/**
 * "Is this model already downloaded?" helper (Decisions.md D-005).
 *
 * Transformers.js v3 persists Hub downloads in the browser Cache API (Cache
 * Storage, cache name "transformers-cache"). We inspect the cached request
 * URLs and match them against catalog model ids. Used by `ModelPicker` for the
 * downloaded badge (M2) and reused by the offline indicator (M3).
 *
 * `matchCachedModels` is pure so it can be unit-tested; only
 * `getDownloadedModels` touches the `caches` global.
 */

/** Cache name used by Transformers.js v3 (`env.cacheName` default). */
export const TRANSFORMERS_CACHE_NAME = "transformers-cache";

/**
 * Pure matcher: which of `modelIds` have at least one cached ONNX weight file?
 *
 * Cached URLs look like
 * `https://huggingface.co/<modelId>/resolve/main/onnx/<file>.onnx`. We require
 * an `.onnx` hit (not just tokenizer/config JSON) so a model whose weights
 * never finished downloading does not show as available.
 */
export function matchCachedModels(
  urls: Iterable<string>,
  modelIds: readonly string[],
): Set<string> {
  const downloaded = new Set<string>();
  for (const url of urls) {
    if (!url.split("?")[0]?.endsWith(".onnx")) continue;
    for (const modelId of modelIds) {
      if (!downloaded.has(modelId) && url.includes(`/${modelId}/`)) {
        downloaded.add(modelId);
      }
    }
  }
  return downloaded;
}

/**
 * Query the browser Cache API for models with cached weights. Returns an
 * empty set where Cache Storage is unavailable (non-secure contexts, tests).
 */
export async function getDownloadedModels(
  modelIds: readonly string[],
): Promise<Set<string>> {
  if (typeof caches === "undefined") return new Set();
  try {
    const urls: string[] = [];
    // Match any transformers-owned cache, in case the name is ever versioned.
    for (const name of await caches.keys()) {
      if (!name.includes("transformers")) continue;
      const cache = await caches.open(name);
      for (const request of await cache.keys()) urls.push(request.url);
    }
    return matchCachedModels(urls, modelIds);
  } catch {
    return new Set();
  }
}