using Unity.Burst;
using Unity.Collections;
using Unity.Entities;
using Unity.Mathematics;
using Unity.NetCode;
using Unity.Transforms;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Predicted "fire" ability: on the single fully-predicting pass of each tick, spawns a
    /// Projectile ghost for every player whose PlayerInput.Fire event is set this tick and whose
    /// AbilityCooldown has elapsed. Runs in both worlds: the owning client predict-spawns the
    /// projectile (classified into the authoritative ghost by ProjectileClassificationSystem via the
    /// Projectile.SpawnId key), and the server spawns the replicated truth.
    ///
    /// M3 data-driven: ability stats are read from the per-entity EffectiveAbilityStats (authored base
    /// from the AbilityDatabase blob keyed by AbilityRef, folded with the replicated StatModifier buffer
    /// by StatRecomputeSystem earlier this tick). The projectile ghost prefab is resolved per ability via
    /// the AbilityPrefabElement buffer on the AbilityDatabase singleton. Effective Speed/Damage/Range are
    /// snapshotted into the spawned Projectile, so the downstream move/damage systems are unchanged and
    /// predicted + server projectiles match (both folded the same replicated modifiers).
    ///
    /// Determinism / idempotency: the prediction loop re-runs this system on rollback, so all
    /// non-idempotent effects (spawning, cooldown advance) are gated behind
    /// NetworkTime.IsFirstTimeFullyPredictingTick so they happen exactly once per tick. The absolute
    /// fire count comes from the replicated input command buffer at NetworkTime.ServerTick (not a
    /// local counter) so the SpawnId matches on client and server. No wall-clock, no System.Random,
    /// no UnityEngine.Time.
    ///
    /// Auto-target is intentionally server-only: the client fires along raw aim, and the server's
    /// authoritative Projectile.Direction GhostField reconciles the predicted projectile to the
    /// assisted heading.
    /// </summary>
    [UpdateInGroup(typeof(PredictedSimulationSystemGroup))]
    [UpdateAfter(typeof(PlayerAimSystem))]
    [BurstCompile]
    public partial struct AbilityFireSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<AbilityDatabase>();
            state.RequireForUpdate<NetworkTime>();
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            // Spawning is a one-off effect: only run on the unique fully-predicting pass of this tick
            // so a rollback re-simulation does not double-spawn.
            var networkTime = SystemAPI.GetSingleton<NetworkTime>();
            if (!networkTime.IsFirstTimeFullyPredictingTick)
                return;

            var serverTick = networkTime.ServerTick;
            if (!serverTick.IsValid)
                return;

            // Per-ability projectile ghost prefabs live on the AbilityDatabase singleton's companion buffer.
            var dbEntity = SystemAPI.GetSingletonEntity<AbilityDatabase>();
            var abilityPrefabs = SystemAPI.GetBuffer<AbilityPrefabElement>(dbEntity);

            bool isServer = state.WorldUnmanaged.IsServer();

            // Server-only auto-target candidate set: training-dummy world XZ positions, collected once.
            var candidatePositions = new NativeList<float3>(Allocator.Temp);
            if (isServer)
            {
                foreach (var dummyTransform in
                         SystemAPI.Query<RefRO<LocalTransform>>().WithAll<TrainingDummyTag>())
                {
                    candidatePositions.Add(dummyTransform.ValueRO.Position);
                }
            }
            var candidates = candidatePositions.AsArray();

            var ecb = new EntityCommandBuffer(state.WorldUpdateAllocator);

            foreach (var (input, facing, xform, eff, abilityRef, cd, owner, entity) in
                     SystemAPI.Query<RefRO<PlayerInput>, RefRO<PlayerFacing>, RefRO<LocalTransform>,
                             RefRO<EffectiveAbilityStats>, RefRO<AbilityRef>, RefRW<AbilityCooldown>,
                             RefRO<GhostOwner>>()
                         .WithAll<Simulate>()
                         .WithEntityAccess())
            {
                // The InputEvent on the component carries the per-tick delta: set => fired this tick.
                if (!input.ValueRO.Fire.IsSet)
                    continue;

                // Cooldown gate. NextFireTick == 0 means "ready". Otherwise the player may fire only
                // once serverTick is at-or-newer than the stored tick (i.e. the stored tick is not
                // strictly newer than now).
                uint nextFireRaw = cd.ValueRO.NextFireTick;
                if (nextFireRaw != 0)
                {
                    var nextTick = new NetworkTick(nextFireRaw);
                    if (nextTick.IsValid && nextTick.IsNewerThan(serverTick))
                        continue; // still cooling down
                }

                // Resolve the projectile ghost prefab for this player's selected ability id.
                Entity prefab = Entity.Null;
                for (int i = 0; i < abilityPrefabs.Length; i++)
                {
                    if (abilityPrefabs[i].Id == abilityRef.ValueRO.Id)
                    {
                        prefab = abilityPrefabs[i].Prefab;
                        break;
                    }
                }
                if (prefab == Entity.Null)
                    continue; // ability has no projectile prefab wired

                // Absolute (monotonic) fire count from the replicated command buffer at this tick.
                // This is the classification key shared by client prediction and server truth.
                var inputBuffer = SystemAPI.GetBuffer<InputBufferData<PlayerInput>>(entity);
                if (!inputBuffer.GetDataAtTick(serverTick, out var applied))
                    continue;
                uint absoluteFireCount = applied.InternalInput.Fire.Count;

                float2 rawAim = facing.ValueRO.Direction;
                if (math.lengthsq(rawAim) < 1e-6f)
                    rawAim = new float2(0f, 1f);
                else
                    rawAim = math.normalize(rawAim);

                // Client fires along raw aim; only the server applies the auto-target assist cone.
                float2 dir = rawAim;
                if (isServer && eff.ValueRO.AutoTargetRange > 0f)
                {
                    dir = AutoTarget.Resolve(
                        xform.ValueRO.Position,
                        rawAim,
                        eff.ValueRO.AutoTargetRange,
                        eff.ValueRO.AutoTargetConeRadians,
                        candidates);
                }

                uint spawnId = (uint)owner.ValueRO.NetworkId << 16 | absoluteFireCount;

                var projectile = ecb.Instantiate(prefab);

                float3 planarDir = new float3(dir.x, 0f, dir.y);
                float3 spawnPos = xform.ValueRO.Position + planarDir * 0.6f;
                spawnPos.y = xform.ValueRO.Position.y;
                quaternion rot = quaternion.LookRotationSafe(planarDir, math.up());

                ecb.SetComponent(projectile, LocalTransform.FromPositionRotation(spawnPos, rot));
                ecb.SetComponent(projectile, new GhostOwner { NetworkId = owner.ValueRO.NetworkId });
                // Snapshot the effective ability stats into the projectile (base + modifiers, computed
                // identically on both worlds), so the move/damage systems need no modifier lookup.
                ecb.SetComponent(projectile, new Projectile
                {
                    Direction = math.normalize(dir),
                    SpawnId = spawnId,
                    Speed = eff.ValueRO.ProjectileSpeed,
                    Damage = eff.ValueRO.Damage,
                    Range = eff.ValueRO.Range,
                    DistanceTravelled = 0f,
                });

                // Earliest raw tick the player may fire again. Clamp cooldown to >= 1 tick.
                uint cooldownTicks = (uint)math.max(1, eff.ValueRO.CooldownTicks);
                cd.ValueRW.NextFireTick = serverTick.TickIndexForValidTick + cooldownTicks;
            }

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