private static String unescapeFieldName()

in sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/firestore/QueryUtils.java [249:353]
99 lines of code
33 McCabe index (conditional complexity)

    private static String unescapeFieldName(String fieldName) {
      if (fieldName.isEmpty()) {
        throw new IllegalArgumentException("quoted identifier cannot be empty");
      }
      StringBuilder buf = new StringBuilder();
      for (int i = 0; i < fieldName.length(); i++) {
        char c = fieldName.charAt(i);
        // Roughly speaking, there are 4 cases we care about:
        //   - carriage returns: \r and \r\n
        //   - unescaped quotes: `
        //   - non-escape sequences
        //   - escape sequences
        if (c == '`') {
          throw new IllegalArgumentException("quoted identifier cannot contain unescaped quote");
        } else if (c == '\r') {
          buf.append('\n');
          // Convert '\r\n' into '\n'
          if (i + 1 < fieldName.length() && fieldName.charAt(i + 1) == '\n') {
            i++;
          }
        } else if (c != '\\') {
          buf.append(c);
        } else if (i + 1 >= fieldName.length()) {
          throw new IllegalArgumentException("illegal trailing backslash");
        } else {
          i++;
          switch (fieldName.charAt(i)) {
            case 'a':
              buf.appendCodePoint(Ascii.BEL); // "Alert" control character
              break;
            case 'b':
              buf.append('\b');
              break;
            case 'f':
              buf.append('\f');
              break;
            case 'n':
              buf.append('\n');
              break;
            case 'r':
              buf.append('\r');
              break;
            case 't':
              buf.append('\t');
              break;
            case 'v':
              buf.appendCodePoint(Ascii.VT); // vertical tab
              break;
            case '?':
              buf.append('?'); // artifact of ancient C grammar
              break;
            case '\\':
              buf.append('\\');
              break;
            case '\'':
              buf.append('\'');
              break;
            case '"':
              buf.append('\"');
              break;
            case '`':
              buf.append('`');
              break;
            case '0':
            case '1':
            case '2':
            case '3':
              if (i + 3 > fieldName.length()) {
                throw new IllegalArgumentException("illegal octal escape sequence");
              }
              buf.appendCodePoint(unescapeOctal(fieldName.substring(i, i + 3)));
              i += 3;
              break;
            case 'x':
            case 'X':
              i++;
              if (i + 2 > fieldName.length()) {
                throw new IllegalArgumentException("illegal hex escape sequence");
              }
              buf.appendCodePoint(unescapeHex(fieldName.substring(i, i + 2)));
              i += 2;
              break;
            case 'u':
              i++;
              if (i + 4 > fieldName.length()) {
                throw new IllegalArgumentException("illegal unicode escape sequence");
              }
              buf.appendCodePoint(unescapeHex(fieldName.substring(i, i + 4)));
              i += 4;
              break;
            case 'U':
              i++;
              if (i + 8 > fieldName.length()) {
                throw new IllegalArgumentException("illegal unicode escape sequence");
              }
              buf.appendCodePoint(unescapeHex(fieldName.substring(i, i + 8)));
              i += 8;
              break;
            default:
              throw new IllegalArgumentException("illegal escape");
          }
        }
      }
      return buf.toString();
    }