Implementing Event Sourced Entities

@PostMapping("/add")
public Effect<String> addItem(@RequestBody LineItem item) {
  if (currentState().checkedOut())
    return effects().error("Cart is already checked out.");
  if (item.quantity() <= 0) { (1)
    return effects().error("Quantity for item " + item.productId() + " must be greater than zero.");
  }

  var event = new ShoppingCartEvent.ItemAdded(item); (2)

  return effects()
      .emitEvent(event) (3)
      .thenReply(newState -> "OK"); (4)
}

@EventHandler (5)
public ShoppingCart itemAdded(ShoppingCartEvent.ItemAdded itemAdded) {
  return currentState().onItemAdded(itemAdded); (6)
}

public ShoppingCart onItemAdded(ShoppingCartEvent.ItemAdded itemAdded) {
  var item = itemAdded.item();
  var lineItem = updateItem(item, this); (1)
  List<LineItem> lineItems =
      removeItemByProductId(this, item.productId()); (2)
  lineItems.add(lineItem); (3)
  lineItems.sort(Comparator.comparing(LineItem::productId));
  return new ShoppingCart(cartId, lineItems, checkedOut); (4)
}

private static List<LineItem> removeItemByProductId(
    ShoppingCart cart, String productId) {
  return cart.items().stream()
      .filter(lineItem -> !lineItem.productId().equals(productId))
      .collect(Collectors.toList());
}

private static LineItem updateItem(LineItem item, ShoppingCart cart) {
  return cart.findItemByProductId(item.productId())
      .map(li -> li.withQuantity(li.quantity() + item.quantity()))
      .orElse(item);
}

public Optional<LineItem> findItemByProductId(String productId) {
  Predicate<LineItem> lineItemExists =
      lineItem -> lineItem.productId().equals(productId);
  return items.stream().filter(lineItemExists).findFirst();
}

private final String entityId;

public ShoppingCartEntity(EventSourcedEntityContext context) {
  this.entityId = context.entityId(); (1)
}

@Override
public ShoppingCart emptyState() { (2)
  return new ShoppingCart(entityId, Collections.emptyList(), false);
}

@GetMapping() (3)
public Effect<ShoppingCart> getCart() {
  return effects().reply(currentState()); (4)
}

package com.example.shoppingcart.domain;

import com.example.shoppingcart.ShoppingCartEntity;
import kalix.javasdk.testkit.EventSourcedResult;
import kalix.javasdk.testkit.EventSourcedTestKit;
import org.junit.jupiter.api.Test;

import java.util.List;

import static com.example.shoppingcart.domain.ShoppingCartEvent.*;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class ShoppingCartTest {

  private final ShoppingCart.LineItem akkaTshirt = new ShoppingCart.LineItem("kalix-tshirt", "Akka Tshirt", 10);


  @Test
  public void testAddLineItem() {

    var testKit = EventSourcedTestKit.of(ShoppingCartEntity::new); (1)

    {
      var result = testKit.call(e -> e.addItem(akkaTshirt)); (2)
      assertEquals("OK", result.getReply()); (3)

      var itemAdded = result.getNextEventOfType(ItemAdded.class);
      assertEquals(10, itemAdded.item().quantity()); (4)
    }

    // actually we want more akka tshirts
    {
      var result = testKit.call(e -> e.addItem( akkaTshirt.withQuantity(5))); (5)
      assertEquals("OK", result.getReply());

      var itemAdded = result.getNextEventOfType(ItemAdded.class);
      assertEquals(5, itemAdded.item().quantity());
    }

    {
      assertEquals(testKit.getAllEvents().size(), 2); (6)
      var result = testKit.call(ShoppingCartEntity::getCart); (7)
      assertEquals(
        new ShoppingCart("testkit-entity-id", List.of(akkaTshirt.withQuantity(15)), false),
        result.getReply());
    }

  }

}

import kalix.spring.testkit.KalixIntegrationTestKitSupport;
// ...

@SpringBootTest(classes = Main.class)
public class IntegrationTest extends KalixIntegrationTestKitSupport { (1)

  @Autowired
  private WebClient webClient; (2)

  private Duration timeout = Duration.of(5, SECONDS);

  @Test
  public void createAndManageCart() {

    String cartId = "card-abc";
    ResponseEntity<String> created =
      webClient.post() (3)
        .uri("/cart/" + cartId + "/create")
        .retrieve()
        .toEntity(String.class)
        .block(timeout);
    assertEquals(HttpStatus.OK, created.getStatusCode());

    var item1 = new LineItem("tv", "Super TV 55'", 1);
    ResponseEntity<String> itemOne =
      webClient.post() (4)
        .uri("/cart/" + cartId + "/add")
        .bodyValue(item1)
        .retrieve()
        .toEntity(String.class)
        .block(timeout);
    assertEquals(HttpStatus.OK, itemOne.getStatusCode());

    ShoppingCart cartUpdated =
      webClient.get() (5)
        .uri("/cart/" + cartId)
        .retrieve()
        .bodyToMono(ShoppingCart.class)
        .block(timeout);
    assertEquals(1, cartUpdated.items().size());
    assertEquals(item2, cartUpdated.items().get(0));
  }
}