function findScript(src: string): HTMLScriptElement | undefined {
  const scripts = Array.prototype.slice.call(
    window.document.querySelectorAll("script"),
  );
  return scripts.find((s) => s.src === src);
}

/**
 * Load a script from a URL and append it to the document head
 */
export function loadScript(
  src: string,
  attributes?: Record<string, string>,
): Promise<HTMLScriptElement> {
  const found = findScript(src);

  if (found !== undefined) {
    const status = found?.getAttribute("status");

    if (status === "loaded") {
      return Promise.resolve(found);
    }

    if (status === "loading") {
      return new Promise((resolve, reject) => {
        found.addEventListener("load", () => resolve(found));
        found.addEventListener("error", (err) => reject(err));
      });
    }
  }

  return new Promise((resolve, reject) => {
    const script = window.document.createElement("script");

    script.type = "text/javascript";
    script.src = src;
    script.async = true;

    script.setAttribute("status", "loading");
    for (const [k, v] of Object.entries(attributes ?? {})) {
      script.setAttribute(k, v);
    }

    script.onload = (): void => {
      script.onerror = script.onload = null;
      script.setAttribute("status", "loaded");
      resolve(script);
    };

    script.onerror = (): void => {
      script.onerror = script.onload = null;
      script.setAttribute("status", "error");
      reject(new Error(`Failed to load ${src}`));
    };

    const firstExistingScript = window.document.querySelector("script");
    if (!firstExistingScript) {
      window.document.head.appendChild(script);
    } else {
      firstExistingScript.parentElement?.insertBefore(
        script,
        firstExistingScript,
      );
    }
  });
}