Add mention suggestions and admin list

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

@@ -196,6 +196,16 @@ public class UserController {
                 .collect(java.util.stream.Collectors.toList());
     }
 
+    /**
+     * List all administrator users.
+     */
+    @GetMapping("/admins")
+    public java.util.List<UserDto> admins() {
+        return userService.getAdmins().stream()
+                .map(this::toDto)
+                .collect(java.util.stream.Collectors.toList());
+    }
+
     @GetMapping("/{identifier}/all")
     public ResponseEntity<UserAggregateDto> userAggregate(@PathVariable("identifier") String identifier,
                                                           @RequestParam(value = "postsLimit", required = false) Integer postsLimit,

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

@@ -31,5 +31,7 @@ public enum NotificationType {
     /** A user requested registration approval */
     REGISTER_REQUEST,
     /** A user redeemed an activity reward */
-    ACTIVITY_REDEEM
+    ACTIVITY_REDEEM,
+    /** You were mentioned in a post or comment */
+    MENTION
 }

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

@@ -64,6 +64,7 @@ public class CommentService {
                 notificationService.createNotification(u, NotificationType.USER_ACTIVITY, post, comment, null, null, null, null);
             }
         }
+        notificationService.notifyMentions(content, author, post, comment);
         return comment;
     }
 
@@ -102,6 +103,7 @@ public class CommentService {
                 notificationService.createNotification(u, NotificationType.USER_ACTIVITY, parent.getPost(), comment, null, null, null, null);
             }
         }
+        notificationService.notifyMentions(content, author, parent.getPost(), comment);
         return comment;
     }
 

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

@@ -11,6 +11,11 @@ import org.springframework.stereotype.Service;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import java.util.Map;
 
+import java.util.regex.Pattern;
+import java.util.regex.Matcher;
+import java.util.Set;
+import java.util.HashSet;
+
 import java.util.List;
 import java.util.concurrent.Executor;
 
@@ -28,6 +33,8 @@ public class NotificationService {
     @Value("${app.website-url}")
     private String websiteUrl;
 
+    private static final Pattern MENTION_PATTERN = Pattern.compile("@([A-Za-z0-9_]+)");
+
     private String buildPayload(String body, String url) {
 //        try {
 //            return new ObjectMapper().writeValueAsString(Map.of(
@@ -144,4 +151,22 @@ public class NotificationService {
                 .orElseThrow(() -> new com.openisle.exception.NotFoundException("User not found"));
         return notificationRepository.countByUserAndRead(user, false);
     }
+
+    public void notifyMentions(String content, User fromUser, Post post, Comment comment) {
+        if (content == null || fromUser == null) {
+            return;
+        }
+        Matcher matcher = MENTION_PATTERN.matcher(content);
+        Set<String> names = new HashSet<>();
+        while (matcher.find()) {
+            names.add(matcher.group(1));
+        }
+        for (String name : names) {
+            userRepository.findByUsername(name).ifPresent(target -> {
+                if (!target.getId().equals(fromUser.getId())) {
+                    createNotification(target, NotificationType.MENTION, post, comment, null, fromUser, null, null);
+                }
+            });
+        }
+    }
 }

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

@@ -139,6 +139,7 @@ public class PostService {
                         null);
             }
         }
+        notificationService.notifyMentions(content, author, post, null);
         return post;
     }
 
@@ -407,6 +408,7 @@ public class PostService {
         post.setTags(new java.util.HashSet<>(tags));
         Post updated = postRepository.save(post);
         imageUploader.adjustReferences(oldContent, content);
+        notificationService.notifyMentions(content, user, updated, null);
         return updated;
     }
 

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

@@ -185,4 +185,11 @@ public class UserService {
         user.setPassword(passwordEncoder.encode(newPassword));
         return userRepository.save(user);
     }
+
+    /**
+     * Get all administrator accounts.
+     */
+    public java.util.List<User> getAdmins() {
+        return userRepository.findByRole(Role.ADMIN);
+    }
 }