module Substrings {
    void run(String[] args = []) {
        @Inject Console console;
        if (args.size < 4) {
            console.print(
                $|
                 |Usage:
                 |
                 |  xec Substrings <str> <offset> <count> <substr>
                 |
            );
            return;
        }

        String s   = args[0];
        Int    n   = new Int(args[1]);
        Int    m   = new Int(args[2]);
        String sub = args[3];
        Char   c   = sub[0];

        console.print($|
                       |{s                   .quoted()=}
                       |{substring(s, n, m  ).quoted()=}
                       |{substring(s, n     ).quoted()=}
                       |{substring(s        ).quoted()=}
                       |{substring(s, c, m  ).quoted()=}
                       |{substring(s, sub, m).quoted()=}
                       |
                     );
    }

    // starting from n characters in and of m length
    static String substring(String s, Int n, Int m) {
        assert 0 <= n <= n+m;
        return n < s.size ? s[n..<(n+m).notGreaterThan(s.size)] : "";
    }

    // starting from n characters in, up to the end of the string
    static String substring(String s, Int n) {
        assert 0 <= n;
        return s.substring(n);
    }

    // whole string minus the last character
    static String substring(String s) {
        return s.size > 1 ? s[0..<s.size-1] : "";
    }

    // starting from a known character within the string and of m length
    static String substring(String s, Char c, Int m){
        assert 0 <= m;
        return substring(s, s.indexOf(c) ?: 0, m);
    }

    // starting from a known substring within the string and of m length
    static String substring(String s, String sub, Int m){
        assert 0 <= m;
        return substring(s, s.indexOf(sub) ?: 0, m);
    }
}