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

namespace ytLive.Tests;

/// <summary>
/// TASK 21: the media decoder path. <see cref="RawVideoFrameReader"/> is pure
/// (synthetic bytes, no ffmpeg); the one integration test drives the real
/// <see cref="MediaVideoSource"/> source loop against a fake decoder process.
/// </summary>
public class MediaVideoSourceTests
{
    // ─── Pure reader (unit) ───

    [Fact]
    public void Reader_EmitsOneFramePerFrameBytes()
    {
        var w = 2; var h = 2;
        var reader = new RawVideoFrameReader(w, h);
        var frameBytes = new byte[w * h * 4];

        var frames = reader.Feed(frameBytes);
        Assert.Single(frames);
        Assert.Equal(w, frames[0].Width);
        Assert.Equal(h, frames[0].Height);
    }

    [Fact]
    public void Reader_SplitsMultipleFramesFromOneFeed()
    {
        var reader = new RawVideoFrameReader(1, 1); // 4 bytes each
        var frames = reader.Feed(new byte[12]);     // 3 frames
        Assert.Equal(3, frames.Count);
    }

    [Fact]
    public void Reader_KeepsPartialBytesAcrossFeeds()
    {
        var reader = new RawVideoFrameReader(1, 1);
        Assert.Empty(reader.Feed(new byte[2]));     // half a frame
        Assert.Empty(reader.Feed(new byte[1]));     // 3/4
        var frames = reader.Feed(new byte[1]);      // completes the frame
        Assert.Single(frames);
        Assert.Empty(reader.Feed(new byte[0]));     // no leftover
    }

    // ─── The one integration test: source loop against a fake decode process ───

    [Fact]
    public async Task MediaVideoSource_EmitsFramesInOrderFromFakeDecoder()
    {
        const int w = 2, h = 1; // frame bytes = 8
        var frameA = new byte[] { 1, 2, 3, 4, 5, 6, 7, 8 };
        var frameB = new byte[] { 9, 10, 11, 12, 13, 14, 15, 16 };
        var payload = new byte[frameA.Length + frameB.Length];
        Buffer.BlockCopy(frameA, 0, payload, 0, frameA.Length);
        Buffer.BlockCopy(frameB, 0, payload, frameA.Length, frameB.Length);

        using var source = new MediaVideoSource(
            "clip.mp4", w, h,
            new FakeLocator(),
            new FakeDecodeProcess(payload));

        var seen = new List<byte[]>();
        var completed = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
        source.FrameAvailable += f => seen.Add(((byte[])f.BgraPixels.Clone()));
        source.Completed += () => completed.TrySetResult(true);

        await source.StartAsync();
        await completed.Task.WaitAsync(TimeSpan.FromSeconds(5));

        Assert.Equal(2, seen.Count);
        Assert.Equal(frameA, seen[0]);
        Assert.Equal(frameB, seen[1]);
    }

    private sealed class FakeDecodeProcess : IDecodeProcess
    {
        private readonly MemoryStream _stream;
        public FakeDecodeProcess(byte[] bytes) => _stream = new MemoryStream(bytes);
        public void Start(ProcessStartInfo startInfo) { }
        public Stream StandardOutput => _stream;
        public bool HasExited => _stream.Position >= _stream.Length;
        public int ExitCode => 0;
        public void Kill() { }
        public Task WaitForExitAsync(CancellationToken ct = default) => Task.CompletedTask;
        public void Dispose() => _stream.Dispose();
    }

    [Fact]
    public async Task MediaVideoSource_PacesFramesByProbedFps()
    {
        const int w = 2, h = 1; // frame bytes = 8
        var payload = new byte[16]; // two frames
        var delays = new List<TimeSpan>();

        using var source = new MediaVideoSource(
            "clip.mp4", w, h,
            new FakeLocator(),
            new FakeDecodeProcess(payload),
            frameRateProbe: new FakeFrameRateProbe(1000.0),
            delay: (_d, _) => { delays.Add(_d); return Task.CompletedTask; });

        var completed = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
        source.Completed += () => completed.TrySetResult(true);

        await source.StartAsync();
        await completed.Task.WaitAsync(TimeSpan.FromSeconds(5));

        // One pacing delay per emitted frame, each = 1/1000s.
        Assert.Equal(2, delays.Count);
        foreach (var d in delays)
            Assert.True(Math.Abs((d - TimeSpan.FromMilliseconds(1)).TotalMilliseconds) < 0.001,
                $"expected ~1ms, got {d.TotalMilliseconds}ms");
    }

    private sealed class FakeFrameRateProbe : IFrameRateProbe
    {
        private readonly double? _fps;
        public FakeFrameRateProbe(double? fps) => _fps = fps;
        public Task<double?> ProbeAsync(string path, CancellationToken ct = default)
            => Task.FromResult(_fps);
    }

    private sealed class FakeLocator : IFfmpegLocator
    {
        public Task<string> LocateAsync(CancellationToken ct = default) => Task.FromResult("ffmpeg.exe");
    }
}