feat: add dedicated mappers

backend/src/main/java/com/openisle/mapper/CommentMapper.java

@@ -0,0 +1,42 @@
+package com.openisle.mapper;
+
+import com.openisle.dto.CommentDto;
+import com.openisle.model.Comment;
+import com.openisle.service.CommentService;
+import com.openisle.service.ReactionService;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+
+import java.util.stream.Collectors;
+
+/** Mapper for comments including replies and reactions. */
+@Component
+@RequiredArgsConstructor
+public class CommentMapper {
+
+    private final CommentService commentService;
+    private final ReactionService reactionService;
+    private final ReactionMapper reactionMapper;
+    private final UserMapper userMapper;
+
+    public CommentDto toDto(Comment comment) {
+        CommentDto dto = new CommentDto();
+        dto.setId(comment.getId());
+        dto.setContent(comment.getContent());
+        dto.setCreatedAt(comment.getCreatedAt());
+        dto.setAuthor(userMapper.toAuthorDto(comment.getAuthor()));
+        dto.setReward(0);
+        return dto;
+    }
+
+    public CommentDto toDtoWithReplies(Comment comment) {
+        CommentDto dto = toDto(comment);
+        dto.setReplies(commentService.getReplies(comment.getId()).stream()
+                .map(this::toDtoWithReplies)
+                .collect(Collectors.toList()));
+        dto.setReactions(reactionService.getReactionsForComment(comment.getId()).stream()
+                .map(reactionMapper::toDto)
+                .collect(Collectors.toList()));
+        return dto;
+    }
+}