using StbImageSharp;
using StbImageWriteSharp;
using Xunit;

namespace MrGameEng.Atlases.Tests;

public sealed class AtlasBuilderTests : IDisposable
{
    private readonly string _root = Directory.CreateTempSubdirectory("mrge-atlas-tests-").FullName;

    private string SourceDir => Path.Combine(_root, "Textures");
    private string OutputDir => Path.Combine(_root, "Atlases");

    public void Dispose() => Directory.Delete(_root, recursive: true);

    /// <summary>Writes a PNG filled with one RGBA color.</summary>
    private void WritePng(string relativePath, int width, int height, byte r, byte g, byte b, byte a = 255)
    {
        var fullPath = Path.Combine(SourceDir, relativePath);
        Directory.CreateDirectory(Path.GetDirectoryName(fullPath)!);
        var data = new byte[width * height * 4];
        for (var i = 0; i < data.Length; i += 4)
        {
            data[i] = r;
            data[i + 1] = g;
            data[i + 2] = b;
            data[i + 3] = a;
        }

        using var stream = File.Create(fullPath);
        new ImageWriter().WritePng(data, width, height, StbImageWriteSharp.ColorComponents.RedGreenBlueAlpha, stream);
    }

    private AtlasBuildOptions Options(int groupDepth = 1, bool force = false) => new()
    {
        SourceDirectory = SourceDir,
        OutputDirectory = OutputDir,
        GroupDepth = groupDepth,
        MaxPageSize = 128,
        Padding = 2,
        Force = force,
    };

    [Theory]
    [InlineData("Terrain/Surfaces/Marsh.png", 1, "Terrain", "Terrain/Surfaces/Marsh")]
    [InlineData("Terrain/Surfaces/Marsh.png", 2, "Terrain.Surfaces", "Terrain/Surfaces/Marsh")]
    [InlineData("Terrain/Surfaces/Marsh.png", 0, "Root", "Terrain/Surfaces/Marsh")]
    [InlineData("loose.png", 3, "Root", "loose")]
    public void ClassifyPath_GroupsByDepth(string path, int depth, string expectedAtlas, string expectedKey)
    {
        var (atlas, key) = AtlasBuilder.ClassifyPath(path, depth, "Root");

        Assert.Equal(expectedAtlas, atlas);
        Assert.Equal(expectedKey, key);
    }

    [Fact]
    public void Build_WritesMetadataAndPages_PixelsSurviveRoundtrip()
    {
        WritePng("Terrain/Grass.png", 16, 16, 10, 200, 30);
        WritePng("Terrain/Water.png", 16, 8, 30, 40, 250);

        var result = AtlasBuilder.Build(Options());

        var group = Assert.Single(result.Groups);
        Assert.Equal("Terrain", group.Name);
        Assert.Equal(2, group.RegionCount);
        Assert.False(group.Skipped);

        var metadata = AtlasMetadata.FromJson(File.ReadAllText(Path.Combine(OutputDir, "Terrain.atlas")));
        Assert.Equal(["Terrain/Grass", "Terrain/Water"], metadata.Regions.Select(x => x.Key));

        var grass = metadata.Regions.Single(x => x.Key == "Terrain/Grass");
        var page = metadata.Pages[grass.Page];
        using var stream = File.OpenRead(Path.Combine(OutputDir, page.File));
        var pixels = ImageResult.FromStream(stream, StbImageSharp.ColorComponents.RedGreenBlueAlpha);

        // Центральный пиксель региона должен быть цветом исходной картинки.
        var center = ((grass.Y + 8) * pixels.Width + grass.X + 8) * 4;
        Assert.Equal((byte)10, pixels.Data[center]);
        Assert.Equal((byte)200, pixels.Data[center + 1]);
        Assert.Equal((byte)30, pixels.Data[center + 2]);
    }

    [Fact]
    public void Build_SecondRunWithoutChanges_SkipsGroup()
    {
        WritePng("UI/button.png", 8, 8, 1, 2, 3);

        var first = AtlasBuilder.Build(Options());
        var second = AtlasBuilder.Build(Options());

        Assert.False(Assert.Single(first.Groups).Skipped);
        Assert.True(Assert.Single(second.Groups).Skipped);
    }

    [Fact]
    public void Build_ChangedSource_Rebuilds()
    {
        WritePng("UI/button.png", 8, 8, 1, 2, 3);
        AtlasBuilder.Build(Options());

        File.SetLastWriteTimeUtc(
            Path.Combine(SourceDir, "UI/button.png"), DateTime.UtcNow.AddMinutes(1));
        var result = AtlasBuilder.Build(Options());

        Assert.False(Assert.Single(result.Groups).Skipped);
    }

    [Fact]
    public void Build_AddedFile_RebuildsGroup()
    {
        WritePng("UI/button.png", 8, 8, 1, 2, 3);
        AtlasBuilder.Build(Options());

        WritePng("UI/icon.png", 8, 8, 4, 5, 6);
        var result = AtlasBuilder.Build(Options());

        var group = Assert.Single(result.Groups);
        Assert.False(group.Skipped);
        Assert.Equal(2, group.RegionCount);
    }

    [Fact]
    public void Build_RemovedGroup_DeletesOrphanedAtlas()
    {
        WritePng("UI/button.png", 8, 8, 1, 2, 3);
        WritePng("World/rock.png", 8, 8, 7, 8, 9);
        AtlasBuilder.Build(Options());

        Directory.Delete(Path.Combine(SourceDir, "World"), recursive: true);
        var result = AtlasBuilder.Build(Options());

        Assert.NotEmpty(result.DeletedOrphans);
        Assert.False(File.Exists(Path.Combine(OutputDir, "World.atlas")));
        Assert.False(File.Exists(Path.Combine(OutputDir, "World.atlas.0.png")));
        Assert.True(File.Exists(Path.Combine(OutputDir, "UI.atlas")));
    }

    [Fact]
    public void Build_ManyImages_SpillToMultiplePages()
    {
        for (var i = 0; i < 12; i++)
        {
            WritePng($"Things/sprite{i:D2}.png", 60, 60, (byte)i, 0, 0);
        }

        var result = AtlasBuilder.Build(Options());

        // 60² с padding 2 на страницу 128² помещаются по 4 — минимум 3 страницы.
        Assert.True(Assert.Single(result.Groups).PageCount >= 3);
    }

    [Fact]
    public void Build_ContentChangedWithSameTimestamp_Rebuilds()
    {
        WritePng("UI/button.png", 8, 8, 1, 2, 3);
        AtlasBuilder.Build(Options());

        // Копия «с сохранением времени» (robocopy, zip): mtime прежний, контент другой.
        var path = Path.Combine(SourceDir, "UI/button.png");
        var timestamp = File.GetLastWriteTimeUtc(path);
        WritePng("UI/button.png", 16, 16, 9, 9, 9);
        File.SetLastWriteTimeUtc(path, timestamp);

        var result = AtlasBuilder.Build(Options());

        Assert.False(Assert.Single(result.Groups).Skipped);
    }

    [Fact]
    public void Build_OldMetadataVersion_Rebuilds()
    {
        WritePng("UI/button.png", 8, 8, 1, 2, 3);
        AtlasBuilder.Build(Options());

        var metadataPath = Path.Combine(OutputDir, "UI.atlas");
        var json = File.ReadAllText(metadataPath)
            .Replace($"\"version\": {AtlasMetadata.CurrentVersion}", "\"version\": 1");
        File.WriteAllText(metadataPath, json);

        var result = AtlasBuilder.Build(Options());

        Assert.False(Assert.Single(result.Groups).Skipped);
    }

    [Fact]
    public void Metadata_JsonRoundtrip_PreservesEverything()
    {
        var metadata = new AtlasMetadata
        {
            Name = "Things.Pawn",
            PageSize = 2048,
            Padding = 2,
            Pages = [new AtlasPage { File = "Things.Pawn.atlas.0.png", Width = 256, Height = 128 }],
            Regions = [new AtlasRegion { Key = "Things/Pawn/Fox", Page = 0, X = 2, Y = 4, Width = 64, Height = 32 }],
        };

        var parsed = AtlasMetadata.FromJson(metadata.ToJson());

        Assert.Equal("Things.Pawn", parsed.Name);
        Assert.Equal(2048, parsed.PageSize);
        var page = Assert.Single(parsed.Pages);
        Assert.Equal(("Things.Pawn.atlas.0.png", 256, 128), (page.File, page.Width, page.Height));
        var region = Assert.Single(parsed.Regions);
        Assert.Equal(("Things/Pawn/Fox", 0, 2, 4, 64, 32),
            (region.Key, region.Page, region.X, region.Y, region.Width, region.Height));
    }

    [Fact]
    public void TextureAtlas_LooksUpRegions_FromMetadata()
    {
        var metadata = new AtlasMetadata
        {
            Name = "Test",
            Pages = [new AtlasPage { File = "Test.atlas.0.png", Width = 64, Height = 64 }],
            Regions =
            [
                new AtlasRegion { Key = "a/b", Page = 0, X = 2, Y = 2, Width = 10, Height = 12 },
            ],
        };

        // Texture2D == null допустим в headless-тестах (см. Texture2DRegion).
        var atlas = new TextureAtlas(metadata, new Microsoft.Xna.Framework.Graphics.Texture2D[1]);

        var region = atlas.GetRegion("a/b");
        Assert.Equal(new Microsoft.Xna.Framework.Rectangle(2, 2, 10, 12), region.Bounds);
        Assert.True(atlas.TryGetRegion("a/b", out _));
        Assert.False(atlas.TryGetRegion("missing", out _));
        Assert.Throws<KeyNotFoundException>(() => atlas.GetRegion("missing"));
    }
}