using System;
using System.IO;

namespace Susurrus.UnitTests
{
    /// <summary>
    /// A seekable stream that reports a length different from the bytes it holds, as a damaged or hostile source can.
    /// </summary>
    public class ClaimedLengthStream : Stream
    {
        private readonly byte[] data;
        private readonly long claimedLength;

        public ClaimedLengthStream(byte[] data, long claimedLength)
        {
            this.data = data;
            this.claimedLength = claimedLength;
        }

        public override bool CanRead => true;

        public override bool CanSeek => true;

        public override bool CanWrite => false;

        public override long Length => claimedLength;

        public override long Position { get; set; }

        public override int Read(byte[] buffer, int offset, int count)
        {
            if (Position >= data.Length)
            {
                return 0;
            }

            int read = (int)Math.Min(count, data.Length - Position);
            Buffer.BlockCopy(data, (int)Position, buffer, offset, read);
            Position += read;
            return read;
        }

        public override void Flush()
        {
        }

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

            return Position;
        }

        public override void SetLength(long value)
        {
            throw new NotSupportedException();
        }

        public override void Write(byte[] buffer, int offset, int count)
        {
            throw new NotSupportedException();
        }
    }
}