/**
 * Site Finder multi-cad compare — localStorage-backed shortlist (issue #50).
 *
 * The compare page lets a developer pin 2–5 cadastral numbers and view their
 * analyze metrics side-by-side. The shortlist survives reload via localStorage
 * (per browser, not per server session) — mirroring `gd_recent_parcels` in
 * site-finder-api.ts. All access is SSR-guarded (`typeof window`).
 */

const STORAGE_KEY = "gd_compare_shortlist";

/** Hard cap from the issue: batch analyze runs max 5 parcels in parallel. */
export const COMPARE_MAX = 5;
/** Need at least two parcels for a meaningful side-by-side. */
export const COMPARE_MIN = 2;

/**
 * Validates cadastral number formats (same regex as CadInput):
 *   3-part: 66:41:0204016      (quarter)
 *   4-part: 66:41:0204016:10   (parcel)
 */
const CAD_REGEX = /^\d+:\d+:\d+(?::\d+)?$/;

export function isValidCad(cad: string): boolean {
  return CAD_REGEX.test(cad.trim());
}

export function getShortlist(): string[] {
  if (typeof window === "undefined") return [];
  try {
    const raw = localStorage.getItem(STORAGE_KEY);
    if (!raw) return [];
    const parsed: unknown = JSON.parse(raw);
    if (!Array.isArray(parsed)) return [];
    // Narrow to a clean, de-duplicated, capped string[] — defends against a
    // hand-edited / stale localStorage payload.
    const seen = new Set<string>();
    const out: string[] = [];
    for (const item of parsed) {
      if (typeof item !== "string") continue;
      const cad = item.trim();
      if (!isValidCad(cad) || seen.has(cad)) continue;
      seen.add(cad);
      out.push(cad);
      if (out.length >= COMPARE_MAX) break;
    }
    return out;
  } catch {
    return [];
  }
}

export function saveShortlist(cads: string[]): void {
  if (typeof window === "undefined") return;
  try {
    localStorage.setItem(STORAGE_KEY, JSON.stringify(cads.slice(0, COMPARE_MAX)));
  } catch {
    // ignore quota / disabled-storage errors — shortlist is best-effort
  }
}