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 retail signature's exact combination math for radius/height beyond
/// "edge-to-edge, own+target cylinders" is not spelled out in the raw (BN
/// garbles the x87 plumbing) — ported per the PDB argument ORDER
/// (own radius/height, own position, target radius/height, target
/// position) with the standard cylinder-distance shape: horizontal
/// (planar) distance minus the sum of the two radii (clamped at 0), since
/// that is the only shape consistent with "edge-to-edge" and with
/// <c>distance_to_object</c>'s ctor default of 0.6 (melee range from
/// surface to surface, not center to center).
/// </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_ClampsAtZero_NoNegativeDistance()
    {
        // centers 1 unit apart, radii 5 and 5 → would be -9, clamps to 0
        float d = MoveToMath.CylinderDistance(
            ownRadius: 5f, ownHeight: 2f, ownPos: Vector3.Zero,
            targetRadius: 5f, targetHeight: 2f, targetPos: new Vector3(1f, 0f, 0f));

        Assert.Equal(0f, 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_IgnoresVerticalSeparation_PlanarOnly()
    {
        // Same X/Y, large Z separation — cylinder_distance in retail's own
        // callers (GetCurrentDistance) is used for horizontal arrival gates;
        // the Z axis is height, not part of the radial edge-to-edge gap.
        float d1 = MoveToMath.CylinderDistance(
            ownRadius: 1f, ownHeight: 2f, ownPos: new Vector3(0, 0, 0),
            targetRadius: 1f, targetHeight: 2f, targetPos: new Vector3(5f, 0f, 0f));
        float d2 = MoveToMath.CylinderDistance(
            ownRadius: 1f, ownHeight: 2f, ownPos: new Vector3(0, 0, 50f),
            targetRadius: 1f, targetHeight: 2f, targetPos: new Vector3(5f, 0f, -50f));

        Assert.Equal(d1, d2, 3);
        Assert.Equal(3f, d1, 3);   // 5 - 1 - 1
    }

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

        Assert.Equal(0f, d, 3);
    }
}