using System;
using System.IO;

namespace Susurrus.UnitTests
{
    /// <summary>
    /// A forward-only stream that hands out at most a few bytes per read, as a network or compressed stream can.
    /// </summary>
    public class TrickleStream : Stream
    {
        private readonly byte[] data;
        private readonly int bytesPerRead;
        private int position;

        public TrickleStream(byte[] data, int bytesPerRead)
        {
            this.data = data;
            this.bytesPerRead = bytesPerRead;
        }

        public override bool CanRead => true;

        public override bool CanSeek => false;

        public override bool CanWrite => false;

        public override long Length => throw new NotSupportedException();

        public override long Position
        {
            get => throw new NotSupportedException();
            set => throw new NotSupportedException();
        }

        public override int Read(byte[] buffer, int offset, int count)
        {
            int read = Math.Min(Math.Min(count, bytesPerRead), data.Length - position);
            Buffer.BlockCopy(data, position, buffer, offset, read);
            position += read;
            return read;
        }

        public override void Flush()
        {
        }

        public override long Seek(long offset, SeekOrigin origin)
        {
            throw new NotSupportedException();
        }

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

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