using System.Collections.Generic;
using System.Numerics;
using AcDream.App.Rendering;
using AcDream.App.Rendering.Gpu;
using AcDream.App.Tests.Rendering.Gpu;
using AcDream.App.UI;
using DatReaderWriter.Types;

namespace AcDream.App.Tests.UI;

/// <summary>
/// Campaign CH slice CH6c: pins the window-opacity ALPHA CHOKEPOINT —
/// <see cref="UiRenderContext"/>'s private <c>ApplyAlpha</c>, reached by every
/// public draw call (<see cref="UiRenderContext.DrawSprite"/>,
/// <see cref="UiRenderContext.DrawRect"/>/<see cref="UiRenderContext.DrawFill"/>,
/// and — new this slice — <see cref="UiRenderContext.DrawStringDat"/> and
/// <see cref="UiRenderContext.DrawString"/>). Retail's <c>ChatInterface::SetOpacity
/// @0x004F3120</c> sets ONE alpha on the whole composited window surface, chrome
/// AND text together — before this slice, <c>DrawStringDat</c> passed
/// <c>applyAlpha: false</c> so glyphs stayed opaque over a translucent window.
///
/// <para>
/// Builds a real <see cref="TextRenderer"/> over the in-memory
/// <see cref="RecordingGpuDevice"/> test double (no live GPU, no shader
/// compile — <c>RecordingGpuDevice.CreatePipeline</c> just wraps the
/// description) so <c>TextRenderer.DebugSpriteSegments</c> can be read back
/// directly instead of asserting through a GPU flush.
/// </para>
/// </summary>
public sealed class UiRenderContextAlphaTests
{
    private sealed class NullGpuFrameSource : ICurrentGpuFrameSource
    {
        public IGpuFrame? CurrentFrame => null;
    }

    private static (TextRenderer renderer, UiRenderContext ctx) Build()
    {
        var device = new RecordingGpuDevice();
        var renderer = new TextRenderer(device, new NullGpuFrameSource(), "unused");
        renderer.Begin(new Vector2(800f, 600f));
        var ctx = new UiRenderContext(renderer, new Vector2(800f, 600f));
        return (renderer, ctx);
    }

    private static UiDatFont BuildFont() => new(
        fgTex: 1, fgW: 64, fgH: 64,
        bgTex: 0, bgW: 0, bgH: 0,
        lineHeight: 16f, baselineOffset: 12f,
        glyphs: new Dictionary<char, FontCharDesc>
        {
            ['A'] = new FontCharDesc
            {
                Unicode = 'A',
                Width = 8,
                Height = 16,
                OffsetX = 0,
                OffsetY = 0,
                HorizontalOffsetBefore = 0,
                HorizontalOffsetAfter = 0,
                VerticalOffsetBefore = 0,
            },
        });

    // -- DrawSprite: full-opacity identity ---------------------------------

    [Fact]
    public void FullOpacity_DrawSprite_MatchesRequestedAlpha_Identity()
    {
        // Pin: with no window opacity pushed (AlphaMod == 1, matching every
        // production window today), output is byte-identical to a tint's own
        // alpha — this slice must not change ANY existing full-opacity render.
        (TextRenderer renderer, UiRenderContext ctx) = Build();
        Assert.Equal(1f, ctx.AlphaMod);

        ctx.DrawSprite(7u, 0, 0, 10, 10, 0, 0, 1, 1, new Vector4(1f, 1f, 1f, 1f));

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(7u, seg.Texture);
        Assert.Equal(1f, seg.Alpha);
    }

    [Fact]
    public void HalfOpacityWindow_MultipliesEverySpriteEmission()
    {
        (TextRenderer renderer, UiRenderContext ctx) = Build();

        ctx.PushAlpha(0.5f);
        Assert.Equal(0.5f, ctx.AlphaMod);
        ctx.DrawSprite(7u, 0, 0, 10, 10, 0, 0, 1, 1, new Vector4(1f, 1f, 1f, 1f));
        ctx.PopAlpha();

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(0.5f, seg.Alpha);

        // Pop restores full opacity for whatever draws next.
        Assert.Equal(1f, ctx.AlphaMod);
    }

    [Fact]
    public void NestedPushAlpha_ComposesMultiplicatively()
    {
        (TextRenderer renderer, UiRenderContext ctx) = Build();

        ctx.PushAlpha(0.5f);
        ctx.PushAlpha(0.4f);
        Assert.Equal(0.2f, ctx.AlphaMod, 5);
        ctx.DrawSprite(7u, 0, 0, 10, 10, 0, 0, 1, 1, new Vector4(1f, 1f, 1f, 1f));
        ctx.PopAlpha();
        ctx.PopAlpha();

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(0.2f, seg.Alpha, 5);
    }

    [Fact]
    public void NestedPushAlpha_MultipliesAgainstAnAlreadyTintedColor()
    {
        // A widget that already draws at partial alpha (e.g. a translucent
        // background sprite, tint.W = 0.8) fades FURTHER when its window is
        // also translucent — the two multipliers compose, they don't clobber.
        (TextRenderer renderer, UiRenderContext ctx) = Build();

        ctx.PushAlpha(0.5f);
        ctx.DrawSprite(7u, 0, 0, 10, 10, 0, 0, 1, 1, new Vector4(1f, 1f, 1f, 0.8f));
        ctx.PopAlpha();

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(0.4f, seg.Alpha, 5);
    }

    [Fact]
    public void PopAlpha_WithoutMatchingPush_IsANoOp()
    {
        (TextRenderer renderer, UiRenderContext ctx) = Build();
        ctx.PopAlpha();
        Assert.Equal(1f, ctx.AlphaMod);
    }

    // -- DrawStringDat: the CH6c fix (text now respects window alpha) -----

    [Fact]
    public void FullOpacity_DrawStringDat_MatchesRequestedAlpha_Identity()
    {
        (TextRenderer renderer, UiRenderContext ctx) = Build();
        UiDatFont font = BuildFont();

        ctx.DrawStringDat(font, "A", 0, 0, new Vector4(1f, 1f, 1f, 1f));

        // bgTex == 0, so only the foreground (fill) pass draws — one segment
        // on the font's foreground texture (id 1).
        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(1u, seg.Texture);
        Assert.Equal(1f, seg.Alpha);
    }

    [Fact]
    public void HalfOpacityWindow_MultipliesDatFontGlyphAlpha()
    {
        // The retail-faithful fix: ChatInterface::SetOpacity (0x004F3120) fades
        // the WHOLE composited window surface, glyphs included — before this
        // slice, DrawStringDat's applyAlpha:false meant text stayed sharp over
        // a translucent window (see the retired class-doc comment this test
        // replaces the assumption of).
        (TextRenderer renderer, UiRenderContext ctx) = Build();
        UiDatFont font = BuildFont();

        ctx.PushAlpha(0.5f);
        ctx.DrawStringDat(font, "A", 0, 0, new Vector4(1f, 1f, 1f, 1f));
        ctx.PopAlpha();

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(0.5f, seg.Alpha);
    }
}