// ESRI World Imagery Wayback — catalog helper for the "Satelit istoric"
// basemap. Wayback is a free, public, CORS-open WMTS service that keeps
// every snapshot of Esri's World Imagery layer back to 2014 (~193
// releases as of 2026-05). Each release is identified by a numeric
// `releaseId` baked into the tile URL:
//
//   https://wayback.maptiles.arcgis.com/arcgis/rest/services/World_Imagery
//     /WMTS/1.0.0/default028mm/MapServer/tile/<releaseId>/{z}/{y}/{x}
//
// The catalog at /waybackconfig.json lists every release with its title
// ("World Imagery (Wayback 2026-04-30)") which is the only place the
// date lives. We parse the title to expose a sortable timeline.
//
// Caching: catalog is ~100 KB and updates monthly when Esri ships a new
// release. Module-level cache + lazy fetch keeps the picker responsive
// while still picking up new releases without a panel reload.

export type WaybackRelease = {
  /** Numeric release id baked into the tile URL (e.g. 49059). */
  id: string;
  /** Parsed release date — "2026-04-30" — from the item title. */
  date: string;
  /** Human-readable title verbatim from catalog. */
  title: string;
  /** Templated tile URL with {level}/{row}/{col} placeholders. */
  itemUrl: string;
};

const CATALOG_URL =
  "https://s3-us-west-2.amazonaws.com/config.maptiles.arcgis.com/waybackconfig.json";

type CatalogEntry = {
  itemID?: string;
  itemTitle?: string;
  itemURL?: string;
};

type Catalog = Record<string, CatalogEntry>;

let cache: { at: number; data: WaybackRelease[] } | null = null;
let inflight: Promise<WaybackRelease[]> | null = null;

const CACHE_TTL_MS = 24 * 60 * 60 * 1000;

function parseDate(title: string): string | null {
  // "World Imagery (Wayback 2026-04-30)" → 2026-04-30
  const m = /(\d{4}-\d{2}-\d{2})/.exec(title);
  return m?.[1] ?? null;
}

/** Fetch + parse the Wayback catalog. Memoized 24h. */
export async function loadWaybackReleases(): Promise<WaybackRelease[]> {
  if (cache && Date.now() - cache.at < CACHE_TTL_MS) return cache.data;
  if (inflight) return inflight;
  inflight = (async () => {
    try {
      const res = await fetch(CATALOG_URL, { cache: "no-store" });
      if (!res.ok) throw new Error(`wayback catalog ${res.status}`);
      const json = (await res.json()) as Catalog;
      const releases: WaybackRelease[] = [];
      for (const [id, entry] of Object.entries(json)) {
        if (!entry?.itemTitle || !entry?.itemURL) continue;
        const date = parseDate(entry.itemTitle);
        if (!date) continue;
        releases.push({
          id,
          date,
          title: entry.itemTitle,
          itemUrl: entry.itemURL,
        });
      }
      // Newest first — date string comparison works because ISO yyyy-mm-dd.
      releases.sort((a, b) => (a.date < b.date ? 1 : -1));
      cache = { at: Date.now(), data: releases };
      return releases;
    } finally {
      inflight = null;
    }
  })();
  return inflight;
}

/** Build the tile-URL template MapLibre expects for a given release id.
 *  WMTS uses {z}/{y}/{x} order in the path (NOT {z}/{x}/{y}). */
export function waybackTileUrl(releaseId: string): string {
  return `https://wayback.maptiles.arcgis.com/arcgis/rest/services/World_Imagery/WMTS/1.0.0/default028mm/MapServer/tile/${releaseId}/{z}/{y}/{x}`;
}

/** Pick a reasonable default release: the most recent one. */
export function latestWaybackRelease(releases: WaybackRelease[]): WaybackRelease | null {
  return releases[0] ?? null;
}