// Tracks an ordered set of vertices contributed by <leaflet-line> children,
// built entirely from the leaflet-line-sync/leaflet-line-remove events they
// fire (see register.ts) -- never by querying the DOM or reading a child's
// property directly. Shared by leaflet-polygon and leaflet-polyline.
//
// Order matters (it's the vertex sequence), so membership changes are
// inserted at their actual document position via compareDocumentPosition --
// that's a structural question about the tree, not a read of child state,
// and there's no other sane source of truth for "which vertex comes first."
export type LatLngTuple = [number, number];

export class VertexTracker {
  #vertices = new Map<HTMLElement, LatLngTuple>();
  #order: HTMLElement[] = [];

  sync(element: HTMLElement, latlng: LatLngTuple): void {
    if (!this.#vertices.has(element)) this.#insertOrdered(element);
    this.#vertices.set(element, latlng);
  }

  remove(element: HTMLElement): void {
    this.#vertices.delete(element);
    this.#order = this.#order.filter((el) => el !== element);
  }

  coords(): LatLngTuple[] {
    return this.#order.map((el) => this.#vertices.get(el)!);
  }

  #insertOrdered(el: HTMLElement): void {
    const idx = this.#order.findIndex(
      (existing) => (existing.compareDocumentPosition(el) & Node.DOCUMENT_POSITION_PRECEDING) !== 0,
    );
    if (idx === -1) this.#order.push(el);
    else this.#order.splice(idx, 0, el);
  }
}