private static PatternExpr expandLookahead()

in spectator-api/src/main/java/com/netflix/spectator/impl/matcher/PatternUtils.java [337:366]

• 20 lines of code
• 8 McCabe index (conditional complexity)

  private static PatternExpr expandLookahead(Matcher matcher) {
    List<PatternExpr> exprs = new ArrayList<>();
    // 0 - positive matcher to append
    // 1 - negative matcher to append
    // 2 - remaining matcher to keep processing
    Matcher[] results = new Matcher[3];

    // Keep processing until no lookaheads remain
    removeNextLookahead(matcher, results);
    while (results[2] != null) {
      if (results[0] != null)
        exprs.add(PatternExpr.simple(results[0]));
      if (results[1] != null)
        exprs.add(PatternExpr.not(PatternExpr.simple(results[1])));
      removeNextLookahead(results[2], results);
    }

    // If the results array is all null, then something was incompatible, return null
    // to indicate this regex cannot be simplified
    if (results[0] == null && results[1] == null) {
      return null;
    }

    // Add final expression
    if (results[0] != null)
      exprs.add(PatternExpr.simple(results[0]));
    if (results[1] != null)
      exprs.add(PatternExpr.not(PatternExpr.simple(results[1])));
    return PatternExpr.and(exprs);
  }