JavaUtils/DrinkingBar.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.math.BigDecimal;
import java.math.MathContext;
import java.math.RoundingMode;
import java.nio.charset.StandardCharsets;
import java.text.DecimalFormat;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.concurrent.TimeUnit;

public class DrinkingBar {

   private static final DateTimeFormatter TIME_FORMATTER = DateTimeFormatter.ofPattern("HH:mm");
   private static final int MINS_PER_HOUR = 60;
   private static final int MINS_PER_HALF_HOUR = MINS_PER_HOUR / 2;
   private static final int MINUTES_BEFORE_PAUSE = 4 * MINS_PER_HOUR + MINS_PER_HALF_HOUR;
   private static final int MINUTES_WITH_PAUSE = 6 * MINS_PER_HOUR;
   private static final int DEFAULT_TOTAL_TIME = 8 * MINS_PER_HOUR + MINS_PER_HALF_HOUR;
   private static final BigDecimal DEFAULT_TOTAL_TIME_BD = BigDecimal.valueOf(DEFAULT_TOTAL_TIME);
   private static final BigDecimal DEFAULT_TOTAL_LITRES = BigDecimal.valueOf(2.0);
   private static final BigDecimal QUARTER_LITRE = BigDecimal.valueOf(0.25);
   private static final DecimalFormat LITRE_FORMAT = new DecimalFormat("0.00");
   private static final DecimalFormat PERCENTAGE_FORMAT = new DecimalFormat("00.00");
   private static final BigDecimal MINS_PER_HOUR_BD = BigDecimal.valueOf(MINS_PER_HOUR);
   private static final MathContext MC_INTEGER = new MathContext(1, RoundingMode.HALF_EVEN);

   private final LocalTime startTime;
   private LocalTime endTime;
   private long totalMinutes;
   private BigDecimal totalMinutesBD;
   private BigDecimal totalLitres;


   private DrinkingBar(LocalTime startTime) {
      this.startTime = startTime;
      this.totalMinutes = DEFAULT_TOTAL_TIME;
      this.totalMinutesBD = BigDecimal.valueOf(totalMinutes);
      this.endTime = startTime.plusMinutes(totalMinutes);
      this.totalLitres = DEFAULT_TOTAL_LITRES;
   }


   public static void main(String[] args) throws IOException {
      var br = new BufferedReader(new InputStreamReader(System.in, StandardCharsets.UTF_8));
      print("Ankunftszeit: ");
      var startTime = LocalTime.parse(br.readLine(), TIME_FORMATTER).truncatedTo(ChronoUnit.MINUTES);
      var db = new DrinkingBar(startTime);
      db.showLoadingBar();
   }


   private static void println(Object o) {
      System.out.println(o);
   }


   private static void print(Object o) {
      System.out.print(o);
   }


   protected long getPassedMinutes() {
      return startTime.until(LocalTime.now().truncatedTo(ChronoUnit.MINUTES), ChronoUnit.MINUTES);
   }


   private void setEndTime(LocalTime endTime) {
      this.endTime = endTime;
      this.totalMinutes = startTime.until(endTime, ChronoUnit.MINUTES);
      this.totalMinutesBD = BigDecimal.valueOf(totalMinutes);
      extraInitEndTimeTotalMinutes();
   }


   protected void extraInitEndTimeTotalMinutes() {
      // correct necessary litres to drink based on the end time.
      // lower the volume in quarter litre steps
      BigDecimal calcTotalLitres = DEFAULT_TOTAL_LITRES;
      BigDecimal totalLitresFromMinutes = DEFAULT_TOTAL_LITRES
         .multiply(totalMinutesBD) // reverse dreisatz
         .divide(DEFAULT_TOTAL_TIME_BD, MathContext.DECIMAL64);
      do {
         calcTotalLitres = calcTotalLitres.subtract(QUARTER_LITRE);
      } while (calcTotalLitres.compareTo(totalLitresFromMinutes) >= 0);
      // add quarter since we always did a step "too many", due to the do ... while loop
      this.totalLitres = calcTotalLitres.add(QUARTER_LITRE);
   }


   private void showLoadingBar() {
      long passedMinutes = getPassedMinutes();
      // long passedMinutes = 0; // DEBUG
      if (passedMinutes > totalMinutes) {
         passedMinutes = totalMinutes;
      } else if (passedMinutes < 0) {
         var now = LocalTime.now().truncatedTo(ChronoUnit.SECONDS);
         println("!ACHTUNG! Startzeit \"" + startTime + ":00\" liegt in der Zukunft von jetzt an (" + now + ") gesehen.");
      }
      println(minutesToTimeString(totalMinutesBD) + " gesamt; Endzeit: " + TIME_FORMATTER.format(endTime));
      while (passedMinutes < totalMinutes) {
         print(fillLoadingBar(passedMinutes, true));
         waitUntilNextMinute();
         passedMinutes++;
      }
      println(fillLoadingBar(passedMinutes, false));
   }


   private String fillLoadingBar(long passedMinutes, boolean progressive) {
      long effectivePassedMinutes = passedMinutes < 0 ? 0 : passedMinutes;
      if (totalMinutes > MINUTES_WITH_PAUSE && passedMinutes > MINUTES_BEFORE_PAUSE && passedMinutes <= MINUTES_WITH_PAUSE) {
         effectivePassedMinutes = MINUTES_BEFORE_PAUSE;
      }
      var effectivePassedMinutesBD = BigDecimal.valueOf(effectivePassedMinutes);
      BigDecimal currentLitres = totalLitres
         .multiply(effectivePassedMinutesBD) // reverse dreisatz
         .divide(totalMinutesBD, MathContext.DECIMAL64)
         .add(QUARTER_LITRE);
      BigDecimal printedLitres = currentLitres.subtract(currentLitres.remainder(QUARTER_LITRE, MathContext.DECIMAL64));
      /* BigDecimal currentProgressToNextStep = ONE_HUNDRED_PERCENT
         .multiply(currentLitres.subtract(printedLitres)) // reverse dreisatz
         .divide(QUARTER_LITRE, MathContext.DECIMAL64); */
      BigDecimal minutesToNextStep = getMinutesToNextStep(currentLitres);
      String progressivePart = progressive ? "\r" : "";
      return progressivePart + "Aktuelles Volumen: " + LITRE_FORMAT.format(printedLitres) + "L - "
         // + PERCENTAGE_FORMAT.format(currentProgressToNextStep) + "% - "
         + minutesToTimeString(minutesToNextStep);
   }


   private BigDecimal getMinutesToNextStep(BigDecimal currentLitres) {
      // berechne Liter benötigt bis zum nächsten 0.25er Schritt
      BigDecimal litresToNextStep = QUARTER_LITRE.subtract(currentLitres.remainder(QUARTER_LITRE));
      // berechne Minuten benötigt für 1 Liter
      BigDecimal minutesPerLitre = totalMinutesBD.divide(totalLitres, MathContext.DECIMAL64);
      // berechne Minuten benötigt bis zum nächsten 0.25er Schritt
      return minutesPerLitre.multiply(litresToNextStep).setScale(0, RoundingMode.HALF_EVEN);
   }


   private String minutesToTimeString(BigDecimal minutes) {
      BigDecimal[] hoursAndMinutes = minutes.divideAndRemainder(MINS_PER_HOUR_BD, MC_INTEGER);
      return LocalTime.of(hoursAndMinutes[0].intValue(), hoursAndMinutes[1].intValue()).format(TIME_FORMATTER);
   }


   private void waitUntilNextMinute() {
      try {
         var now = LocalTime.now();
         var oneMinuteLater = now.plusMinutes(1).truncatedTo(ChronoUnit.MINUTES);
         /* We wait whole seconds to not make it overly complicated.
            That results in cut milliseconds: if we would have to wait 1 second and 526 milliseconds, we wait only 1 second.
            So, adjust for ignored milliseconds, add +1 second as it is better to switch between 00 and 01 as between 59 and 00 */
         TimeUnit.SECONDS.sleep(now.until(oneMinuteLater, ChronoUnit.SECONDS) + 1);
         // TimeUnit.MILLISECONDS.sleep(100L); // DEBUG
      } catch (InterruptedException ie) {
         Thread.currentThread().interrupt();
         throw new RuntimeException(ie);
      }
   }
}