using System.Numerics;
using AcDream.App.Rendering;
using AcDream.App.Rendering.Gpu;
using AcDream.App.Tests.Rendering.Gpu;
using Xunit;

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// Campaign LA gate round 2 (register AD-98 filtering fidelity, 2026-08-15):
/// pins <see cref="TextRenderer.DrawSprite"/>'s texture-swap seam —
/// <see cref="TextRenderer.LinearTwinResolver"/>, consulted only while
/// <see cref="TextRenderer.CanvasScale"/> is not <see cref="Vector2.One"/> — the
/// half of the fix that doesn't need a live GPU. The user-visible symptom this
/// answers: the fixed-canvas char-select stretch (73041d70) reported JAGGED
/// text, because dat-font glyph atlases upload nearest (pixel-exact at 1:1) and
/// stayed nearest even while every quad was being magnified 2.4×1.8. The actual
/// linear-twin CREATION lives in <c>TextureCache.GetOrCreateLinearUiTwin</c>
/// (GPU-backed, see <c>TextureCacheLinearTwinTests</c>); this file proves the
/// RENDERER SIDE of the seam — segment handle selection — using a fake resolver
/// so the assertion doesn't depend on TextureCache's own wiring being correct.
/// </summary>
public sealed class TextRendererLinearTwinTests
{
    private sealed class NullGpuFrameSource : ICurrentGpuFrameSource
    {
        public IGpuFrame? CurrentFrame => null;
    }

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

    [Fact]
    public void CanvasScaleOne_DrawSprite_NeverConsultsResolver_KeepsOriginalHandle()
    {
        // At the native 1:1 scale (every in-world/UI frame today) the resolver
        // must not even be CALLED, not just "called and return the same value" —
        // a resolver that throws proves the ordinary path pays zero overhead for
        // a feature it never activates, exactly the "lazy" design constraint the
        // Campaign LA round-2 follow-up was scoped to.
        TextRenderer renderer = BuildRenderer();
        renderer.LinearTwinResolver = _ => throw new System.InvalidOperationException(
            "LinearTwinResolver must not be consulted while CanvasScale == One.");

        renderer.DrawSprite(5u, 0, 0, 10, 10, 0, 0, 1, 1, Vector4.One);

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(5u, seg.Texture);
    }

    [Fact]
    public void CanvasScaleNotOne_DrawSprite_SwapsHandleThroughResolver()
    {
        // The fixed-canvas case: CanvasScale is set by UiRoot.Draw for the
        // duration of a fixed-canvas screen's tree. A nearest-registered dat-font
        // glyph handle (5) must draw through its linear twin (999), not itself.
        TextRenderer renderer = BuildRenderer();
        renderer.CanvasScale = new Vector2(2.4f, 1.8f);
        renderer.LinearTwinResolver = handle => handle == 5u ? 999u : handle;

        renderer.DrawSprite(5u, 0, 0, 10, 10, 0, 0, 1, 1, Vector4.One);

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(999u, seg.Texture);
    }

    [Fact]
    public void CanvasScaleNotOne_ResolverIsIdentityForUnknownHandles()
    {
        // Chrome/background art (never registered nearest) and
        // UiTextureTableHandle.None (DrawFill's untextured branch) are the
        // majority of scaled-canvas draws. TextureCache.GetOrCreateLinearUiTwin
        // returns them unchanged; this pins that TextRenderer forwards whatever
        // the resolver returns without a separate "was this swapped" branch.
        TextRenderer renderer = BuildRenderer();
        renderer.CanvasScale = new Vector2(2.4f, 1.8f);
        renderer.LinearTwinResolver = handle => handle == 5u ? 999u : handle;

        renderer.DrawSprite(7u, 0, 0, 10, 10, 0, 0, 1, 1, Vector4.One);

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

    [Fact]
    public void CanvasScaleNotOne_NoResolverWired_KeepsOriginalHandle_DoesNotThrow()
    {
        // A host/test that never wires LinearTwinResolver (every existing
        // TextRenderer construction site before this change, and any future
        // test double) must keep drawing — nearest stays nearest, the
        // pre-existing (if jagged) behavior, rather than a null-reference
        // failure the moment a fixed-canvas screen activates.
        TextRenderer renderer = BuildRenderer();
        renderer.CanvasScale = new Vector2(2.4f, 1.8f);

        renderer.DrawSprite(5u, 0, 0, 10, 10, 0, 0, 1, 1, Vector4.One);

        var seg = Assert.Single(renderer.DebugSpriteSegments);
        Assert.Equal(5u, seg.Texture);
    }
}