using System.IO;
using File = System.IO.File;

namespace DTLib;

/// <summary>
/// Stream wrapper for some operations over data chunks.
/// You can add multiple transform operations.
/// <example><code>
/// using var pipe = new TransformStream(File.OpenRead("encrypted"))
///     .AddTransform(ReportProgress)
///     .AddTransform(Decrypt);
/// using var o = File.OpenWrite("decrypted");
/// pipe.CopyTo(o);
/// </code></example>
/// </summary>
public class TransformStream : Stream
{
    private readonly Stream _inputStream;
    
    public delegate void TransformFuncDelegate(byte[] buffer, int offset, int count);
    private List<TransformFuncDelegate> _transformFunctions = new();

    public TransformStream(Stream inputStream)
    {
        _inputStream = inputStream;
    }

    public TransformStream AddTransform(TransformFuncDelegate f)
    {
        _transformFunctions.Add(f);
        return this;
    }
    
    public TransformStream AddTransforms(IEnumerable<TransformFuncDelegate> f)
    {
        _transformFunctions.AddRange(f);
        return this;
    }
    
    public override bool CanRead => _inputStream.CanRead;
    public override bool CanSeek => _inputStream.CanSeek;
    public override bool CanWrite => false;
    public override long Length => _inputStream.Length;
    public override long Position { get => _inputStream.Position; set => _inputStream.Position = value; }
    
    public override int Read(byte[] buffer, int offset, int count)
    {
        int read = _inputStream.Read(buffer, offset, count);
        if(read > 0)
        {
            for (int i = 0; i < _transformFunctions.Count; i++)
            {
                _transformFunctions[i].Invoke(buffer, offset, read);
            }
        }
        return read;
    }
    
    public override void Flush() {}

    public override long Seek(long offset, SeekOrigin origin) => _inputStream.Seek(offset, origin);

    public override void SetLength(long value) => throw new NotImplementedException();

    public override void Write(byte[] buffer, int offset, int count) => throw new NotImplementedException();

    public override void Close() => _inputStream.Close();
}