andreschaffer/event-sourcing-cqrs-examples

package bankservice.domain.model;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;
import static java.lang.String.format;
import static java.util.Collections.emptyList;

import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableList;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

public abstract class Aggregate {

  private UUID id;
  private int baseVersion;
  private List<Event> newEvents;

  protected Aggregate(UUID id) {
    this(id, emptyList());
  }

  protected Aggregate(UUID id, List<Event> eventStream) {
    checkNotNull(id);
    checkNotNull(eventStream);
    this.id = id;
    eventStream.forEach(e -> {
      apply(e);
      this.baseVersion = e.getVersion();
    });
    this.newEvents = new ArrayList<>();
  }

  protected void applyNewEvent(Event event) {
    checkArgument(event.getVersion() == getNextVersion(),
        "New event version '%s' does not match expected next version '%s'",
        event.getVersion(), getNextVersion());
    apply(event);
    newEvents.add(event);
  }

  private void apply(Event event) {
    try {
      Method method = this.getClass().getDeclaredMethod("apply", event.getClass());
      method.setAccessible(true);
      method.invoke(this, event);
    } catch (InvocationTargetException e) {
      Throwables.propagate(e.getCause());
    } catch (NoSuchMethodException | IllegalAccessException e) {
      throw new UnsupportedOperationException(
          format("Aggregate '%s' doesn't apply event type '%s'", this.getClass(), event.getClass()),
          e);
    }
  }

  public UUID getId() {
    return id;
  }

  public int getBaseVersion() {
    return baseVersion;
  }

  public List<Event> getNewEvents() {
    return ImmutableList.copyOf(newEvents);
  }

  protected int getNextVersion() {
    return baseVersion + newEvents.size() + 1;
  }
}