using System;
using Xunit;
using ytLive.Services;
using ytLive.ViewModels;

namespace ytLive.Tests;

/// <summary>
/// Proves the zoom layer's pixels are the GENUINE 2x magnification of the
/// backdrop: the source window is the box/2 interior centred on the box centre
/// (the same region as the preview's VisualBrush), with the static art composited
/// over the live capture exactly as the SceneCompositor draws the backdrop. This
/// is the "don't ship a magnifier you only think exists" proof — a 1x box, a
/// mis-positioned window, or a wrong backdrop layer all fail hard below.
/// </summary>
public sealed class ZoomFrameBuilderTests
{
    private static VideoFrame BandedBackdrop(int bandW, int bandCount)
    {
        var w = bandW * bandCount;
        const int h = 1080;
        var buf = new byte[w * h * 4];
        var bandColors = new (byte B, byte G, byte R)[]
        {
            (10, 20, 30),  // band 0
            (0, 0, 255),   // band 1 red
            (0, 255, 0),   // band 2 green — the box window lands here
            (255, 0, 0),   // band 3 blue
        };
        for (var y = 0; y < h; y++)
        {
            for (var x = 0; x < w; x++)
            {
                var (b, g, r) = bandColors[Math.Min(bandCount - 1, x / bandW)];
                var i = (y * w + x) * 4;
                buf[i] = b;
                buf[i + 1] = g;
                buf[i + 2] = r;
                buf[i + 3] = 255;
            }
        }
        return new VideoFrame(w, h, buf);
    }

    private static VideoFrame SolidFrame(int w, int h, byte b, byte g, byte r)
    {
        var buf = new byte[w * h * 4];
        for (var i = 0; i < w * h; i++)
        {
            buf[i * 4] = b;
            buf[i * 4 + 1] = g;
            buf[i * 4 + 2] = r;
            buf[i * 4 + 3] = 255;
        }
        return new VideoFrame(w, h, buf);
    }

    [Fact]
    public void Build_Produces_2x_Centered_ArtOverLive_Magnification()
    {
        var art = BandedBackdrop(480, 4); // [0,480) 1/4 dim, [480,960) red, [960,1440) green, [1440,1920) blue
        var live = SolidFrame(1920, 1080, 200, 60, 60); // magenta-ish — must never show through

        // Box [840,1320)x[100,580). 2x window = [960,1200)x[160,520) = band 2, all green.
        // A 1x (broken) magnifier samples [840,1320) → red+green+blue mixed.
        var zoom = ZoomFrameBuilder.Build(live, art, 840, 100, 480, 480, 1920, 1080);

        Assert.NotNull(zoom);
        Assert.Equal(480, zoom.Width);
        Assert.Equal(480, zoom.Height);
        for (var y = 0; y < zoom.Height; y++)
        {
            for (var x = 0; x < zoom.Width; x++)
            {
                var i = (y * zoom.Width + x) * 4;
                Assert.Equal(0, zoom.BgraPixels[i]);       // B
                Assert.Equal(255, zoom.BgraPixels[i + 1]); // G
                Assert.Equal(0, zoom.BgraPixels[i + 2]);   // R
                Assert.Equal(255, zoom.BgraPixels[i + 3]); // A
            }
        }
    }
}