/**
 * Fetches Twemoji glyphs from the jsDelivr CDN, for `lib/site-icons.ts` to
 * render the favicons from.
 *
 * @module
 */

/** Pinned, so a new Twemoji release can't change the icons unasked. */
const TWEMOJI_VERSION = "16.0.1";

/**
 * Glyphs by codepoint. It only lives as long as the process, and the `icons`
 * task renders one emoji per process.
 */
const glyphCache = new Map<string, string>();

/**
 * Returns Twemoji's SVG for `emoji`, whose file name `cp` comes from
 * `emojiToCodepoint`. `emoji` only serves the error message. It fetches with
 * plain `fetch`, since the host is fixed.
 *
 * @throws {Error} When the glyph can't be fetched.
 */
export async function fetchTwemojiSvg(
  emoji: string,
  cp: string,
): Promise<string> {
  const cached = glyphCache.get(cp);
  if (cached) return cached;
  const url =
    `https://cdn.jsdelivr.net/gh/jdecked/twemoji@${TWEMOJI_VERSION}/assets/svg/${cp}.svg`;
  let res: Response;
  try {
    res = await fetch(url);
  } catch (cause) {
    throw new Error(
      `Failed to fetch Twemoji glyph for "${emoji}" (${cp}) from ${url}`,
      { cause },
    );
  }
  if (!res.ok) {
    throw new Error(
      `Failed to fetch Twemoji glyph for "${emoji}" (${cp}) from ${url}: ${res.status} ${res.statusText}`,
    );
  }
  const svg = await res.text();
  glyphCache.set(cp, svg);
  return svg;
}