#region PDFsharp - A .NET library for processing PDF
//
// Authors:
//   Stefan Lange (mailto:Stefan.Lange@pdfsharp.com)
//
// Copyright (c) 2005-2008 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.Diagnostics;
using System.Text;
using PdfSharp.Internal;
using PdfSharp.Pdf.Internal;

namespace PdfSharp.Pdf.Filters
{
  /// <summary>
  /// Implements the ASCII85Decode filter.
  /// </summary>
  public class ASCII85Decode : Filter
  {
    /// <summary>
    /// Encodes the specified data.
    /// </summary>
    public override byte[] Encode(byte[] data)
    {
      if (data == null)
        throw new ArgumentNullException("data");

      int length = data.Length;  // length == 0 is must not be treated as a special case
      int words = length / 4;
      int rest = length - (words * 4);
      byte[] result = new byte[words * 5 + (rest == 0 ? 0 : rest + 1) + 2];

      int idxIn = 0, idxOut = 0;
      int wCount = 0;
      while (wCount < words)
      {
        uint val = ((uint)data[idxIn++] << 24) + ((uint)data[idxIn++] << 16) + ((uint)data[idxIn++] << 8) + data[idxIn++];
        if (val == 0)
        {
          result[idxOut++] = (byte)'z';
        }
        else
        {
          byte c5 = (byte)(val % 85 + '!');
          val /= 85;
          byte c4 = (byte)(val % 85 + '!');
          val /= 85;
          byte c3 = (byte)(val % 85 + '!');
          val /= 85;
          byte c2 = (byte)(val % 85 + '!');
          val /= 85;
          byte c1 = (byte)(val + '!');

          result[idxOut++] = c1;
          result[idxOut++] = c2;
          result[idxOut++] = c3;
          result[idxOut++] = c4;
          result[idxOut++] = c5;
        }
        wCount++;
      }
      if (rest == 1)
      {
        uint val = (uint)data[idxIn++] << 24;
        val /= 85 * 85 * 85;
        byte c2 = (byte)(val % 85 + '!');
        val /= 85;
        byte c1 = (byte)(val + '!');

        result[idxOut++] = c1;
        result[idxOut++] = c2;
      }
      else if (rest == 2)
      {
        uint val = ((uint)data[idxIn++] << 24) + ((uint)data[idxIn++] << 16);
        val /= 85 * 85;
        byte c3 = (byte)(val % 85 + '!');
        val /= 85;
        byte c2 = (byte)(val % 85 + '!');
        val /= 85;
        byte c1 = (byte)(val + '!');

        result[idxOut++] = c1;
        result[idxOut++] = c2;
        result[idxOut++] = c3;
      }
      else if (rest == 3)
      {
        uint val = ((uint)data[idxIn++] << 24) + ((uint)data[idxIn++] << 16) + ((uint)data[idxIn++] << 8);
        val /= 85;
        byte c4 = (byte)(val % 85 + '!');
        val /= 85;
        byte c3 = (byte)(val % 85 + '!');
        val /= 85;
        byte c2 = (byte)(val % 85 + '!');
        val /= 85;
        byte c1 = (byte)(val + '!');

        result[idxOut++] = c1;
        result[idxOut++] = c2;
        result[idxOut++] = c3;
        result[idxOut++] = c4;
      }
      result[idxOut++] = (byte)'~';
      result[idxOut++] = (byte)'>';

      if (idxOut < result.Length)
        Array.Resize<byte>(ref result, idxOut);

      return result;
    }

    /// <summary>
    /// Decodes the specified data.
    /// </summary>
    public override byte[] Decode(byte[] data, FilterParms parms)
    {
      if (data == null)
        throw new ArgumentNullException("data");

      int idx;
      int length = data.Length;
      int zCount = 0;
      int idxOut = 0;
      for (idx = 0; idx < length; idx++)
      {
        char ch = (char)data[idx];
        if (ch >= '!' && ch <= 'u')
          data[idxOut++] = (byte)ch;
        else if (ch == 'z')
        {
          data[idxOut++] = (byte)ch;
          zCount++;
        }
        else if (ch == '~')
        {
          if ((char)data[idx + 1] != '>')
            throw new ArgumentException("Illegal character.", "data");
          break;
        }
        else
        {
          // ingnore unknown character
        }
      }
      // Loop not ended with break?
      if (idx == length)
        throw new ArgumentException("Illegal character.", "date");

      length = idxOut;
      int nonZero = length - zCount;
      int byteCount = 4 * (zCount + (nonZero / 5)); // full 4 byte blocks

      int remainder = nonZero % 5;
      if (remainder == 1)
        throw new InvalidOperationException("Illegal character.");

      if (remainder != 0)
        byteCount += remainder - 1;

      byte[] output = new byte[byteCount];

      idxOut = 0;
      idx = 0;
      while (idx + 4 < length)
      {
        char ch = (char)data[idx];
        if (ch == 'z')
        {
          idx++;
          idxOut += 4;
        }
        else
        {
          uint val =
            (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
            (uint)(data[idx++] - '!') * (85 * 85 * 85) +
            (uint)(data[idx++] - '!') * (85 * 85) +
            (uint)(data[idx++] - '!') * 85 +
            (uint)(data[idx++] - '!');

          output[idxOut++] = (byte)(val >> 24);
          output[idxOut++] = (byte)(val >> 16);
          output[idxOut++] = (byte)(val >> 8);
          output[idxOut++] = (byte)val;
        }
      }

      // I've found no appropriate algorithm, so I write my own. In some rare cases the value must not
      // increased by one, but I cannot found a general formula or a proof.
      // All possible cases are tested programmatically.
      if (remainder == 2) // one byte
      {
        int idxIn = idx;
        uint value =
          (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85 * 85);

        // Always increase if not zero (tried out)
        if (value != 0)
          value += 0x01000000;

        output[idxOut++] = (byte)(value >> 24);
      }
      else if (remainder == 3) // two bytes
      {
        int idxIn = idx;
        uint val;
        uint value =
          (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85);

        if (value != 0)
        {
          value &= 0xFFFF0000;
          val = value / (85 * 85);
          byte c3 = (byte)(val % 85 + '!');
          val /= 85;
          byte c2 = (byte)(val % 85 + '!');
          val /= 85;
          byte c1 = (byte)(val + '!');
          if (c1 != data[idxIn] || c2 != data[idxIn + 1] || c3 != data[idxIn + 2])
          {
            value += 0x00010000;
            //Count2++;
          }
        }
        output[idxOut++] = (byte)(value >> 24);
        output[idxOut++] = (byte)(value >> 16);
      }
      else if (remainder == 4) // three bytes
      {
        int idxIn = idx;
        uint val;
        uint value =
          (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85) +
          (uint)(data[idx++] - '!') * 85;

        if (value != 0)
        {
          value &= 0xFFFFFF00;
          val = value / 85;
          byte c4 = (byte)(val % 85 + '!');
          val /= 85;
          byte c3 = (byte)(val % 85 + '!');
          val /= 85;
          byte c2 = (byte)(val % 85 + '!');
          val /= 85;
          byte c1 = (byte)(val + '!');
          if (c1 != data[idxIn] || c2 != data[idxIn + 1] || c3 != data[idxIn + 2] || c4 != data[idxIn + 3])
          {
            value += 0x00000100;
            //Count3++;
          }
        }
        output[idxOut++] = (byte)(value >> 24);
        output[idxOut++] = (byte)(value >> 16);
        output[idxOut++] = (byte)(value >> 8);
      }
      return output;
    }

    //public static int Count1;
    //public static int Count2;
    //public static int Count3;
  }
}
