using NUnit.Framework;
using ProjectM.Simulation;
using Unity.Core;
using Unity.Entities;
using Unity.Mathematics;
using Unity.Transforms;

namespace ProjectM.Tests
{
    /// <summary>
    /// Plain-Entities determinism test for <see cref="ProjectileMoveSystem"/> (the M2 predicted
    /// projectile integrator). Boots a bare ECS world, registers the system in the
    /// SimulationSystemGroup, creates a synthetic projectile (LocalTransform + Projectile + enabled
    /// Simulate), injects a fixed delta-time, ticks N times, and asserts the position advanced by
    /// exactly Speed * dt * N along the planar (XZ) Direction and that DistanceTravelled accumulated
    /// the same total. Version-independent and netcode-free, mirroring PlayerMoveSystemTests.
    /// The system's <c>[UpdateInGroup(PredictedSimulationSystemGroup)]</c> attribute is inert here
    /// because the system is added to the SimulationSystemGroup manually.
    /// </summary>
    public class ProjectileMoveSystemTests
    {
        [Test]
        public void Projectile_Advances_By_Speed_Times_Dt_Each_Tick()
        {
            using var world = new World("ProjectileMoveTestWorld");
            var simulationGroup = world.GetOrCreateSystemManaged<SimulationSystemGroup>();
            var moveSystem = world.GetOrCreateSystem<ProjectileMoveSystem>();
            simulationGroup.AddSystemToUpdateList(moveSystem);
            simulationGroup.SortSystems();

            var em = world.EntityManager;
            var entity = em.CreateEntity(
                typeof(LocalTransform), typeof(Projectile), typeof(Simulate));

            const float speed = 10f;
            const float dt = 0.1f;
            const int ticks = 5;

            em.SetComponentData(entity, LocalTransform.FromPosition(float3.zero));
            em.SetComponentData(entity, new Projectile
            {
                Direction = new float2(1f, 0f),
                SpawnId = 0u,
                Speed = speed,
                Damage = 20f,
                Range = 100f,
                DistanceTravelled = 0f,
            });

            for (int i = 0; i < ticks; i++)
            {
                // Fixed delta so the predicted integration is fully deterministic (no wall-clock).
                world.SetTime(new TimeData(elapsedTime: dt * (i + 1), deltaTime: dt));
                simulationGroup.Update();
            }

            var position = em.GetComponentData<LocalTransform>(entity).Position;
            var distance = em.GetComponentData<Projectile>(entity).DistanceTravelled;

            Assert.AreEqual(speed * dt * ticks, position.x, 1e-3f,
                "X should advance by Speed * dt each tick for Direction=(1,0).");
            Assert.AreEqual(0f, position.y, 1e-3f, "Travel is planar; Y should stay 0.");
            Assert.AreEqual(0f, position.z, 1e-3f, "Direction=(1,0) maps to +X only; Z should stay 0.");
            Assert.AreEqual(speed * dt * ticks, distance, 1e-3f,
                "DistanceTravelled should accumulate Speed * dt each tick.");
        }

        [Test]
        public void Projectile_Integration_Is_Idempotent_Across_Equal_Tick_Batches()
        {
            // Determinism/idempotence: the same Direction, Speed and dt must yield the same result
            // regardless of how the ticks are grouped (mirrors the prediction loop re-simulating a
            // tick on rollback). Returns (finalPosition, distanceTravelled).
            (float3 Position, float Distance) RunTicks(int ticks)
            {
                using var world = new World("ProjectileMoveDetWorld");
                var group = world.GetOrCreateSystemManaged<SimulationSystemGroup>();
                group.AddSystemToUpdateList(world.GetOrCreateSystem<ProjectileMoveSystem>());
                group.SortSystems();

                var em = world.EntityManager;
                var e = em.CreateEntity(
                    typeof(LocalTransform), typeof(Projectile), typeof(Simulate));
                em.SetComponentData(e, LocalTransform.FromPosition(float3.zero));
                em.SetComponentData(e, new Projectile
                {
                    Direction = new float2(0f, 1f),
                    SpawnId = 0u,
                    Speed = 7f,
                    Damage = 20f,
                    Range = 100f,
                    DistanceTravelled = 0f,
                });

                for (int i = 0; i < ticks; i++)
                {
                    world.SetTime(new TimeData(0.05f * (i + 1), 0.05f));
                    group.Update();
                }

                var proj = em.GetComponentData<Projectile>(e);
                return (em.GetComponentData<LocalTransform>(e).Position, proj.DistanceTravelled);
            }

            var a = RunTicks(20);
            var b = RunTicks(20);

            Assert.AreEqual(a.Position.z, b.Position.z, 1e-4f,
                "Two identical runs must produce identical positions.");
            Assert.AreEqual(a.Distance, b.Distance, 1e-4f,
                "Two identical runs must produce identical DistanceTravelled.");
            Assert.AreEqual(7f * 0.05f * 20f, a.Position.z, 1e-3f,
                "Direction=(0,1) maps to +Z by Speed*dt*N.");
            Assert.AreEqual(7f * 0.05f * 20f, a.Distance, 1e-3f,
                "DistanceTravelled equals Speed*dt*N.");
        }
    }
}