import npmurl from "url";

function loadJSON(url: string, defaultValue: any, cb: (...args: any[]) => void) {
  fetch(url, {
    mode: "cors",
    credentials: "same-origin"
  })
    .then((response) => {
      if (!response.ok) {
        throw new Error("Failed to load metadata for " + url);
      }
      return response.json();
    })
    .then((body) => {
      cb(body);
    })
    .catch(() => {
      console.warn("Can not load metadata for " + url + ", using default value " + defaultValue);
      cb(defaultValue);
    });
}

export function downloadGlyphsMetadata(urlTemplate: string, cb: (...args: any[]) => void) {
  if(!urlTemplate) return cb([]);

  // Special handling because Tileserver GL serves the fontstacks metadata differently
  // https://github.com/klokantech/tileserver-gl/pull/104#issuecomment-274444087
  const urlObj = npmurl.parse(urlTemplate);
  const normPathPart = "/%7Bfontstack%7D/%7Brange%7D.pbf";
  if(urlObj.pathname === normPathPart) {
    urlObj.pathname = "/fontstacks.json";
  } else {
    urlObj.pathname = urlObj.pathname!.replace(normPathPart, ".json");
  }
  const url = npmurl.format(urlObj);

  loadJSON(url, [], cb);
}

export function downloadSpriteMetadata(baseUrl: string, cb: (...args: any[]) => void) {
  if(!baseUrl) return cb([]);
  const url = baseUrl + ".json";
  loadJSON(url, {}, glyphs => cb(Object.keys(glyphs)));
}