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). 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"/> (cone)
    /// and <see cref="MeleeComboSystem"/> (melee cleave). Callers still gate their own speed/window (e.g. the melee
    /// KnockSpeed &gt; 0 check) before calling.
    ///
    /// The former BossState knockback-immunity gate was removed with the boss purge (2026-08-07 audit): the boss
    /// query required LungeState, which no prefab baked, so BossAISystem matched nothing and the immunity branch
    /// was unreachable. Reintroduce a per-target immunity flag when the LANTERN shelf-boss lands (Phase 6).
    /// </summary>
    static class KnockbackUtil
    {
        public static void Stamp(ref ComponentLookup<KnockbackState> lookup,
            Entity target, float3 sourcePos, float3 targetPos, float2 faceFallback, float speed, uint untilTick, bool pull = false)
        {
            if (!lookup.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 };
        }
    }
}