using System;
using System.IO;
using System.Collections;

namespace System.Windows.Forms
{
	/// <summary>
	/// Byte provider for (big) files.
	/// </summary>
	public class FileByteProvider : IByteProvider, IDisposable
	{
		#region WriteCollection class
		/// <summary>
		/// Represents the write buffer class
		/// </summary>
		class WriteCollection : DictionaryBase
		{
			/// <summary>
			/// Gets or sets a byte in the collection
			/// </summary>
			public byte this[long index]
			{
				get { return (byte)this.Dictionary[index]; }
				set { Dictionary[index] = value; }
			}

			/// <summary>
			/// Adds a byte into the collection
			/// </summary>
			/// <param name="index">the index of the byte</param>
			/// <param name="value">the value of the byte</param>
			public void Add(long index, byte value)
			{ Dictionary.Add(index, value); }

			/// <summary>
			/// Determines if a byte with the given index exists.
			/// </summary>
			/// <param name="index">the index of the byte</param>
			/// <returns>true, if the is in the collection</returns>
			public bool Contains(long index)
			{ return Dictionary.Contains(index); }

		}
		#endregion

		/// <summary>
		/// Occurs, when the write buffer contains new changes.
		/// </summary>
		public event EventHandler Changed;

		/// <summary>
		/// Contains all changes
		/// </summary>
		WriteCollection _writes = new WriteCollection();

		/// <summary>
		/// Contains the file name.
		/// </summary>
		string _fileName;
		/// <summary>
		/// Contains the file stream.
		/// </summary>
		FileStream _fileStream;
        /// <summary>
        /// Read-only access.
        /// </summary>
        bool _readOnly;

		/// <summary>
		/// Initializes a new instance of the FileByteProvider class.
		/// </summary>
		/// <param name="fileName"></param>
		public FileByteProvider(string fileName)
		{
			_fileName = fileName;

            try
            {
                // try to open in write mode
                _fileStream = File.Open(fileName, FileMode.Open, FileAccess.ReadWrite, FileShare.Read);
            }
            catch
            {
                // write mode failed, try to open in read-only and fileshare friendly mode.
                try
                {
                    _fileStream = File.Open(fileName, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                    _readOnly = true;
                }
                catch
                {
                    throw;
                }
            }
		}

		/// <summary>
		/// Terminates the instance of the FileByteProvider class.
		/// </summary>
		~FileByteProvider()
		{
			Dispose();
		}

		/// <summary>
		/// Raises the Changed event.
		/// </summary>
		/// <remarks>Never used.</remarks>
		void OnChanged(EventArgs e)
		{
			if(Changed != null)
				Changed(this, e);
		}

		/// <summary>
		/// Gets the name of the file the byte provider is using.
		/// </summary>
		public string FileName
		{
			get { return _fileName; }
		}

		/// <summary>
		/// Returns a value if there are some changes.
		/// </summary>
		/// <returns>true, if there are some changes</returns>
		public bool HasChanges()
		{ 
			return (_writes.Count > 0); 
		}

		/// <summary>
		/// Updates the file with all changes the write buffer contains.
		/// </summary>
		public void ApplyChanges()
		{
            if (this._readOnly)
            {
                throw new Exception("File is in read-only mode.");
            }

			if(!HasChanges())
				return;

			IDictionaryEnumerator en = _writes.GetEnumerator();
			while(en.MoveNext())
			{
				long index = (long)en.Key;
				byte value = (byte)en.Value;
				if(_fileStream.Position != index)
					_fileStream.Position = index;
				_fileStream.Write(new byte[]{value}, 0, 1);
			}
			_writes.Clear();
		}

		/// <summary>
		/// Clears the write buffer and reject all changes made.
		/// </summary>
		public void RejectChanges()
		{
			_writes.Clear();
		}

		#region IByteProvider Members
		/// <summary>
		/// Never used.
		/// </summary>
#pragma warning disable 67
        public event EventHandler LengthChanged;
#pragma warning restore 67

        /// <summary>
		/// Reads a byte from the file.
		/// </summary>
		/// <param name="index">the index of the byte to read</param>
		/// <returns>the byte</returns>
		public byte ReadByte(long index)
		{
			if(_writes.Contains(index))
				return _writes[index];

			if(_fileStream.Position != index)
				_fileStream.Position = index;

			byte res = (byte)_fileStream.ReadByte();
			return res;
		}

		/// <summary>
		/// Gets the length of the file.
		/// </summary>
		public long Length
		{
			get
			{
				return _fileStream.Length;
			}
		}

		/// <summary>
		/// Writes a byte into write buffer
		/// </summary>
		public void WriteByte(long index, byte value)
		{
			if(_writes.Contains(index))
				_writes[index] = value;
			else
				_writes.Add(index, value);

			OnChanged(EventArgs.Empty);
		}

		/// <summary>
		/// Not supported
		/// </summary>
		public void DeleteBytes(long index, long length)
		{
			throw new NotSupportedException("FileByteProvider.DeleteBytes");
		}

		/// <summary>
		/// Not supported
		/// </summary>
		public void InsertBytes(long index, byte[] bs)
		{  
			throw new NotSupportedException("FileByteProvider.InsertBytes");
		}

		/// <summary>
		/// Returns true
		/// </summary>
		public bool SupportsWriteByte()
		{
			return !_readOnly;
		}

		/// <summary>
		/// Returns false
		/// </summary>
		public bool SupportsInsertBytes()
		{
			return false;
		}

		/// <summary>
		/// Returns false
		/// </summary>
		public bool SupportsDeleteBytes()
		{
			return false;
		}
		#endregion

		#region IDisposable Members
		/// <summary>
		/// Releases the file handle used by the FileByteProvider.
		/// </summary>
		public void Dispose()
		{
			if(_fileStream != null)
			{
				_fileName = null;

				_fileStream.Close();
				_fileStream = null;
			}

			GC.SuppressFinalize(this);
		}
		#endregion
	}
}
