using AcDream.Core.Textures;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using DatReaderWriter.Types;

namespace AcDream.Core.Tests.Textures;

public class SurfaceDecoderTests
{
    [Fact]
    public void Decode_A8R8G8B8_ConvertsToRgba8()
    {
        // Source format is B, G, R, A in memory (little-endian ARGB).
        // One 2x2 image: red, green, blue, white pixels.
        var src = new byte[]
        {
            0x00, 0x00, 0xFF, 0xFF,  // red   (B=0, G=0, R=255, A=255)
            0x00, 0xFF, 0x00, 0xFF,  // green
            0xFF, 0x00, 0x00, 0xFF,  // blue
            0xFF, 0xFF, 0xFF, 0xFF,  // white
        };
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 2,
            Format = PixelFormat.PFID_A8R8G8B8,
            SourceData = src,
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Equal(2, decoded.Width);
        Assert.Equal(2, decoded.Height);
        Assert.Equal(16, decoded.Rgba8.Length);  // 2*2*4
        // red pixel, in RGBA: 255, 0, 0, 255
        Assert.Equal(0xFF, decoded.Rgba8[0]);
        Assert.Equal(0x00, decoded.Rgba8[1]);
        Assert.Equal(0x00, decoded.Rgba8[2]);
        Assert.Equal(0xFF, decoded.Rgba8[3]);
    }

    [Fact]
    public void Decode_UnsupportedFormat_ReturnsMagenta()
    {
        var rs = new RenderSurface
        {
            Width = 4,
            Height = 4,
            Format = PixelFormat.PFID_INDEX16,  // not implemented path
            SourceData = new byte[32],
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }

    [Fact]
    public void Decode_A8_NonAdditive_ProducesWhitePlusAlpha()
    {
        // Default (isAdditive: false) = WB FillA8 semantics: R=G=B=255, A=val.
        // Used for non-additive entity surfaces where A8 is a pure alpha channel.
        var src = new byte[] { 0x00, 0x40, 0x80, 0xFF };  // 2x2 image
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 2,
            Format = PixelFormat.PFID_A8,
            SourceData = src,
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Equal(2, decoded.Width);
        Assert.Equal(2, decoded.Height);
        Assert.Equal(16, decoded.Rgba8.Length);
        // Each input byte expands to (255, 255, 255, val) — white with varying alpha
        Assert.Equal(new byte[]
        {
            255, 255, 255, 0x00,
            255, 255, 255, 0x40,
            255, 255, 255, 0x80,
            255, 255, 255, 0xFF,
        }, decoded.Rgba8);
    }

    [Fact]
    public void Decode_A8_Additive_ReplicatesByteToAllChannels()
    {
        // isAdditive=true = WB FillA8Additive semantics: R=G=B=A=val.
        // Used for terrain blending alpha masks (TerrainAtlas always passes isAdditive:true).
        var src = new byte[] { 0x00, 0x40, 0x80, 0xFF };  // 2x2 image
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 2,
            Format = PixelFormat.PFID_A8,
            SourceData = src,
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs, palette: null, isClipMap: false, isAdditive: true);

        Assert.Equal(16, decoded.Rgba8.Length);
        // Each input byte fans out to all four channels
        Assert.Equal(new byte[]
        {
            0x00, 0x00, 0x00, 0x00,
            0x40, 0x40, 0x40, 0x40,
            0x80, 0x80, 0x80, 0x80,
            0xFF, 0xFF, 0xFF, 0xFF,
        }, decoded.Rgba8);
    }

    [Fact]
    public void Decode_CustomLscapeAlpha_TreatedIdenticallyToA8()
    {
        // PFID_CUSTOM_LSCAPE_ALPHA (0xF4) is AC's custom format for terrain
        // blending alpha maps. Pixel layout is identical to PFID_A8 — one
        // byte of alpha per pixel — so the decoder routes both through the
        // same DecodeA8 implementation. Default (isAdditive:false) → R=G=B=255, A=val.
        var src = new byte[] { 0x10, 0x20, 0x30, 0x40 };  // 2x2
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 2,
            Format = PixelFormat.PFID_CUSTOM_LSCAPE_ALPHA,
            SourceData = src,
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Equal(16, decoded.Rgba8.Length);
        Assert.Equal(new byte[]
        {
            255, 255, 255, 0x10,
            255, 255, 255, 0x20,
            255, 255, 255, 0x30,
            255, 255, 255, 0x40,
        }, decoded.Rgba8);
    }

    [Fact]
    public void Decode_A8_WithShortSourceData_ReturnsMagenta()
    {
        var rs = new RenderSurface
        {
            Width = 4,
            Height = 4,
            Format = PixelFormat.PFID_A8,
            SourceData = new byte[8],  // expects 16
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }

    [Fact]
    public void Decode_NullSourceData_ReturnsMagenta()
    {
        var rs = new RenderSurface
        {
            Width = 4,
            Height = 4,
            Format = PixelFormat.PFID_A8R8G8B8,
            SourceData = null!,
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }

    [Fact]
    public void Decode_TruncatedA8R8G8B8_ReturnsMagenta()
    {
        // Buffer too small for width*height*4.
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 2,
            Format = PixelFormat.PFID_A8R8G8B8,
            SourceData = new byte[8],  // should be 16
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }

    [Fact]
    public void DecodeSolidColor_Opaque_PreservesAlpha()
    {
        var color = new ColorARGB { Alpha = 0xFF, Red = 0x11, Green = 0x22, Blue = 0x33 };

        var decoded = SurfaceDecoder.DecodeSolidColor(color, translucency: 0f);

        Assert.Equal(1, decoded.Width);
        Assert.Equal(1, decoded.Height);
        Assert.Equal(new byte[] { 0x11, 0x22, 0x33, 0xFF }, decoded.Rgba8);
    }

    [Fact]
    public void DecodeSolidColor_FullyTranslucent_AlphaGoesToZero()
    {
        // Surfaces marked Base1Solid + Translucent with Translucency=1.0 are
        // AC's convention for "invisible placeholder surfaces" — the engine renders
        // them as nothing. Alpha must go to 0 so the mesh shader's discard rule
        // makes them invisible.
        var color = new ColorARGB { Alpha = 0xFF, Red = 0xC8, Green = 0xC8, Blue = 0xC8 };

        var decoded = SurfaceDecoder.DecodeSolidColor(color, translucency: 1f);

        Assert.Equal(0, decoded.Rgba8[3]);  // alpha must be zero
    }

    [Fact]
    public void DecodeIndex16_ClipMap_ZerosAlphaForLowIndices()
    {
        // Build a 4x1 INDEX16 surface with indices 0, 1, 7, 8.
        // On a clipmap surface, indices 0..7 should be fully transparent and
        // index 8 should render with its palette color.
        var rs = new RenderSurface
        {
            Width = 4,
            Height = 1,
            Format = PixelFormat.PFID_INDEX16,
            SourceData = new byte[]
            {
                0x00, 0x00,  // index 0
                0x01, 0x00,  // index 1
                0x07, 0x00,  // index 7
                0x08, 0x00,  // index 8
            },
        };
        var palette = new Palette();
        for (int i = 0; i < 16; i++)
            palette.Colors.Add(new ColorARGB { Alpha = 0xFF, Red = 0xAA, Green = 0xBB, Blue = 0xCC });

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs, palette, isClipMap: true);

        // Pixels 0, 1, 2 (indices 0, 1, 7) should be fully transparent.
        Assert.Equal(0, decoded.Rgba8[3]);   // pixel 0 alpha
        Assert.Equal(0, decoded.Rgba8[7]);   // pixel 1 alpha
        Assert.Equal(0, decoded.Rgba8[11]);  // pixel 2 alpha
        // Pixel 3 (index 8) should have the palette alpha.
        Assert.Equal(0xFF, decoded.Rgba8[15]);
        Assert.Equal(0xAA, decoded.Rgba8[12]);
    }

    // ---- PFID_P8 tests -------------------------------------------------------

    [Fact]
    public void Decode_P8_LooksUpPaletteForEachByte()
    {
        // 2x1 surface: pixel 0 → palette index 0 (red), pixel 1 → palette index 1 (blue).
        var palette = new Palette();
        palette.Colors.Add(new ColorARGB { Alpha = 0xFF, Red = 0xFF, Green = 0x00, Blue = 0x00 }); // index 0 = red
        palette.Colors.Add(new ColorARGB { Alpha = 0xFF, Red = 0x00, Green = 0x00, Blue = 0xFF }); // index 1 = blue

        var rs = new RenderSurface
        {
            Width = 2,
            Height = 1,
            Format = PixelFormat.PFID_P8,
            SourceData = new byte[] { 0x00, 0x01 },  // indices
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs, palette);

        Assert.Equal(8, decoded.Rgba8.Length);  // 2 pixels * 4 channels
        // Pixel 0: red
        Assert.Equal(new byte[] { 0xFF, 0x00, 0x00, 0xFF }, decoded.Rgba8[0..4]);
        // Pixel 1: blue
        Assert.Equal(new byte[] { 0x00, 0x00, 0xFF, 0xFF }, decoded.Rgba8[4..8]);
    }

    [Fact]
    public void Decode_P8_ClipMap_ZerosAlphaForLowIndices()
    {
        // 4x1 surface with indices 0, 3, 7, 8.
        // isClipMap=true → indices 0..7 should be fully transparent; index 8 opaque.
        var palette = new Palette();
        for (int i = 0; i < 16; i++)
            palette.Colors.Add(new ColorARGB { Alpha = 0xFF, Red = 0xCC, Green = 0xDD, Blue = 0xEE });

        var rs = new RenderSurface
        {
            Width = 4,
            Height = 1,
            Format = PixelFormat.PFID_P8,
            SourceData = new byte[] { 0x00, 0x03, 0x07, 0x08 },
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs, palette, isClipMap: true);

        // Indices 0, 3, 7 should be transparent.
        Assert.Equal(0, decoded.Rgba8[3]);   // pixel 0 alpha
        Assert.Equal(0, decoded.Rgba8[7]);   // pixel 1 alpha
        Assert.Equal(0, decoded.Rgba8[11]);  // pixel 2 alpha
        // Index 8 should be opaque with palette color.
        Assert.Equal(0xFF, decoded.Rgba8[15]);
        Assert.Equal(0xCC, decoded.Rgba8[12]);
    }

    [Fact]
    public void Decode_P8_WithoutPalette_ReturnsMagenta()
    {
        // P8 without palette passed → falls through to magenta.
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 1,
            Format = PixelFormat.PFID_P8,
            SourceData = new byte[] { 0x00, 0x01 },
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }

    [Fact]
    public void Decode_P8_TruncatedData_ReturnsMagenta()
    {
        var palette = new Palette();
        palette.Colors.Add(new ColorARGB { Alpha = 0xFF, Red = 0xAA, Green = 0xBB, Blue = 0xCC });

        var rs = new RenderSurface
        {
            Width = 4,
            Height = 1,
            Format = PixelFormat.PFID_P8,
            SourceData = new byte[] { 0x00, 0x00 },  // expects 4 bytes
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs, palette);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }

    // ---- PFID_R8G8B8 tests ---------------------------------------------------

    [Fact]
    public void Decode_R8G8B8_ConvertsToRgba8WithOpaqueAlpha()
    {
        // PFID_R8G8B8 is stored on disk as B,G,R (little-endian 24-bit BGR).
        // 2x1 surface: first pixel = red (B=0,G=0,R=255), second = green (B=0,G=255,R=0).
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 1,
            Format = PixelFormat.PFID_R8G8B8,
            SourceData = new byte[]
            {
                0x00, 0x00, 0xFF,  // B=0, G=0, R=255 → red
                0x00, 0xFF, 0x00,  // B=0, G=255, R=0 → green
            },
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Equal(8, decoded.Rgba8.Length);
        // Red pixel → R=255, G=0, B=0, A=255
        Assert.Equal(new byte[] { 0xFF, 0x00, 0x00, 0xFF }, decoded.Rgba8[0..4]);
        // Green pixel → R=0, G=255, B=0, A=255
        Assert.Equal(new byte[] { 0x00, 0xFF, 0x00, 0xFF }, decoded.Rgba8[4..8]);
    }

    [Fact]
    public void Decode_R8G8B8_TruncatedData_ReturnsMagenta()
    {
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 1,
            Format = PixelFormat.PFID_R8G8B8,
            SourceData = new byte[] { 0x00, 0x00 },  // expects 6 bytes
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }

    // ---- PFID_X8R8G8B8 tests -------------------------------------------------

    [Fact]
    public void Decode_X8R8G8B8_ConvertsToRgba8DiscardingXByte()
    {
        // PFID_X8R8G8B8 is stored on disk as B,G,R,X (DirectX little-endian 32-bit).
        // The X byte is unused padding — NOT alpha. Output alpha must be 255.
        // 2x1: first pixel = blue (B=255,G=0,R=0,X=0xDE), second = white (B=255,G=255,R=255,X=0xAD).
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 1,
            Format = PixelFormat.PFID_X8R8G8B8,
            SourceData = new byte[]
            {
                0xFF, 0x00, 0x00, 0xDE,  // B=255, G=0, R=0, X=0xDE → blue, alpha forced 255
                0xFF, 0xFF, 0xFF, 0xAD,  // B=255, G=255, R=255, X=0xAD → white, alpha forced 255
            },
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Equal(8, decoded.Rgba8.Length);
        // Blue pixel → R=0, G=0, B=255, A=255 (X byte discarded)
        Assert.Equal(new byte[] { 0x00, 0x00, 0xFF, 0xFF }, decoded.Rgba8[0..4]);
        // White pixel → R=255, G=255, B=255, A=255 (X byte discarded)
        Assert.Equal(new byte[] { 0xFF, 0xFF, 0xFF, 0xFF }, decoded.Rgba8[4..8]);
    }

    [Fact]
    public void Decode_X8R8G8B8_TruncatedData_ReturnsMagenta()
    {
        var rs = new RenderSurface
        {
            Width = 2,
            Height = 1,
            Format = PixelFormat.PFID_X8R8G8B8,
            SourceData = new byte[] { 0xFF, 0x00, 0x00, 0xDE },  // expects 8 bytes (2 pixels)
        };

        var decoded = SurfaceDecoder.DecodeRenderSurface(rs);

        Assert.Same(DecodedTexture.Magenta, decoded);
    }
}