LlamaCasty/ytLive.Tests/ChromaKeyDetectorTests.cs

using System;
using System.Collections.Generic;
using Xunit;
using ytLive.Services;

namespace ytLive.Tests;

/// <summary>
/// TASK 64 unit tests (pure): does the detector recognise a real green/blue screen, and does it
/// keep its mouth shut about things that merely contain green? Plus the decoder filter chain the
/// key turns into — asserted as a string, the same way the encoder's ffmpeg args are pinned.
/// </summary>
public class ChromaKeyDetectorTests
{
    private const byte GreenR = 0x00, GreenG = 0xB1, GreenB = 0x40;   // #00B140 — a real screen
    private const byte BlueR = 0x00, BlueG = 0x47, BlueB = 0xBB;      // #0047BB

    [Fact]
    public void GreenScreen_IsDetected_WithTheColourActuallyShot()
    {
        var frame = Build(120, 68, (x, y) => InCentre(x, y, 120, 68) ? Skin() : (GreenR, GreenG, GreenB));

        var suggestion = ChromaKeyDetector.Detect(frame);

        Assert.Equal(ChromaScreen.Green, suggestion.Screen);
        Assert.True(suggestion.IsHighConfidence, $"confidence {suggestion.Confidence:0.00} should be high");
        Assert.Equal("#00B140", suggestion.ColorHex);
    }

    [Fact]
    public void BlueScreen_IsDetected()
    {
        var frame = Build(120, 68, (x, y) => InCentre(x, y, 120, 68) ? Skin() : (BlueR, BlueG, BlueB));

        var suggestion = ChromaKeyDetector.Detect(frame);

        Assert.Equal(ChromaScreen.Blue, suggestion.Screen);
        Assert.True(suggestion.IsHighConfidence);
    }

    [Fact]
    public void LetterboxedScreen_IsStillDetected()
    {
        // The clip is wider than the screen: black bars top and bottom. Bars must not count
        // against the screen, or every letterboxed clip reads as "no backdrop".
        var frame = Build(120, 68, (x, y) =>
            y < 12 || y >= 56 ? ((byte)0, (byte)0, (byte)0) : (GreenR, GreenG, GreenB));

        var suggestion = ChromaKeyDetector.Detect(frame);

        Assert.Equal(ChromaScreen.Green, suggestion.Screen);
        Assert.True(suggestion.Confidence >= ChromaKeySuggestion.SuggestFloor,
            $"letterboxing dropped confidence to {suggestion.Confidence:0.00}");
    }

    [Fact]
    public void LawnOrPitch_SaysNothing()
    {
        // Green, but the greens disagree with each other (hue 100 vs 145 alternating). Keying
        // this would eat the picture, so "None" is the correct answer.
        var frame = Build(120, 68, (x, y) => (x / 4 + y / 4) % 2 == 0
            ? ((byte)20, (byte)150, (byte)30)     // hue ≈ 125, dark-ish grass
            : ((byte)80, (byte)180, (byte)10));   // hue ≈ 95, sunlit grass

        var suggestion = ChromaKeyDetector.Detect(frame);

        Assert.Equal(ChromaScreen.None, suggestion.Screen);
    }

    [Fact]
    public void MixedScene_SaysNothing()
    {
        var frame = Build(120, 68, (x, y) => ((byte)(x % 255), (byte)(y % 255), (byte)((x + y) % 255)));

        var suggestion = ChromaKeyDetector.Detect(frame);

        Assert.Equal(ChromaScreen.None, suggestion.Screen);
    }

    [Fact]
    public void DarkFrames_AreNotAScreen()
    {
        var frame = Build(120, 68, (x, y) => ((byte)0, (byte)(y % 20), (byte)0));

        Assert.Equal(ChromaScreen.None, ChromaKeyDetector.Detect(frame).Screen);
    }

    // ─── the filter chain the key turns into ───

    [Fact]
    public void UnkeyedClip_KeepsThePlainScaleChain()
        => Assert.Equal("scale=1920:1080", VideoFilterChain.BuildVideo(1920, 1080, ChromaKeyOptions.Off));

    [Fact]
    public void KeyedClip_ScalesThenKeysThenDespillsThenForcesBgra()
    {
        var options = new ChromaKeyOptions(true, "#00B140", 0.12, 0.08, Spill: true);

        Assert.Equal(
            "scale=1920:1080,colorkey=0x00B140:0.12:0.08,despill=type=green,format=bgra",
            VideoFilterChain.BuildVideo(1920, 1080, options));
    }

    [Fact]
    public void BlueScreen_DespillsBlue()
    {
        var options = new ChromaKeyOptions(true, "#0047BB", 0.1, 0.05, Spill: true, ChromaScreen.Blue);

        Assert.Contains("despill=type=blue", VideoFilterChain.BuildVideo(1920, 1080, options));
    }

    [Fact]
    public void SpillOff_AndBadColour_StillProduceAValidChain()
    {
        var noSpill = new ChromaKeyOptions(true, "not-a-colour", 2.0, -1, Spill: false);
        var chain = VideoFilterChain.BuildVideo(1280, 720, noSpill);

        // Out-of-range numbers clamp, an unparseable colour falls back to the app default, and
        // no despill term is appended — ffmpeg must never be handed a filter it will reject.
        Assert.Equal("scale=1280:720,colorkey=0x00B140:1:0,format=bgra", chain);
    }

    [Fact]
    public void Signature_IsTheSameForIdenticalLooks_AndDiffersOtherwise()
    {
        var a = new ChromaKeyOptions(true, "#00b140", 0.12, 0.08, true);
        var b = new ChromaKeyOptions(true, "#00B140", 0.12, 0.08, true);
        var c = new ChromaKeyOptions(true, "#00B140", 0.30, 0.08, true);

        Assert.Equal(a.Signature, b.Signature);       // shared decoder for identical looks
        Assert.NotEqual(a.Signature, c.Signature);
        Assert.Equal("off", ChromaKeyOptions.Off.Signature);
    }

    // ─── helpers ───

    private static bool InCentre(int x, int y, int w, int h)
        => x > w * 0.35 && x < w * 0.65 && y > h * 0.25 && y < h * 0.75;

    private static (byte R, byte G, byte B) Skin() => (0xE0, 0xB0, 0x90);

    private static VideoFrame Build(int width, int height, Func<int, int, (byte R, byte G, byte B)> pixel)
    {
        var bytes = new byte[width * height * 4];
        for (var y = 0; y < height; y++)
        for (var x = 0; x < width; x++)
        {
            var (r, g, b) = pixel(x, y);
            var i = (y * width + x) * 4;
            bytes[i] = b;
            bytes[i + 1] = g;
            bytes[i + 2] = r;
            bytes[i + 3] = 255;
        }
        return new VideoFrame(width, height, bytes);
    }
}