feat: implement post subscription notifications

src/main/java/com/openisle/controller/PostController.java

@@ -8,6 +8,7 @@ import com.openisle.service.PostService;
 import com.openisle.service.ReactionService;
 import com.openisle.service.CaptchaService;
 import com.openisle.service.DraftService;
+import com.openisle.service.SubscriptionService;
 import lombok.Data;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.ResponseEntity;
@@ -26,6 +27,7 @@ public class PostController {
     private final PostService postService;
     private final CommentService commentService;
     private final ReactionService reactionService;
+    private final SubscriptionService subscriptionService;
     private final CaptchaService captchaService;
     private final DraftService draftService;
 
@@ -50,7 +52,7 @@ public class PostController {
     public ResponseEntity<PostDto> getPost(@PathVariable Long id, Authentication auth) {
         String viewer = auth != null ? auth.getName() : null;
         Post post = postService.viewPost(id, viewer);
-        return ResponseEntity.ok(toDto(post));
+        return ResponseEntity.ok(toDto(post, viewer));
     }
 
     @GetMapping
@@ -134,6 +136,16 @@ public class PostController {
         return dto;
     }
 
+    private PostDto toDto(Post post, String viewer) {
+        PostDto dto = toDto(post);
+        if (viewer != null) {
+            dto.setSubscribed(subscriptionService.isPostSubscribed(viewer, post.getId()));
+        } else {
+            dto.setSubscribed(false);
+        }
+        return dto;
+    }
+
     private CommentDto toCommentDtoWithReplies(Comment comment) {
         CommentDto dto = toCommentDto(comment);
         List<CommentDto> replies = commentService.getReplies(comment.getId()).stream()
@@ -223,6 +235,7 @@ public class PostController {
         private List<CommentDto> comments;
         private List<ReactionDto> reactions;
         private java.util.List<AuthorDto> participants;
+        private boolean subscribed;
     }
 
     @Data

src/main/java/com/openisle/model/NotificationType.java

@@ -14,6 +14,10 @@ public enum NotificationType {
     POST_REVIEWED,
     /** A subscribed post received a new comment */
     POST_UPDATED,
+    /** Someone subscribed to your post */
+    POST_SUBSCRIBED,
+    /** Someone unsubscribed from your post */
+    POST_UNSUBSCRIBED,
     /** Someone you follow published a new post */
     FOLLOWED_POST,
     /** Someone started following you */

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

@@ -26,6 +26,10 @@ public class SubscriptionService {
             PostSubscription ps = new PostSubscription();
             ps.setUser(user);
             ps.setPost(post);
+            if (!user.getId().equals(post.getAuthor().getId())) {
+                notificationService.createNotification(post.getAuthor(),
+                        NotificationType.POST_SUBSCRIBED, post, null, null, user, null);
+            }
             return postSubRepo.save(ps);
         });
     }
@@ -33,7 +37,13 @@ public class SubscriptionService {
     public void unsubscribePost(String username, Long postId) {
         User user = userRepo.findByUsername(username).orElseThrow();
         Post post = postRepo.findById(postId).orElseThrow();
-        postSubRepo.findByUserAndPost(user, post).ifPresent(postSubRepo::delete);
+        postSubRepo.findByUserAndPost(user, post).ifPresent(ps -> {
+            postSubRepo.delete(ps);
+            if (!user.getId().equals(post.getAuthor().getId())) {
+                notificationService.createNotification(post.getAuthor(),
+                        NotificationType.POST_UNSUBSCRIBED, post, null, null, user, null);
+            }
+        });
     }
 
     public void subscribeComment(String username, Long commentId) {
@@ -117,6 +127,15 @@ public class SubscriptionService {
         return userSubRepo.findBySubscriberAndTarget(subscriber, target).isPresent();
     }
 
+    public boolean isPostSubscribed(String username, Long postId) {
+        if (username == null || postId == null) {
+            return false;
+        }
+        User user = userRepo.findByUsername(username).orElseThrow();
+        Post post = postRepo.findById(postId).orElseThrow();
+        return postSubRepo.findByUserAndPost(user, post).isPresent();
+    }
+
     private Optional<User> findUser(String identifier) {
         if (identifier.matches("\\d+")) {
             return userRepo.findById(Long.parseLong(identifier));