Add GotErrorsResource (#24)

Fixes #21

src/main/java/org/kiwiproject/dropwizard/error/resource/GotErrorsResource.java

@@ -0,0 +1,53 @@
+package org.kiwiproject.dropwizard.error.resource;
+
+import static javax.ws.rs.core.MediaType.APPLICATION_JSON;
+
+import org.kiwiproject.dropwizard.error.model.DataStoreType;
+
+import javax.ws.rs.GET;
+import javax.ws.rs.Path;
+import javax.ws.rs.Produces;
+import javax.ws.rs.core.Response;
+import java.util.Map;
+
+/**
+ * A simple JAX-RS resource for clients to determine if application errors are available or not.
+ * <p>
+ * Clients can check if application errors are available using a HTTP GET request that returns a
+ * {@code 200 OK} response if available. The response entity contains information on whether the
+ * underlying data store is shared or not. A shared database means it is shared between separate
+ * service/application instances, whereas a database that is <em>not</em> shared is local to the
+ * specific service/application instance being queried.
+ * <p>
+ * For example, an in-memory H2 database is not shared, whereas a Postgres database used by all
+ * instances of one specific service/application (e.g. an "Order Service" that has 3 running
+ * instances that all use the same Postgres database).
+ * <p>
+ * Obviously, a {@code 404 Not Found} is returned if this resource is not registered and available.
+ */
+@Path("/kiwi/got-errors")
+@Produces(APPLICATION_JSON)
+public class GotErrorsResource {
+
+    private final DataStoreType dataStoreType;
+
+    /**
+     * Construct a new instance.
+     *
+     * @param dataStoreType the DataStoreType of the service/application this resource is registered with
+     */
+    public GotErrorsResource(DataStoreType dataStoreType) {
+        this.dataStoreType = dataStoreType;
+    }
+
+    /**
+     * Check if application errors are available. Clients always receive a 200 response from this endpoint.
+     *
+     * @return the Response
+     */
+    @GET
+    public Response gotErrors() {
+        var entity = Map.of("shared", dataStoreType.shared());
+        return Response.ok(entity).build();
+    }
+}

src/test/java/org/kiwiproject/dropwizard/error/resource/GotErrorsResourceTest.java

@@ -0,0 +1,40 @@
+package org.kiwiproject.dropwizard.error.resource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
+import static org.kiwiproject.jaxrs.KiwiGenericTypes.MAP_OF_STRING_TO_OBJECT_GENERIC_TYPE;
+import static org.kiwiproject.test.jaxrs.JaxrsTestHelper.assertOkResponse;
+
+import io.dropwizard.testing.junit5.DropwizardExtensionsSupport;
+import io.dropwizard.testing.junit5.ResourceExtension;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.kiwiproject.dropwizard.error.model.DataStoreType;
+
+@DisplayName("GotErrorsResource")
+@ExtendWith(DropwizardExtensionsSupport.class)
+class GotErrorsResourceTest {
+
+    private static final DataStoreType DATA_STORE_TYPE = DataStoreType.NOT_SHARED;
+
+    private static final ResourceExtension RESOURCES = ResourceExtension.builder()
+            .addResource(new GotErrorsResource(DATA_STORE_TYPE))
+            .build();
+
+    @Test
+    void shouldReturnOkResponse() {
+        var response = RESOURCES.client()
+                .target("/kiwi/got-errors?")
+                .request()
+                .get();
+
+        assertOkResponse(response);
+
+        var entity = response.readEntity(MAP_OF_STRING_TO_OBJECT_GENERIC_TYPE);
+
+        assertThat(entity).containsOnly(
+                entry("shared", DATA_STORE_TYPE.shared())
+        );
+    }
+}