using System;

namespace SevenZip.Compression.RangeCoder
{
	class Decoder
	{
		public const uint kTopValue = (1 << 24);
		public uint Range;
		public uint Code;
		// public Buffer.InBuffer Stream = new Buffer.InBuffer(1 << 16);
		public System.IO.Stream Stream;

		public void Init(System.IO.Stream stream)
		{
			// Stream.Init(stream);
			Stream = stream;

			Code = 0;
			Range = 0xFFFFFFFF;
			for (int i = 0; i < 5; i++)
				Code = (Code << 8) | (byte)Stream.ReadByte();
		}

		public void ReleaseStream()
		{
			// Stream.ReleaseStream();
			Stream = null;
		}

		public void CloseStream()
		{
			Stream.Close();
		}

		public void Normalize()
		{
			while (Range < kTopValue)
			{
				Code = (Code << 8) | (byte)Stream.ReadByte();
				Range <<= 8;
			}
		}

		public void Normalize2()
		{
			if (Range < kTopValue)
			{
				Code = (Code << 8) | (byte)Stream.ReadByte();
				Range <<= 8;
			}
		}

		public uint GetThreshold(uint total)
		{
			return Code / (Range /= total);
		}

		public void Decode(uint start, uint size, uint total)
		{
			Code -= start * Range;
			Range *= size;
			Normalize();
		}

		public uint DecodeDirectBits(int numTotalBits)
		{
			uint range = Range;
			uint code = Code;
			uint result = 0;
			for (int i = numTotalBits; i > 0; i--)
			{
				range >>= 1;
				/*
				result <<= 1;
				if (code >= range)
				{
					code -= range;
					result |= 1;
				}
				*/
				uint t = (code - range) >> 31;
				code -= range & (t - 1);
				result = (result << 1) | (1 - t);

				if (range < kTopValue)
				{
					code = (code << 8) | (byte)Stream.ReadByte();
					range <<= 8;
				}
			}
			Range = range;
			Code = code;
			return result;
		}

		public uint DecodeBit(uint size0, int numTotalBits)
		{
			uint newBound = (Range >> numTotalBits) * size0;
			uint symbol;
			if (Code < newBound)
			{
				symbol = 0;
				Range = newBound;
			}
			else
			{
				symbol = 1;
				Code -= newBound;
				Range -= newBound;
			}
			Normalize();
			return symbol;
		}

		// ulong GetProcessedSize() {return Stream.GetProcessedSize(); }
	}
}