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

namespace ProjectM.Server
{
    /// <summary>
    /// Server-only walk-in gate transit: a player who walks within a gate's radius (and whose region matches the
    /// gate's <see cref="ExpeditionGate.FromRegion"/>) is transited to the gate's ToRegion at its ArrivalPos
    /// (RegionTag flipped + LocalTransform teleported — GhostRelevancy re-scopes their ghosts, as in
    /// <c>RegionTransitSystem</c>). Returning to BASE signals the ThreatDirector (a completed expedition can draw a
    /// retaliation siege) by incrementing <see cref="ProjectM.Simulation.ThreatState.PendingReturns"/>. Plain server
    /// SimulationSystemGroup, ordered BEFORE CyclePhaseSystem (Gate -> ThreatDirector -> RunState) so the return is
    /// consumed the same tick. Arrival points are offset from the destination gate so a transited player does not
    /// immediately re-trigger.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateBefore(typeof(CyclePhaseSystem))]
    public partial struct ExpeditionGateSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<ExpeditionGate>();
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            // Snapshot gates once.
            var gateFrom = new NativeList<byte>(Allocator.Temp);
            var gateTo = new NativeList<byte>(Allocator.Temp);
            var gateRadiusSq = new NativeList<float>(Allocator.Temp);
            var gatePos = new NativeList<float2>(Allocator.Temp);
            var gateArrival = new NativeList<float3>(Allocator.Temp);
            foreach (var (gate, xform) in SystemAPI.Query<RefRO<ExpeditionGate>, RefRO<LocalTransform>>())
            {
                gateFrom.Add(gate.ValueRO.FromRegion);
                gateTo.Add(gate.ValueRO.ToRegion);
                gateRadiusSq.Add(gate.ValueRO.Radius * gate.ValueRO.Radius);
                gatePos.Add(xform.ValueRO.Position.xz);
                gateArrival.Add(gate.ValueRO.ArrivalPos);
            }

            bool returnedToBase = false;
            foreach (var (region, xform) in
                     SystemAPI.Query<RefRW<RegionTag>, RefRW<LocalTransform>>().WithAll<PlayerTag>())
            {
                byte r = region.ValueRO.Region;
                float2 pp = xform.ValueRO.Position.xz;
                for (int i = 0; i < gateFrom.Length; i++)
                {
                    if (gateFrom[i] != r) continue;
                    if (math.distancesq(pp, gatePos[i]) > gateRadiusSq[i]) continue;
                    region.ValueRW.Region = gateTo[i];
                    xform.ValueRW.Position = gateArrival[i];
                    if (gateTo[i] == RegionId.Base)
                        returnedToBase = true;
                    break;
                }
            }

            gateFrom.Dispose();
            gateTo.Dispose();
            gateRadiusSq.Dispose();
            gatePos.Dispose();
            gateArrival.Dispose();

            // A player returned to base from an expedition -> signal the ThreatDirector (it sizes/arms any
            // retaliation siege). The gate teleports the returner out of its radius, so this fires once per return.
            if (returnedToBase && SystemAPI.TryGetSingletonEntity<ThreatState>(out var threatEntity))
            {
                var threat = SystemAPI.GetComponent<ThreatState>(threatEntity);
                threat.PendingReturns += 1;
                threat.ExpeditionsCompleted += 1;
                SystemAPI.SetComponent(threatEntity, threat);
            }
        }
    }
}