 
                        if (this.CurerntChar == ':') {   // "foo::"
                            NextChar(); 
                            kind = LexKind.Axe; 
                        }
                        else {                          // "foo:*", "foo:bar" or "foo: " 
                            this.prefix = this.name;
                            if (this.CurerntChar == '*') {
 	                            NextChar();
                                this.name = "*"; 
                            }
                            else if (xmlCharType.IsStartNCNameChar(this.CurerntChar)) { 
                                this.name = ScanName(); 
                            }
                            else { 
                                throw XPathException.Create(Res.Xp_InvalidName, SourceText);
                            }
                        }
 
                    }
                    else { 
                        SkipSpace(); 
                        if (this.CurerntChar == ':') {
                            NextChar(); 
                            // it can be "foo ::" or just "foo :"
                            if (this.CurerntChar == ':') {
                                NextChar();
                                kind = LexKind.Axe; 
                            }
                            else { 
                                throw XPathException.Create(Res.Xp_InvalidName, SourceText); 
                            }
                        } 
                    }
                    SkipSpace();
                    this.canBeFunction = (this.CurerntChar == '(');
                } 
                else {
                    throw XPathException.Create(Res.Xp_InvalidToken, SourceText); 
                } 
 		        break;
            } 
            return true;
        }

        private double ScanNumber() { 
            Debug.Assert(this.CurerntChar == '.' || xmlCharType.IsDigit(this.CurerntChar));
            int start = xpathExprIndex - 1; 
			int len = 0; 
 			while (xmlCharType.IsDigit(this.CurerntChar)) {
				NextChar(); len ++; 
			}
            if (this.CurerntChar == '.') {
				NextChar(); len ++;
 				while (xmlCharType.IsDigit(this.CurerntChar)) { 
					NextChar(); len ++;
 				} 
            } 
 			return XmlConvert.ToXPathDouble(this.xpathExpr.Substring(start, len));
        } 

        private double ScanFraction() {
            Debug.Assert(xmlCharType.IsDigit(this.CurerntChar));
            int start = xpathExprIndex - 2; 
            Debug.Assert(0 <= start && this.xpathExpr[start] == '.');
			int len = 1; // '.' 
 			while (xmlCharType.IsDigit(this.CurerntChar)) { 
				NextChar(); len ++;
			} 
			return XmlConvert.ToXPathDouble(this.xpathExpr.Substring(start, len));
        }

        private string ScanString() { 
            char endChar = this.CurerntChar;
            NextChar(); 
            int start = xpathExprIndex - 1; 
 			int len = 0;
            while(this.CurerntChar != endChar) { 
				if (! NextChar()) {
 	                throw XPathException.Create(Res.Xp_UnclosedString);
 				}
				len ++; 
 			}
            Debug.Assert(this.CurerntChar == endChar); 
            NextChar(); 
            return this.xpathExpr.Substring(start, len);
        } 

        private string ScanName() {
            Debug.Assert(xmlCharType.IsStartNCNameChar(this.CurerntChar));
            int start = xpathExprIndex - 1; 
			int len = 0;
            while (xmlCharType.IsNCNameChar(this.CurerntChar)) { 
				NextChar(); len ++; 
			}
            return this.xpathExpr.Substring(start, len); 
        }

        public enum LexKind  {
            Comma                 = ',', 
            Slash                 = '/',
            At                    = '@', 
            Dot                   = '.', 
            LParens               = '(',
            RParens               = ')', 
            LBracket              = '[',
            RBracket              = ']',
            Star                  = '*',
            Plus                  = '+', 
            Minus                 = '-',
            Eq                    = '=', 
            Lt                    = '<', 
            Gt                    = '>',
            Bang                  = '!', 
            Dollar                = '$',
            Apos                  = '\'',
            Quote                 = '"',
            Union                 = '|', 
            Ne                    = 'N',   // !=
            Le                    = 'L',   // <= 
            Ge                    = 'G',   // >= 
            And                   = 'A',   // &&
            Or                    = 'O',   // || 
            DotDot                = 'D',   // ..
            SlashSlash            = 'S',   // //
            Name                  = 'n',   // XML _Name
            String                = 's',   // Quoted string constant 
            Number                = 'd',   // _Number constant
            Axe                   = 'a',   // Axe (like child::) 
            Eof                   = 'E', 
        };
    } 
}


// File provided for Reference Use Only by Microsoft Corporation (c) 2007.
// Copyright (c) Microsoft Corporation. All rights reserved.
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