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))]
    // Pin the drain AFTER DashSystem: a same-tick player-sourced projectile (ProjectileDamageSystem stamps
    // SourceTick = now and this system drains the SAME tick) must see a dash window STARTED this tick —
    // without the edge the negation at src == StartTick is an unconstrained sorter tiebreak. The Dash chain
    // (StatRecompute→PlayerControl→Dash) and the projectile chain (PlayerAim→AbilityFire→ProjectileMove→
    // ProjectileDamage→here) are otherwise disjoint, so this edge cannot form a cycle (Play-validated).
    [UpdateAfter(typeof(DashSystem))]
    [BurstCompile]
    public partial struct HealthApplyDamageSystem : ISystem
    {
        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var ecb = new EntityCommandBuffer(Allocator.Temp);
            bool haveTick = SystemAPI.TryGetSingleton<NetworkTime>(out var netTime);
            uint negatedThisTick = 0;
            uint punishesThisTick = 0;

            foreach (var (health, dmg, entity) in
                     SystemAPI.Query<RefRW<Health>, DynamicBuffer<DamageEvent>>()
                         .WithEntityAccess())
            {
                if (dmg.Length == 0)
                    continue;
                // Dev god-mode: while enabled, this entity ignores ALL damage (server-authoritative, once per tick).
                if (SystemAPI.HasComponent<DebugGodMode>(entity) && SystemAPI.IsComponentEnabled<DebugGodMode>(entity))
                {
                    dmg.Clear();
                    continue;
                }


                // Respawn invulnerability: a freshly-recovered player ignores damage for a window.
                if (haveTick && netTime.ServerTick.IsValid && SystemAPI.HasComponent<RespawnInvuln>(entity))
                {
                    uint until = SystemAPI.GetComponent<RespawnInvuln>(entity).UntilTick;
                    if (until != 0)
                    {
                        var untilTick = new NetworkTick(until);
                        if (untilTick.IsValid && untilTick.IsNewerThan(netTime.ServerTick))
                        {
                            dmg.Clear();
                            continue;
                        }
                    }
                }

                bool hasDash = haveTick && netTime.ServerTick.IsValid && SystemAPI.HasComponent<DashState>(entity);
                DashState ds = hasDash ? SystemAPI.GetComponent<DashState>(entity) : default;

                bool isCharger = haveTick && netTime.ServerTick.IsValid && SystemAPI.HasComponent<LungeState>(entity);
                uint negatedForThisEntity = 0u;
                float total = 0f;
                for (int i = 0; i < dmg.Length; i++)
                {
                    uint src = dmg[i].SourceTick;
                    if (hasDash && src != 0u && ds.IFrameUntilTick != 0u)
                    {
                        var srcTick = new NetworkTick(src);
                        var startTick = new NetworkTick(ds.StartTick);
                        var untilTick = new NetworkTick(ds.IFrameUntilTick);
                        // Dash i-frames cover the HALF-OPEN window [StartTick, IFrameUntilTick): negate iff src >= start AND src < until.
                        bool atOrAfterStart = srcTick.IsValid && startTick.IsValid && !startTick.IsNewerThan(srcTick);
                        bool beforeUntil = untilTick.IsValid && untilTick.IsNewerThan(srcTick);
                        if (atOrAfterStart && beforeUntil)
                        {
                            negatedThisTick++;
                            negatedForThisEntity++;
                            continue; // dash i-frame negates this hit (per-element, not a whole-buffer clear)
                        }
                    }
                    total += dmg[i].Amount;

                    // MC-1 punish scoring: a player-sourced hit (SourceNetworkId >= 0) landing inside a Charger's
                    // whiff-stagger window counts ONCE — zeroing StaggerUntilTick keeps punishes:windows <= 1.
                    if (isCharger && dmg[i].SourceNetworkId >= 0)
                    {
                        var lunge = SystemAPI.GetComponent<LungeState>(entity);
                        if (lunge.StaggerUntilTick != 0u)
                        {
                            var stag = new NetworkTick(lunge.StaggerUntilTick);
                            if (stag.IsValid && stag.IsNewerThan(netTime.ServerTick))
                            {
                                punishesThisTick++;
                                lunge.StaggerUntilTick = 0u;
                                SystemAPI.SetComponent(entity, lunge);
                            }
                        }
                    }
                }
                dmg.Clear();
                if (negatedForThisEntity != 0u)
                {
                    ds.NegatedCount += negatedForThisEntity; // server-side spam signal; DashSystem reads it at window-close
                    SystemAPI.SetComponent(entity, ds);
                }

                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 + enemies + EB-1 Destructible structures despawn;
                // player death is deferred (clamp only). A structure carries NO EffectiveCharacterStats, so it took
                // the math.max(0,..) branch above and CAN reach 0 — never give a structure stats (it would clamp to
                // a non-zero floor and become immortal).
                if (health.ValueRO.Current <= 0f && (SystemAPI.HasComponent<TrainingDummyTag>(entity) || SystemAPI.HasComponent<EnemyTag>(entity) || SystemAPI.HasComponent<Destructible>(entity)))
                    ecb.DestroyEntity(entity);
            }
            if ((negatedThisTick != 0u || punishesThisTick != 0u) && SystemAPI.HasSingleton<DevTelemetry>())
            {
                var telem = SystemAPI.GetSingletonRW<DevTelemetry>();
                telem.ValueRW.DashIFrameNegatedHits += negatedThisTick;
                telem.ValueRW.ChargerWhiffPunishesLanded += punishesThisTick;
            }

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