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"/>/<see cref="PendingStructureIo"/> 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), re-stamp the rebased tick fields
    /// (<see cref="ProductionMath.RestoreNextTick"/>; LastProcessed = now so within-session catch-up resumes from now,
    /// never a wall-clock mint), re-tag RegionTag{Base} + RuntimePlacedTag, refill the in-flight conveyor item + the
    /// machine I/O buffers, then DESTROY the carrier so it never runs again. The ledger/goal restore 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<Conveyor> m_ConveyorLookup;

        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            m_TransformLookup = state.GetComponentLookup<LocalTransform>(isReadOnly: true);
            m_ConveyorLookup = state.GetComponentLookup<Conveyor>(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_ConveyorLookup.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, ioBuf, carrier) in
                     SystemAPI.Query<DynamicBuffer<PendingStructure>, DynamicBuffer<PendingStructureIo>>().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 = ProductionMath.RestoreNextTick(now, p.RemainingTicks),
                        LastProcessedTick = TickUtil.NonZero(now),
                    });
                    ecb.AddComponent(structure, new RegionTag { Region = RegionId.Base });
                    ecb.AddComponent<RuntimePlacedTag>(structure);

                    if (p.Type == StructureType.Conveyor && m_ConveyorLookup.HasComponent(prefab))
                    {
                        var conv = m_ConveyorLookup[prefab];
                        conv.Direction = p.Direction;
                        ecb.SetComponent(structure, conv);
                        ecb.SetComponent(structure, new ConveyorItem { ResourceId = p.ConveyorResId, Count = p.ConveyorCount });
                        ecb.SetComponentEnabled<ConveyorItem>(structure, p.ConveyorCount > 0);
                    }

                    // Refill machine I/O buffers from the flat io table (only slots with saved rows -> the prefab has them).
                    bool inInit = false, outInit = false;
                    DynamicBuffer<MachineInput> inBuf = default;
                    DynamicBuffer<MachineOutput> outBuf = default;
                    for (int r = 0; r < ioBuf.Length; r++)
                    {
                        if (ioBuf[r].StructureIndex != s)
                            continue;
                        if (ioBuf[r].Slot == 0)
                        {
                            if (!inInit) { inBuf = ecb.SetBuffer<MachineInput>(structure); inInit = true; }
                            inBuf.Add(new MachineInput { ResourceId = ioBuf[r].ResourceId, Count = ioBuf[r].Count });
                        }
                        else
                        {
                            if (!outInit) { outBuf = ecb.SetBuffer<MachineOutput>(structure); outInit = true; }
                            outBuf.Add(new MachineOutput { ResourceId = ioBuf[r].ResourceId, Count = ioBuf[r].Count });
                        }
                    }
                }

                ecb.DestroyEntity(carrier);
            }

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