using NUnit.Framework;
using ProjectM.Server;
using ProjectM.Simulation;
using Unity.Core;
using Unity.Entities;

namespace ProjectM.Tests
{
    /// <summary>
    /// Plain-Entities EditMode tests for the server-only HealthApplyDamageSystem.
    /// Boots a bare ECS world, registers the system in the SimulationSystemGroup, and ticks it.
    /// The system carries [WorldSystemFilter(ServerSimulation)], but world-system filtering is only
    /// applied by the netcode bootstrap; when we GetOrCreateSystem and add it to a group manually the
    /// filter is ignored, so it still runs in this netcode-free world. The system plays its
    /// EntityCommandBuffer back to state.EntityManager immediately (Temp allocator) per the build
    /// contract, so no separate ECB system is required for destruction to take effect within a single
    /// group update. Mirrors PlayerMoveSystemTests and HeartbeatSystemTests.
    /// </summary>
    public class HealthApplyDamageSystemTests
    {
        /// <summary>
        /// Builds a bare world, registers HealthApplyDamageSystem in the SimulationSystemGroup, and
        /// returns both so each test can create entities and tick.
        /// </summary>
        static (World world, SimulationSystemGroup group) MakeWorld(string name)
        {
            var world = new World(name);
            var group = world.GetOrCreateSystemManaged<SimulationSystemGroup>();
            group.AddSystemToUpdateList(world.GetOrCreateSystem<HealthApplyDamageSystem>());
            group.SortSystems();
            // Fixed time so the (time-independent) system runs cleanly; deterministic regardless.
            world.SetTime(new TimeData(elapsedTime: 0f, deltaTime: 1f / 60f));
            return (world, group);
        }

        [Test]
        public void Damage_Events_Are_Summed_Subtracted_And_Buffer_Cleared()
        {
            var (world, group) = MakeWorld("HealthApplyDamageTestWorld");
            using (world)
            {
                var em = world.EntityManager;
                // TrainingDummyTag included so this entity is a valid death candidate too, but with
                // 50 HP and 35 total damage it survives, so it must NOT be destroyed here.
                var entity = em.CreateEntity(typeof(Health), typeof(DamageEvent), typeof(TrainingDummyTag));
                em.SetComponentData(entity, new Health { Current = 50f, Max = 50f });

                var dmg = em.GetBuffer<DamageEvent>(entity);
                dmg.Add(new DamageEvent { Amount = 20f, SourceNetworkId = 1 });
                dmg.Add(new DamageEvent { Amount = 15f, SourceNetworkId = 2 });

                group.Update();

                Assert.IsTrue(em.Exists(entity),
                    "Non-lethal damage (35 of 50) must not destroy the entity.");
                Assert.AreEqual(15f, em.GetComponentData<Health>(entity).Current, 1e-4f,
                    "Health.Current should be 50 minus (20 plus 15) = 15.");
                Assert.AreEqual(0, em.GetBuffer<DamageEvent>(entity).Length,
                    "The DamageEvent buffer must be cleared after the events are applied.");
            }
        }

        [Test]
        public void Lethal_Damage_Clamps_Health_To_Zero_And_Destroys_TrainingDummy()
        {
            var (world, group) = MakeWorld("HealthApplyDamageLethalDummyWorld");
            using (world)
            {
                var em = world.EntityManager;
                var entity = em.CreateEntity(typeof(Health), typeof(DamageEvent), typeof(TrainingDummyTag));
                em.SetComponentData(entity, new Health { Current = 50f, Max = 50f });

                var dmg = em.GetBuffer<DamageEvent>(entity);
                dmg.Add(new DamageEvent { Amount = 80f, SourceNetworkId = 7 });

                group.Update();

                // The system clamps Current to a floor of 0 then destroys the dummy via an
                // immediately-played ECB, so the entity is gone within this single group update.
                Assert.IsFalse(em.Exists(entity),
                    "A lethally-hit TrainingDummyTag entity must be destroyed by the system's ECB.");

                using var remaining = em.CreateEntityQuery(typeof(TrainingDummyTag));
                Assert.AreEqual(0, remaining.CalculateEntityCount(),
                    "No TrainingDummyTag entities should remain after a lethal hit.");
            }
        }

        [Test]
        public void Lethal_Damage_On_NonDummy_Clamps_To_Zero_Without_Destroying()
        {
            // Player death is deferred in M2; only TrainingDummyTag entities are destroyed.
            // A non-dummy (no TrainingDummyTag) at zero HP must be clamped to 0 and kept alive.
            var (world, group) = MakeWorld("HealthApplyDamageLethalPlayerWorld");
            using (world)
            {
                var em = world.EntityManager;
                var entity = em.CreateEntity(typeof(Health), typeof(DamageEvent));
                em.SetComponentData(entity, new Health { Current = 30f, Max = 30f });

                var dmg = em.GetBuffer<DamageEvent>(entity);
                dmg.Add(new DamageEvent { Amount = 100f, SourceNetworkId = 3 });

                group.Update();

                Assert.IsTrue(em.Exists(entity),
                    "A non-dummy (player) entity must survive lethal damage in M2; death is deferred.");
                Assert.AreEqual(0f, em.GetComponentData<Health>(entity).Current, 1e-4f,
                    "Health.Current must be clamped to 0 (never negative).");
                Assert.AreEqual(0, em.GetBuffer<DamageEvent>(entity).Length,
                    "The DamageEvent buffer must be cleared after the events are applied.");
            }
        }

        [Test]
        public void No_Damage_Events_Leaves_Health_Untouched()
        {
            // Guards the dmg.Length == 0 early-continue: an empty buffer must not alter Health.
            var (world, group) = MakeWorld("HealthApplyDamageNoEventsWorld");
            using (world)
            {
                var em = world.EntityManager;
                var entity = em.CreateEntity(typeof(Health), typeof(DamageEvent), typeof(TrainingDummyTag));
                em.SetComponentData(entity, new Health { Current = 42f, Max = 60f });

                group.Update();

                Assert.IsTrue(em.Exists(entity), "An undamaged entity must not be destroyed.");
                Assert.AreEqual(42f, em.GetComponentData<Health>(entity).Current, 1e-4f,
                    "Health.Current must be untouched when there are no DamageEvents.");
            }
        }
    }
}