// dnlib: See LICENSE.txt for more info

using System;
using System.IO;

namespace dnlib.IO {
	sealed class DataReaderStream : Stream {
		public override bool CanRead => true;
		public override bool CanSeek => true;
		public override bool CanWrite => false;
		public override long Length => reader.Length;

		public override long Position {
			get => position;
			set => position = value;
		}

		DataReader reader;
		long position;

		public DataReaderStream(in DataReader reader) {
			this.reader = reader;
			position = reader.Position;
		}

		public override void Flush() { }

		bool CheckAndSetPosition() {
			if ((ulong)position > reader.Length)
				return false;
			reader.Position = (uint)position;
			return true;
		}

		public override long Seek(long offset, SeekOrigin origin) {
			switch (origin) {
			case SeekOrigin.Begin:		Position = offset; break;
			case SeekOrigin.Current:	Position += offset; break;
			case SeekOrigin.End:		Position = Length + offset; break;
			}
			return Position;
		}

		public override int Read(byte[] buffer, int offset, int count) {
			if (buffer is null)
				throw new ArgumentNullException(nameof(buffer));
			if (offset < 0)
				throw new ArgumentOutOfRangeException(nameof(offset));
			if (count < 0)
				throw new ArgumentOutOfRangeException(nameof(count));
			if (!CheckAndSetPosition())
				return 0;
			int bytesToRead = (int)Math.Min((uint)count, reader.BytesLeft);
			reader.ReadBytes(buffer, offset, bytesToRead);
			Position += bytesToRead;
			return bytesToRead;
		}

		public override int ReadByte() {
			if (!CheckAndSetPosition() || !reader.CanRead(1U))
				return -1;
			Position++;
			return reader.ReadByte();
		}

		public override void SetLength(long value) => throw new NotSupportedException();
		public override void Write(byte[] buffer, int offset, int count) => throw new NotSupportedException();
	}
}