import { SpecifyError, specifyErrors } from '../../errors/index.js';
import { BuiltInParserRuleSignature } from '../internals/BuiltInParserRuleSignature.js';

export function pickLastParserInParserRule(rule: BuiltInParserRuleSignature) {
  const index = rule.parsers?.length > 0 ? rule.parsers?.length - 1 : 0;
  const maybeParserConfig = rule.parsers?.[index];
  if (!maybeParserConfig) {
    throw new SpecifyError({
      errorKey: specifyErrors.PARSERS_ENGINE_INVALID_PARSER_INPUT.errorKey,
      publicMessage: `Unknown built-in parser at index #${index}" on rule "${
        rule.name ?? 'Unknown rule'
      }".`,
    });
  }
  return maybeParserConfig;
}