Roman.java

    /**
     * Build the Roman-numeral regex fragment via Sift. Mirrors the structure of
     * the canonical Python guessit/rebulk Roman regex: a lookahead asserting at
     * least one Roman character, followed by greedy thousands / hundreds / tens
     * / ones blocks with subtractive pairs listed first so they bind before the
     * base letters.
     */
    private static SiftPattern<Fragment> buildRomanFragment() {
        var romanChar = SiftPatterns.anyOf(
                SiftPatterns.literal("M"), SiftPatterns.literal("C"),
                SiftPatterns.literal("D"), SiftPatterns.literal("L"),
                SiftPatterns.literal("X"), SiftPatterns.literal("V"),
                SiftPatterns.literal("I"));
        var romanRun = Sift.fromAnywhere().oneOrMore().of(romanChar);

        var thousands = Sift.between(0, 4).character('M');
        var hundreds = SiftPatterns.anyOf(
                SiftPatterns.literal("CM"),
                SiftPatterns.literal("CD"),
                Sift.fromAnywhere().optional().character('D')
                        .then().between(0, 3).character('C'));
        var tens = SiftPatterns.anyOf(
                SiftPatterns.literal("XC"),
                SiftPatterns.literal("XL"),
                Sift.fromAnywhere().optional().character('L')
                        .then().between(0, 3).character('X'));
        var ones = SiftPatterns.anyOf(
                SiftPatterns.literal("IX"),
                SiftPatterns.literal("IV"),
                Sift.fromAnywhere().optional().character('V')
                        .then().between(0, 3).character('I'));

        return Sift.fromAnywhere()
                .mustBeFollowedBy(romanRun)
                .followedBy(List.of(thousands, hundreds, tens, ones));
    }