import { createErr, createOk, Result } from "../option-t/mod.ts";

export interface InvalidURLError {
  name: "InvalidURLError";
  message: string;
}
export interface NotFoundError {
  name: "NotFoundError";
  message: string;
}
/**
 * Extracts the source map URL from the given code.
 *
 * This code is based on https://github.com/evanw/source-map-visualization/blob/f3e9dfec20e7bfd9625d03dd0d427affa74a9c43/code.js#L103-L145 under @evanw 's license.
 *
 * @param code - The code from which to extract the source map URL.
 * @param _lang - The language of the code (currently only supports `"js"`).
 * @returns The extracted source map URL as a `URL` object, or `null` if no source map URL is found.
 */
export const extractSourceMapURL = (
  code: string,
  base: string | URL | undefined,
): Result<URL, InvalidURLError | NotFoundError> => {
  let url;

  // Check for both "//" and "/*" comments. This is mostly done manually
  // instead of doing it all with a regular expression because Firefox's
  // regular expression engine crashes with an internal error when the
  // match is too big.
  for (const match of code.matchAll(/\/([*/])[#@] *sourceMappingURL=/g)) {
    const start = match.index + match[0].length;
    const n = code.length;
    let end = start;
    while (end < n && code.charCodeAt(end) > 32) {
      end++;
    }
    if (end === start) continue;
    if (match[1] === "/" || code.indexOf("*/", end) > 0) {
      url = code.slice(start, end);
      break;
    }
  }

  return url
    ? URL.canParse(url, base)
      ? createOk(new URL(url, base))
      : createErr({ name: "InvalidURLError", message: `Invalid URL: ${url}` })
    : notFoundError;
};

const notFoundError = createErr<NotFoundError>({
  name: "NotFoundError",
  message: "Source map URL is not found",
});