//
// File.cs: Provides a basic framework for reading from and writing to
// a file, as well as accessing basic tagging and media properties.
//
// Author:
//   Brian Nickel (brian.nickel@gmail.com)
//   Aaron Bockover (abockover@novell.com)
//
// Original Source:
//   tfile.cpp from TagLib
//
// Copyright (C) 2005, 2007 Brian Nickel
// Copyright (C) 2006 Novell, Inc.
// Copyright (C) 2002,2003 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;
using System.Collections.Generic;
using System.Globalization;
using System.IO;
using System.Runtime.Serialization;

namespace TagLib
{

	/// <summary>
	///    Specifies the options to use when reading the media.
	/// </summary>
	[Flags]
	public enum ReadStyle
	{
		/// <summary>
		///    The media properties will not be read.
		/// </summary>
		None = 0,

		// Fast = 1,

		/// <summary>
		///    The media properties will be read with average accuracy.
		/// </summary>
		Average = 2,

		/// <summary>
		///    Use the <see cref="PictureLazy"/> class in the 
		///    the property <see cref="Tag.Pictures"/>. 
		///    This will avoid loading picture content when reading the Tag.
		///    Picture will be read lazily, when the picture content is 
		///    accessed.
		/// </summary>
		PictureLazy = 4
	}

	/// <summary>
	///    This abstract class provides a basic framework for reading from
	///    and writing to a file, as well as accessing basic tagging and
	///    media properties.
	/// </summary>
	/// <remarks>
	///    <para>This class is agnostic to all specific media types. Its
	///    child classes, on the other hand, support the the intricacies of
	///    different media and tagging formats. For example, <see
	///    cref="Mpeg4.File" /> supports the MPEG-4 specificication and
	///    Apple's tagging format.</para>
	///    <para>Each file type can be created using its format specific
	///    constructors, ie. <see cref="Mpeg4.File(string)" />, but the
	///    preferred method is to use <see
	///    cref="Create(string,string,ReadStyle)" /> or one of its
	///    variants, as it automatically detects the appropriate class from
	///    the file extension or provided mime-type.</para>
	/// </remarks>
	public abstract class File : IDisposable
	{
		#region Enums

		/// <summary>
		///   Specifies the type of file access operations currently
		///   permitted on an instance of <see cref="File" />.
		/// </summary>
		public enum AccessMode
		{
			/// <summary>
			///    Read operations can be performed.
			/// </summary>
			Read,

			/// <summary>
			///    Read and write operations can be performed.
			/// </summary>
			Write,

			/// <summary>
			///    The file is closed for both read and write
			///    operations.
			/// </summary>
			Closed
		}

		#endregion



		#region Delegates

		/// <summary>
		///    This delegate is used for intervening in <see
		///    cref="Create(string)" /> by resolving the file type
		///    before any standard resolution operations.
		/// </summary>
		/// <param name="abstraction">
		///    A <see cref="IFileAbstraction" /> object representing the
		///    file to be read.
		/// </param>
		/// <param name="mimetype">
		///    A <see cref="string" /> object containing the mime-type
		///    of the file.
		/// </param>
		/// <param name="style">
		///    A <see cref="ReadStyle" /> value specifying how to read
		///    media properties from the file.
		/// </param>
		/// <returns>
		///    A new instance of <see cref="File" /> or <see
		///    langword="null" /> if the resolver could not match it.
		/// </returns>
		/// <remarks>
		///    <para>A <see cref="FileTypeResolver" /> is one way of
		///    altering the behavior of <see cref="Create(string)" />
		///    .</para>
		///    <para>When <see cref="Create(string)" /> is called, the
		///    registered resolvers are invoked in the reverse order in
		///    which they were registered. The resolver may then perform
		///    any operations necessary, including other type-finding
		///    methods.</para>
		///    <para>If the resolver returns a new <see cref="File" />,
		///    it will instantly be returned, by <see
		///    cref="Create(string)" />. If it returns <see 
		///    langword="null" />, <see cref="Create(string)" /> will
		///    continue to process. If the resolver throws an exception
		///    it will be uncaught.</para>
		///    <para>To register a resolver, use <see
		///    cref="AddFileTypeResolver" />.</para>
		/// </remarks>
		public delegate File FileTypeResolver (IFileAbstraction abstraction, string mimetype, ReadStyle style);

		#endregion



		#region Private Properties

		/// <summary>
		///    Contains the current stream used in reading/writing.
		/// </summary>
		Stream file_stream;

		/// <summary>
		///    Contains the internal file abstraction.
		/// </summary>
		protected IFileAbstraction file_abstraction;

		/// <summary>
		///    Contains buffer size to use when reading.
		/// </summary>
		static readonly int buffer_size = 1024;

		/// <summary>
		///    Contains the file type resolvers to use in <see
		///    cref="Create(string)" />.
		/// </summary>
		static readonly List<FileTypeResolver> file_type_resolvers = new List<FileTypeResolver> ();

		/// <summary>
		///    The reasons (if any) why this file is marked as corrupt.
		/// </summary>
		List<string> corruption_reasons;

		#endregion



		#region Public Static Properties

		/// <summary>
		///    The buffer size to use when reading large blocks of data
		///    in the <see cref="File" /> class.
		/// </summary>
		/// <value>
		///    A <see cref="uint" /> containing the buffer size to use
		///    when reading large blocks of data.
		/// </value>
		public static uint BufferSize => (uint)buffer_size;

		#endregion


		#region Constructors

		/// <summary>
		///    Constructs and initializes a new instance of <see
		///    cref="File" /> for a specified path in the local file
		///    system.
		/// </summary>
		/// <param name="path">
		///    A <see cref="string" /> object containing the path of the
		///    file to use in the new instance.
		/// </param>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="path" /> is <see langword="null" />.
		/// </exception>
		protected File (string path)
		{
			if (path == null)
				throw new ArgumentNullException (nameof (path));

			file_abstraction = new LocalFileAbstraction (path);
		}

		/// <summary>
		///    Constructs and initializes a new instance of <see
		///    cref="File" /> for a specified file abstraction.
		/// </summary>
		/// <param name="abstraction">
		///    A <see cref="IFileAbstraction" /> object to use when
		///    reading from and writing to the file.
		/// </param>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="abstraction" /> is <see langword="null"
		///    />.
		/// </exception>
		protected File (IFileAbstraction abstraction)
		{
			if (abstraction == null)
				throw new ArgumentNullException (nameof (abstraction));

			file_abstraction = abstraction;
		}

		#endregion



		#region Public Properties

		/// <summary>
		///    Gets a abstract representation of all tags stored in the
		///    current instance.
		/// </summary>
		/// <value>
		///    A <see cref="TagLib.Tag" /> object representing all tags
		///    stored in the current instance.
		/// </value>
		/// <remarks>
		///    <para>This property provides generic and general access
		///    to the most common tagging features of a file. To access
		///    or add a specific type of tag in the file, use <see
		///    cref="GetTag(TagLib.TagTypes,bool)" />.</para>
		/// </remarks>
		public abstract Tag Tag { get; }

		/// <summary>
		///    Gets the media properties of the file represented by the
		///    current instance.
		/// </summary>
		/// <value>
		///    A <see cref="TagLib.Properties" /> object containing the
		///    media properties of the file represented by the current
		///    instance.
		/// </value>
		public abstract Properties Properties { get; }

		/// <summary>
		///    Gets the tag types contained in the physical file
		///    represented by the current instance.
		/// </summary>
		/// <value>
		///    A bitwise combined <see cref="TagLib.TagTypes" /> value
		///    containing the tag types stored in the physical file as
		///    it was read or last saved.
		/// </value>
		public TagTypes TagTypesOnDisk { get; protected set; } = TagTypes.None;

		/// <summary>
		///    Gets the tag types contained in the current instance.
		/// </summary>
		/// <value>
		///    A bitwise combined <see cref="TagLib.TagTypes" /> value
		///    containing the tag types stored in the current instance.
		/// </value>
		public TagTypes TagTypes => Tag?.TagTypes ?? TagTypes.None;

		/// <summary>
		///    Gets the name of the file as stored in its file
		///    abstraction.
		/// </summary>
		/// <value>
		///    A <see cref="string" /> object containing the name of the
		///    file as stored in the <see cref="IFileAbstraction" />
		///    object used to create it or the path if created with a
		///    local path.
		/// </value>
		public string Name => file_abstraction.Name;

		/// <summary>
		///    Gets the mime-type of the file as determined by <see
		///    cref="Create(IFileAbstraction,string,ReadStyle)" /> if
		///    that method was used to create the current instance.
		/// </summary>
		/// <value>
		///    A <see cref="string" /> object containing the mime-type
		///    used to create the file or <see langword="null" /> if <see
		///    cref="Create(IFileAbstraction,string,ReadStyle)" /> was
		///    not used to create the current instance.
		/// </value>
		public string MimeType { get; internal set; }

		/// <summary>
		///    Gets the seek position in the internal stream used by the
		///    current instance.
		/// </summary>
		/// <value>
		///    A <see cref="long" /> value representing the seek
		///    position, or 0 if the file is not open for reading.
		/// </value>
		public long Tell => (Mode == AccessMode.Closed) ? 0 : file_stream.Position;

		/// <summary>
		///    Gets the length of the file represented by the current
		///    instance.
		/// </summary>
		/// <value>
		///    A <see cref="long" /> value representing the size of the
		///    file, or 0 if the file is not open for reading.
		/// </value>
		public long Length => (Mode == AccessMode.Closed) ? 0 : file_stream.Length;

		/// <summary>
		///    Gets the position at which the invariant portion of the
		///    current instance begins.
		/// </summary>
		/// <value>
		///    A <see cref="long" /> value representing the seek
		///    position at which the file's invariant (media) data
		///    section begins. If the value could not be determined,
		///    <c>-1</c> is returned.
		/// </value>
		public long InvariantStartPosition { get; protected set; } = -1;

		/// <summary>
		///    Gets the position at which the invariant portion of the
		///    current instance ends.
		/// </summary>
		/// <value>
		///    A <see cref="long" /> value representing the seek
		///    position at which the file's invariant (media) data
		///    section ends. If the value could not be determined,
		///    <c>-1</c> is returned.
		/// </value>
		public long InvariantEndPosition { get; protected set; } = -1;

		/// <summary>
		///    Gets and sets the file access mode in use by the current
		///    instance.
		/// </summary>
		/// <value>
		///    A <see cref="AccessMode" /> value describing the features
		///    of stream currently in use by the current instance.
		/// </value>
		/// <remarks>
		///    Changing the value will cause the stream currently in use
		///    to be closed, except when a change is made from <see
		///    cref="AccessMode.Write" /> to <see cref="AccessMode.Read"
		///    /> which has no effect.
		/// </remarks>
		public AccessMode Mode {
			get {
				if (file_stream == null)
					return AccessMode.Closed;

				if (file_stream.CanWrite)
					return AccessMode.Write;

				return AccessMode.Read;
			}
			set {
				if (Mode == value || (Mode == AccessMode.Write && value == AccessMode.Read))
					return;

				if (file_stream != null)
					file_abstraction.CloseStream (file_stream);

				file_stream = null;

				if (value == AccessMode.Read)
					file_stream = file_abstraction.ReadStream;
				else if (value == AccessMode.Write)
					file_stream = file_abstraction.WriteStream;

				Mode = value;
			}
		}

		/// <summary>
		/// Gets the <see cref="IFileAbstraction"/> representing the file.
		/// </summary>
		public IFileAbstraction FileAbstraction => file_abstraction;

		/// <summary>
		///    Indicates if tags can be written back to the current file or not
		/// </summary>
		/// <value>
		///    A <see cref="bool" /> which is true if tags can be written to the
		///    current file, otherwise false.
		/// </value>
		public virtual bool Writeable => !PossiblyCorrupt;

		/// <summary>
		///   Indicates whether or not this file may be corrupt.
		/// </summary>
		/// <value>
		/// <c>true</c> if possibly corrupt; otherwise, <c>false</c>.
		/// </value>
		/// <remarks>
		///    Files with unknown corruptions should not be written.
		/// </remarks>
		public bool PossiblyCorrupt => corruption_reasons != null;

		/// <summary>
		///   The reasons for which this file is marked as corrupt.
		/// </summary>
		public IEnumerable<string> CorruptionReasons => corruption_reasons;

		#endregion



		#region Public Methods

		/// <summary>
		///	   Mark the file as corrupt.
		/// </summary>
		/// <param name="reason">
		///    The reason why this file is considered to be corrupt.
		/// </param>
		internal void MarkAsCorrupt (string reason)
		{
			if (corruption_reasons == null)
				corruption_reasons = new List<string> ();
			corruption_reasons.Add (reason);
		}

		/// <summary>
		///    Dispose the current file. Equivalent to setting the
		///    mode to closed
		/// </summary>
		public void Dispose ()
		{
			Mode = AccessMode.Closed;
		}

		/// <summary>
		///    Saves the changes made in the current instance to the
		///    file it represents.
		/// </summary>
		public abstract void Save ();

		/// <summary>
		///    Removes a set of tag types from the current instance.
		/// </summary>
		/// <param name="types">
		///    A bitwise combined <see cref="TagLib.TagTypes" /> value
		///    containing tag types to be removed from the file.
		/// </param>
		/// <remarks>
		///    In order to remove all tags from a file, pass <see
		///    cref="TagTypes.AllTags" /> as <paramref name="types" />.
		/// </remarks>
		public abstract void RemoveTags (TagTypes types);

		/// <summary>
		///    Gets a tag of a specified type from the current instance,
		///    optionally creating a new tag if possible.
		/// </summary>
		/// <param name="type">
		///    A <see cref="TagLib.TagTypes" /> value indicating the
		///    type of tag to read.
		/// </param>
		/// <param name="create">
		///    A <see cref="bool" /> value specifying whether or not to
		///    try and create the tag if one is not found.
		/// </param>
		/// <returns>
		///    A <see cref="Tag" /> object containing the tag that was
		///    found in or added to the current instance. If no
		///    matching tag was found and none was created, <see
		///    langword="null" /> is returned.
		/// </returns>
		/// <remarks>
		///    <para>Passing <see langword="true" /> to <paramref
		///    name="create" /> does not guarantee the tag will be
		///    created. For example, trying to create an ID3v2 tag on an
		///    OGG Vorbis file will always fail.</para>
		///    <para>It is safe to assume that if <see langword="null"
		///    /> is not returned, the returned tag can be cast to the
		///    appropriate type.</para>
		/// </remarks>
		/// <example>
		///    <para>The following example sets the mood of a file to
		///    several tag types.</para>
		///    <code lang="C#">string [] SetMoods (TagLib.File file, params string[] moods)
		///{
		///   TagLib.Id3v2.Tag id3 = file.GetTag (TagLib.TagTypes.Id3v2, true);
		///   if (id3 != null)
		///      id3.SetTextFrame ("TMOO", moods);
		///   
		///   TagLib.Asf.Tag asf = file.GetTag (TagLib.TagTypes.Asf, true);
		///   if (asf != null)
		///      asf.SetDescriptorStrings (moods, "WM/Mood", "Mood");
		///   
		///   TagLib.Ape.Tag ape = file.GetTag (TagLib.TagTypes.Ape);
		///   if (ape != null)
		///      ape.SetValue ("MOOD", moods);
		///      
		///   // Whatever tag types you want...
		///}</code>
		/// </example>
		public abstract Tag GetTag (TagTypes type, bool create);

		/// <summary>
		///    Gets a tag of a specified type from the current instance.
		/// </summary>
		/// <param name="type">
		///    A <see cref="TagLib.TagTypes" /> value indicating the
		///    type of tag to read.
		/// </param>
		/// <returns>
		///    A <see cref="Tag" /> object containing the tag that was
		///    found in the current instance. If no matching tag
		///    was found, <see langword="null" /> is returned.
		/// </returns>
		/// <remarks>
		///    <para>This class merely accesses the tag if it exists.
		///    <see cref="GetTag(TagTypes,bool)" /> provides the option
		///    of adding the tag to the current instance if it does not
		///    exist.</para>
		///    <para>It is safe to assume that if <see langword="null"
		///    /> is not returned, the returned tag can be cast to the
		///    appropriate type.</para>
		/// </remarks>
		/// <example>
		///    <para>The following example reads the mood of a file from
		///    several tag types.</para>
		///    <code lang="C#">static string [] GetMoods (TagLib.File file)
		///{
		///   TagLib.Id3v2.Tag id3 = file.GetTag (TagLib.TagTypes.Id3v2);
		///   if (id3 != null) {
		///      TextIdentificationFrame f = TextIdentificationFrame.Get (this, "TMOO");
		///      if (f != null)
		///         return f.FieldList.ToArray ();
		///   }
		///   
		///   TagLib.Asf.Tag asf = file.GetTag (TagLib.TagTypes.Asf);
		///   if (asf != null) {
		///      string [] value = asf.GetDescriptorStrings ("WM/Mood", "Mood");
		///      if (value.Length &gt; 0)
		///         return value;
		///   }
		///   
		///   TagLib.Ape.Tag ape = file.GetTag (TagLib.TagTypes.Ape);
		///   if (ape != null) {
		///      Item item = ape.GetItem ("MOOD");
		///      if (item != null)
		///         return item.ToStringArray ();
		///   }
		///      
		///   // Whatever tag types you want...
		///   
		///   return new string [] {};
		///}</code>
		/// </example>
		public Tag GetTag (TagTypes type)
		{
			return GetTag (type, false);
		}

		/// <summary>
		///    Reads a specified number of bytes at the current seek
		///    position from the current instance.
		/// </summary>
		/// <param name="length">
		///    A <see cref="int" /> value specifying the number of bytes
		///    to read.
		/// </param>
		/// <returns>
		///    A <see cref="ByteVector" /> object containing the data
		///    read from the current instance.
		/// </returns>
		/// <remarks>
		///    <para>This method reads the block of data at the current
		///    seek position. To change the seek position, use <see
		///    cref="Seek(long,SeekOrigin)" />.</para>
		/// </remarks>
		/// <exception cref="ArgumentException">
		///    <paramref name="length" /> is less than zero.
		/// </exception>
		public ByteVector ReadBlock (int length)
		{
			if (length < 0)
				throw new ArgumentException ("Length must be non-negative", nameof (length));

			if (length == 0)
				return new ByteVector ();

			Mode = AccessMode.Read;

			byte[] buffer = new byte[length];

			int count = 0, read = 0, needed = length;

			do {
				count = file_stream.Read (buffer, read, needed);

				read += count;
				needed -= count;
			} while (needed > 0 && count != 0);

			return new ByteVector (buffer, read);
		}

		/// <summary>
		///    Writes a block of data to the file represented by the
		///    current instance at the current seek position.
		/// </summary>
		/// <param name="data">
		///    A <see cref="ByteVector" /> object containing data to be
		///    written to the current instance.
		/// </param>
		/// <remarks>
		///    This will overwrite any existing data at the seek
		///    position and append new data to the file if writing past
		///    the current end.
		/// </remarks>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="data" /> is <see langword="null" />.
		/// </exception>
		public void WriteBlock (ByteVector data)
		{
			if (data == null)
				throw new ArgumentNullException (nameof (data));

			Mode = AccessMode.Write;

			file_stream.Write (data.Data, 0, data.Count);
		}

		/// <summary>
		///    Searches forwards through a file for a specified
		///    pattern, starting at a specified offset.
		/// </summary>
		/// <param name="pattern">
		///    A <see cref="ByteVector" /> object containing a pattern
		///    to search for in the current instance.
		/// </param>
		/// <param name="startPosition">
		///    A <see cref="int" /> value specifying at what
		///    seek position to start searching.
		/// </param>
		/// <param name="before">
		///    A <see cref="ByteVector" /> object specifying a pattern
		///    that the searched for pattern must appear before. If this
		///    pattern is found first, -1 is returned.
		/// </param>
		/// <returns>
		///    A <see cref="long" /> value containing the index at which
		///    the value was found. If not found, -1 is returned.
		/// </returns>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="pattern" /> is <see langword="null" />.
		/// </exception>
		public long Find (ByteVector pattern, long startPosition, ByteVector before)
		{
			if (pattern == null)
				throw new ArgumentNullException (nameof (pattern));

			Mode = AccessMode.Read;

			if (pattern.Count > buffer_size)
				return -1;

			// The position in the file that the current buffer
			// starts at.

			long buffer_offset = startPosition;
			long original_position = file_stream.Position;

			try {
				// Start the search at the offset.
				file_stream.Position = startPosition;
				for (var buffer = ReadBlock (buffer_size); buffer.Count > 0; buffer = ReadBlock (buffer_size)) {
					var location = buffer.Find (pattern);
					if (before != null) {
						var beforeLocation = buffer.Find (before);
						if (beforeLocation < location)
							return -1;
					}

					if (location >= 0)
						return buffer_offset + location;

					// Ensure that we always rewind the stream a little so we never have a partial
					// match where our data exists between the end of read A and the start of read B.
					buffer_offset += buffer_size - pattern.Count;
					if (before != null && before.Count > pattern.Count)
						buffer_offset -= before.Count - pattern.Count;
					file_stream.Position = buffer_offset;
				}

				return -1;
			} finally {
				file_stream.Position = original_position;
			}
		}

		/// <summary>
		///    Searches forwards through a file for a specified
		///    pattern, starting at a specified offset.
		/// </summary>
		/// <param name="pattern">
		///    A <see cref="ByteVector" /> object containing a pattern
		///    to search for in the current instance.
		/// </param>
		/// <param name="startPosition">
		///    A <see cref="int" /> value specifying at what
		///    seek position to start searching.
		/// </param>
		/// <returns>
		///    A <see cref="long" /> value containing the index at which
		///    the value was found. If not found, -1 is returned.
		/// </returns>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="pattern" /> is <see langword="null" />.
		/// </exception>
		public long Find (ByteVector pattern, long startPosition)
		{
			return Find (pattern, startPosition, null);
		}

		/// <summary>
		///    Searches forwards through a file for a specified
		///    pattern, starting at the beginning of the file.
		/// </summary>
		/// <param name="pattern">
		///    A <see cref="ByteVector" /> object containing a pattern
		///    to search for in the current instance.
		/// </param>
		/// <returns>
		///    A <see cref="long" /> value containing the index at which
		///    the value was found. If not found, -1 is returned.
		/// </returns>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="pattern" /> is <see langword="null" />.
		/// </exception>
		public long Find (ByteVector pattern)
		{
			return Find (pattern, 0);
		}

		/// <summary>
		///    Searches backwards through a file for a specified
		///    pattern, starting at a specified offset.
		/// </summary>
		/// <param name="pattern">
		///    A <see cref="ByteVector" /> object containing a pattern
		///    to search for in the current instance.
		/// </param>
		/// <param name="startPosition">
		///    A <see cref="int" /> value specifying at what
		///    seek position to start searching.
		/// </param>
		/// <param name="after">
		///    A <see cref="ByteVector" /> object specifying a pattern
		///    that the searched for pattern must appear after. If this
		///    pattern is found first, -1 is returned.
		/// </param>
		/// <returns>
		///    A <see cref="long" /> value containing the index at which
		///    the value was found. If not found, -1 is returned.
		/// </returns>
		/// <remarks>
		///    Searching for <paramref name="after" /> is not yet
		///    implemented.
		/// </remarks>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="pattern" /> is <see langword="null" />.
		/// </exception>
		long RFind (ByteVector pattern, long startPosition, ByteVector after)
		{
			if (pattern == null)
				throw new ArgumentNullException (nameof (pattern));

			Mode = AccessMode.Read;

			if (pattern.Count > buffer_size)
				return -1;

			// The position in the file that the current buffer
			// starts at.

			ByteVector buffer;

			// These variables are used to keep track of a partial
			// match that happens at the end of a buffer.

			/*
			int previous_partial_match = -1;
			int after_previous_partial_match = -1;
			*/

			// Save the location of the current read pointer.  We
			// will restore the position using Seek() before all 
			// returns.

			long original_position = file_stream.Position;

			// Start the search at the offset.

			long buffer_offset = Length - startPosition;
			int read_size = buffer_size;

			read_size = (int)Math.Min (buffer_offset, buffer_size);
			buffer_offset -= read_size;
			file_stream.Position = buffer_offset;

			// See the notes in find() for an explanation of this
			// algorithm.

			for (buffer = ReadBlock (read_size); buffer.Count > 0; buffer = ReadBlock (read_size)) {

				// TODO: (1) previous partial match

				// (2) pattern contained in current buffer

				long location = buffer.RFind (pattern);
				if (location >= 0) {
					file_stream.Position = original_position;
					return buffer_offset + location;
				}

				if (after != null && buffer.RFind (after) >= 0) {
					file_stream.Position = original_position;
					return -1;
				}

				read_size = (int)Math.Min (buffer_offset, buffer_size);
				buffer_offset -= read_size;
				if (read_size + pattern.Count > buffer_size)
					buffer_offset += pattern.Count;

				file_stream.Position = buffer_offset;
			}

			// Since we hit the end of the file, reset the status
			// before continuing.

			file_stream.Position = original_position;
			return -1;
		}

		/// <summary>
		///    Searches backwards through a file for a specified
		///    pattern, starting at a specified offset.
		/// </summary>
		/// <param name="pattern">
		///    A <see cref="ByteVector" /> object containing a pattern
		///    to search for in the current instance.
		/// </param>
		/// <param name="startPosition">
		///    A <see cref="int" /> value specifying at what
		///    seek position to start searching.
		/// </param>
		/// <returns>
		///    A <see cref="long" /> value containing the index at which
		///    the value was found. If not found, -1 is returned.
		/// </returns>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="pattern" /> is <see langword="null" />.
		/// </exception>
		public long RFind (ByteVector pattern, long startPosition)
		{
			return RFind (pattern, startPosition, null);
		}

		/// <summary>
		///    Searches backwards through a file for a specified
		///    pattern, starting at the end of the file.
		/// </summary>
		/// <param name="pattern">
		///    A <see cref="ByteVector" /> object containing a pattern
		///    to search for in the current instance.
		/// </param>
		/// <returns>
		///    A <see cref="long" /> value containing the index at which
		///    the value was found. If not found, -1 is returned.
		/// </returns>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="pattern" /> is <see langword="null" />.
		/// </exception>
		public long RFind (ByteVector pattern)
		{
			return RFind (pattern, 0);
		}

		/// <summary>
		///    Inserts a specifed block of data into the file repesented
		///    by the current instance at a specified location,
		///    replacing a specified number of bytes.
		/// </summary>
		/// <param name="data">
		///    A <see cref="ByteVector" /> object containing the data to
		///    insert into the file.
		/// </param>
		/// <param name="start">
		///    A <see cref="long" /> value specifying at which point to
		///    insert the data.
		/// </param>
		/// <param name="replace">
		///    A <see cref="long" /> value specifying the number of
		///    bytes to replace. Typically this is the original size of
		///    the data block so that a new block will replace the old
		///    one.
		/// </param>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="data" /> is <see langword="null" />.
		/// </exception>
		public void Insert (ByteVector data, long start, long replace)
		{
			if (data == null)
				throw new ArgumentNullException (nameof (data));

			Insert (data, data.Count, start, replace);
		}



		/// <summary>
		///    Inserts a specified block of data into the file repesented
		///    by the current instance at a specified location.
		/// </summary>
		/// <param name="data">
		///    A <see cref="ByteVector" /> object containing the data to
		///    insert into the file.
		/// </param>
		/// <param name="start">
		///    A <see cref="long" /> value specifying at which point to
		///    insert the data.
		/// </param>
		/// <remarks>
		///    This method inserts a new block of data into the file. To
		///    replace an existing block, ie. replacing an existing
		///    tag with a new one of different size, use <see
		///    cref="Insert(ByteVector,long,long)" />.
		/// </remarks>
		/// <exception cref="ArgumentNullException">
		///    <paramref name="data" /> is <see langword="null" />.
		/// </exception>
		public void Insert (ByteVector data, long start)
		{
			Insert (data, start, 0);
		}

		/// <summary>
		///   Inserts a specified block-size into the file repesented
		///   by the current instance at a specified location. Former
		///   data at this location is not overwriten and may then 
		///   contain random content.
		/// </summary>
		/// <param name="size">
		///   A <see cref="long" /> value specifying the size in bytes
		///   of the block to be inserted (reserved).
		/// </param>
		/// <param name="start">
		///    A <see cref="long" /> value specifying at which point to
		///    insert the data.
		/// </param>
		/// <remarks>
		///    This method is usefull to reserve some space in the file.
		///    To insert or replace defined data blocks, use <see
		///    cref="Insert(ByteVector,long)" /> or 
		///    <see cref="Insert(ByteVector,long,long)"/> 
		/// </remarks>
		public void Insert (long size, long start)
		{
			Insert (null, size, start, 0);
		}


		/// <summary>
		///    Removes a specified block of data from the file
		///    represented by the current instance.
		/// </summary>
		/// <param name="start">
		///    A <see cref="long" /> value specifying at which point to
		///    remove data.
		/// </param>
		/// <param name="length">
		///    A <see cref="long" /> value specifying the number of
		///    bytes to remove.
		/// </param>
		public void RemoveBlock (long start, long length)
		{
			if (length <= 0)
				return;

			Mode = AccessMode.Write;

			int buffer_length = buffer_size;

			long read_position = start + length;
			long write_position = start;

			ByteVector buffer = (byte)1;

			while (buffer.Count != 0) {
				file_stream.Position = read_position;
				buffer = ReadBlock (buffer_length);
				read_position += buffer.Count;

				file_stream.Position = write_position;
				WriteBlock (buffer);
				write_position += buffer.Count;
			}

			Truncate (write_position);
		}

		/// <summary>
		///    Seeks the read/write pointer to a specified offset in the
		///    current instance, relative to a specified origin.
		/// </summary>
		/// <param name="offset">
		///    A <see cref="long" /> value indicating the byte offset to
		///    seek to.
		/// </param>
		/// <param name="origin">
		///    A <see cref="SeekOrigin" /> value specifying an
		///    origin to seek from.
		/// </param>
		public void Seek (long offset, SeekOrigin origin)
		{
			if (Mode != AccessMode.Closed)
				file_stream.Seek (offset, origin);
		}

		/// <summary>
		///    Seeks the read/write pointer to a specified offset in the
		///    current instance, relative to the beginning of the file.
		/// </summary>
		/// <param name="offset">
		///    A <see cref="long" /> value indicating the byte offset to
		///    seek to.
		/// </param>
		public void Seek (long offset)
		{
			Seek (offset, SeekOrigin.Begin);
		}

		#endregion



		#region Public Static Methods

		/// <summary>
		///    Creates a new instance of a <see cref="File" /> subclass
		///    for a specified path, guessing the mime-type from the
		///    file's extension and using the average read style.
		/// </summary>
		/// <param name="path">
		///    A <see cref="string" /> object specifying the file to
		///    read from and write to.
		/// </param>
		/// <returns>
		///    A new instance of <see cref="File" /> as read from the
		///    specified path.
		/// </returns>
		/// <exception cref="CorruptFileException">
		///    The file could not be read due to corruption.
		/// </exception>
		/// <exception cref="UnsupportedFormatException">
		///    The file could not be read because the mime-type could
		///    not be resolved or the library does not support an
		///    internal feature of the file crucial to its reading.
		/// </exception>
		public static File Create (string path)
		{
			return Create (path, null, ReadStyle.Average);
		}

		/// <summary>
		///    Creates a new instance of a <see cref="File" /> subclass
		///    for a specified file abstraction, guessing the mime-type
		///    from the file's extension and using the average read
		///    style.
		/// </summary>
		/// <param name="abstraction">
		///    A <see cref="IFileAbstraction" /> object to use when
		///    reading to and writing from the current instance.
		/// </param>
		/// <returns>
		///    A new instance of <see cref="File" /> as read from the
		///    specified abstraction.
		/// </returns>
		/// <exception cref="CorruptFileException">
		///    The file could not be read due to corruption.
		/// </exception>
		/// <exception cref="UnsupportedFormatException">
		///    The file could not be read because the mime-type could
		///    not be resolved or the library does not support an
		///    internal feature of the file crucial to its reading.
		/// </exception>
		public static File Create (IFileAbstraction abstraction)
		{
			return Create (abstraction, null, ReadStyle.Average);
		}

		/// <summary>
		///    Creates a new instance of a <see cref="File" /> subclass
		///    for a specified path and read style, guessing the
		///    mime-type from the file's extension.
		/// </summary>
		/// <param name="path">
		///    A <see cref="string" /> object specifying the file to
		///    read from and write to.
		/// </param>
		/// <param name="propertiesStyle">
		///    A <see cref="ReadStyle" /> value specifying the level of
		///    detail to use when reading the media information from the
		///    new instance.
		/// </param>
		/// <returns>
		///    A new instance of <see cref="File" /> as read from the
		///    specified path.
		/// </returns>
		/// <exception cref="CorruptFileException">
		///    The file could not be read due to corruption.
		/// </exception>
		/// <exception cref="UnsupportedFormatException">
		///    The file could not be read because the mime-type could
		///    not be resolved or the library does not support an
		///    internal feature of the file crucial to its reading.
		/// </exception>
		public static File Create (string path, ReadStyle propertiesStyle)
		{
			return Create (path, null, propertiesStyle);
		}

		/// <summary>
		///    Creates a new instance of a <see cref="File" /> subclass
		///    for a specified file abstraction and read style, guessing
		///    the mime-type from the file's extension.
		/// </summary>
		/// <param name="abstraction">
		///    A <see cref="IFileAbstraction" /> object to use when
		///    reading to and writing from the current instance.
		/// </param>
		/// <param name="propertiesStyle">
		///    A <see cref="ReadStyle" /> value specifying the level of
		///    detail to use when reading the media information from the
		///    new instance.
		/// </param>
		/// <returns>
		///    A new instance of <see cref="File" /> as read from the
		///    specified abstraction.
		/// </returns>
		/// <exception cref="CorruptFileException">
		///    The file could not be read due to corruption.
		/// </exception>
		/// <exception cref="UnsupportedFormatException">
		///    The file could not be read because the mime-type could
		///    not be resolved or the library does not support an
		///    internal feature of the file crucial to its reading.
		/// </exception>
		public static File Create (IFileAbstraction abstraction, ReadStyle propertiesStyle)
		{
			return Create (abstraction, null, propertiesStyle);
		}

		/// <summary>
		///    Creates a new instance of a <see cref="File" /> subclass
		///    for a specified path, mime-type, and read style.
		/// </summary>
		/// <param name="path">
		///    A <see cref="string" /> object specifying the file to
		///    read from and write to.
		/// </param>
		/// <param name="mimetype">
		///    A <see cref="string" /> object containing the mime-type
		///    to use when selecting the appropriate class to use, or
		///    <see langword="null" /> if the extension in <paramref
		///    name="path" /> is to be used.
		/// </param>
		/// <param name="propertiesStyle">
		///    A <see cref="ReadStyle" /> value specifying the level of
		///    detail to use when reading the media information from the
		///    new instance.
		/// </param>
		/// <returns>
		///    A new instance of <see cref="File" /> as read from the
		///    specified path.
		/// </returns>
		/// <exception cref="CorruptFileException">
		///    The file could not be read due to corruption.
		/// </exception>
		/// <exception cref="UnsupportedFormatException">
		///    The file could not be read because the mime-type could
		///    not be resolved or the library does not support an
		///    internal feature of the file crucial to its reading.
		/// </exception>
		public static File Create (string path, string mimetype, ReadStyle propertiesStyle)
		{
			return Create (new LocalFileAbstraction (path), mimetype, propertiesStyle);
		}

		/// <summary>
		///    Creates a new instance of a <see cref="File" /> subclass
		///    for a specified file abstraction, mime-type, and read
		///    style.
		/// </summary>
		/// <param name="abstraction">
		///    A <see cref="IFileAbstraction" /> object to use when
		///    reading to and writing from the current instance.
		/// </param>
		/// <param name="mimetype">
		///    A <see cref="string" /> object containing the mime-type
		///    to use when selecting the appropriate class to use, or
		///    <see langword="null" /> if the extension in <paramref
		///    name="abstraction" /> is to be used.
		/// </param>
		/// <param name="propertiesStyle">
		///    A <see cref="ReadStyle" /> value specifying the level of
		///    detail to use when reading the media information from the
		///    new instance.
		/// </param>
		/// <returns>
		///    A new instance of <see cref="File" /> as read from the
		///    specified abstraction.
		/// </returns>
		/// <exception cref="CorruptFileException">
		///    The file could not be read due to corruption.
		/// </exception>
		/// <exception cref="UnsupportedFormatException">
		///    The file could not be read because the mime-type could
		///    not be resolved or the library does not support an
		///    internal feature of the file crucial to its reading.
		/// </exception>
		public static File Create (IFileAbstraction abstraction, string mimetype, ReadStyle propertiesStyle)
		{
			if (mimetype == null) {
				string ext = string.Empty;

				int index = abstraction.Name.LastIndexOf (".") + 1;

				if (index >= 1 && index < abstraction.Name.Length)
					ext = abstraction.Name.Substring (index, abstraction.Name.Length - index);

				mimetype = "taglib/" + ext.ToLower (CultureInfo.InvariantCulture);
			}

			foreach (var resolver in file_type_resolvers) {
				var file = resolver (abstraction, mimetype, propertiesStyle);

				if (file != null)
					return file;
			}

			if (!FileTypes.AvailableTypes.ContainsKey (mimetype))
				throw new UnsupportedFormatException (
					string.Format (CultureInfo.InvariantCulture, "{0} ({1})", abstraction.Name, mimetype));

			var file_type = FileTypes.AvailableTypes[mimetype];

			try {
				var file = (File)Activator.CreateInstance (file_type, new object[] { abstraction, propertiesStyle });

				file.MimeType = mimetype;
				return file;
			} catch (System.Reflection.TargetInvocationException e) {
				PrepareExceptionForRethrow (e.InnerException);
				throw e.InnerException;
			}
		}

		/// <summary>
		///    Adds a <see cref="FileTypeResolver" /> to the <see
		///    cref="File" /> class. The one added last gets run first.
		/// </summary>
		/// <param name="resolver">
		///    A <see cref="FileTypeResolver" /> delegate to add to the
		///    file type recognition stack.
		/// </param>
		/// <remarks>
		///    A <see cref="FileTypeResolver" /> adds support for 
		///    recognizing a file type outside of the standard mime-type
		///    methods.
		/// </remarks>
		public static void AddFileTypeResolver (FileTypeResolver resolver)
		{
			if (resolver != null)
				file_type_resolvers.Insert (0, resolver);
		}

		#endregion



		#region Private/Protected Methods

		/// <summary>
		///    Prepare to Save the file. Thismust be called at the begining 
		///    of every File.Save() method.
		/// </summary>
		protected void PreSave ()
		{
			// Check validity

			if (!Writeable)
				throw new InvalidOperationException ("File not writeable.");

			if (PossiblyCorrupt)
				throw new CorruptFileException ("Corrupted file cannot be saved.");

			// All the Lazy objects must be loaded before opening the file
			// in Write mode
			if (Tag?.Pictures != null) {
				foreach (var pic in Tag.Pictures) {
					if (pic is ILazy lazy) {
						lazy.Load ();
					}
				}
			}
		}

		/// <summary>
		///    Inserts a specified block into the file repesented
		///    by the current instance at a specified location.
		/// </summary>
		/// <param name="data">
		///    A <see cref="ByteVector" /> object containing the data to
		///    insert into the file. if null, no data is writen to the
		///    file and the block is just inserted without overwriting the 
		///    former data at the given location.
		/// </param>
		/// <param name="size">
		///    A <see cref="long" /> value specifying the size of the block
		///    to be inserted.
		/// </param>
		/// <param name="start">
		///    A <see cref="long" /> value specifying at which point to
		///    insert the data.
		/// </param>
		/// <param name="replace">
		///    A <see cref="long" /> value specifying the number of
		///    bytes to replace. Typically this is the original size of
		///    the data block so that a new block will replace the old
		///    one.
		/// </param>
		/// <remarks>
		///    This method inserts a new block of data into the file. To
		///    replace an existing block, ie. replacing an existing
		///    tag with a new one of different size, use <see
		///    cref="Insert(ByteVector,long,long)" />.
		/// </remarks>
		void Insert (ByteVector data, long size, long start, long replace)
		{
			Mode = AccessMode.Write;

			if (size == replace) {
				if (data != null) {
					file_stream.Position = start;
					WriteBlock (data);
				}
				return;
			} else if (size < replace) {
				if (data != null) {
					file_stream.Position = start;
					WriteBlock (data);
				}
				RemoveBlock (start + size, replace - size);
				return;
			}

			// Woohoo!  Faster (about 20%) than id3lib at last. I
			// had to get hardcore and avoid TagLib's high level API
			// for rendering just copying parts of the file that
			// don't contain tag data.
			//
			// Now I'll explain the steps in this ugliness:

			// First, make sure that we're working with a buffer
			// that is longer or equal than the *difference* in the tag sizes,
			// and that is a multiple of buffer_size.
			// We want to avoid overwriting parts that aren't yet in
			// memory, so this is necessary.

			int buffer_length = (int)(size - replace);
			int modulo = buffer_length % buffer_size;
			if (modulo != 0) buffer_length += buffer_size - modulo;


			// Set where to start the reading and writing.

			long read_position = start + replace;
			long write_position = start;

			byte[] buffer;
			byte[] about_to_overwrite;

			// This is basically a special case of the loop below.  
			// Here we're just doing the same steps as below, but 
			// since we aren't using the same buffer size -- instead
			// we're using the tag size -- this has to be handled as
			// a special case.  We're also using File::writeBlock()
			// just for the tag. That's a bit slower than using char
			// *'s so, we're only doing it here.

			file_stream.Position = read_position;
			about_to_overwrite = ReadBlock (buffer_length).Data;
			read_position += buffer_length;

			if (data != null) {
				file_stream.Position = write_position;
				WriteBlock (data);
			} else if (start + size > Length) {
				file_stream.SetLength (start + size);
			}
			write_position += size;

			buffer = new byte[about_to_overwrite.Length];
			Array.Copy (about_to_overwrite, 0, buffer, 0,
				about_to_overwrite.Length);

			// Ok, here's the main loop.  We want to loop until the
			// read fails, which means that we hit the end of the 
			// file.

			while (buffer_length != 0) {
				// Seek to the current read position and read
				// the data that we're about to overwrite. 
				// Appropriately increment the readPosition.

				file_stream.Position = read_position;
				int bytes_read = file_stream.Read (
					about_to_overwrite, 0, buffer_length < about_to_overwrite.Length ?
						buffer_length : about_to_overwrite.Length);
				read_position += buffer_length;

				// Seek to the write position and write our
				// buffer. Increment the writePosition.

				file_stream.Position = write_position;
				file_stream.Write (buffer, 0, buffer_length < buffer.Length ? buffer_length : buffer.Length);
				write_position += buffer_length;

				// Make the current buffer the data that we read
				// in the beginning.

				Array.Copy (about_to_overwrite, 0, buffer, 0, bytes_read);

				// Again, we need this for the last write.  We
				// don't want to write garbage at the end of our
				// file, so we need to set the buffer size to
				// the amount that we actually read.

				buffer_length = bytes_read;
			}
		}

		/// <summary>
		///    Resized the current instance to a specified number of
		///    bytes.
		/// </summary>
		/// <param name="length">
		///    A <see cref="long" /> value specifying the number of
		///    bytes to resize the file to.
		/// </param>
		protected void Truncate (long length)
		{
			var old_mode = Mode;
			Mode = AccessMode.Write;
			file_stream.SetLength (length);
			Mode = old_mode;
		}

		/// <summary>
		/// Causes the original strack trace of the exception to be preserved when it is rethrown
		/// </summary>
		/// <param name="ex"></param>
		static void PrepareExceptionForRethrow (Exception ex)
		{
			var ctx = new StreamingContext (StreamingContextStates.CrossAppDomain);
			var mgr = new ObjectManager (null, ctx);
			var si = new SerializationInfo (ex.GetType (), new FormatterConverter ());

			ex.GetObjectData (si, ctx);
			mgr.RegisterObject (ex, 1, si); // prepare for SetObjectData
			mgr.DoFixups (); // ObjectManager calls SetObjectData
		}

		#endregion



		#region Classes

		/// <summary>
		///    This class implements <see cref="IFileAbstraction" />
		///    to provide support for accessing the local/standard file
		///    system.
		/// </summary>
		/// <remarks>
		///    This class is used as the standard file abstraction
		///    throughout the library.
		/// </remarks>
		public class LocalFileAbstraction : IFileAbstraction
		{
			/// <summary>
			///    Contains the name used to open the file.
			/// </summary>
			readonly string name;

			/// <summary>
			///    Constructs and initializes a new instance of
			///    <see cref="LocalFileAbstraction" /> for a
			///    specified path in the local file system.
			/// </summary>
			/// <param name="path">
			///    A <see cref="string" /> object containing the
			///    path of the file to use in the new instance.
			/// </param>
			/// <exception cref="ArgumentNullException">
			///    <paramref name="path" /> is <see langword="null"
			///    />.
			/// </exception>
			public LocalFileAbstraction (string path)
			{
				if (path == null)
					throw new ArgumentNullException (nameof (path));

				name = path;
			}

			/// <summary>
			///    Gets the path of the file represented by the
			///    current instance.
			/// </summary>
			/// <value>
			///    A <see cref="string" /> object containing the
			///    path of the file represented by the current
			///    instance.
			/// </value>
			public string Name => name;

			/// <summary>
			///    Gets a new readable, seekable stream from the
			///    file represented by the current instance.
			/// </summary>
			/// <value>
			///    A new <see cref="Stream" /> to be used
			///    when reading the file represented by the current
			///    instance.
			/// </value>
			public Stream ReadStream => System.IO.File.Open (Name,
				FileMode.Open,
				FileAccess.Read,
				FileShare.Read);

			/// <summary>
			///    Gets a new writable, seekable stream from the
			///    file represented by the current instance.
			/// </summary>
			/// <value>
			///    A new <see cref="Stream" /> to be used
			///    when writing to the file represented by the
			///    current instance.
			/// </value>
			public Stream WriteStream => System.IO.File.Open (Name,
				FileMode.Open,
				FileAccess.ReadWrite);

			/// <summary>
			///    Closes a stream created by the current instance.
			/// </summary>
			/// <param name="stream">
			///    A <see cref="Stream" /> object
			///    created by the current instance.
			/// </param>
			public void CloseStream (Stream stream)
			{
				if (stream == null)
					throw new ArgumentNullException (nameof (stream));

				stream.Close ();
			}
		}

		#endregion



		#region Interfaces

		/// <summary>
		///    This interface provides abstracted access to a file. It
		///    premits access to non-standard file systems and data
		///    retrieval methods.
		/// </summary>
		/// <remarks>
		///    <para>To use a custom abstraction, use <see
		///    cref="Create(IFileAbstraction)" /> instead of <see
		///    cref="Create(string)" /> when creating files.</para>
		/// </remarks>
		/// <example>
		///    <para>The following example uses Gnome VFS to open a file
		///    and read its title.</para>
		/// <code lang="C#">using TagLib;
		///using Gnome.Vfs;
		///
		///public class ReadTitle
		///{
		///   public static void Main (string [] args)
		///   {
		///      if (args.Length != 1)
		///         return;
		///
		///      Gnome.Vfs.Vfs.Initialize ();
		///      
		///      try {
		///          TagLib.File file = TagLib.File.Create (
		///             new VfsFileAbstraction (args [0]));
		///          System.Console.WriteLine (file.Tag.Title);
		///      } finally {
		///         Vfs.Shutdown()
		///      }
		///   }
		///}
		///
		///public class VfsFileAbstraction : TagLib.File.IFileAbstraction
		///{
		///    private string name;
		///
		///    public VfsFileAbstraction (string file)
		///    {
		///        name = file;
		///    }
		///
		///    public string Name {
		///        get { return name; }
		///    }
		///
		///    public System.IO.Stream ReadStream {
		///        get { return new VfsStream(Name, System.IO.FileMode.Open); }
		///    }
		///
		///    public System.IO.Stream WriteStream {
		///        get { return new VfsStream(Name, System.IO.FileMode.Open); }
		///    }
		///
		///    public void CloseStream (System.IO.Stream stream)
		///    {
		///        stream.Close ();
		///    }
		///}</code>
		///    <code lang="Boo">import TagLib from "taglib-sharp.dll"
		///import Gnome.Vfs from "gnome-vfs-sharp"
		///
		///class VfsFileAbstraction (TagLib.File.IFileAbstraction):
		///        
		///        _name as string
		///        
		///        def constructor(file as string):
		///                _name = file
		///        
		///        Name:
		///                get:
		///                        return _name
		///                
		///        ReadStream:
		///                get:
		///                        return VfsStream(_name, FileMode.Open)
		///                
		///        WriteStream:
		///                get:
		///                        return VfsStream(_name, FileMode.Open)
		///        
		///if len(argv) == 1:
		///        Vfs.Initialize()
		///
		///        try:
		///                file as TagLib.File = TagLib.File.Create (VfsFileAbstraction (argv[0]))
		///                print file.Tag.Title
		///        ensure:
		///                Vfs.Shutdown()</code>
		/// </example>
		public interface IFileAbstraction
		{
			/// <summary>
			///    Gets the name or identifier used by the
			///    implementation.
			/// </summary>
			/// <value>
			///    A <see cref="string" /> object containing the 
			///    name or identifier used by the implementation.
			/// </value>
			/// <remarks>
			///    This value would typically represent a path or
			///    URL to be used when identifying the file in the
			///    file system, but it could be any value
			///    as appropriate for the implementation.
			/// </remarks>
			string Name { get; }

			/// <summary>
			///    Gets a readable, seekable stream for the file
			///    referenced by the current instance.
			/// </summary>
			/// <value>
			///    A <see cref="System.IO.Stream" /> object to be
			///    used when reading a file.
			/// </value>
			/// <remarks>
			///    This property is typically used when creating
			///    constructing an instance of <see cref="File" />.
			///    Upon completion of the constructor, <see
			///    cref="CloseStream" /> will be called to close
			///    the stream. If the stream is to be reused after
			///    this point, <see cref="CloseStream" /> should be
			///    implemented in a way to keep it open.
			/// </remarks>
			Stream ReadStream { get; }

			/// <summary>
			///    Gets a writable, seekable stream for the file
			///    referenced by the current instance.
			/// </summary>
			/// <value>
			///    A <see cref="Stream" /> object to be
			///    used when writing to a file.
			/// </value>
			/// <remarks>
			///    This property is typically used when saving a
			///    file with <see cref="Save" />. Upon completion of
			///    the method, <see cref="CloseStream" /> will be
			///    called to close the stream. If the stream is to
			///    be reused after this point, <see
			///    cref="CloseStream" /> should be implemented in a
			///    way to keep it open.
			/// </remarks>
			Stream WriteStream { get; }

			/// <summary>
			///    Closes a stream originating from the current
			///    instance.
			/// </summary>
			/// <param name="stream">
			///    A <see cref="Stream" /> object
			///    originating from the current instance.
			/// </param>
			/// <remarks>
			///    If the stream is to be used outside of the scope,
			///    of TagLib#, this method should perform no action.
			///    For example, a stream that was created outside of
			///    the current instance, or a stream that will
			///    subsequently be used to play the file.
			/// </remarks>
			void CloseStream (Stream stream);
		}

		#endregion
	}
}