using System.Diagnostics;
using System.IO;
using ytLive.Services.Encoder;

namespace ytLive.Services;

/// <summary>
/// TASK 64: reads ONE frame out of a video file so the app can look at its background before
/// the creator says anything. Kept behind an interface so tests never spawn ffmpeg, and separate
/// from the decode pipe because this is a read, not a playback session.
/// </summary>
public interface IChromaProbe
{
    /// <summary>The file's first usable frame at a small size, or null when it cannot be read
    /// (bad path, unsupported file, ffmpeg gave nothing). Null is a normal answer: the layer
    /// simply gets no suggestion.</summary>
    Task<VideoFrame?> ProbeAsync(string path, CancellationToken cancellationToken = default);
}

/// <summary>Default <see cref="IChromaProbe"/>: one ffmpeg pass, scaled to 160×90 so the look is
/// cheap and the detector sees plenty of the backdrop.</summary>
public sealed class FfmpegChromaProbe : IChromaProbe
{
    private const int ProbeWidth = 160;
    private const int ProbeHeight = 90;

    private readonly IFfmpegLocator _locator;
    private readonly Func<IDecodeProcess> _processFactory;

    public FfmpegChromaProbe(IFfmpegLocator locator, Func<IDecodeProcess> processFactory)
    {
        _locator = locator;
        _processFactory = processFactory;
    }

    public async Task<VideoFrame?> ProbeAsync(string path, CancellationToken cancellationToken = default)
    {
        if (string.IsNullOrWhiteSpace(path)) return null;
        try
        {
            var ffmpegPath = await _locator.LocateAsync(cancellationToken).ConfigureAwait(false);
            var args =
                $"-hide_banner -loglevel error -i \"{path}\" -frames:v 1 -an " +
                $"-f rawvideo -pix_fmt bgra -vf scale={ProbeWidth}:{ProbeHeight} -";

            using var process = _processFactory();
            process.Start(new ProcessStartInfo
            {
                FileName = ffmpegPath,
                Arguments = args,
                UseShellExecute = false,
                RedirectStandardOutput = true,
                RedirectStandardError = true,
                CreateNoWindow = true,
            });

            var frames = await Task.Run(() =>
            {
                using var buffer = new MemoryStream();
                process.StandardOutput.CopyTo(buffer);
                var reader = new RawVideoFrameReader(ProbeWidth, ProbeHeight);
                var fed = reader.Feed(buffer.ToArray());
                return fed;
            }, cancellationToken).ConfigureAwait(false);

            return frames.Count > 0 ? frames[0] : null;
        }
        catch (Exception ex)
        {
            Helpers.AppLog.Write($"ChromaProbe: '{Path.GetFileName(path)}' unreadable: {ex.Message}");
            return null;
        }
    }
}