using Unity.Entities;
using Unity.Mathematics;

namespace ProjectM.Simulation
{
    /// <summary>
    /// Shared knockback stamp for melee/cone hits. Guarded exactly as the two call sites were: the target must own
    /// <see cref="KnockbackState"/> (dummies/structures lacking it would throw at ECB playback if written) and must
    /// NOT be a boss (<see cref="BossState"/> = knockback-immune, A4). The planar (XZ) heading is
    /// normalize(targetPos - sourcePos), falling back to <paramref name="faceFallback"/> when that delta is
    /// degenerate. Deduplicates the identical stamps in <see cref="AbilityFireSystem"/> (Warrior cone) and
    /// <see cref="MeleeComboSystem"/> (melee cleave). Callers still gate their own speed/window (e.g. the melee
    /// KnockSpeed &gt; 0 check) before calling.
    /// </summary>
    static class KnockbackUtil
    {
        public static void Stamp(ref ComponentLookup<KnockbackState> lookup, in ComponentLookup<BossState> bossLookup,
            Entity target, float3 sourcePos, float3 targetPos, float2 faceFallback, float speed, uint untilTick, bool pull = false)
        {
            if (!lookup.HasComponent(target) || bossLookup.HasComponent(target))
                return;

            float3 delta = targetPos - sourcePos;
            float2 dir = math.lengthsq(delta.xz) > 1e-6f ? math.normalize(delta.xz) : faceFallback;
            if (pull) dir = -dir; // Phase 1.7 Gravity Pull: drag the target TOWARD the attacker
            lookup[target] = new KnockbackState { Dir = dir, Speed = speed, UntilTick = untilTick };
        }
    }
}