cofounderella/lib/services/chat/chat_service.dart

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_auth/firebase_auth.dart';

import '../../constants.dart';
import '../../utils/helper.dart';
import '../../models/message.dart';

class ChatService {
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;
  final FirebaseAuth _auth = FirebaseAuth.instance;

  // send message
  Future<void> sendMessage(String receiverID, message) async {
    // get current user info
    final String currentUserID = _auth.currentUser!.uid;
    final String currentUserEmail = _auth.currentUser!.email!;
    final Timestamp timestamp = Timestamp.now();

    // create new message
    Message newMessage = Message(
      senderID: currentUserID,
      senderEmail: currentUserEmail,
      receiverID: receiverID,
      message: message,
      timestamp: timestamp,
    );

    // construct chat room ID for the two users
    String chatRoomID = getCompoundId([currentUserID, receiverID]);

    // create batch to add message and update last message details in one step
    WriteBatch batch = _firestore.batch();

    // add new message to database
    var newMessageRef = _firestore
        .collection(Constants.dbCollectionChatRooms)
        .doc(chatRoomID)
        .collection(Constants.dbCollectionMessages)
        .doc(); // doc generates a random ID for the message
    batch.set(newMessageRef, newMessage.toMap());

    // update last message details in chat room
    var chatRoomRef =
        _firestore.collection(Constants.dbCollectionChatRooms).doc(chatRoomID);

    // add to batch above
    batch.set(
        chatRoomRef,
        {
          Constants.dbFieldMessageSenderId: currentUserID,
          Constants.dbFieldMessageSenderEmail: currentUserEmail,
          Constants.dbFieldMessageTimestamp: timestamp,
        },
        SetOptions(merge: true));

    // commit batch
    await batch.commit();
  }

  /// Retrieves the last message of a chatroom.
  Future<Message> getLastMessage(String chatRoomID) async {
    String senderID = '';
    String senderEmail = '';
    String receiverID = '';
    String message = '';
    Timestamp timestamp = Timestamp.fromDate(DateTime.utc(1970, 01, 01));

    QuerySnapshot messageSnapshot = await _firestore
        .collection(Constants.dbCollectionChatRooms)
        .doc(chatRoomID)
        .collection(Constants.dbCollectionMessages)
        .orderBy(Constants.dbFieldMessageTimestamp, descending: true)
        .limit(1)
        .get();

    DocumentSnapshot lastMessageDoc = messageSnapshot.docs.first;
    if (lastMessageDoc.exists) {
      senderID = lastMessageDoc[Constants.dbFieldMessageSenderId];
      senderEmail = lastMessageDoc[Constants.dbFieldMessageSenderEmail];
      receiverID = lastMessageDoc[Constants.dbFieldMessageReceiverId];
      message = lastMessageDoc[Constants.dbFieldMessageText];
      timestamp = lastMessageDoc[Constants.dbFieldMessageTimestamp];
    }

    return Message(
      senderID: senderID,
      senderEmail: senderEmail,
      receiverID: receiverID,
      message: message,
      timestamp: timestamp,
    );
  }

  // get messages
  Stream<QuerySnapshot> getMessages(String userID, otherUserID) {
    String chatRoomID = getCompoundId([userID, otherUserID]);

    return _firestore
        .collection(Constants.dbCollectionChatRooms)
        .doc(chatRoomID)
        .collection(Constants.dbCollectionMessages)
        .orderBy(Constants.dbFieldMessageTimestamp, descending: false)
        .snapshots();
  }
}