using System.Numerics;
using AcDream.App.Rendering;
using AcDream.Core.World;
using Xunit;

namespace AcDream.App.Tests.Rendering;

/// <summary>
/// Campaign CC gate round 1, Batch D (GF-7/GF-14): pins
/// <see cref="PrivateEntityViewportRenderer.BuildDrawEntities"/>, the pure
/// helper that decides which entities <see cref="PrivateEntityViewportRenderer.Render"/>
/// submits to <c>WbDrawDispatcher</c>. Exercised directly (no GPU device, no
/// constructed <c>WbDrawDispatcher</c>) — the same interface-fake-first
/// testing shape <c>CreatureAppraisalPresentationTests</c> already uses for
/// this renderer family, since <c>PrivateEntityViewportRenderer</c> itself
/// pulls in a live mesh-pipeline object graph too heavy to construct in a
/// unit test.
///
/// <para>
/// This is the paperdoll/creature-appraisal REGRESSION PIN the batch's test
/// plan calls for: both renderers never configure a backdrop slot (see
/// <c>PaperdollViewportRenderer</c>/<c>CreatureAppraisalPresentation.cs</c> —
/// neither passes a <c>backdropRenderId</c> nor exposes <c>SetBackdrop</c>),
/// so every one of their draws calls this helper with <c>backdrop: null</c> —
/// exactly the first case below.
/// </para>
/// </summary>
public sealed class PrivateEntityViewportRendererDrawOrderTests
{
    private static WorldEntity Entity(uint id, IReadOnlyList<MeshRef> meshRefs) => new()
    {
        Id = id,
        ServerGuid = id,
        SourceGfxObjOrSetupId = 0x0200_0001u,
        Position = Vector3.Zero,
        Rotation = Quaternion.Identity,
        MeshRefs = meshRefs,
    };

    private static readonly MeshRef[] OneMesh = [new MeshRef(0x0100_0001u, Matrix4x4.Identity)];

    [Fact]
    public void NoBackdrop_ReturnsExactlyTheMainEntity()
    {
        WorldEntity main = Entity(1u, OneMesh);

        IReadOnlyList<WorldEntity> entities =
            PrivateEntityViewportRenderer.BuildDrawEntities(backdrop: null, main);

        Assert.Same(main, Assert.Single(entities));
    }

    [Fact]
    public void BackdropPresent_ReturnsBackdropFirstThenMain()
    {
        // Decomp-cited: gmCG3DView::Update adds the backdrop object to
        // creature_mode_objects BEFORE the player object is re-added
        // (~0x004eed44 vs ~0x004ef199) — this ordering is retail-faithful,
        // not an arbitrary choice.
        WorldEntity backdrop = Entity(ChargenPreviewEntityBuilder.PreviewBackdropRenderId, OneMesh);
        WorldEntity main = Entity(ChargenPreviewEntityBuilder.PreviewRenderId, OneMesh);

        IReadOnlyList<WorldEntity> entities =
            PrivateEntityViewportRenderer.BuildDrawEntities(backdrop, main);

        Assert.Equal(2, entities.Count);
        Assert.Same(backdrop, entities[0]);
        Assert.Same(main, entities[1]);
    }

    [Fact]
    public void BackdropWithNoDrawableMeshes_DegradesToExactlyTheMainEntity()
    {
        WorldEntity emptyBackdrop = Entity(
            ChargenPreviewEntityBuilder.PreviewBackdropRenderId, []);
        WorldEntity main = Entity(ChargenPreviewEntityBuilder.PreviewRenderId, OneMesh);

        IReadOnlyList<WorldEntity> entities =
            PrivateEntityViewportRenderer.BuildDrawEntities(emptyBackdrop, main);

        Assert.Same(main, Assert.Single(entities));
    }
}