using System;
using System.IO;

namespace Lumpio.Gif {
	public class BitPacker {
		private Stream stream;
		private byte[] buffer;
		private int pos;
		private ushort need;
		
		private ulong bytesWritten;
		public ulong BytesWritten {
			get {
				return bytesWritten;
			}
		}
		
		private int addCodeToBuffer(ulong code, short n) {
			ulong mask;

			if (n < 0) {
				if (need < 8) {
					pos++;
					buffer[pos] = 0x00;
				}
				need = 8;
				return pos;
			}
			while (n >= need) {
				mask = (ulong)(1 << need) - 1;
				buffer[pos] |= (byte)((mask & code) << (8 - need));
				pos++;
				buffer[pos] = 0x00;
				code = code >> need;
				n -= (short)need;
				need = 8;
			}
			if (n > 0) {
				mask = (ulong)(1 << n) - 1;
				buffer[pos] |= (byte)((mask & code) << (8 - need));
				need -= (ushort)n;
			}
			return pos;
		}

		public BitPacker(Stream stream) {
			this.stream = stream;
			need = 8;
			buffer = new byte[260];
			bytesWritten = 0;
			pos = 0;
			buffer[0] = 0x00;
		}

		public int Submit(ulong code, ushort n) {
			addCodeToBuffer(code, (short)n);
			if (pos >= 255) {
				stream.WriteByte(255);
				stream.Write(buffer, 0, 255);
				buffer[0] = buffer[255];
				buffer[1] = buffer[256];
				buffer[2] = buffer[257];
				buffer[3] = buffer[258];
				pos -= 255;
				bytesWritten += 256;
			}
			return pos;
		}

		public void WriteFlush() {
			addCodeToBuffer(0, -1);
			if (pos <= 0) {
				return;
			}
			stream.WriteByte((byte)pos);
			stream.Write(buffer, 0, pos);
			bytesWritten += (ulong)pos + 1;
			pos = 0;
			buffer[0] = 0x00;
			need = 8;
		}
	}
}