package cps;

import java.util.function.Function;

public interface Re {

    boolean match(String s, Function<String, Boolean> kont);
    default boolean match(String s) {
        return match(s, kont -> true);
    }

    /**
     * 匹配字符
     * @param charLiteral
     * @return
     */
    static Re lit(char charLiteral) {
        return (s, kont) -> {
            if (s.isEmpty()) {
                return false;
            }
            return charLiteral == s.charAt(0) && kont.apply(s.substring(1));
        };
    }

    /**
     * 按顺序匹配a b
     * @param a
     * @param b
     * @return
     */
    static Re seq(Re a, Re b) {
        return (s, kont) -> a.match(s, rest -> b.match(rest, kont));
    }

    /**
     * 匹配a或b
     * @param a
     * @param b
     * @return
     */
    static Re either(Re a, Re b) {
        return (s, kont) -> a.match(s, kont) || b.match(s, kont);
    }

    /**
     * 匹配0到N个
     * @param re
     * @return
     */
    static Re star(Re re) {
        return (s, kont) -> re.match(s, rest -> star(re).match(rest, kont))
                || kont.apply(s);
    }

    static Re atLeastOne(Re re) {
        return seq(re, star(re));
    }
}