using ProjectM.Simulation;
using Unity.Mathematics;
using Unity.Physics;

namespace ProjectM.Server
{
    /// <summary>
    /// Shared server-side collide-and-slide mover for OWNERLESS enemy ghosts (extracted from EnemyAISystem so the
    /// boss brain reuses ONE copy — a fix to the tunnelling sweep or wall-glance reaches every enemy at once).
    /// Both EnemyAISystem's three passes and BossAISystem call <see cref="SweptMove"/>. Pure given the CollisionWorld;
    /// Burst-safe (non-generic closest-hit SphereCast, per the CLAUDE.md generic-collector hazard).
    /// </summary>
    public static class EnemyMoveUtil
    {
        /// <summary>Collide-and-slide sphere-cast for server-authoritative enemy movement: sweep the intended step
        /// against the static environment (boundary ring + landmarks + player-built walls) and stop at / glance along
        /// the first wall hit. Y is held flat (top-down movement plane).</summary>
        public static float3 SweptMove(in PhysicsWorldSingleton physics, float3 from, float3 to, float radius, CollisionFilter filter)
        {
            float3 delta = to - from;
            delta.y = 0f;
            float dist = math.length(delta);
            if (dist < 1e-5f)
                return to;
            float3 dir = delta / dist;
            const float skin = 0.05f;
            var cw = physics.CollisionWorld;
            if (!cw.SphereCast(from, radius, dir, dist, out var hit, filter))
                return to;

            float allowed = math.max(0f, hit.Fraction * dist - skin);
            float3 stop = from + dir * allowed;
            stop.y = from.y;

            // Slide the unused motion along the wall, then sweep the slide so we don't tunnel a second wall.
            float3 slide = EnemyAIMath.SlideVelocity(to - stop, hit.SurfaceNormal);
            float slideDist = math.length(slide);
            if (slideDist < 1e-5f)
                return stop;
            float3 sdir = slide / slideDist;
            float3 result = cw.SphereCast(stop, radius, sdir, slideDist, out var hit2, filter)
                ? stop + sdir * math.max(0f, hit2.Fraction * slideDist - skin)
                : stop + slide;
            result.y = from.y;
            return result;
        }
    }
}