Project-M/Assets/_Project/Scripts/Server/Combat/PlayerRespawnSystem.cs

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

namespace ProjectM.Server
{
    /// <summary>
    /// Server-authoritative player death→respawn timing. The "is dead" GATE is derived every predicted tick from
    /// replicated Health by <see cref="PlayerDeathStateSystem"/> (so movement/aim/fire stop on both server and
    /// owner-client); THIS system owns the timer + the authoritative recovery. Runs server-only in the plain
    /// <see cref="SimulationSystemGroup"/> AFTER the predicted group, so it observes this tick's post-damage Health.
    /// On first seeing Health&lt;=0 it schedules a respawn tick; once due it refills Health to the effective max and
    /// repositions the player to its deterministic base spawn slot (<see cref="PlayerSpawnMath"/>). Health.Current
    /// (GhostField) + LocalTransform replicate, so the recovery reaches clients and the derived Dead clears.
    /// </summary>
    [BurstCompile]
    [WorldSystemFilter(WorldSystemFilterFlags.ServerSimulation)]
    [UpdateInGroup(typeof(SimulationSystemGroup))]
    [UpdateAfter(typeof(PredictedSimulationSystemGroup))]
    public partial struct PlayerRespawnSystem : ISystem
    {
        [BurstCompile]
        public void OnCreate(ref SystemState state)
        {
            state.RequireForUpdate<NetworkTime>();
        }

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

            // Resilient spawn reference: prefer the BaseAnchor plot center, fall back to the PlayerSpawner. NEVER
            // hard-require PlayerSpawner (a transiently-missing singleton must not strand dead players downed forever).
            bool haveSpawner = SystemAPI.TryGetSingleton<PlayerSpawner>(out var spawner);
            bool haveAnchor = SystemAPI.TryGetSingleton<BaseAnchor>(out var baseAnchor);
            if (!haveSpawner && !haveAnchor)
                return; // no spawn reference at all this tick — re-try next tick rather than mis-place
            float3 center = haveAnchor ? BaseGridMath.PlotCenter(baseAnchor) : spawner.SpawnPoint;
            float ringRadius = haveSpawner ? spawner.SpawnRingRadius : 2f;
            int ringSlots = haveSpawner ? spawner.RingSlots : 4;
                center = BaseGridMath.PlotCenter(baseAnchor);

            foreach (var (health, respawn, invuln, xform, region, owner, eff) in
                     SystemAPI.Query<RefRW<Health>, RefRW<RespawnState>, RefRW<RespawnInvuln>, RefRW<LocalTransform>,
                             RefRW<RegionTag>, RefRO<GhostOwner>, RefRO<EffectiveCharacterStats>>()
                         .WithAll<PlayerTag>())
            {
                if (health.ValueRO.Current > 0f)
                {
                    respawn.ValueRW.RespawnTick = 0; // alive: clear any pending schedule
                    continue;
                }

                // Dead this tick.
                if (respawn.ValueRO.RespawnTick == 0)
                {
                    // Just died: schedule the recovery.
                    respawn.ValueRW.RespawnTick = RespawnMath.RespawnTick(now, respawn.ValueRO.DelayTicks);
                }
                else if (RespawnMath.IsDue(now, respawn.ValueRO.RespawnTick))
                {
                    // Recover: full health at the deterministic base spawn slot.
                    float maxHealth = eff.ValueRO.MaxHealth > 0f ? eff.ValueRO.MaxHealth : health.ValueRO.Max;
                    health.ValueRW.Current = maxHealth;

                    float3 pos = center + PlayerSpawnMath.SpawnOffset(
                        owner.ValueRO.NetworkId, ringRadius, ringSlots);
                    xform.ValueRW.Position = pos;
                    // Death fix: respawn is at BASE, so the player's server-only RegionTag MUST return to Base too
                    // (every other mover flips RegionTag + Position together). Dying on an expedition otherwise leaves
                    // you at base coords still tagged Expedition -> RegionRelevancy hides all base ghosts (soft-brick).
                    region.ValueRW.Region = RegionId.Base;

                    // Grant brief post-respawn damage immunity so the swarm can't instantly re-kill.
                    invuln.ValueRW.UntilTick = TickUtil.NonZero(now + (uint)math.max(0, respawn.ValueRO.InvulnTicks));

                    respawn.ValueRW.RespawnTick = 0;
                }
            }
        }
    }
}