Create CollectionToDtoMapper in core module.

See commit 689e5ae95645768b024dee52c10451c944a41527.
Useful for hg plugin.

scm-core/src/main/java/sonia/scm/api/v2/resources/BaseMapper.java

@@ -0,0 +1,16 @@
+package sonia.scm.api.v2.resources;
+
+import de.otto.edison.hal.HalRepresentation;
+import org.mapstruct.Mapping;
+
+import java.time.Instant;
+
+abstract class BaseMapper<T, D extends HalRepresentation> {
+
+  @Mapping(target = "attributes", ignore = true) // We do not map HAL attributes
+  public abstract D map(T modelObject);
+
+  Instant mapTime(Long epochMilli) {
+    return epochMilli == null? null: Instant.ofEpochMilli(epochMilli);
+  }
+}

scm-core/src/main/java/sonia/scm/api/v2/resources/CollectionToDtoMapper.java

@@ -0,0 +1,32 @@
+package sonia.scm.api.v2.resources;
+
+import de.otto.edison.hal.HalRepresentation;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static de.otto.edison.hal.Embedded.embeddedBuilder;
+import static de.otto.edison.hal.Links.linkingTo;
+
+abstract class CollectionToDtoMapper<E, D extends HalRepresentation> {
+
+  private final String collectionName;
+  private final BaseMapper<E, D> mapper;
+
+  protected CollectionToDtoMapper(String collectionName, BaseMapper<E, D> mapper) {
+    this.collectionName = collectionName;
+    this.mapper = mapper;
+  }
+
+  public HalRepresentation map(Collection<E> collection) {
+    List<D> dtos = collection.stream().map(mapper::map).collect(Collectors.toList());
+    return new HalRepresentation(
+      linkingTo().self(createSelfLink()).build(),
+      embeddedBuilder().with(collectionName, dtos).build()
+    );
+  }
+
+  protected abstract String createSelfLink();
+
+}