Function fetchUrlMask

src/utils/urlImageFiles.ts:175–230

(
  maskUrlBase: string,
  imageName: string
)

 * @returns The fetched File or null if fetch failed
 */
export async function fetchUrlMask(
  maskUrlBase: string,
  imageName: string
): Promise<File | null> {
  const cached = urlMaskState.getCached(imageName);
  if (cached) {
    return cached;
  }

  // The source has shipped no masks (enough consecutive misses, never a hit):
  // stop probing instead of firing two more doomed 404s for every image.
  if (!urlMaskFoundAny && urlMaskConsecutiveMisses >= URL_MASK_ABSENCE_THRESHOLD) {
    return null;
  }

  if (urlMaskState.isRequestPending(imageName)) {
    return urlMaskState.waitForRequest(imageName);
  }

  urlMaskState.startRequest(imageName);
  let result: File | null = null;

  try {
    for (const { url: maskUrl, filename } of buildMaskUrlCandidates(maskUrlBase, imageName)) {
      try {
        const response = await fetch(maskUrl);
        if (response.ok) {
          const blob = await response.blob();
          const file = new File([blob], filename, { type: blob.type || 'image/png' });
          urlMaskState.setCached(imageName, file);
          result = file;
          appLogger.debug(`[URL Mask] Found mask for ${imageName}`);
          return file;
        }
      } catch (err) {
        appLogger.debug(`[URL Mask] Error trying ${maskUrl}:`, err);
      }
    }

    appLogger.debug(`[URL Mask] No mask found for ${imageName}`);
    return null;
  } finally {
    urlMaskState.completeRequest(imageName, result);
    if (result) {
      urlMaskFoundAny = true;
      urlMaskConsecutiveMisses = 0;
    } else {
      urlMaskConsecutiveMisses += 1;
      if (!urlMaskFoundAny && urlMaskConsecutiveMisses === URL_MASK_ABSENCE_THRESHOLD) {
        appLogger.debug(
          `[URL Mask] No masks found after ${URL_MASK_ABSENCE_THRESHOLD} images; skipping further mask probes for this source.`
        );
      }
    }
  }
}

/**