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

namespace ProjectM.Server
{
    /// <summary>
    /// Server-authoritative upgrade pickup grant. When a player overlaps an <see cref="UpgradePickup"/>
    /// (planar XZ distance within the pickup's <see cref="HitRadius"/>), appends the pickup's modifier to
    /// the player's replicated <see cref="StatModifier"/> buffer (which replicates to the predicting
    /// owner, so StatRecomputeSystem folds identical effective stats on both worlds) and destroys the
    /// pickup. Runs in the default <see cref="SimulationSystemGroup"/> (NOT the prediction loop) since the
    /// grant is a non-predicted server event. The buffer append + pickup destroy are batched through an
    /// <see cref="EntityCommandBuffer"/> played back immediately — so a plain-world EditMode test needs no
    /// separate ECB system.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    public partial struct UpgradePickupSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<UpgradePickup>();
        }

        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            // Snapshot modifiable players (carrying the modifier buffer + a transform) once this tick.
            var playerEntities = new NativeList<Entity>(Allocator.Temp);
            var playerPositions = new NativeList<float3>(Allocator.Temp);
            foreach (var (xform, e) in
                     SystemAPI.Query<RefRO<LocalTransform>>()
                         .WithAll<PlayerTag, StatModifier>()
                         .WithEntityAccess())
            {
                playerEntities.Add(e);
                playerPositions.Add(xform.ValueRO.Position);
            }

            var ecb = new EntityCommandBuffer(Allocator.Temp);

            foreach (var (xform, radius, pickup, pickupEntity) in
                     SystemAPI.Query<RefRO<LocalTransform>, RefRO<HitRadius>, RefRO<UpgradePickup>>()
                         .WithEntityAccess())
            {
                float2 pp = new float2(xform.ValueRO.Position.x, xform.ValueRO.Position.z);
                float r = radius.ValueRO.Value;

                for (int i = 0; i < playerEntities.Length; i++)
                {
                    float2 cp = new float2(playerPositions[i].x, playerPositions[i].z);
                    if (math.distancesq(pp, cp) > r * r)
                        continue;

                    ecb.AppendToBuffer(playerEntities[i], new StatModifier
                    {
                        Target = pickup.ValueRO.Target,
                        Op = pickup.ValueRO.Op,
                        Value = pickup.ValueRO.Value,
                        SourceId = pickup.ValueRO.SourceId,
                    });
                    ecb.DestroyEntity(pickupEntity);
                    break; // granted to the first overlapping player, then despawns
                }
            }

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