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Page.cs

//
// PageHeader.cs:
//
// Author:
//   Brian Nickel (brian.nickel@gmail.com)
//
// Original Source:
//   oggpage.cpp from TagLib
//
// Copyright (C) 2005-2007 Brian Nickel
// Copyright (C) 2003 Scott Wheeler (Original Implementation)
//
// This library is free software; you can redistribute it and/or modify
// it  under the terms of the GNU Lesser General Public License version
// 2.1 as published by the Free Software Foundation.
//
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307
// USA
//

using System.Collections.Generic;
using System;

namespace TagLib.Ogg
{
      /// <summary>
      ///    This class provides a representation of an Ogg page.
      /// </summary>
00036       public class Page
      {
#region Private Properties
            
            /// <summary>
            ///    Contains the page header.
            /// </summary>
00043             private PageHeader header;
            
            /// <summary>
            ///    Contains the packets.
            /// </summary>
00048             private ByteVectorCollection packets;
            
#endregion
            
            
            
#region Constructors
            
            /// <summary>
            ///    Constructs and intializes a new instance of <see
            ///    cref="Page" /> with a specified header and no packets.
            /// </summary>
            /// <param name="header">
            ///    A <see cref="PageHeader"/> object to use as the header of
            ///    the new instance.
            /// </param>
00064             protected Page (PageHeader header)
            {
                  this.header = header;
                  packets = new ByteVectorCollection ();
            }
            
            /// <summary>
            ///    Constructs and initializes a new instance of <see
            ///    cref="Page" /> by reading a raw Ogg page from a specified
            ///    position in a specified file.
            /// </summary>
            /// <param name="file">
            ///    A <see cref="File" /> object containing the file from
            ///    which the contents of the new instance are to be read.
            /// </param>
            /// <param name="position">
            ///    A <see cref="long" /> value specify at what position to
            ///    read.
            /// </param>
            /// <exception cref="ArgumentNullException">
            ///    <paramref name="file" /> is <see langword="null" />.
            /// </exception>
            /// <exception cref="ArgumentOutOfRangeException">
            ///    <paramref name="position" /> is less than zero or greater
            ///    than the size of the file.
            /// </exception>
            /// <exception cref="CorruptFileException">
            ///    The Ogg identifier could not be found at the correct
            ///    location.
            /// </exception>
00094             public Page (File file, long position)
                  : this (new PageHeader (file, position))
            {
                  file.Seek (position + header.Size);
                  
                  foreach (int packet_size in header.PacketSizes)
                        packets.Add (file.ReadBlock (packet_size));
            }
            
            /// <summary>
            ///    Constructs and initializes a new instance of <see
            ///    cref="Page" /> with a specified header and packets.
            /// </summary>
            /// <param name="packets">
            ///    A <see cref="ByteVectorCollection" /> object containing
            ///    packets to use for the new instance.
            /// </param>
            /// <param name="header">
            ///    A <see cref="PageHeader"/> object to use as the header of
            ///    the new instance.
            /// </param>
            /// <exception cref="ArgumentNullException">
            ///    <paramref name="packets" /> is <see langword="null" />.
            /// </exception>
00118             public Page (ByteVectorCollection packets, PageHeader header)
                  : this (header)
            {
                  if (packets == null)
                        throw new ArgumentNullException ("packets");
                  
                  this.packets = new ByteVectorCollection (packets);
                  
                  List<int> packet_sizes = new List<int> ();
                  
                  // Build a page from the list of packets.
                  foreach (ByteVector v in packets)
                        packet_sizes.Add (v.Count);
                  
                  header.PacketSizes = packet_sizes.ToArray ();
            }
            
#endregion
            
            
            
#region Public Methods
            
            /// <summary>
            ///    Renders the current instance as a raw Ogg page.
            /// </summary>
            /// <returns>
            ///    A <see cref="ByteVector" /> object containing the
            ///    rendered version of the current instance.
            /// </returns>
00148             public ByteVector Render ()
            {
                  ByteVector data = header.Render ();
                  
                  foreach (ByteVector v in packets)
                        data.Add (v);
                  
                  // Compute and set the checksum for the Ogg page. The
                  // checksum is taken over the entire page with the 4
                  // bytes reserved for the checksum zeroed and then
                  // inserted in bytes 22-25 of the page header.
                  
                  ByteVector checksum = ByteVector.FromUInt (
                        data.Checksum, false);
                  
                  for (int i = 0; i < 4; i++)
                        data [i + 22] = checksum [i];
                  
                  return data;
            }
            
#endregion
            
            
            
#region Public Properties
            
            /// <summary>
            ///    Gets the header of the current instance.
            /// </summary>
            /// <value>
            ///    A <see cref="PageHeader" /> object that applies to the
            ///    current instance.
            /// </value>
00182             public PageHeader Header {
                  get {return header;}
            }
            
            /// <summary>
            ///    Gets the packets contained in the current instance.
            /// </summary>
            /// <value>
            ///    A <see cref="ByteVector[]" /> containing the packets
            ///    contained in the current instance.
            /// </value>
00193             public ByteVector[] Packets {
                  get {return packets.ToArray ();}
            }
            
            /// <summary>
            ///    Gets the total size of the current instance as it
            ///    appeared on disk.
            /// </summary>
            /// <value>
            ///    A <see cref="uint" /> value containing the size of the
            ///    page, including the header, as it appeared on disk.
            /// </value>
00205             public uint Size {
                  get {return header.Size + header.DataSize;}
            }
            
#endregion
            
            
            
#region Public Static Methods
            
            /// <summary>
            ///    Overwrites all page headers in a file starting at a
            ///    specified position, shifting the page sequence numbers
            ///    a set amount.
            /// </summary>
            /// <param name="file">
            ///    A <see cref="File" /> object containing the file to
            ///    update.
            /// </param>
            /// <param name="position">
            ///    A <see cref="long" /> value specify at what position to
            ///    start updating.
            /// </param>
            /// <param name="shiftTable">
            ///    A <see cref="T:System.Collections.Generic.IDictionary`2"
            ///    /> object where the key is the serial number of the
            ///    stream to update and the value is the amount to offset
            ///    the page sequence numbers in the stream.
            /// </param>
            /// <exception cref="ArgumentNullException">
            ///    <paramref name="file" /> or <paramref name="shiftTable"
            ///    /> is <see langword="null" />.
            /// </exception>
            /// <remarks>
            ///    When the number of pages in a stream changes, all
            ///    subsequent pages in the stream need to have their page
            ///    sequence number update in order to remain valid.
            ///    Additionally, when the page sequence number changes, the
            ///    page needs to have its checksum recomputed. This makes
            ///    for a costly recalculation if large comment data is
            ///    added.
            /// </remarks>
00247             public static void OverwriteSequenceNumbers (File file,
                                                         long position,
                                                         IDictionary<uint, int> shiftTable)
            {
                  if (file == null)
                        throw new ArgumentNullException ("file");
                  
                  if (shiftTable == null)
                        throw new ArgumentNullException ("shiftTable");
                  
                  // Check to see if there are no changes to be made.
                  bool done = true;
                  foreach (KeyValuePair<uint, int> pair in shiftTable)
                        if (pair.Value != 0) {
                              done = false;
                              break;
                        }
                  
                  // If the file is fine, quit.
                  if (done)
                        return;
                  
                  while (position < file.Length - 27) {
                        PageHeader header = new PageHeader (file, position);
                        int size = (int) (header.Size + header.DataSize);
                        
                        if (shiftTable.ContainsKey (header.StreamSerialNumber)
                              && shiftTable [header.StreamSerialNumber] != 0) {
                              file.Seek (position);
                              ByteVector page_data = file.ReadBlock (size);
                              
                              ByteVector new_data = ByteVector.FromUInt (
                                    (uint)(header.PageSequenceNumber +
                                    shiftTable [header.StreamSerialNumber]),
                                    false);
                              
                              for (int i = 18; i < 22; i ++)
                                    page_data [i] = new_data [i - 18];
                              for (int i = 22; i < 26; i++)
                                    page_data [i] = 0;
                              
                              new_data.Add (ByteVector.FromUInt (
                                    page_data.Checksum, false));
                              file.Seek (position + 18);
                              file.WriteBlock (new_data);
                        }
                        position += size;
                  }
            }
            
#endregion
      }
}

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