using System;
using System.IO;

namespace NetVips;

/// <summary>
/// An target connected to a writable <see cref="Stream"/>.
/// </summary>
internal class TargetStream : TargetCustom
{
    /// <summary>
    /// Write to this stream.
    /// </summary>
    private readonly Stream _stream;

    /// <summary>
    /// The start position within the stream.
    /// </summary>
    private readonly long _startPosition;

    /// <inheritdoc cref="GObject"/>
    internal TargetStream(Stream stream)
    {
        var readable = stream.CanRead;
        var seekable = stream.CanSeek;

        _stream = stream;
        _startPosition = seekable ? _stream.Position : 0;

        OnWrite += Write;
        if (readable)
        {
            OnRead += Read;
        }
        if (seekable)
        {
            OnSeek += Seek;
        }
        OnEnd += End;
    }

    /// <summary>
    /// Create a <see cref="TargetStream"/> which will output to a <see cref="Stream"/>.
    /// </summary>
    /// <param name="stream">Write to this stream.</param>
    /// <returns>A new <see cref="TargetStream"/>.</returns>
    /// <exception cref="T:System.ArgumentException">If <paramref name="stream"/> is not writable.</exception>
    internal static TargetStream NewFromStream(Stream stream)
    {
        if (!stream.CanWrite)
        {
            throw new ArgumentException("The stream should be writable.", nameof(stream));
        }

        return new TargetStream(stream);
    }

    /// <summary>
    /// Attach a write handler.
    /// </summary>
    /// <param name="buffer">An array of bytes.</param>
    /// <param name="length">The number of bytes to be written to the current stream.</param>
    /// <returns>The total number of bytes written to the stream.</returns>
    private long Write(byte[] buffer, int length)
    {
        try
        {
            _stream.Write(buffer, 0, length);
        }
        catch
        {
            return -1;
        }

        return length;
    }

    /// <summary>
    /// Attach a read handler.
    /// </summary>
    /// <param name="buffer">An array of bytes.</param>
    /// <param name="length">The maximum number of bytes to be read.</param>
    /// <returns>The total number of bytes read into the buffer.</returns>
    public int Read(byte[] buffer, int length)
    {
        return _stream.Read(buffer, 0, length);
    }

    /// <summary>
    /// Attach a seek handler.
    /// </summary>
    /// <param name="offset">A byte offset relative to the <paramref name="origin"/>
    /// parameter.</param>
    /// <param name="origin">A value of type <see cref="SeekOrigin"/> indicating the
    /// reference point used to obtain the new position.</param>
    /// <returns>The new position within the current stream.</returns>
    public long Seek(long offset, SeekOrigin origin)
    {
        try
        {
            return origin switch
            {
                SeekOrigin.Begin => _stream.Seek(_startPosition + offset, SeekOrigin.Begin) - _startPosition,
                SeekOrigin.Current => _stream.Seek(offset, SeekOrigin.Current) - _startPosition,
                SeekOrigin.End => _stream.Seek(offset, SeekOrigin.End) - _startPosition,
                _ => -1
            };
        }
        catch
        {
            return -1;
        }
    }

    /// <summary>
    /// Attach a end handler.
    /// </summary>
    /// <returns>0 on success, -1 on error.</returns>
    public int End()
    {
        try
        {
            _stream.Flush();
        }
        catch
        {
            return -1;
        }

        return 0;
    }
}