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 {
  // get instance of firestore and auth
  final FirebaseFirestore _firestore = FirebaseFirestore.instance;
  final FirebaseAuth _auth = FirebaseAuth.instance;

  // get user stream
  Stream<List<Map<String, dynamic>>> getUsersStream() {
    return _firestore
        .collection(Constants.dbCollectionUsers)
        .snapshots()
        .map((snapshot) {
      return snapshot.docs.map((doc) {
        // iterate each user
        final user = doc.data();

        //return user
        return user;
      }).toList();
    });
  }

  // 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]);

    // add new message to database
    await _firestore
        .collection(Constants.dbCollectionChatRooms)
        .doc(chatRoomID)
        .collection(Constants.dbCollectionMessages)
        .add(newMessage.toMap());
  }

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

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