// ═══ utils.js ═══
// ============================================================
//  UTILS — shared pure helpers
// ============================================================

function distSq(ax, ay, bx, by) {
  const dx = ax - bx;
  const dy = ay - by;
  return dx * dx + dy * dy;
}

function normalizeAngle(angle) {
  while (angle > Math.PI) angle -= Math.PI * 2;
  while (angle < -Math.PI) angle += Math.PI * 2;
  return angle;
}

function shortestAngleDelta(from, to) {
  return normalizeAngle(to - from);
}

function stepTowardAngle(current, desired, maxStep) {
  const delta = shortestAngleDelta(current, desired);
  if (Math.abs(delta) <= maxStep) return normalizeAngle(desired);
  return normalizeAngle(current + Math.sign(delta) * maxStep);
}

function compactLiveArray(items, isLive) {
  let write = 0;
  for (let i = 0; i < items.length; i++) {
    const item = items[i];
    if (isLive(item)) items[write++] = item;
  }
  items.length = write;
}

function clamp(value, min, max) {
  return Math.max(min, Math.min(max, value));
}

function cheapestEnemyCost() {
  const tier = G?.difficultyTier ?? 0;
  const prestige = G?.prestigeLevel ?? 0;
  return ENEMY_DEFS
    .filter(d => (d.minTier ?? 0) <= tier && (d.minPrestige ?? 0) <= prestige)
    .reduce((min, d) => Math.min(min, d.cost), Infinity);
}

function countAliveEnemies() {
  let count = 0;
  for (const e of G.enemies) if (e.alive) count++;
  return count;
}

function getEquippedWeapons() {
  return G.weapons.slice(0, G.tower.weaponSlots).filter(Boolean);
}

function findWeaponInstance(instanceId) {
  for (const w of G.weapons) if (w && w.instanceId === instanceId) return w;
  return null;
}