start adding Link repo

3-Domain/src/main/java/link/Link.java

@@ -21,4 +21,42 @@ public class Link {
 		this.categoryIds = categoryIds;
 		this.tags = tags;
 	}
+
+	public LinkId getId() {
+		return id;
+	}
+
+	public Username getCreator() {
+		return creator;
+	}
+
+	public LinkUrl getUrl() {
+		return url;
+	}
+
+	public Set<CategoryId> getCategoryIds() {
+		return categoryIds;
+	}
+
+	public Set<Tag> getTags() {
+		return tags;
+	}
+
+	@Override
+	public boolean equals(Object o) {
+		if (this == o) return true;
+		if (o == null || getClass() != o.getClass()) return false;
+
+		Link link = (Link) o;
+
+		if (!id.equals(link.id)) return false;
+		return url.equals(link.url);
+	}
+
+	@Override
+	public int hashCode() {
+		int result = id.hashCode();
+		result = 31 * result + url.hashCode();
+		return result;
+	}
 }

3-Domain/src/main/java/link/LinkPersistenceAdapter.java

@@ -0,0 +1,10 @@
+package link;
+
+import java.util.Set;
+
+public interface LinkPersistenceAdapter {
+
+	Set<Link> getAll();
+	Boolean add(Link link);
+
+}

3-Domain/src/main/java/link/LinkRepository.java

@@ -0,0 +1,41 @@
+package link;
+
+import exeptions.LinkAlreadyExists;
+
+import java.util.Optional;
+import java.util.Set;
+
+public class LinkRepository {
+
+	final private LinkPersistenceAdapter linkPersistenceAdapter;
+	final private Set<Link> links;
+
+	public LinkRepository(LinkPersistenceAdapter linkPersistenceAdapter) {
+		this.linkPersistenceAdapter = linkPersistenceAdapter;
+		this.links = linkPersistenceAdapter.getAll();
+	}
+
+	public Optional<Link> getById(LinkId id) {
+		return links.stream().filter(link -> link.getId().equals(id)).findFirst();
+	}
+
+	public Optional<Link> getByUrl(LinkUrl url) {
+		return links.stream().filter(link -> link.getUrl().equals(url)).findFirst();
+	}
+
+	public void add(Link link) {
+		checkDuplicates(link);
+
+
+	}
+
+	private void checkDuplicates(Link newLink) {
+		if (this.getById(newLink.getId()).isPresent()) {
+			throw new LinkAlreadyExists("A link with the id " + newLink.getId() + " already exitsts");
+		}
+
+		if (this.getByUrl(newLink.getUrl()).isPresent()) {
+			throw new LinkAlreadyExists("A link with the url " + newLink.getUrl() + " already exitsts");
+		}
+	}
+}