using System;
using System.Numerics;
using AcDream.Core.Selection;
using AcDream.Core.World;
using Xunit;

namespace AcDream.Core.Tests.Selection;

public class WorldPickerTests
{
    private const float Epsilon = 0.01f;

    private static (Matrix4x4 View, Matrix4x4 Projection) MakeIdentityCamera()
    {
        var view = Matrix4x4.Identity;
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            fieldOfView: MathF.PI / 3f,
            aspectRatio: 16f / 9f,
            nearPlaneDistance: 0.1f,
            farPlaneDistance: 100f);
        return (view, proj);
    }

    [Fact]
    public void BuildRay_CenterOfViewport_ReturnsForwardRay()
    {
        var (view, proj) = MakeIdentityCamera();
        const float vpW = 1920f, vpH = 1080f;

        var (_, direction) = WorldPicker.BuildRay(
            mouseX: vpW / 2f, mouseY: vpH / 2f,
            viewportW: vpW, viewportH: vpH,
            view, proj);

        // Right-handed perspective + identity view -> camera looks down -Z.
        // Center pixel ray = (0, 0, -1) within float epsilon.
        Assert.True(MathF.Abs(direction.X) < Epsilon, $"direction.X = {direction.X}");
        Assert.True(MathF.Abs(direction.Y) < Epsilon, $"direction.Y = {direction.Y}");
        Assert.True(direction.Z < -0.99f,             $"direction.Z = {direction.Z}");
    }

    [Fact]
    public void BuildRay_OffsetMouseRight_DeflectsRayPositiveX()
    {
        var (view, proj) = MakeIdentityCamera();
        const float vpW = 1920f, vpH = 1080f;

        var (_, direction) = WorldPicker.BuildRay(
            mouseX: vpW * 0.75f, mouseY: vpH / 2f,
            viewportW: vpW, viewportH: vpH,
            view, proj);

        Assert.True(direction.X > 0.1f, $"direction.X = {direction.X} (expected > 0.1)");
    }

    private static WorldEntity MakeEntity(uint serverGuid, Vector3 position) => new()
    {
        Id = serverGuid == 0u ? 1u : serverGuid,
        ServerGuid = serverGuid,
        SourceGfxObjOrSetupId = 0u,
        Position = position,
        Rotation = Quaternion.Identity,
        MeshRefs = Array.Empty<MeshRef>(),
    };

    [Fact]
    public void Pick_RayThroughEntity_ReturnsServerGuid()
    {
        var entity = MakeEntity(0xABCDu, new Vector3(0, 0, -10));

        var result = WorldPicker.Pick(
            origin: Vector3.Zero,
            direction: -Vector3.UnitZ,
            candidates: new[] { entity },
            skipServerGuid: 0u);

        Assert.Equal(0xABCDu, result);
    }

    [Fact]
    public void Pick_RayMisses_ReturnsNull()
    {
        var entity = MakeEntity(0xABCDu, new Vector3(0, 0, -10));

        var result = WorldPicker.Pick(
            origin: Vector3.Zero,
            direction: Vector3.UnitX,
            candidates: new[] { entity },
            skipServerGuid: 0u);

        Assert.Null(result);
    }

    [Fact]
    public void Pick_TwoEntitiesInLine_ReturnsCloser()
    {
        var near = MakeEntity(0x1111u, new Vector3(0, 0, -5));
        var far  = MakeEntity(0x2222u, new Vector3(0, 0, -20));

        var result = WorldPicker.Pick(
            origin: Vector3.Zero,
            direction: -Vector3.UnitZ,
            candidates: new[] { far, near },  // iteration order shouldn't matter
            skipServerGuid: 0u);

        Assert.Equal(0x1111u, result);
    }

    [Fact]
    public void Pick_SkipsSkipGuid()
    {
        var entity = MakeEntity(0xABCDu, new Vector3(0, 0, -10));

        var result = WorldPicker.Pick(
            origin: Vector3.Zero,
            direction: -Vector3.UnitZ,
            candidates: new[] { entity },
            skipServerGuid: 0xABCDu);

        Assert.Null(result);
    }

    [Fact]
    public void Pick_SkipsZeroServerGuid()
    {
        // Atlas-tier scenery / dat-hydrated statics carry ServerGuid=0
        // and aren't valid Use targets — server would reject guid=0.
        var entity = MakeEntity(0u, new Vector3(0, 0, -10));

        var result = WorldPicker.Pick(
            origin: Vector3.Zero,
            direction: -Vector3.UnitZ,
            candidates: new[] { entity },
            skipServerGuid: 0xDEADu);

        Assert.Null(result);
    }

    [Fact]
    public void Pick_BeyondMaxDistance_ReturnsNull()
    {
        var entity = MakeEntity(0xABCDu, new Vector3(0, 0, -100));

        var result = WorldPicker.Pick(
            origin: Vector3.Zero,
            direction: -Vector3.UnitZ,
            candidates: new[] { entity },
            skipServerGuid: 0u);  // default maxDistance = 50f

        Assert.Null(result);
    }

    [Fact]
    public void Pick_RayOriginInsideEntitySphere_StillReturnsServerGuid()
    {
        // Player ~3m from a door -> camera near-plane sits INSIDE the door's
        // 5m bounding sphere. Naive t_near < 0 guard would skip; correct
        // behavior is to fall through to t_far (the sphere exit point).
        var entity = MakeEntity(0xABCDu, new Vector3(0, 0, -3));

        var result = WorldPicker.Pick(
            origin: Vector3.Zero,
            direction: -Vector3.UnitZ,
            candidates: new[] { entity },
            skipServerGuid: 0u);

        Assert.Equal(0xABCDu, result);
    }
}