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

namespace ProjectM.Server
{
    /// <summary>
    /// One-shot server restore of player-built structures for a "Continue" session. The menu (WorldLauncher) stages a
    /// <see cref="PendingStructure"/> carrier in the fresh ServerWorld BEFORE the gameplay subscene streams; this
    /// system waits (RequireForUpdate) for the streamed <see cref="StructureCatalog"/> + <see cref="BaseAnchor"/> +
    /// a valid NetworkTime, then replays each saved structure CHARGE-FREE: Instantiate the catalog prefab at the
    /// saved cell (preserving the baked Scale), restore the wounded HP born-correct, re-tag RegionTag{Base} +
    /// RuntimePlacedTag, then DESTROY the carrier so it never runs again. The ledger restores separately +
    /// absolutely via CycleDirectorSpawnSystem's born-correct load (no double-spend, no Withdraw here).
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    public partial struct BaseRestoreSystem : ISystem
    {
        ComponentLookup<LocalTransform> m_TransformLookup;
        ComponentLookup<Health> m_HealthLookup;

        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            m_TransformLookup = state.GetComponentLookup<LocalTransform>(isReadOnly: true);
            m_HealthLookup = state.GetComponentLookup<Health>(isReadOnly: true);
            state.RequireForUpdate<StructureCatalog>();
            state.RequireForUpdate<BaseAnchor>();
            state.RequireForUpdate<NetworkTime>();
            state.RequireForUpdate(state.GetEntityQuery(ComponentType.ReadOnly<PendingStructure>()));
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            var serverTick = SystemAPI.GetSingleton<NetworkTime>().ServerTick;
            if (!serverTick.IsValid)
                return;
            uint now = serverTick.TickIndexForValidTick;

            m_TransformLookup.Update(ref state);
            m_HealthLookup.Update(ref state);

            var anchor = SystemAPI.GetSingleton<BaseAnchor>();
            var catalog = SystemAPI.GetBuffer<StructureCatalogEntry>(SystemAPI.GetSingletonEntity<StructureCatalog>());

            var ecb = new EntityCommandBuffer(Allocator.Temp);

            foreach (var (pending, carrier) in
                     SystemAPI.Query<DynamicBuffer<PendingStructure>>().WithEntityAccess())
            {
                for (int s = 0; s < pending.Length; s++)
                {
                    var p = pending[s];

                    int entryIdx = -1;
                    for (int i = 0; i < catalog.Length; i++)
                        if (catalog[i].Type == p.Type) { entryIdx = i; break; }
                    if (entryIdx < 0 || catalog[entryIdx].Prefab == Entity.Null)
                        continue; // type not in the catalog (e.g. a save from a newer build) -> skip, don't crash

                    var prefab = catalog[entryIdx].Prefab;
                    var structure = ecb.Instantiate(prefab);

                    int2 cell = new int2(p.CellX, p.CellZ);
                    var xform = m_TransformLookup[prefab];
                    xform.Position = BaseGridMath.CellToWorld(anchor, cell); // preserve baked Scale (FromPosition would reset it)
                    ecb.SetComponent(structure, xform);

                    ecb.SetComponent(structure, new PlacedStructure
                    {
                        Type = p.Type,
                        Cell = cell,
                        NextTick = 0u, // cooldown restore retired with the automation chain (LANTERN purge)
                        LastProcessedTick = TickUtil.NonZero(now),
                    });
                    // EB-1: restore the wounded HP born-correct in the SAME ecb as Instantiate (Health.Current is a
                    // [GhostField]; a deferred set would leak baked Max to clients for one snapshot). Max + the
                    // 0->full fallback come from the BAKED prefab, never the save.
                    if (m_HealthLookup.HasComponent(prefab))
                    {
                        var hm = m_HealthLookup[prefab];
                        ecb.SetComponent(structure, new Health { Current = p.HP > 0f ? p.HP : hm.Max, Max = hm.Max });
                    }
                    ecb.AddComponent(structure, new RegionTag { Region = RegionId.Base });
                    ecb.AddComponent<RuntimePlacedTag>(structure);
                }

                ecb.DestroyEntity(carrier);
            }

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