feat: add channel support

backend/src/main/java/com/openisle/service/ChannelService.java

@@ -0,0 +1,76 @@
+package com.openisle.service;
+
+import com.openisle.dto.ChannelDto;
+import com.openisle.model.MessageConversation;
+import com.openisle.model.MessageParticipant;
+import com.openisle.model.User;
+import com.openisle.repository.MessageConversationRepository;
+import com.openisle.repository.MessageParticipantRepository;
+import com.openisle.repository.MessageRepository;
+import com.openisle.repository.UserRepository;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.time.LocalDateTime;
+import java.util.List;
+import java.util.stream.Collectors;
+
+@Service
+@RequiredArgsConstructor
+public class ChannelService {
+    private final MessageConversationRepository conversationRepository;
+    private final MessageParticipantRepository participantRepository;
+    private final MessageRepository messageRepository;
+    private final UserRepository userRepository;
+
+    @Transactional(readOnly = true)
+    public List<ChannelDto> listChannels(Long userId) {
+        List<MessageConversation> channels = conversationRepository.findByChannelTrue();
+        return channels.stream().map(c -> toDto(c, userId)).collect(Collectors.toList());
+    }
+
+    @Transactional
+    public ChannelDto joinChannel(Long channelId, Long userId) {
+        MessageConversation channel = conversationRepository.findById(channelId)
+                .orElseThrow(() -> new IllegalArgumentException("Channel not found"));
+        User user = userRepository.findById(userId)
+                .orElseThrow(() -> new IllegalArgumentException("User not found"));
+        participantRepository.findByConversationIdAndUserId(channelId, userId)
+                .orElseGet(() -> {
+                    MessageParticipant p = new MessageParticipant();
+                    p.setConversation(channel);
+                    p.setUser(user);
+                    MessageParticipant saved = participantRepository.save(p);
+                    channel.getParticipants().add(saved);
+                    return saved;
+                });
+        return toDto(channel, userId);
+    }
+
+    private ChannelDto toDto(MessageConversation channel, Long userId) {
+        ChannelDto dto = new ChannelDto();
+        dto.setId(channel.getId());
+        dto.setName(channel.getName());
+        dto.setDescription(channel.getDescription());
+        dto.setAvatar(channel.getAvatar());
+        dto.setMemberCount(channel.getParticipants().size());
+        boolean joined = channel.getParticipants().stream()
+                .anyMatch(p -> p.getUser().getId().equals(userId));
+        dto.setJoined(joined);
+        if (joined) {
+            MessageParticipant participant = channel.getParticipants().stream()
+                    .filter(p -> p.getUser().getId().equals(userId))
+                    .findFirst().orElse(null);
+            LocalDateTime lastRead = participant.getLastReadAt() == null
+                    ? LocalDateTime.of(1970, 1, 1, 0, 0)
+                    : participant.getLastReadAt();
+            long unread = messageRepository
+                    .countByConversationIdAndCreatedAtAfterAndSenderIdNot(channel.getId(), lastRead, userId);
+            dto.setUnreadCount(unread);
+        } else {
+            dto.setUnreadCount(0);
+        }
+        return dto;
+    }
+}

backend/src/main/java/com/openisle/service/MessageService.java

@@ -82,6 +82,49 @@ public class MessageService {
         return message;
     }
 
+    @Transactional
+    public Message sendMessageToConversation(Long senderId, Long conversationId, String content) {
+        User sender = userRepository.findById(senderId)
+                .orElseThrow(() -> new IllegalArgumentException("Sender not found"));
+        MessageConversation conversation = conversationRepository.findById(conversationId)
+                .orElseThrow(() -> new IllegalArgumentException("Conversation not found"));
+
+        // Join the conversation if not already a participant (useful for channels)
+        participantRepository.findByConversationIdAndUserId(conversationId, senderId)
+                .orElseGet(() -> {
+                    MessageParticipant p = new MessageParticipant();
+                    p.setConversation(conversation);
+                    p.setUser(sender);
+                    return participantRepository.save(p);
+                });
+
+        Message message = new Message();
+        message.setConversation(conversation);
+        message.setSender(sender);
+        message.setContent(content);
+        message = messageRepository.save(message);
+
+        conversation.setLastMessage(message);
+        conversationRepository.save(conversation);
+
+        MessageDto messageDto = toDto(message);
+        String conversationDestination = "/topic/conversation/" + conversation.getId();
+        messagingTemplate.convertAndSend(conversationDestination, messageDto);
+
+        // Notify all participants except sender for updates
+        for (MessageParticipant participant : conversation.getParticipants()) {
+            if (participant.getUser().getId().equals(senderId)) continue;
+            String userDestination = "/topic/user/" + participant.getUser().getId() + "/messages";
+            messagingTemplate.convertAndSend(userDestination, messageDto);
+
+            long unreadCount = getUnreadMessageCount(participant.getUser().getId());
+            String username = participant.getUser().getUsername();
+            messagingTemplate.convertAndSendToUser(username, "/queue/unread-count", unreadCount);
+        }
+
+        return message;
+    }
+
     private MessageDto toDto(Message message) {
         MessageDto dto = new MessageDto();
         dto.setId(message.getId());
@@ -134,12 +177,18 @@ public class MessageService {
     @Transactional(readOnly = true)
     public List<ConversationDto> getConversations(Long userId) {
         List<MessageConversation> conversations = conversationRepository.findConversationsByUserIdOrderByLastMessageDesc(userId);
-        return conversations.stream().map(c -> toDto(c, userId)).collect(Collectors.toList());
+        return conversations.stream()
+                .filter(c -> !c.isChannel())
+                .map(c -> toDto(c, userId))
+                .collect(Collectors.toList());
     }
 
     private ConversationDto toDto(MessageConversation conversation, Long userId) {
         ConversationDto dto = new ConversationDto();
         dto.setId(conversation.getId());
+        dto.setChannel(conversation.isChannel());
+        dto.setName(conversation.getName());
+        dto.setAvatar(conversation.getAvatar());
         dto.setCreatedAt(conversation.getCreatedAt());
         if (conversation.getLastMessage() != null) {
             dto.setLastMessage(toDto(conversation.getLastMessage()));
@@ -189,6 +238,9 @@ public class MessageService {
 
         ConversationDetailDto detailDto = new ConversationDetailDto();
         detailDto.setId(conversation.getId());
+        detailDto.setName(conversation.getName());
+        detailDto.setChannel(conversation.isChannel());
+        detailDto.setAvatar(conversation.getAvatar());
         detailDto.setParticipants(participants);
         detailDto.setMessages(messageDtoPage);