using System.Numerics;
using AcDream.Core.Physics;
using AcDream.Core.Physics.Motion;
using Xunit;

namespace AcDream.Core.Tests.Physics.Motion;

/// <summary>
/// R4-V1 — <c>Position::cylinder_distance</c>, the pure-math shape per
/// r4-moveto-decomp.md §5a (<c>MoveToManager::GetCurrentDistance</c>,
/// <c>005291b0</c>): edge-to-edge distance between two vertical cylinders
/// (own radius/height, target radius/height, both positions). Object moves
/// (use_spheres set on the wire) use this; position moves use plain
/// Euclidean <c>Position::distance</c> (§5a: "position moves use center
/// distance" — <see cref="MoveToMath.CylinderDistance"/> is the object-move
/// variant only; center distance is <c>Vector3.Distance</c>, already
/// available, not re-ported here).
///
/// <para>
/// The exact branch structure is visible at named-retail
/// <c>Position::cylinder_distance @ 0x005A97F0</c> and independently matches
/// ACE <c>Physics.Common.Position.CylinderDistance</c>. It uses full 3D center
/// distance, both radii, both heights, and returns signed overlap.
/// </para>
/// </summary>
public sealed class MoveToMathCylinderDistanceTests
{
    [Fact]
    public void TwoCylinders_HorizontallySeparated_SubtractsBothRadii()
    {
        // centers 10 units apart on X, radii 1 and 2 → edge distance = 10-1-2=7
        float d = MoveToMath.CylinderDistance(
            ownRadius: 1f, ownHeight: 2f, ownPos: Vector3.Zero,
            targetRadius: 2f, targetHeight: 2f, targetPos: new Vector3(10f, 0f, 0f));

        Assert.Equal(7f, d, 3);
    }

    [Fact]
    public void TwoCylinders_Overlapping_ReturnsSignedThreeDimensionalOverlap()
    {
        // radial gap = 1 - 10 = -9; vertical gap = 0 - 2 = -2.
        float d = MoveToMath.CylinderDistance(
            ownRadius: 5f, ownHeight: 2f, ownPos: Vector3.Zero,
            targetRadius: 5f, targetHeight: 2f, targetPos: new Vector3(1f, 0f, 0f));

        Assert.Equal(-MathF.Sqrt(85f), d, 3);
    }

    [Fact]
    public void TwoCylinders_ZeroRadii_ReducesToCenterDistance()
    {
        float d = MoveToMath.CylinderDistance(
            ownRadius: 0f, ownHeight: 2f, ownPos: Vector3.Zero,
            targetRadius: 0f, targetHeight: 2f, targetPos: new Vector3(3f, 4f, 0f));

        Assert.Equal(5f, d, 3);   // 3-4-5 triangle
    }

    [Fact]
    public void TwoCylinders_VerticallyAndRadiallySeparated_CombinesBothGaps()
    {
        // full center gap = 5, radial gap = 3; vertical gap = 4 - 2 = 2.
        float d = MoveToMath.CylinderDistance(
            ownRadius: 1f, ownHeight: 2f, ownPos: Vector3.Zero,
            targetRadius: 1f, targetHeight: 2f, targetPos: new Vector3(3f, 0f, 4f));

        Assert.Equal(MathF.Sqrt(13f), d, 3);
    }

    [Fact]
    public void SamePosition_ReturnsSignedOverlap()
    {
        float d = MoveToMath.CylinderDistance(
            ownRadius: 0.5f, ownHeight: 2f, ownPos: Vector3.Zero,
            targetRadius: 0.5f, targetHeight: 2f, targetPos: Vector3.Zero);

        Assert.Equal(-MathF.Sqrt(5f), d, 3);
    }

    [Fact]
    public void OppositeGapSigns_ReturnsRadialGapVerbatim()
    {
        float d = MoveToMath.CylinderDistance(
            ownRadius: 5f, ownHeight: 1f, ownPos: Vector3.Zero,
            targetRadius: 5f, targetHeight: 1f, targetPos: new Vector3(0f, 0f, 3f));

        Assert.Equal(-7f, d, 3);
    }
}