using System;
using System.Collections.Generic;
using System.Threading;
using System.Threading.Tasks;
using Xunit;
using ytLive.Models;
using ytLive.Services;
using ytLive.Services.Compositor;
using ytLive.Services.Encoder;

namespace ytLive.Tests;

/// <summary>
/// TASK 33 slice 3 — the step-down's one dangerous act: relaunching the encoder mid-broadcast.
///
/// <para>The restart is a full pump stop/start rather than an encoder swap, and this test is why: a swap
/// leaves an in-flight submit pointing at a disposed process, which faults the loop and ends the
/// broadcast. Here the pump must come back and produce a frame with a <b>new</b> encoder instance and
/// the tier the policy landed on.</para>
/// </summary>
public sealed class EncoderRestartTests
{
    [Fact]
    public async Task ChangeEncoder_RelauchesWithANewEncoderAtTheNewTier()
    {
        var tier = (Width: 1920, Height: 1080, Fps: 60, Bitrate: 8.0);
        var started = new List<EncoderOptions>();
        var frames = new List<CapturingEncoder>();

        var scene = new Scene { Name = "Live" };
        scene.Elements.Add(new Source { Name = "Background", Type = SourceType.Background, IsBackground = true });
        var black = new VideoFrame(1920, 1080, new byte[1920 * 1080 * 4]);

        using var pump = new FramePump(
            sceneProvider: () => scene,
            frameResolver: _ => black,
            compositorOptions: () => new CompositorOptions
            {
                SourceRectX = 0, SourceRectY = 0,
                SourceRectWidth = 1920, SourceRectHeight = 1080,
                OutputWidth = 1920, OutputHeight = 1080,
            },
            encoderOptions: () => new EncoderOptions
            {
                RtmpUrl = "rtmp://a.rtmp.youtube.com/live2/abc",
                Width = tier.Width, Height = tier.Height, Fps = tier.Fps,
                BitrateKbps = (int)(tier.Bitrate * 1000),
            },
            encoderFactory: () =>
            {
                var encoder = new CapturingEncoder();
                encoder.Started += options => started.Add(options);
                frames.Add(encoder);
                return encoder;
            },
            log: _ => { },
            pacingDelay: (_, _) => Task.Delay(5));

        await pump.StartAsync();
        Assert.True(await frames[0].FirstFrame.Task.WaitAsync(TimeSpan.FromSeconds(5)), "first session never produced a frame");

        // The policy lands on 1080p30 @ 6.4 Mbps; the VM has already written the override, so the
        // options func now reports the new tier — which the restart must re-read.
        tier = (1920, 1080, 30, 6.4);

        Assert.True(await pump.ChangeEncoderAsync());
        Assert.True(await frames[1].FirstFrame.Task.WaitAsync(TimeSpan.FromSeconds(5)), "restarted session never produced a frame");

        Assert.Equal(2, started.Count);
        Assert.Equal(60, started[0].Fps);
        Assert.Equal(30, started[1].Fps);
        Assert.Equal(6400, started[1].BitrateKbps);
        Assert.NotSame(frames[0], frames[1]);

        await pump.StopAsync();
    }

    private sealed class CapturingEncoder : IFfmpegEncoder
    {
        public readonly TaskCompletionSource<bool> FirstFrame = new(TaskCreationOptions.RunContinuationsAsynchronously);
        public event Action<EncoderOptions>? Started;

        public int DroppedFrames => 0;

        public event EventHandler<StreamHealth>? HealthUpdated { add { } remove { } }
        public event EventHandler<string>? ProcessFailed { add { } remove { } }

        public Task StartAsync(EncoderOptions options, CancellationToken cancellationToken = default)
        {
            Started?.Invoke(options);
            return Task.CompletedTask;
        }

        public Task SubmitFrameAsync(VideoFrame frame, CancellationToken cancellationToken = default)
        {
            FirstFrame.TrySetResult(true);
            return Task.CompletedTask;
        }

        public Task StopAsync(CancellationToken cancellationToken = default) => Task.CompletedTask;

        public void Dispose() { }
    }
}