/**
 * Combat rules — the pure arithmetic shared by the sandbox's actors
 * (the player's armor, the enemy craft, and whatever system ports out of
 * the range into the real game). No Phaser, no scene, so it runs in bare
 * Node: dev/combat.test.mjs exercises exactly this file.
 *
 * An armor block is `{ shields, hull }` (both ≥ 0): a hit spends the
 * shields first, then the hull, and the craft is dead at hull ≤ 0 — the
 * same rule for the player (data/combat.json → playerShip) and the
 * hostiles (→ enemy).
 */

/**
 * Spend damage off an armor block (mutates it).
 *
 * @param {{shields: number, hull: number}} armor the block to hit
 * @param {number} amount damage (negative/NaN treated as 0)
 * @returns {{shieldHit: number, hullHit: number, dead: boolean}}
 *   shieldHit/hullHit = how much each layer absorbed; dead = hull ≤ 0.
 */
export function applyDamage(armor, amount) {
  let rem = Math.max(0, Number(amount) || 0);

  const shields = Math.max(0, armor.shields ?? 0);
  const shieldHit = Math.min(shields, rem);
  rem -= shieldHit;

  const hull = Math.max(0, armor.hull ?? 0);
  const hullHit = Math.min(hull, rem);
  rem -= hullHit;

  armor.shields = shields - shieldHit;
  armor.hull = hull - hullHit;
  return { shieldHit, hullHit, dead: armor.hull <= 0 };
}

/**
 * The render heading (rad) of a ship sprite: its rotation minus the
 * art's facing offset (ship.artOffset — the sheet art may not face east,
 * js/entities/Ship.js). A plain object with a .rotation is fine.
 */
export function headingOf(ship) {
  return ship.rotation - (ship.artOffset || 0);
}

/**
 * One step of the standoff-ring AI: advance the craft's orbit angle and
 * return the point on the ring it should steer to (pure — the craft
 * does the steering, js/combat/EnemyShip.js).
 *
 * @returns {{angle: number, x: number, y: number}} the new orbit angle + target
 */
export function orbitStep(px, py, orbitAngle, orbitDir, orbitSpeed, dt, orbitRadius) {
  const angle = orbitAngle + orbitDir * orbitSpeed * dt;
  return {
    angle,
    x: px + Math.cos(angle) * orbitRadius,
    y: py + Math.sin(angle) * orbitRadius,
  };
}