using NUnit.Framework;
using ProjectM.Simulation;
using Unity.Mathematics;

namespace ProjectM.Tests
{
    /// <summary>
    /// Pure-function tests for <see cref="PlayerSpawnMath.SpawnOffset"/> (no ECS world), mirroring
    /// StatMathTests. Pins the M4 co-op deterministic spawn spread: stable, distinct per-NetworkId ring
    /// positions so players never stack on connect.
    /// </summary>
    public class PlayerSpawnRingTests
    {
        const float R = 2.5f;
        const int Slots = 4;
        const float Eps = 1e-4f;

        [Test]
        public void Deterministic_SameInputs_SameOffset()
        {
            var a = PlayerSpawnMath.SpawnOffset(2, R, Slots);
            var b = PlayerSpawnMath.SpawnOffset(2, R, Slots);
            Assert.AreEqual(a.x, b.x, Eps);
            Assert.AreEqual(a.y, b.y, Eps);
            Assert.AreEqual(a.z, b.z, Eps);
        }

        [Test]
        public void FirstFour_Land_On_Cardinal_Ring_Slots()
        {
            // NetworkIds start at 1; slots=4 -> 0, 90, 180, 270 degrees on a ring of radius R.
            AssertXz(PlayerSpawnMath.SpawnOffset(1, R, Slots), R, 0f);
            AssertXz(PlayerSpawnMath.SpawnOffset(2, R, Slots), 0f, R);
            AssertXz(PlayerSpawnMath.SpawnOffset(3, R, Slots), -R, 0f);
            AssertXz(PlayerSpawnMath.SpawnOffset(4, R, Slots), 0f, -R);
        }

        [Test]
        public void Distinct_NetworkIds_Give_Distinct_Positions()
        {
            var seen = new System.Collections.Generic.List<float3>();
            for (int id = 1; id <= 8; id++)
            {
                var p = PlayerSpawnMath.SpawnOffset(id, R, Slots);
                foreach (var q in seen)
                    Assert.Greater(math.distance(p, q), 1e-3f, $"id {id} collides with an earlier slot");
                seen.Add(p);
            }
        }

        [Test]
        public void FifthPlayer_Spills_To_Outer_Ring()
        {
            // idx 4 with slots 4 -> ring 1, slot 0 -> radius doubled, angle 0.
            AssertXz(PlayerSpawnMath.SpawnOffset(5, R, Slots), 2f * R, 0f);
        }

        [Test]
        public void NonPositiveRadius_Returns_Zero()
        {
            Assert.AreEqual(0f, math.length(PlayerSpawnMath.SpawnOffset(3, 0f, Slots)), Eps);
            Assert.AreEqual(0f, math.length(PlayerSpawnMath.SpawnOffset(3, -1f, Slots)), Eps);
        }

        [Test]
        public void DegenerateSlots_DoNotThrow_AndStayDistinct()
        {
            // slots < 1 is clamped to 1 (every player on its own concentric ring).
            var a = PlayerSpawnMath.SpawnOffset(1, R, 0);
            var b = PlayerSpawnMath.SpawnOffset(2, R, 0);
            Assert.Greater(math.distance(a, b), 1e-3f);
        }

        [Test]
        public void Offset_Is_Planar_NoVerticalComponent()
        {
            for (int id = 1; id <= 6; id++)
                Assert.AreEqual(0f, PlayerSpawnMath.SpawnOffset(id, R, Slots).y, Eps);
        }

        static void AssertXz(float3 p, float x, float z)
        {
            Assert.AreEqual(x, p.x, Eps);
            Assert.AreEqual(z, p.z, Eps);
        }
    }
}