import org.junit.Test;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;
import java.util.logging.Logger;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.math.BigInteger;

public class MaxNumberTest {    
  
    private static final Logger logger = Logger.getLogger(MaxNumberTest.class.getName());
    
    // Adjust as needed
    public static final double MAX_EXECUTION_TIME_MS = 5;
    public static final int MAX_WAIT_TIME_LOOP_IN_SEC = 10;
  
    public static String concatenateCharacters(List<Character> charList) {
        StringBuilder sb = new StringBuilder();
        for (Character ch : charList) {
            sb.append(ch);
        }
        return sb.toString();
    }
  
  @Test
  public void testFour() {
    assertEquals(BigInteger.valueOf(4), MaxNumber.print(4));
  }
  
  @Test
  public void testTwelve() {
    assertEquals(BigInteger.valueOf(21), MaxNumber.print(12));
  }
  
  @Test
  public void testOneHundred() {
    assertEquals(BigInteger.valueOf(110), MaxNumber.print(101));
  }
  
  @Test
  public void testHuge1() {
    assertEquals(BigInteger.valueOf(754000000000000000L), MaxNumber.print(400000005000007000L));
  }
  
  @Test
  public void testHuge2() {
    assertEquals(BigInteger.valueOf(988777666444322200L), MaxNumber.print(307778062924466824L));
  }
  
  @Test
  public void testMaxInt() {
    assertTrue(MaxNumber.print(Long.MAX_VALUE).compareTo(BigInteger.valueOf(Long.MAX_VALUE)) >= 0);
  }
  
    
  @Test
  public void testFunctionTimePerformance() {
      ThreadLocalRandom random = ThreadLocalRandom.current();

      long beforeWarmup = System.currentTimeMillis();
      // warmup of CPU cache
      for (int i = 0; i < 200; i++) {
          MaxNumber.print(random.nextLong(0, Long.MAX_VALUE / 10));
      }
      long afterWarmup = System.currentTimeMillis();
      double warmupTimeSec = (afterWarmup - beforeWarmup) / 1_000D;
      assertTrue(warmupTimeSec < MAX_WAIT_TIME_LOOP_IN_SEC, "Rough execution time is too high: "
              + String.format("%.1f", warmupTimeSec * 5) + "ms");    // factor of 5 is due to 1000 (ms/s) / 200 iterations

      long startTime = System.nanoTime();
      int iterations = 10_000;
      // ------
      for (int i = 0; i < iterations; i++) {
          MaxNumber.print(random.nextLong(0, Long.MAX_VALUE / 10));
      }
      // ------
      long endTime = System.nanoTime();

      // Calculate the execution time in milliseconds
      long totalExecutionTimeMs = (endTime - startTime) / 1_000_000;
      double avgExecTimeMs = totalExecutionTimeMs / (double) iterations;
      logger.info("Average execution time was: " + String.format("%.3f", avgExecTimeMs) + "ms");
      assertTrue(avgExecTimeMs <= MAX_EXECUTION_TIME_MS,
              "Execution time exceeded the " + MAX_EXECUTION_TIME_MS + "ms limit");
  }
  
  @Test
  public void testRandomValues() {
      char[] almostAllDigits = new char[]{'0','0','1','2','2','3','3','3','4','5','6','7','7','8','8','9','9'};

      for (int i = 0; i < 100; i++) {
          List<Character> allDigitList = new ArrayList<>();
          for (char digit : almostAllDigits) {
              allDigitList.add(digit);
          }
          Collections.shuffle(allDigitList);
          allDigitList.add(0, '1');   // to prevent starting with 0
          String shuffledDigits = concatenateCharacters(allDigitList);
          long randomNumber = Long.parseLong(shuffledDigits);

          BigInteger actualMaxNumber = MaxNumber.print(randomNumber);

          BigInteger expectedMaxNumber = BigInteger.valueOf(998877654333221100L);  // allMostAllDigits joined with {'1'}, in descending order
          assertEquals(expectedMaxNumber, actualMaxNumber, "Expected: " + expectedMaxNumber + " from " + randomNumber +", but got: " + actualMaxNumber);
      }
  }
}