// WRONG — legacy style
@Value
public class User {
    String username;
    String email;
}

// WRONG — hand-written boilerplate
public class User {
    private final String username;
    private final String email;
    // constructor, getters, equals, hashCode, toString...
}

// CORRECT
public record User(String username, String email) {}

public sealed interface PaymentResult
    permits PaymentSuccess, PaymentFailure, PaymentPending {
}

public record PaymentSuccess(String transactionId, Money amount) implements PaymentResult {}
public record PaymentFailure(String reason, ErrorCode code) implements PaymentResult {}
public record PaymentPending(String transactionId) implements PaymentResult {}

// CORRECT
String message = switch (result) {
    case PaymentSuccess success ->
        "Paid %s".formatted(success.amount());
    case PaymentFailure failure ->
        "Failed: %s".formatted(failure.reason());
    case PaymentPending pending ->
        "Pending: %s".formatted(pending.transactionId());
};

// WRONG — old-style switch statement with break
switch (result.getType()) {
    case SUCCESS:
        message = "Paid";
        break;
    // ...
}

// CORRECT — null is an explicit case
return switch (status) {
    case null -> "unknown";
    case ACTIVE -> "active";
    case PAUSED -> "paused";
};

// WRONG — null handled outside the switch
if (status == null) return "unknown";
return switch (status) {
    case ACTIVE -> "active";
    case PAUSED -> "paused";
};

// CORRECT
if (obj instanceof String s && !s.isBlank()) {
    process(s);
}

// WRONG
if (obj instanceof String) {
    String s = (String) obj;
    process(s);
}

String query = """
    SELECT u.id, u.name
    FROM users u
    WHERE u.active = true
    ORDER BY u.name
    """;

// CORRECT — type is obvious
var users = userRepository.findAll();
var mapper = new ObjectMapper();

// WRONG — type is not obvious, use explicit type
var result = process(data);

// CORRECT
if (obj instanceof Point(int x, int y)) {
    System.out.println(x + ", " + y);
}

String desc = switch (shape) {
    case Circle(double r) -> "Circle r=" + r;
    case Rect(double w, double h) -> "Rect " + w + "x" + h;
};

// WRONG — old style: cast + field access
if (obj instanceof Point p) {
    System.out.println(p.x() + ", " + p.y());
}

// CORRECT
try { ... } catch (Exception _) { ... }
try (var _ = ScopedValue.where(KEY, value)) { ... }
list.stream().map(_ -> "constant").toList();

// WRONG
try { ... } catch (Exception ignored) { ... }
try { ... } catch (Exception e) { ... } // when e is never used

// CORRECT
var roles = List.of("ADMIN", "USER");
var config = Map.of("timeout", 30, "retries", 3);
var tags = Set.of("java", "backend");

// WRONG
var roles = Arrays.asList("ADMIN", "USER");
var roles = new ArrayList<>(List.of("ADMIN", "USER"));
var roles = Collections.unmodifiableList(Arrays.asList("ADMIN", "USER"));

// CORRECT
var first = list.getFirst();
var last = list.getLast();
var rev = list.reversed();

// WRONG
var first = list.get(0);
var last = list.get(list.size() - 1);
var rev = new ArrayList<>(list); Collections.reverse(rev);

// CORRECT
str.isBlank()               // replaces str.trim().isEmpty()
str.strip()                 // Unicode-aware trim
"ha".repeat(3)              // "hahaha"
"Hello %s".formatted(name) // replaces String.format(...)
str.lines()                 // Stream<String> of lines

// WRONG
str.trim().isEmpty()
String.format("Hello %s", name)

// CORRECT — Optional for methods that may return nothing
public Optional<User> findByEmail(String email) {
    return Optional.ofNullable(repository.get(email));
}

// WRONG — returning null
public User findByEmail(String email) {
    return repository.get(email); // might return null
}

// CORRECT
userService.findByEmail(email)
    .map(User::username)
    .orElseThrow(() -> new UserNotFoundException(email));

// WRONG
User user = userService.findByEmail(email).get();

// CORRECT
catch (IOException | SQLException e) {
    log.error("Data access failed", e);
}

// WRONG — duplicated handlers
catch (IOException e) { log.error("...", e); }
catch (SQLException e) { log.error("...", e); }

// CORRECT
public User getUser(UserId id) {
    return userRepository.findById(id)
        .orElseThrow(() -> new UserNotFoundException(id));
}

// WRONG — returning null on error
public User getUser(UserId id) {
    try {
        return userRepository.findById(id).orElse(null);
    } catch (Exception e) {
        return null;
    }
}

// CORRECT
var activeEmails = users.stream()
    .filter(User::isActive)
    .map(User::email)
    .toList();

// WRONG — manual loop for simple transformation
var activeEmails = new ArrayList<String>();
for (User user : users) {
    if (user.isActive()) {
        activeEmails.add(user.getEmail());
    }
}

// WRONG — side effect in intermediate operation
users.stream()
    .map(user -> { emailService.send(user); return user.email(); })
    .toList();

// WRONG — unnecessary stream() when there is no pipeline
users.stream().forEach(user -> emailService.send(user));

// CORRECT — Iterable.forEach for simple side effects
users.forEach(user -> emailService.send(user));

// CORRECT — pure filter, side effect only in terminal forEach
users.stream()
    .filter(User::isActive)
    .forEach(user -> emailService.send(user));

// CORRECT — plain loop when you need break/continue or checked exceptions
for (var user : users) {
    emailService.send(user);
}

methodName_shouldExpectedBehavior_whenCondition

@Test
void findByEmail_shouldReturnUser_whenUserExists() { ... }

@Test
void findByEmail_shouldThrowNotFoundException_whenUserDoesNotExist() { ... }

@Test
void processPayment_shouldReturnSuccess_whenBalanceSufficient() { ... }

// CORRECT — Virtual Threads
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
    var future = executor.submit(() -> fetchData(url));
    return future.get();
}

// WRONG — reactive chains for simple I/O
Mono.fromCallable(() -> fetchData(url))
    .subscribeOn(Schedulers.boundedElastic())
    .flatMap(data -> process(data))
    .subscribe();

// CORRECT
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
    var user = scope.fork(() -> fetchUser(id));
    var order = scope.fork(() -> fetchOrder(id));
    scope.join().throwIfFailed();
    return new Response(user.get(), order.get());
}

// WRONG — manual executor management, no automatic lifecycle
var executor = Executors.newFixedThreadPool(2);
var f1 = executor.submit(() -> fetchUser(id));
var f2 = executor.submit(() -> fetchOrder(id));
executor.shutdown();
return new Response(f1.get(), f2.get());

// CORRECT
String content = Files.readString(Path.of("config.json"));
Files.writeString(Path.of("output.txt"), data);
var path = Path.of("src", "main", "java");

// WRONG
var br = new BufferedReader(new FileReader("config.json"));
// ... manual read loop ...
var path = Paths.get("src", "main", "java");

// CORRECT
var client = HttpClient.newHttpClient();
var request = HttpRequest.newBuilder(URI.create(url)).GET().build();
var response = client.send(request, HttpResponse.BodyHandlers.ofString());

// WRONG — HttpURLConnection with manual stream handling
var conn = (HttpURLConnection) new URL(url).openConnection();
conn.setRequestMethod("GET");
var reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
// ...

// CORRECT
LocalDate today = LocalDate.now();
LocalDate date = LocalDate.of(2025, Month.JANUARY, 15);
Instant now = Instant.now();
long days = ChronoUnit.DAYS.between(start, end);
Duration duration = Duration.ofMinutes(30);

// WRONG
Date date = new Date();
Calendar cal = Calendar.getInstance();
cal.set(2025, 0, 15); // zero-indexed months

// CORRECT
log.info("Processing order {} for user {}", orderId, userId);

// WRONG
log.info("Processing order " + orderId + " for user " + userId);