Fix the loading time of puzzle list

This merge request should improve the performance of the puzzle list page on Pupple. It is ensured in two ways:

1. The controller no longer fetches the list of all puzzles from the database, but only a portion of the data that is displayed on the given page (i.e. 14 rows instead of 150 and going up)
2. Non-blocking calls using puzzleAttemptService are no longer blocked in a loop (which defeated the whole purpose of having them non-blocking), now Mono.when is used instead to wait for all tasks to finish simultaneously.

Furthermore a DTO is used, which might improve performance, but not as significantly.

I've checked the changes manually and they seem to not break anything while (potentially) improving performance.

Changelog:

## [0.0.4]

### Added

### Changed

- Pass a single DTO instead of multiple HashMap inside PuzzleList.html ( @cbaraya)

- Fetch only the puzzles from the database that will be used ( @kradziwilowicz)

### Fixed

- Made retrieving display names no longer block to increase performance ( @kradziwilowicz)

src/main/java/nl/tudelft/pupple/controller/PersonController.java

@@ -36,7 +36,9 @@ import nl.tudelft.labracore.api.dto.PersonDetailsDTO;
 import nl.tudelft.labracore.lib.security.user.AuthenticatedPerson;
 import nl.tudelft.labracore.lib.security.user.Person;
 import nl.tudelft.pupple.controller.utility.PageUtil;
+import nl.tudelft.pupple.dto.view.PuzzleOverviewDTO;
 import nl.tudelft.pupple.model.Puzzle;
+import nl.tudelft.pupple.model.PuzzleAttempt;
 import nl.tudelft.pupple.model.labracore.PupplePerson;
 import nl.tudelft.pupple.repository.PuzzleAttemptRepository;
 import nl.tudelft.pupple.repository.PuzzleRepository;
@@ -90,53 +92,42 @@ public class PersonController {
 
 		PersonDetailsDTO otherPerson = personControllerApi.getPersonById(personId).block();
 
-		List<Puzzle> puzzlesFeatured;
+		// List<Puzzle> puzzlesFeatured;
+		Page<Puzzle> puzzlesFeatured;
 		boolean isOwner = person.getId() == personId;
 		boolean canViewFuturePuzzles = isOwner || authorisationService.isAdmin();
 
 		if (unassigned != null) {
 			if (canViewFuturePuzzles) {
-				puzzlesFeatured = puzzleRepository.findByDayUsedIsNullAndCreator(pupplePerson);
+				puzzlesFeatured = puzzleRepository.findByDayUsedIsNullAndCreator(pupplePerson, pageable);
 			} else {
-				puzzlesFeatured = new ArrayList<>();
+				puzzlesFeatured = PageUtil.pageFromList(new ArrayList<>(), pageable);
 			}
 		} else {
 			if (canViewFuturePuzzles) {
-				puzzlesFeatured = puzzleRepository.findByCreator(pupplePerson);
+				puzzlesFeatured = puzzleRepository.findByCreator(pupplePerson, pageable);
 			} else {
 				puzzlesFeatured = puzzleRepository.findByDayUsedIsBeforeAndCreator(LocalDate
-						.now().plusDays(1), pupplePerson);
+						.now().plusDays(1), pupplePerson, pageable);
 			}
 		}
 
-		HashMap<Long, String> displayNames = new HashMap<>();
-		puzzlesFeatured.stream()
-				.filter(puzzle -> puzzle.getCreator() != null && puzzle.getCreator().getPublicProfile())
-				.map(puzzle -> puzzle.getCreator().getId())
-				.forEach((id) -> displayNames.put(id,
-						personControllerApi.getPersonById(id).block().getDisplayName()));
-		HashMap<Long, Long> attempts = new HashMap<>();
-		puzzlesFeatured.stream()
-				.filter(puzzle -> puzzleAttemptRepository.getByPersonIdAndPuzzleId(person.getId(),
-						puzzle.getId()) != null)
-				.forEach((puzzle) -> attempts.put(puzzle.getId(),
-						(long) puzzleAttemptRepository.getByPersonIdAndPuzzleId(
-								person.getId(), puzzle.getId()).getGuesses().size()));
+		List<PuzzleOverviewDTO> overviewPuzzles = new ArrayList<>();
 
-		puzzlesFeatured.sort(Comparator
-				.comparing(Puzzle::getDayUsed, Comparator.nullsFirst(Comparator.naturalOrder()))
-				.reversed());
-		Page<Puzzle> puzzlePage = PageUtil.pageFromList(puzzlesFeatured, pageable);
-		Set<Puzzle> puzzlesSolved = new HashSet<>(puzzleAttemptService
-				.filterSolvedPuzzles(person, puzzlesFeatured));
+		Set<Puzzle> puzzlesSolved = new HashSet<>(
+				puzzleAttemptService.filterSolvedPuzzles(person, new ArrayList<>()));
+		for (Puzzle p : puzzlesFeatured) {
+			PuzzleAttempt attempt = puzzleAttemptRepository.getByPersonIdAndPuzzleId(person.getId(),
+					p.getId());
+			int guesses = (attempt == null) ? 0 : attempt.getGuesses().size(); // 0 if not attempt
+			overviewPuzzles.add(new PuzzleOverviewDTO(p, null, guesses, puzzlesSolved.contains(p)));
+		}
 
 		model.addAttribute("displayName", otherPerson.getDisplayName());
 		model.addAttribute("pupplePerson", pupplePerson);
-		model.addAttribute("solved", puzzlesSolved);
-		model.addAttribute("puzzles", puzzlePage);
+		model.addAttribute("puzzles", puzzlesFeatured);
+		model.addAttribute("overviewPuzzles", overviewPuzzles);
 		model.addAttribute("isOwner", isOwner);
-		model.addAttribute("displayNames", displayNames);
-		model.addAttribute("guessAmounts", attempts);
 		return "profile/view";
 	}