TimeUtil.java

import lombok.experimental.UtilityClass;

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.time.format.DateTimeFormatter;
import java.time.format.DateTimeFormatterBuilder;
import java.time.format.DateTimeParseException;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;
import java.util.StringJoiner;

@UtilityClass
public class TimeUtil {

    public final ZoneOffset ZONE = ZoneOffset.UTC;

    public DateTimeFormatter f = new DateTimeFormatterBuilder().appendPattern("[dd'd':]HH'h':mm'm':ss's'")
            .parseDefaulting(ChronoField.DAY_OF_MONTH, 1).parseDefaulting(ChronoField.MONTH_OF_YEAR, 1)
            .parseDefaulting(ChronoField.YEAR, 1970).toFormatter();

    private final ChronoUnit[] units = { ChronoUnit.DAYS, ChronoUnit.HOURS, ChronoUnit.MINUTES, ChronoUnit.SECONDS };

    private LocalDateTime fromMillis(long millis) {
        return Instant.ofEpochMilli(millis).atZone(ZONE).toLocalDateTime();
    }

    private String fix(String toFix) {
        String d = "00d";
        String h = "00h";
        String m = "00m";
        String s = "00s";
        String[] a = toFix.split(":");
        for (String st : a) {
            if (st.length() == 2)
                st = "0" + st;
            if (st.contains("d"))
                d = st;
            if (st.contains("h"))
                h = st;
            if (st.contains("m"))
                m = st;
            if (st.contains("s"))
                s = st;
        }
        StringJoiner j = new StringJoiner(":");
        j.add(d);
        j.add(h);
        j.add(m);
        j.add(s);
        return j.toString();
    }

    public String millisToString(long targetMilli) {

        LocalDateTime past = fromMillis(0);
        LocalDateTime future = fromMillis(targetMilli);

        Object[] times = new Long[units.length];

        for (int i = 0; i < units.length; i++) {
            long time = past.until(future, units[i]);
            past = past.plus((Long) (times[i] = time), units[i]);
        }

        return String.format("&a%d&7d &a%d&7h &a%d&7m &a%d&7s", times);
    }

    public long stringToMillis(String input) {
        if (input == null || input.isEmpty())
            return -1;
        input = fix(input);
        boolean zero = input.startsWith("00");
        try {
            return LocalDateTime.parse(zero ? input.substring(4) : input, f).plusDays(zero ? 0 : 1).toInstant(ZONE)
                    .toEpochMilli();
        } catch (DateTimeParseException e) {
            return -1;
        }
    }

    public int getDifference(long targetMilli, ChronoUnit unit) {
        return (int) unit.between(fromMillis(targetMilli), fromMillis(System.currentTimeMillis()));
    }

}