const UTF8Prefix = "data:application/json;utf-8" as const;
type UTF8String = `${typeof UTF8Prefix},${string}`;

/**
 * Checks if a given string is a UTF-8 encoded JSON string.
 * @param input - The string to be checked.
 * @returns True if the input string starts with "data:application/json;utf-8", false otherwise.
 * @example
 * ```ts
 * isUTF8JSONString("data:application/json;utf-8,{ \"test\": \"utf8\" }")
 * // true
 * ```
 */
export function isUTF8JSONString(input: string): input is UTF8String {
  if (input.toLowerCase().startsWith(UTF8Prefix)) {
    return true;
  }
  return false;
}

/**
 * Parses a UTF-8 string and returns the decoded string.
 * @param input - The UTF-8 string to parse.
 * @returns The decoded string.
 * @example
 * ```ts
 * parseUTF8String("data:application/json;utf-8,{ \"test\": \"utf8\" }")
 * // '{"test":"utf8"}'
 * ```
 */
export function parseUTF8String(input: UTF8String) {
  const commaIndex = input.indexOf(",");
  const utf8 = input.slice(commaIndex + 1);
  try {
    // try to decode the UTF-8 string, if it fails, return the original string
    return decodeURIComponent(utf8);
  } catch {
    return utf8;
  }
}