Add comment module

src/main/java/com/openisle/service/CommentService.java

@@ -0,0 +1,57 @@
+package com.openisle.service;
+
+import com.openisle.model.Comment;
+import com.openisle.model.Post;
+import com.openisle.model.User;
+import com.openisle.repository.CommentRepository;
+import com.openisle.repository.PostRepository;
+import com.openisle.repository.UserRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+@Service
+@RequiredArgsConstructor
+public class CommentService {
+    private final CommentRepository commentRepository;
+    private final PostRepository postRepository;
+    private final UserRepository userRepository;
+
+    public Comment addComment(String username, Long postId, String content) {
+        User author = userRepository.findByUsername(username)
+                .orElseThrow(() -> new IllegalArgumentException("User not found"));
+        Post post = postRepository.findById(postId)
+                .orElseThrow(() -> new IllegalArgumentException("Post not found"));
+        Comment comment = new Comment();
+        comment.setAuthor(author);
+        comment.setPost(post);
+        comment.setContent(content);
+        return commentRepository.save(comment);
+    }
+
+    public Comment addReply(String username, Long parentId, String content) {
+        User author = userRepository.findByUsername(username)
+                .orElseThrow(() -> new IllegalArgumentException("User not found"));
+        Comment parent = commentRepository.findById(parentId)
+                .orElseThrow(() -> new IllegalArgumentException("Comment not found"));
+        Comment comment = new Comment();
+        comment.setAuthor(author);
+        comment.setPost(parent.getPost());
+        comment.setParent(parent);
+        comment.setContent(content);
+        return commentRepository.save(comment);
+    }
+
+    public List<Comment> getCommentsForPost(Long postId) {
+        Post post = postRepository.findById(postId)
+                .orElseThrow(() -> new IllegalArgumentException("Post not found"));
+        return commentRepository.findByPostAndParentIsNullOrderByCreatedAtAsc(post);
+    }
+
+    public List<Comment> getReplies(Long parentId) {
+        Comment parent = commentRepository.findById(parentId)
+                .orElseThrow(() -> new IllegalArgumentException("Comment not found"));
+        return commentRepository.findByParentOrderByCreatedAtAsc(parent);
+    }
+}