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

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

/** How close (screen pixels) a tap must be to a location or ship: about a fingertip. */
export const TAP_RADIUS = 22;

/**
 * What a tap at `tap` (screen pixels) selects: the nearest ship marker or
 * location within reach. Ships win ties, since they are drawn on top.
 */
export function hitTest(
  scene: Scene,
  tap: MapPoint,
  viewport: Viewport,
  camera: Camera,
): MapSelection | null {
  let best: { selection: MapSelection; distance: number } | null = null;
  const consider = (point: MapPoint, selection: MapSelection, bias: number) => {
    const p = toScreen(point, viewport, camera);
    const distance = Math.hypot(p.x - tap.x, p.y - tap.y) - bias;
    if (distance <= TAP_RADIUS && (!best || distance < best.distance)) {
      best = { selection, distance };
    }
  };
  for (const location of scene.locations) {
    consider(location.point, { kind: "location", id: location.id }, 0);
  }
  for (const flight of scene.flights) {
    consider(flight.marker, { kind: "flight", dispatchId: flight.dispatchId }, 4);
  }
  return (best as { selection: MapSelection } | null)?.selection ?? null;
}