Implement event domain model and application service

Add Event entity, CreateEventCommand, ports (CreateEventUseCase,
EventRepository), and EventService with Clock injection for
deterministic testing. Expiry date must be in the future.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/src/main/java/de/fete/application/service/EventService.java

@@ -0,0 +1,44 @@
+package de.fete.application.service;
+
+import de.fete.domain.model.CreateEventCommand;
+import de.fete.domain.model.Event;
+import de.fete.domain.port.in.CreateEventUseCase;
+import de.fete.domain.port.out.EventRepository;
+import java.time.Clock;
+import java.time.LocalDate;
+import java.time.OffsetDateTime;
+import java.util.UUID;
+import org.springframework.stereotype.Service;
+
+/** Application service implementing event creation. */
+@Service
+public class EventService implements CreateEventUseCase {
+
+  private final EventRepository eventRepository;
+  private final Clock clock;
+
+  /** Creates a new EventService with the given repository and clock. */
+  public EventService(EventRepository eventRepository, Clock clock) {
+    this.eventRepository = eventRepository;
+    this.clock = clock;
+  }
+
+  @Override
+  public Event createEvent(CreateEventCommand command) {
+    if (!command.expiryDate().isAfter(LocalDate.now(clock))) {
+      throw new ExpiryDateInPastException(command.expiryDate());
+    }
+
+    var event = new Event();
+    event.setEventToken(UUID.randomUUID());
+    event.setOrganizerToken(UUID.randomUUID());
+    event.setTitle(command.title());
+    event.setDescription(command.description());
+    event.setDateTime(command.dateTime());
+    event.setLocation(command.location());
+    event.setExpiryDate(command.expiryDate());
+    event.setCreatedAt(OffsetDateTime.now(clock));
+
+    return eventRepository.save(event);
+  }
+}

backend/src/main/java/de/fete/application/service/ExpiryDateInPastException.java

@@ -0,0 +1,20 @@
+package de.fete.application.service;
+
+import java.time.LocalDate;
+
+/** Thrown when an event's expiry date is not in the future. */
+public class ExpiryDateInPastException extends RuntimeException {
+
+  private final LocalDate expiryDate;
+
+  /** Creates a new exception for the given invalid expiry date. */
+  public ExpiryDateInPastException(LocalDate expiryDate) {
+    super("Expiry date must be in the future: " + expiryDate);
+    this.expiryDate = expiryDate;
+  }
+
+  /** Returns the invalid expiry date. */
+  public LocalDate getExpiryDate() {
+    return expiryDate;
+  }
+}

backend/src/main/java/de/fete/config/WebConfig.java

@@ -1,6 +1,8 @@
 package de.fete.config;
 
 import java.io.IOException;
+import java.time.Clock;
+import org.springframework.context.annotation.Bean;
 import org.springframework.context.annotation.Configuration;
 import org.springframework.core.io.ClassPathResource;
 import org.springframework.core.io.Resource;
@@ -14,6 +16,11 @@ import org.springframework.web.servlet.resource.PathResourceResolver;
 @Configuration
 public class WebConfig implements WebMvcConfigurer {
 
+  @Bean
+  Clock clock() {
+    return Clock.systemDefaultZone();
+  }
+
   @Override
   public void configurePathMatch(PathMatchConfigurer configurer) {
     configurer.addPathPrefix("/api", c -> c.isAnnotationPresent(RestController.class));

backend/src/main/java/de/fete/domain/model/CreateEventCommand.java

@@ -0,0 +1,13 @@
+package de.fete.domain.model;
+
+import java.time.LocalDate;
+import java.time.OffsetDateTime;
+
+/** Command carrying the data needed to create an event. */
+public record CreateEventCommand(
+    String title,
+    String description,
+    OffsetDateTime dateTime,
+    String location,
+    LocalDate expiryDate
+) {}

backend/src/main/java/de/fete/domain/model/Event.java

@@ -0,0 +1,109 @@
+package de.fete.domain.model;
+
+import java.time.LocalDate;
+import java.time.OffsetDateTime;
+import java.util.UUID;
+
+/** Domain entity representing an event. */
+public class Event {
+
+  private Long id;
+  private UUID eventToken;
+  private UUID organizerToken;
+  private String title;
+  private String description;
+  private OffsetDateTime dateTime;
+  private String location;
+  private LocalDate expiryDate;
+  private OffsetDateTime createdAt;
+
+  /** Returns the internal database ID. */
+  public Long getId() {
+    return id;
+  }
+
+  /** Sets the internal database ID. */
+  public void setId(Long id) {
+    this.id = id;
+  }
+
+  /** Returns the public event token (UUID). */
+  public UUID getEventToken() {
+    return eventToken;
+  }
+
+  /** Sets the public event token. */
+  public void setEventToken(UUID eventToken) {
+    this.eventToken = eventToken;
+  }
+
+  /** Returns the secret organizer token (UUID). */
+  public UUID getOrganizerToken() {
+    return organizerToken;
+  }
+
+  /** Sets the secret organizer token. */
+  public void setOrganizerToken(UUID organizerToken) {
+    this.organizerToken = organizerToken;
+  }
+
+  /** Returns the event title. */
+  public String getTitle() {
+    return title;
+  }
+
+  /** Sets the event title. */
+  public void setTitle(String title) {
+    this.title = title;
+  }
+
+  /** Returns the event description. */
+  public String getDescription() {
+    return description;
+  }
+
+  /** Sets the event description. */
+  public void setDescription(String description) {
+    this.description = description;
+  }
+
+  /** Returns the event date and time with UTC offset. */
+  public OffsetDateTime getDateTime() {
+    return dateTime;
+  }
+
+  /** Sets the event date and time. */
+  public void setDateTime(OffsetDateTime dateTime) {
+    this.dateTime = dateTime;
+  }
+
+  /** Returns the event location. */
+  public String getLocation() {
+    return location;
+  }
+
+  /** Sets the event location. */
+  public void setLocation(String location) {
+    this.location = location;
+  }
+
+  /** Returns the expiry date after which event data is deleted. */
+  public LocalDate getExpiryDate() {
+    return expiryDate;
+  }
+
+  /** Sets the expiry date. */
+  public void setExpiryDate(LocalDate expiryDate) {
+    this.expiryDate = expiryDate;
+  }
+
+  /** Returns the creation timestamp. */
+  public OffsetDateTime getCreatedAt() {
+    return createdAt;
+  }
+
+  /** Sets the creation timestamp. */
+  public void setCreatedAt(OffsetDateTime createdAt) {
+    this.createdAt = createdAt;
+  }
+}

backend/src/main/java/de/fete/domain/port/in/CreateEventUseCase.java

@@ -0,0 +1,11 @@
+package de.fete.domain.port.in;
+
+import de.fete.domain.model.CreateEventCommand;
+import de.fete.domain.model.Event;
+
+/** Inbound port for creating a new event. */
+public interface CreateEventUseCase {
+
+  /** Creates an event from the given command and returns the persisted event. */
+  Event createEvent(CreateEventCommand command);
+}

backend/src/main/java/de/fete/domain/port/out/EventRepository.java

@@ -0,0 +1,15 @@
+package de.fete.domain.port.out;
+
+import de.fete.domain.model.Event;
+import java.util.Optional;
+import java.util.UUID;
+
+/** Outbound port for persisting and retrieving events. */
+public interface EventRepository {
+
+  /** Persists the given event and returns it with generated fields populated. */
+  Event save(Event event);
+
+  /** Finds an event by its public event token. */
+  Optional<Event> findByEventToken(UUID eventToken);
+}