using ProjectM.Simulation;
using Unity.Burst;
using Unity.Collections;
using Unity.Entities;
using Unity.Mathematics;
using Unity.NetCode;

namespace ProjectM.Server
{
    /// <summary>
    /// Server-authoritative damage application. Drains each damageable entity's
    /// <see cref="DamageEvent"/> buffer (appended by <see cref="ProjectileDamageSystem"/> earlier
    /// this tick), subtracts the summed amount from <see cref="Health"/>, then clears the buffer so
    /// each hit is applied exactly once. Entities that carry character stats (players) clamp to their
    /// data-driven <see cref="EffectiveCharacterStats.MaxHealth"/> ceiling; others (training dummies)
    /// clamp at zero. A dead <see cref="TrainingDummyTag"/> is destroyed; player death is deferred.
    /// Health.Current is a <c>[GhostField]</c>, so the new value replicates to clients for display.
    ///
    /// Runs server-only (<see cref="WorldSystemFilterFlags.ServerSimulation"/>) inside the prediction
    /// group so it shares tick timing with movement/damage, where it executes once per tick. The
    /// single structural change (destroying a dead dummy) is batched through a frame-allocator
    /// <see cref="EntityCommandBuffer"/> that is played back immediately to the entity manager — so a
    /// plain-world EditMode test needs no separate ECB system.
    /// </summary>
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(PredictedSimulationSystemGroup))]
    [UpdateAfter(typeof(ProjectileDamageSystem))]
    [BurstCompile]
    public partial struct HealthApplyDamageSystem : ISystem
    {
        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var ecb = new EntityCommandBuffer(Allocator.Temp);

            foreach (var (health, dmg, entity) in
                     SystemAPI.Query<RefRW<Health>, DynamicBuffer<DamageEvent>>()
                         .WithEntityAccess())
            {
                if (dmg.Length == 0)
                    continue;

                float total = 0f;
                for (int i = 0; i < dmg.Length; i++)
                    total += dmg[i].Amount;
                dmg.Clear();

                float newHp = health.ValueRO.Current - total;

                // Effective max health (base + modifiers) is the runtime ceiling for entities that carry
                // character stats (players); others just clamp at zero. No auto-heal on a max increase.
                if (SystemAPI.HasComponent<EffectiveCharacterStats>(entity))
                    newHp = math.clamp(newHp, 0f, SystemAPI.GetComponent<EffectiveCharacterStats>(entity).MaxHealth);
                else
                    newHp = math.max(0f, newHp);

                health.ValueRW.Current = newHp;

                // Server-authoritative death: training dummies despawn; player death is deferred (clamp only).
                if (health.ValueRO.Current <= 0f && SystemAPI.HasComponent<TrainingDummyTag>(entity))
                    ecb.DestroyEntity(entity);
            }

            ecb.Playback(state.EntityManager);
            ecb.Dispose();
        }
    }
}