#region PDFsharp - A .NET library for processing PDF
//
// Authors:
//   Stefan Lange (mailto:Stefan.Lange@pdfsharp.com)
//
// Copyright (c) 2005-2007 empira Software GmbH, Cologne (Germany)
//
// http://www.pdfsharp.com
// http://sourceforge.net/projects/pdfsharp
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
// DEALINGS IN THE SOFTWARE.
#endregion

using System;
using System.Globalization;
using System.Diagnostics;
using System.Collections;
using System.Text;
using System.IO;
using PdfSharp.Pdf.Internal;

namespace PdfSharp.Pdf.IO
{
  /// <summary>
  /// Lexical analyser for PDF files. Technically a PDF file is a stream of bytes. Some chunks
  /// of bytes represent strings in serveral encodings. The actual encoding depends on the
  /// context where the string is used. Therefore the bytes are 'raw encoded' into characters,
  /// i.e. a character or token read by the lexer has always character values in the range from
  /// 0 to 255.
  /// </summary>
  internal class Lexer
  {
    /// <summary>
    /// Initializes a new instance of the Lexer class.
    /// </summary>
    public Lexer(Stream pdfInputStream)
    {
      this.pdf = pdfInputStream;
      this.pdfLength = (int)pdf.Length;
      this.idxChar = 0;
      Position = 0;
    }

    /// <summary>
    /// Initializes fields after position has changed.
    /// </summary>
    void Initialize()
    {
      this.currChar = (char)this.pdf.ReadByte();
      this.nextChar = (char)this.pdf.ReadByte();
      this.token = new StringBuilder();
      //this.symbol = Symbol.None;
    }

    /// <summary>
    /// Gets or sets the position within the PDF stream.
    /// </summary>
    public int Position
    {
      get { return this.idxChar; }
      set
      {
        this.idxChar = value;
        this.pdf.Position = value;
        Initialize();
      }
    }

    /// <summary>
    /// Reads the next token and returns its type. If the token starts with a digit, the parameter
    /// testReference specifies how to treat it. If it is flase, the lexer scans for a single integer.
    /// If it is true, the lexer checks if the digit is the prefix of a reference. If it is a reference,
    /// the token is set to the object ID followed by the generation number separated by a blank
    /// (the 'R' is omited from the token).
    /// </summary>
    // /// <param name="testReference">Indicates whether to test the next token if it is a reference.</param>
    public Symbol ScanNextToken()
    {
    Again:
      this.token = new StringBuilder();
      char ch = MoveToNonWhiteSpace();
      switch (ch)
      {
        case '%':
          // Eat comments, the parser doesn't handle them
          //return this.symbol = ScanComment();
          ScanComment();
          goto Again;

        case '/':
          return this.symbol = ScanName();

        //case 'R':
        //  if (Lexer.IsWhiteSpace(this.nextChar))
        //  {
        //    ScanNextChar();
        //    return Symbol.R;
        //  }
        //  break;

        case '+': //TODO is it so easy?
        case '-':
          return this.symbol = ScanNumber();

        case '(':
          return this.symbol = ScanLiteralString();

        case '[':
          ScanNextChar();
          return this.symbol = Symbol.BeginArray;

        case ']':
          ScanNextChar();
          return this.symbol = Symbol.EndArray;

        case '<':
          if (this.nextChar == '<')
          {
            ScanNextChar();
            ScanNextChar();
            return this.symbol = Symbol.BeginDictionary;
          }
          return this.symbol = ScanHexadecimalString();

        case '>':
          if (this.nextChar == '>')
          {
            ScanNextChar();
            ScanNextChar();
            return this.symbol = Symbol.EndDictionary;
          }
          Debug.Assert(false, ">???");
          break;

        case '.':
          return this.symbol = ScanNumber();
      }
      if (Char.IsDigit(ch))
        return this.symbol = ScanNumber();

      if (Char.IsLetter(ch))
        return this.symbol = ScanKeyword();

      if (ch == Chars.EOF)
        return this.symbol = Symbol.Eof;
      Debug.Assert(false, "not implemented");
      return this.symbol = Symbol.None;
    }

    ////public Symbol ScanNextToken(bool x)
    ////{
    ////  throw new NotImplementedException();
    ////}

    /// <summary>
    /// Reads the raw content of a stream.
    /// </summary>
    public byte[] ReadStream(int length)
    {
      int pos = 0;
      // Skip new line behind «stream»
      if (this.currChar == Chars.CR)
      {
        if (this.nextChar == Chars.LF)
          pos = this.idxChar + 2;
        else
          pos = this.idxChar + 1;
      }
      else
        pos = this.idxChar + 1;

      this.pdf.Position = pos;
      byte[] bytes = new byte[length];
      int read = this.pdf.Read(bytes, 0, length);
      Debug.Assert(read == length);
      // synchronize idxChar etc.
      this.Position = pos + length;
      return bytes;
    }

    /// <summary>
    /// 
    /// </summary>
    public String ReadRawString(int position, int length)
    {
      this.pdf.Position = position;
      byte[] bytes = new byte[length];
      this.pdf.Read(bytes, 0, length);
      return PdfEncoders.RawEncoding.GetString(bytes);
    }

    /// <summary>
    /// Scans a comment line.
    /// </summary>
    public Symbol ScanComment()
    {
      Debug.Assert(this.currChar == Chars.Percent);

      this.token = new StringBuilder();
      while (AppendAndScanNextChar() != Chars.LF) ;
      // TODO: not correct
      if (this.token.ToString().StartsWith("%%EOF"))
        return Symbol.Eof;
      return this.symbol = Symbol.Comment;
    }

    /// <summary>
    /// Scans a name.
    /// </summary>
    public Symbol ScanName()
    {
      Debug.Assert(this.currChar == Chars.Slash);

      this.token = new StringBuilder();
      while (true)
      {
        char ch = AppendAndScanNextChar();
        if (IsWhiteSpace(ch) || IsDelimiter(ch))
        {
          return this.symbol = Symbol.Name;
        }
        else if (ch == '#')
        {
          ScanNextChar();
          char[] hex = new char[2];
          hex[0] = this.currChar;
          hex[1] = this.nextChar;
          ScanNextChar();
          // TODO Check syntax
          ch = (char)(ushort)int.Parse(new string(hex), NumberStyles.AllowHexSpecifier);
          this.currChar = ch;
        }
      }
    }

    public Symbol ScanNumber()
    {
      // I found a PDF file created with Acrobat 7 with this entry 
      //   /Checksum 2996984786
      // What is this? It is neither an integer nor a real.
      // I introduced an UInteger...
      bool period = false;
      bool sign = false;
      period.GetType();
      sign.GetType();

      this.token = new StringBuilder();
      char ch = this.currChar;
      if (ch == '+' || ch == '-')
      {
        sign = true;
        this.token.Append(ch);
        ch = ScanNextChar();
      }
      while (true)
      {
        if (char.IsDigit(ch))
        {
          this.token.Append(ch);
        }
        else if (ch == '.')
        {
          if (period)
            throw new PdfReaderException("More than one period in number.");
          period = true;
          this.token.Append(ch);
        }
        else
          break;
        ch = ScanNextChar();
      }

      if (period)
        return Symbol.Real;
      long l = Int64.Parse(this.token.ToString(), CultureInfo.InvariantCulture);
      if (l >= Int32.MinValue && l <= Int32.MaxValue)
        return Symbol.Integer;
      if (l > 0 && l <= UInt32.MaxValue)
        return Symbol.UInteger;
      throw new PdfReaderException("Number exceeds integer range.");
    }

    public Symbol ScanKeyword()
    {
      this.token = new StringBuilder();
      char ch = this.currChar;
      // Scan token
      while (true)
      {
        if (char.IsLetter(ch))
        {
          this.token.Append(ch);
        }
        else
          break;
        ch = ScanNextChar();
      }

      // Check known tokens
      switch (this.token.ToString())
      {
        case "obj":
          return this.symbol = Symbol.Obj;

        case "endobj":
          return this.symbol = Symbol.EndObj;

        case "null":
          return this.symbol = Symbol.Null;

        case "true":
        case "false":
          return this.symbol = Symbol.Boolean;

        case "R":
          return this.symbol = Symbol.R;

        case "stream":
          return this.symbol = Symbol.BeginStream;

        case "endstream":
          return this.symbol = Symbol.EndStream;

        case "xref":
          return this.symbol = Symbol.XRef;

        case "trailer":
          return this.symbol = Symbol.Trailer;

        case "startxref":
          return this.symbol = Symbol.StartXRef;
      }

      // Anything else is treated as a keyword. Samples are f or n in iref.
      return this.symbol = Symbol.Keyword;
    }

    public Symbol ScanLiteralString()
    {
      Debug.Assert(this.currChar == Chars.ParenLeft);

      this.token = new StringBuilder();
      int parenLevel = 0;
      char ch = ScanNextChar();
      // Test UNICODE string
      if (ch == '\xFE' && this.nextChar == '\xFF')
      {
        // I'm not sure if the code is correct in any case.
        // ? Can a UNICODE character not start with ')' as hibyte
        // ? What about \# escape sequences

        // BUG: The code is not correct. I got a file containing the following sting:
        // (þÿñùãfØÚ\rÞF`:7.2.5 Acceptable daily intake \(ADI\) and other guideline levels)
        // It starts as unicode but ends as Ascii. No idea how to parse.
        char chHi, chLo;
        ScanNextChar();
        chHi = ScanNextChar();
        if (chHi == ')')
        {
          // The empty unicode string...
          ScanNextChar();
          return this.symbol = Symbol.String;
        }
        chLo = ScanNextChar();
        ch = (char)((int)chHi * 256 + (int)chLo);
        while (true)
        {
        SkipChar:
          switch (ch)
          {
            case '(':
              parenLevel++;
              break;

            case ')':
              if (parenLevel == 0)
              {
                ScanNextChar();
                return this.symbol = Symbol.String;
              }
              else
                parenLevel--;
              break;

            case '\\':
              {
                // TODO: not sure that this is correct...
                ch = ScanNextChar();
                switch (ch)
                {
                  case 'n':
                    ch = Chars.LF;
                    break;

                  case 'r':
                    ch = Chars.CR;
                    break;

                  case 't':
                    ch = Chars.HT;
                    break;

                  case 'b':
                    ch = Chars.BS;
                    break;

                  case 'f':
                    ch = Chars.FF;
                    break;

                  case '(':
                    ch = Chars.ParenLeft;
                    break;

                  case ')':
                    ch = Chars.ParenRight;
                    break;

                  case '\\':
                    ch = Chars.BackSlash;
                    break;

                  case Chars.LF:
                    ch = ScanNextChar();
                    goto SkipChar;

                  default:
                    if (Char.IsDigit(ch))
                    {
                      // Octal character code
                      int n = ch - '0';
                      if (Char.IsDigit(this.nextChar))
                      {
                        n = n * 8 + ScanNextChar() - '0';
                        if (Char.IsDigit(this.nextChar))
                          n = n * 8 + ScanNextChar() - '0';
                      }
                      ch = (char)n;
                    }
                    break;
                }
                break;
              }

            // TODO ???
            //case '#':
            //  Debug.Assert(false, "Not yet implemented");
            //  break;

            default:
              break;
          }
          this.token.Append(ch);
          chHi = ScanNextChar();
          if (chHi == ')')
          {
            ScanNextChar();
            return this.symbol = Symbol.String;
          }
          chLo = ScanNextChar();
          ch = (char)((int)chHi * 256 + (int)chLo);
        }
      }
      else
      {
        // 8-bit characters
        while (true)
        {
        SkipChar:
          switch (ch)
          {
            case '(':
              parenLevel++;
              break;

            case ')':
              if (parenLevel == 0)
              {
                ScanNextChar();
                return this.symbol = Symbol.String;
              }
              else
                parenLevel--;
              break;

            case '\\':
              {
                ch = ScanNextChar();
                switch (ch)
                {
                  case 'n':
                    ch = Chars.LF;
                    break;

                  case 'r':
                    ch = Chars.CR;
                    break;

                  case 't':
                    ch = Chars.HT;
                    break;

                  case 'b':
                    ch = Chars.BS;
                    break;

                  case 'f':
                    ch = Chars.FF;
                    break;

                  case '(':
                    ch = Chars.ParenLeft;
                    break;

                  case ')':
                    ch = Chars.ParenRight;
                    break;

                  case '\\':
                    ch = Chars.BackSlash;
                    break;

                  case Chars.LF:
                    ch = ScanNextChar();
                    goto SkipChar;

                  default:
                    if (char.IsDigit(ch))
                    {
                      //TODO
                      Debug.Assert(false, "Not implemented; unknown escape charachter.");
                    }
                    // Simply ignore backslash
                    break;
                }
                break;
              }

            // TODO ???
            //case '#':
            //  Debug.Assert(false, "Not yet implemented");
            //  break;

            default:
              break;
          }
          this.token.Append(ch);
          ch = ScanNextChar();
        }
      }
    }

    public Symbol ScanHexadecimalString()
    {
      Debug.Assert(this.currChar == Chars.Less);

      this.token = new StringBuilder();
      char[] hex = new char[2];
      ScanNextChar();
      while (true)
      {
        MoveToNonWhiteSpace();
        if (this.currChar == '>')
        {
          ScanNextChar();
          break;
        }
        if (char.IsLetterOrDigit(this.currChar))
        {
          hex[0] = char.ToUpper(this.currChar);
          hex[1] = char.ToUpper(this.nextChar);
          int ch = int.Parse(new string(hex), NumberStyles.AllowHexSpecifier);
          this.token.Append(Convert.ToChar(ch));
          ScanNextChar();
          ScanNextChar();
        }
      }
      string chars = this.token.ToString();
      int count = chars.Length;
      if (count > 2 && chars[0] == (char)0xFE && chars[1] == (char)0xFF)
      {
        Debug.Assert(count % 2 == 0);
        this.token.Length = 0;
        for (int idx = 2; idx < count; idx += 2)
          this.token.Append((char)(chars[idx] * 256 + chars[idx + 1]));
      }
      return this.symbol = Symbol.HexString;
    }

    /// <summary>
    /// Move current position one character further in PDF stream.
    /// </summary>
    internal char ScanNextChar()
    {
      if (this.pdfLength <= this.idxChar)
      {
        this.currChar = Chars.EOF;
        this.nextChar = Chars.EOF;
      }
      else
      {
        this.currChar = this.nextChar;
        this.nextChar = (char)this.pdf.ReadByte();
        this.idxChar++;
        if (this.currChar == Chars.CR)
        {
          if (this.nextChar == Chars.LF)
          {
            // Treat CR LF as LF
            this.currChar = this.nextChar;
            this.nextChar = (char)this.pdf.ReadByte();
            this.idxChar++;
          }
          else
          {
            // Treat single CR as LF
            this.currChar = Chars.LF;
          }
        }
      }
      return currChar;
    }

    /// <summary>
    /// Resets the current token to the empty string.
    /// </summary>
    void ClearToken()
    {
      this.token.Length = 0;
    }

    /// <summary>
    /// Appends current character to the token and reads next one.
    /// </summary>
    internal char AppendAndScanNextChar()
    {
      token.Append(this.currChar);
      return ScanNextChar();
    }

    /// <summary>
    /// If the current character is not a white space, the function immediately returns it.
    /// Otherwise the PDF cursor is moved forward to the first non-white space or EOF.
    /// White spaces are NUL, HT, LF, FF, CR, and SP.
    /// </summary>
    public char MoveToNonWhiteSpace()
    {
      while (this.currChar != Chars.EOF)
      {
        switch (this.currChar)
        {
          case Chars.NUL:
          case Chars.HT:
          case Chars.LF:
          case Chars.FF:
          case Chars.CR:
          case Chars.SP:
            ScanNextChar();
            break;

          default:
            return currChar;
        }
      }
      return currChar;
    }

    /// <summary>
    /// Gets the current symbol.
    /// </summary>
    public Symbol Symbol
    {
      get { return this.symbol; }
      set { this.symbol = value; }
    }

    /// <summary>
    /// Gets the current token.
    /// </summary>
    internal string Token
    {
      get { return this.token.ToString(); }
    }

    /// <summary>
    /// Interprets current token as boolean literal.
    /// </summary>
    internal bool TokenToBoolean
    {
      get
      {
        Debug.Assert(this.token.ToString() == "true" || this.token.ToString() == "false");
        return this.token.ToString()[0] == 't';
      }
    }

    /// <summary>
    /// Interprets current token as integer literal.
    /// </summary>
    internal int TokenToInteger
    {
      get
      {
        //Debug.Assert(this.token.ToString().IndexOf('.') == -1);
        return Int32.Parse(this.token.ToString(), CultureInfo.InvariantCulture);
      }
    }

    /// <summary>
    /// Interprets current token as unsigned integer literal.
    /// </summary>
    internal uint TokenToUInteger
    {
      get
      {
        //Debug.Assert(this.token.ToString().IndexOf('.') == -1);
        return UInt32.Parse(this.token.ToString(), CultureInfo.InvariantCulture);
      }
    }

    /// <summary>
    /// Interpret current token as real or interger literal.
    /// </summary>
    internal double TokenToReal
    {
      get { return double.Parse(token.ToString(), CultureInfo.InvariantCulture); }
    }

    /// <summary>
    /// Indicates whether the specified character is a PDF white-space character.
    /// </summary>
    internal static bool IsWhiteSpace(char ch)
    {
      switch (ch)
      {
        case Chars.NUL:  // 0 Null
        case Chars.HT:   // 9 Tab
        case Chars.LF:   // 10 Line feed
        case Chars.FF:   // 12 Form feed
        case Chars.CR:   // 13 Carriage return
        case Chars.SP:   // 32 Space
          return true;
      }
      return false;
    }

    /// <summary>
    /// Indicates whether the specified character is a PDF delimiter character.
    /// </summary>
    internal static bool IsDelimiter(char ch)
    {
      switch (ch)
      {
        case '(':
        case ')':
        case '<':
        case '>':
        case '[':
        case ']':
        case '{':
        case '}':
        case '/':
        case '%':
          return true;
      }
      return false;
    }

    public int PdfLength
    {
      get { return this.pdfLength; }
    }

    int pdfLength;
    int idxChar;
    char currChar;
    char nextChar;
    StringBuilder token;
    Symbol symbol = Symbol.None;

    private Stream pdf;
  }
}
