import java.text.DecimalFormat;
import java.time.LocalTime;
import java.time.format.DateTimeFormatter;
import java.time.temporal.ChronoUnit;
import java.util.Objects;
import java.util.concurrent.TimeUnit;
import java.util.regex.Pattern;

public class SimpleLoadingBar {

   private static final String TIME_FORMAT = "HH:mm";
   private static final DateTimeFormatter TIME_FORMATTER = DateTimeFormatter.ofPattern(TIME_FORMAT);
   private static final Pattern TIME_PATTERN = Pattern.compile("(?>[01]\\d|2[0-4]):[0-5]\\d");
   private static final DecimalFormat PERCENTAGE_FORMAT = new DecimalFormat("00.00");
   private static final int MINS_PER_HOUR = 60;
   private static final int LINE_LENGTH = 100;


   public static void main(String[] args) {
      if (args.length > 0 && Objects.equals(args[0], "--help")) {
         printHelp();
         return;
      }
      verifyMinimumNumberOfArgs(args);
      String nextArg = args[0];
      verifyTimeFormat(nextArg, "Erstes Argument"); // FSFIXME package
      var firstTime = LocalTime.parse(nextArg, TIME_FORMATTER); // FSFIXME package
      LocalTime startTime = null;
      String title = "";
      LocalTime endTime = null;
      if (args.length > 1) {
         startTime = firstTime;
         nextArg = args[1];
         if ("-msg".equals(nextArg)) {
            title = args.length > 2 ? args[2] : title;
         } else {
            verifyTimeFormat(nextArg, "Zweites Argument");
            endTime = LocalTime.parse(nextArg, TIME_FORMATTER);
         }
      }
      if (endTime == null) {
         startTime = LocalTime.now();
         endTime = firstTime;
      }
      String fallbackTitle = "Ende! Endzeit " + TIME_FORMATTER.format(endTime) + " erreicht.";
      if (args.length == 2 || !title.isBlank()) {
         title = title.isBlank() ? fallbackTitle : title;
         showLoadingBar(startTime, endTime, title);
         return;
      }
      // if there are 3 arguments, the third will be discarded.
      boolean hasTitleArg = args.length > 3 && "-msg".equals(args[2]);
      title = hasTitleArg ? args[3] : title;
      title = title.isBlank() ? fallbackTitle : title;
      showLoadingBar(startTime, endTime, title);
   }


   private static void printHelp() {
      System.out.println("Mögliche Argumente für LoadingBar:\n"
          + "Startzeit, Endzeit, Endnachricht (Optional)\n"
          + TIME_FORMAT + " " + TIME_FORMAT + " -msg <Nachricht>\n"
          + "Endzeit (Startzeit = jetzt), Endnachricht (Optional)\n"
          + TIME_FORMAT + " -msg <Nachricht>\n"
      );
   }


   private static void verifyMinimumNumberOfArgs(String[] args) {
      if (args.length >= 1) {
         return;
      }
      System.out.println("Mindestens 1 Argument muss gegeben sein.");
      printHelp();
      System.exit(1);
   }


   private static void verifyTimeFormat(String param, String errMsgPrefix) {
      if (TIME_PATTERN.matcher(param).matches()) {
         return;
      }
      System.out.println(errMsgPrefix + " \"" + param + "\" muss Uhrzeitformat (" + TIME_FORMAT + ") entsprechen.");
      System.exit(1);
   }


   public static void showLoadingBar(LocalTime startTime, LocalTime endTime, String title) {
      long initialMinutes = startTime.until(endTime, ChronoUnit.MINUTES);
      System.out.print(minutesToTimeString(initialMinutes) + " gesamt; Endzeit: " + TIME_FORMATTER.format(endTime) + "\n");
      long passedMinutes = startTime.until(LocalTime.now(), ChronoUnit.MINUTES);
      if (passedMinutes > initialMinutes) {
         passedMinutes = initialMinutes;
      } else if (passedMinutes < 0) {
         System.out.println(fillLoadingBar(initialMinutes, 0, false));
         return;
      }
      while (passedMinutes < initialMinutes) {
         System.out.print(fillLoadingBar(initialMinutes, passedMinutes, true));
         try {
            var now = LocalTime.now();
            var oneMinuteLater = now.plusMinutes(1).truncatedTo(ChronoUnit.MINUTES);
            // +1 second to adjust for ignored milliseconds 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.SECONDS.sleep(1L); // DEBUG
         } catch (InterruptedException ie) {
            throw new RuntimeException(ie);
         }
         passedMinutes++;
      }
      System.out.println(fillLoadingBar(initialMinutes, passedMinutes, false));
      System.out.println(formatTitle(title));
   }


   private static String fillLoadingBar(long initialMinutes, long passedMinutes, boolean progressive) {
      double wholePercentage = ((double) passedMinutes / initialMinutes) * 100;
      long remainingMinutes = initialMinutes - passedMinutes;
      int numberOfEquals = (int) wholePercentage;
      var sb = new StringBuilder("[");
      for (int i = 0; i < LINE_LENGTH; i++) {
         if (i < numberOfEquals) {
            sb.append("=");
         } else {
            sb.append("-");
         }
      }
      sb.append("] ").append(PERCENTAGE_FORMAT.format(wholePercentage)).append("% ")
          .append(minutesToTimeString(passedMinutes)).append(" - ").append(minutesToTimeString(remainingMinutes));
      if (progressive) {
         sb.append("\r");
      }
      return sb.toString();
   }


   private static String minutesToTimeString(long minutes) {
      return LocalTime.of((int) minutes / MINS_PER_HOUR, (int) minutes % MINS_PER_HOUR).format(TIME_FORMATTER);
   }


   private static String formatTitle(String title) {
      String separator = "*".repeat(title.length());
      return separator + "\n" + title + "\n" + separator;
   }
}