//
// System.IO.MemoryStream 
//
// Authors:	Marcin Szczepanski (marcins@zipworld.com.au)
//		Patrik Torstensson
//		Gonzalo Paniagua Javier (gonzalo@ximian.com)
//
// (c) 2001,2002 Marcin Szczepanski, Patrik Torstensson
// (c) 2003 Ximian, Inc. (http://www.ximian.com)
//

namespace System.IO
{
	[Serializable]
	public class MemoryStream : Stream
	{
		bool canWrite;
		bool allowGetBuffer;
		int capacity;
		int length;
		byte [] internalBuffer;
		int initialIndex;
		bool expandable;
		bool streamClosed;
		int position;

		public MemoryStream () : this (0)
		{
		}

		public MemoryStream (int capacity)
		{
			if (capacity < 0)
				throw new ArgumentOutOfRangeException ("capacity");

			canWrite = true;

			this.capacity = capacity;
			internalBuffer = new byte [capacity];

			expandable = true;
			allowGetBuffer = true;
		}

		public MemoryStream (byte [] buffer)
		{
			InternalConstructor (buffer, 0, buffer.Length, true, false);                        
		}

		public MemoryStream (byte [] buffer, bool writeable)
		{
			InternalConstructor (buffer, 0, buffer.Length, writeable, false);
		}

		public MemoryStream (byte [] buffer, int index, int count)
		{
			InternalConstructor (buffer, index, count, true, false);
		}

		public MemoryStream (byte [] buffer, int index, int count, bool writeable)
		{
			InternalConstructor (buffer, index, count, writeable, false);
		}

		public MemoryStream (byte [] buffer, int index, int count, bool writeable, bool publicallyVisible)
		{
			InternalConstructor (buffer, index, count, writeable, publicallyVisible);
		}

		void InternalConstructor (byte [] buffer, int index, int count, bool writeable, bool publicallyVisible)
		{
			if (buffer == null)
				throw new ArgumentNullException ("buffer");

			if (index < 0 || count < 0)
				throw new ArgumentOutOfRangeException ("index or count is less than 0.");

			if (buffer.Length - index < count)
				throw new ArgumentException ("index+count", 
							     "The size of the buffer is less than index + count.");

			canWrite = writeable;

			internalBuffer = buffer;
			capacity = count + index;
			length = capacity;
			position = index;
			initialIndex = index;

			allowGetBuffer = publicallyVisible;
			expandable = false;                
		}

		void CheckIfClosedThrowDisposed ()
		{
			if (streamClosed)
				throw new ObjectDisposedException ("MemoryStream");
		}
		
		void CheckIfClosedThrowIO ()
		{
			if (streamClosed)
				throw new IOException ("MemoryStream is closed");
		}
		
		public override bool CanRead {
			get { return !streamClosed; }
		}

		public override bool CanSeek {
			get { return !streamClosed; }
		}

		public override bool CanWrite {
			get { return (!streamClosed && canWrite); }
		}

		public virtual int Capacity {
			get {
				CheckIfClosedThrowDisposed ();
				return capacity - initialIndex;
			}

			set {
				CheckIfClosedThrowDisposed ();
				if (value == capacity)
					return; // LAMENESS: see MemoryStreamTest.ConstructorFive

				if (!expandable)
					throw new NotSupportedException ("Cannot expand this MemoryStream");

				if (value < 0 || value < length)
					throw new ArgumentOutOfRangeException ("value",
					"New capacity cannot be negative or less than the current capacity " + value + " " + capacity);

				byte [] newBuffer = null;
				if (value != 0) {
					newBuffer = new byte [value];
					Buffer.BlockCopyInternal (internalBuffer, 0, newBuffer, 0, length);
				}

				internalBuffer = newBuffer; // It's null when capacity is set to 0
				capacity = value;
			}
		}

		public override long Length {
			get {
				// LAMESPEC: The spec says to throw an IOException if the
				// stream is closed and an ObjectDisposedException if
				// "methods were called after the stream was closed".  What
				// is the difference?

				CheckIfClosedThrowIO ();

				// This is ok for MemoryStreamTest.ConstructorFive
				return length - initialIndex;
			}
		}

		public override long Position {
			get {
				CheckIfClosedThrowIO ();
				return position - initialIndex;
			}

			set {
				CheckIfClosedThrowIO ();
				if (value < 0)
					throw new ArgumentOutOfRangeException ("value",
								"Position cannot be negative" );

				if (value > Int32.MaxValue)
					throw new ArgumentOutOfRangeException ("value",
					"Position must be non-negative and less than 2^31 - 1 - origin");

				position = initialIndex + (int) value;
			}
		}

		public override void Close ()
		{
			streamClosed = true;
			expandable = false;
		}

		public override void Flush ()
		{
			// Do nothing
		}

		public virtual byte [] GetBuffer ()
		{
			if (!allowGetBuffer)
				throw new UnauthorizedAccessException ();

			return internalBuffer;
		}

		public override int Read (byte [] buffer, int offset, int count)
		{
			CheckIfClosedThrowDisposed ();

			if (buffer == null)
				throw new ArgumentNullException ("buffer");

			if (offset < 0 || count < 0)
				throw new ArgumentOutOfRangeException ("offset or count less than zero.");

			if (buffer.Length - offset < count )
				throw new ArgumentException ("offset+count",
							      "The size of the buffer is less than offset + count.");

			if (position >= length || count == 0)
				return 0;

			if (position > length - count)
				count = length - position;

			Buffer.BlockCopyInternal (internalBuffer, position, buffer, offset, count);
			position += count;
			return count;
		}

		public override int ReadByte ()
		{
			CheckIfClosedThrowDisposed ();
			if (position >= length)
				return -1;

			return internalBuffer [position++];
		}

		public override long Seek (long offset, SeekOrigin loc)
		{
			CheckIfClosedThrowDisposed ();

			// It's funny that they don't throw this exception for < Int32.MinValue
			if (offset > (long) Int32.MaxValue)
				throw new ArgumentOutOfRangeException ("Offset out of range. " + offset);

			int refPoint;
			switch (loc) {
			case SeekOrigin.Begin:
				if (offset < 0)
					throw new IOException ("Attempted to seek before start of MemoryStream.");
				refPoint = initialIndex;
				break;
			case SeekOrigin.Current:
				refPoint = position;
				break;
			case SeekOrigin.End:
				refPoint = length;
				break;
			default:
				throw new ArgumentException ("loc", "Invalid SeekOrigin");
			}

			// LAMESPEC: My goodness, how may LAMESPECs are there in this
			// class! :)  In the spec for the Position property it's stated
			// "The position must not be more than one byte beyond the end of the stream."
			// In the spec for seek it says "Seeking to any location beyond the length of the 
			// stream is supported."  That's a contradiction i'd say.
			// I guess seek can go anywhere but if you use position it may get moved back.

			refPoint += (int) offset;
			if (refPoint < initialIndex)
				throw new IOException ("Attempted to seek before start of MemoryStream.");

			position = refPoint;
			return position;
		}

		int CalculateNewCapacity (int minimum)
		{
			if (minimum < 256)
				minimum = 256; // See GetBufferTwo test

			if (minimum < capacity * 2)
				minimum = capacity * 2;

			return minimum;
		}

		public override void SetLength (long value)
		{
			CheckIfClosedThrowDisposed ();
			if (!expandable && value > capacity)
				throw new NotSupportedException ("Expanding this MemoryStream is not supported");

			if (!canWrite)
				throw new IOException ("Cannot write to this MemoryStream");

			// LAMESPEC: AGAIN! It says to throw this exception if value is
			// greater than "the maximum length of the MemoryStream".  I haven't
			// seen anywhere mention what the maximum length of a MemoryStream is and
			// since we're this far this memory stream is expandable.
			if (value < 0 || (value + initialIndex) > (long) Int32.MaxValue)
				throw new ArgumentOutOfRangeException ();

			int newSize = (int) value + initialIndex;
			if (newSize > capacity) {
				Capacity = CalculateNewCapacity (newSize);
			} else if (newSize > length) {
				for (int i = newSize; i < length; i++)
					Buffer.SetByte (internalBuffer, i, 0);
			}

			length = newSize;
			if (position > length)
				position = length;
		}

		public virtual byte [] ToArray ()
		{
			int l = length - initialIndex;
			byte[] outBuffer = new byte [l];

			Buffer.BlockCopyInternal (internalBuffer, initialIndex, outBuffer, 0, l);
			return outBuffer; 
		}

		public override void Write (byte [] buffer, int offset, int count)
		{
			CheckIfClosedThrowDisposed ();

			if (!canWrite)
				throw new NotSupportedException ("Cannot write to this stream.");

			if (buffer == null)
				throw new ArgumentNullException ("buffer");
			
			if (offset < 0 || count < 0)
				throw new ArgumentOutOfRangeException ();

			if (buffer.Length - offset < count)
				throw new ArgumentException ("offset+count",
							     "The size of the buffer is less than offset + count.");

			if (position + count > capacity)
				Capacity = CalculateNewCapacity (position + count);

			Buffer.BlockCopyInternal (buffer, offset, internalBuffer, position, count);
			position += count;
			if (position >= length)
				length = position;
		}

		public override void WriteByte (byte value)
		{
			CheckIfClosedThrowDisposed ();
			if (!canWrite)
				throw new NotSupportedException ("Cannot write to this stream.");

			if (position + 1 >= capacity)
				Capacity = CalculateNewCapacity (position + 1);

			if (position >= length)
				length = position + 1;

			internalBuffer [position++] = value;
		}

		public virtual void WriteTo (Stream stream)
		{
			CheckIfClosedThrowDisposed ();

			if (stream == null)
				throw new ArgumentNullException ("stream");

			stream.Write (internalBuffer, initialIndex, length - initialIndex);
		}
	}               
}