import type { Camera, Viewport } from "./camera";
import { layoutScene } from "./layout";
import type { MapPoint } from "./projection";
import type { Scene } from "./scene";

export type MapSelection =
  { kind: "location"; id: string } | { kind: "flight"; dispatchId: string };

/**
 * What a tap at `tap` (screen pixels) selects: the nearest ship or location
 * whose tap target (at least `minTapPx`, Step 10C.6) contains it, as laid out
 * on screen. Ships win ties, since they are drawn on top.
 */
export function hitTest(
  scene: Scene,
  tap: MapPoint,
  viewport: Viewport,
  camera: Camera,
): MapSelection | null {
  const layout = layoutScene(scene, viewport, camera);
  let best: { selection: MapSelection; distance: number } | null = null;
  const consider = (center: MapPoint, size: number, selection: MapSelection, bias: number) => {
    const distance = Math.hypot(center.x - tap.x, center.y - tap.y);
    if (distance <= size / 2 && (!best || distance - bias < best.distance)) {
      best = { selection, distance: distance - bias };
    }
  };
  for (const location of layout.locations) {
    consider(location.center, location.tap, { kind: "location", id: location.id }, 0);
  }
  for (const flight of layout.flights) {
    consider(flight.center, flight.tap, { kind: "flight", dispatchId: flight.dispatchId }, 4);
  }
  return (best as { selection: MapSelection } | null)?.selection ?? null;
}