Add add Link usecase

2-Application/src/main/java/link/LinkIdGenerator.java

@@ -0,0 +1,8 @@
+package link;
+
+import category.CategoryId;
+
+public interface LinkIdGenerator {
+
+	LinkId generateId();
+}

2-Application/src/main/java/link/LinkUseCase.java

@@ -0,0 +1,44 @@
+package link;
+
+import category.CategoryName;
+import category.CategoryRepository;
+import tag.TaggingUseCase;
+import user.Username;
+
+import java.util.Set;
+import java.util.stream.Collectors;
+
+public class LinkUseCase {
+
+	private final LinkRepository linkRepository;
+	private final CategoryRepository categoryRepository;
+	private final TaggingUseCase taggingUseCase;
+	private final LinkIdGenerator linkIdGenerator;
+
+	public LinkUseCase(LinkRepository linkRepository,
+	                   CategoryRepository categoryRepository,
+	                   TaggingUseCase taggingUseCase,
+	                   LinkIdGenerator linkIdGenerator) {
+		this.linkRepository = linkRepository;
+		this.categoryRepository = categoryRepository;
+		this.taggingUseCase = taggingUseCase;
+		this.linkIdGenerator = linkIdGenerator;
+	}
+
+	public void addLink(LinkUrl url, Set<CategoryName> categoryNames, Username creator) {
+
+		OnlineCheck.of(url);
+
+		var categoryIds = categoryNames.stream().map(categoryRepository::getIdByName).collect(Collectors.toSet());
+
+		var tags = taggingUseCase.getTagsFor(url);
+
+		var id = linkIdGenerator.generateId();
+
+		var link = new Link(id, creator, url, categoryIds, tags);
+
+		linkRepository.add(link);
+
+	}
+
+}