.NET Shell Extensions - Shell Property Sheets

using System;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.InteropServices.ComTypes;
using STATSTG = System.Runtime.InteropServices.ComTypes.STATSTG;

namespace SharpShell.Helpers
{
    /// <summary>
    /// A ComStream is a wrapper around the COM IStream interface,
    /// providing direct .NET style access to a COM IStream.
    /// </summary>
    public class ComStream : Stream
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="ComStream" /> class.
        /// </summary>
        /// <param name="comStream">The source COM stream.</param>
        public ComStream(IStream comStream)
        {
            //  Set the stream.
            this.comStream = comStream;
            bufferPointer = Marshal.AllocCoTaskMem(8);
        }

        /// <summary>
        /// Finalizes an instance of the <see cref="ComStream"/> class.
        /// </summary>
        ~ComStream()
        {
            Marshal.FreeCoTaskMem(bufferPointer);
        }

        /// <summary>
        /// When overridden in a derived class, clears all buffers for this stream and causes 
        /// any buffered data to be written to the underlying device.
        /// </summary>
        public override void Flush()
        {
            //  Commit the underlying COM stream.
            comStream.Commit(0);
        }


        public override int Read(byte[] buffer, int offset, int count)
        {
            if (offset != 0) 
                throw new NotImplementedException();
            comStream.Read(buffer, count, bufferPointer);
            return Marshal.ReadInt32(bufferPointer);
        }

        /// <summary>
        /// When overridden in a derived class, sets the position within the current stream.
        /// </summary>
        /// <param name="offset">A byte offset relative to the <paramref name="origin" /> parameter.</param>
        /// <param name="origin">A value of type <see cref="T:System.IO.SeekOrigin" /> indicating the reference point used to obtain the new position.</param>
        /// <returns>
        /// The new position within the current stream.
        /// </returns>
        public override long Seek(long offset, SeekOrigin origin)
        {
            comStream.Seek(offset, (int)origin, bufferPointer);
            return Marshal.ReadInt64(bufferPointer);
        }

        /// <summary>
        /// When overridden in a derived class, sets the length of the current stream.
        /// </summary>
        /// <param name="value">The desired length of the current stream in bytes.</param>
        public override void SetLength(long value)
        {
            comStream.SetSize(value);
        }

        /// <summary>
        /// When overridden in a derived class, writes a sequence of bytes to the current stream and advances the current position within this stream by the number of bytes written.
        /// </summary>
        /// <param name="buffer">An array of bytes. This method copies <paramref name="count" /> bytes from <paramref name="buffer" /> to the current stream.</param>
        /// <param name="offset">The zero-based byte offset in <paramref name="buffer" /> at which to begin copying bytes to the current stream.</param>
        /// <param name="count">The number of bytes to be written to the current stream.</param>
        /// <exception cref="System.NotImplementedException"></exception>
        public override void Write(byte[] buffer, int offset, int count)
        {
            if (offset != 0) 
                throw new NotImplementedException();
            comStream.Write(buffer, count, IntPtr.Zero);
        }

        /// <summary>
        /// The COM stream instance.
        /// </summary>
        private readonly IStream comStream;

        /// <summary>
        /// The buffer pointer.
        /// </summary>
        private readonly IntPtr bufferPointer;

        /// <summary>
        /// When overridden in a derived class, gets a value indicating whether the current stream supports reading.
        /// </summary>
        /// <returns>true if the stream supports reading; otherwise, false.</returns>
        public override bool CanRead
        {
            get { return true; }
        }

        /// <summary>
        /// When overridden in a derived class, gets a value indicating whether the current stream supports seeking.
        /// </summary>
        /// <returns>true if the stream supports seeking; otherwise, false.</returns>
        public override bool CanSeek
        {
            get { return true; }
        }

        /// <summary>
        /// When overridden in a derived class, gets a value indicating whether the current stream supports writing.
        /// </summary>
        /// <returns>true if the stream supports writing; otherwise, false.</returns>
        public override bool CanWrite
        {
            get { return true; }
        }

        /// <summary>
        /// When overridden in a derived class, gets the length in bytes of the stream.
        /// </summary>
        /// <returns>A long value representing the length of the stream in bytes.</returns>
        public override long Length
        {
            get
            {
                //  Get the statistics of the COM stream, return the size.
                STATSTG stat;
                comStream.Stat(out stat, 1);
                return stat.cbSize;
            }
        }

        /// <summary>
        /// When overridden in a derived class, gets or sets the position within the current stream.
        /// </summary>
        /// <returns>The current position within the stream.</returns>
        /// <exception cref="System.NotImplementedException">
        /// </exception>
        public override long Position
        {
            get { throw new NotImplementedException(); }
            set { throw new NotImplementedException(); }
        }
    }
}