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

namespace ProjectM.Simulation
{
    /// <summary>
    /// Predicted projectile integrator: advances every live <see cref="Projectile"/> along its
    /// replicated planar (XZ) <see cref="Projectile.Direction"/> at its baked <see cref="Projectile.Speed"/>,
    /// accumulating <see cref="Projectile.DistanceTravelled"/>. Runs inside the prediction loop on the
    /// owning client (re-simulated on rollback) and once per tick on the server, after
    /// <see cref="AbilityFireSystem"/> has spawned this tick's shots; filtered to <see cref="Simulate"/>
    /// so only predicted ghosts move. Deterministic by construction: uses <c>SystemAPI.Time.DeltaTime</c>
    /// (the fixed tick step) only — no wall-clock, no <c>System.Random</c>. Pure motion: range expiry and
    /// destruction are server-authoritative in <c>ProjectileDamageSystem</c>, so this system never
    /// performs structural changes and is fully idempotent across rollback re-simulation.
    /// </summary>
    [UpdateInGroup(typeof(PredictedSimulationSystemGroup))]
    [UpdateAfter(typeof(AbilityFireSystem))]
    [BurstCompile]
    public partial struct ProjectileMoveSystem : ISystem
    {
        [BurstCompile]
        public void OnUpdate(ref SystemState state)
        {
            float dt = SystemAPI.Time.DeltaTime;

            foreach (var (transform, projectile) in
                     SystemAPI.Query<RefRW<LocalTransform>, RefRW<Projectile>>()
                         .WithAll<Simulate>())
            {
                float step = projectile.ValueRO.Speed * dt;
                projectile.ValueRW.LastStep = step;
                float3 dir = new float3(projectile.ValueRO.Direction.x, 0f, projectile.ValueRO.Direction.y);

                transform.ValueRW.Position += dir * step;
                projectile.ValueRW.DistanceTravelled += step;
            }
        }
    }
}