Added disease services

FrontEnd/lib/services/disease_service.dart

+import 'package:cloud_firestore/cloud_firestore.dart';
+
+import '../models/error_model.dart';
+
+class DiseaseService {
+  static final _leafs = FirebaseFirestore.instance.collection('leafs');
+
+  static Future<QuerySnapshot<Map<String, dynamic>>?> getLeafsById(
+      int id) async {
+    QuerySnapshot<Map<String, dynamic>>? documentSnapshot;
+    try {
+      documentSnapshot = await _leafs.where('id', isEqualTo: id).get();
+    } on FirebaseException catch (e) {
+      ErrorModel.errorMessage = e.message!;
+    } on Exception catch (e) {
+      ErrorModel.errorMessage = e.toString();
+    }
+    return documentSnapshot;
+  }
+
+  static Future<QuerySnapshot<Map<String, dynamic>>?> getDiseaseById(
+      String leafRef, int id) async {
+    QuerySnapshot<Map<String, dynamic>>? documentSnapshot;
+    try {
+      documentSnapshot = await _leafs
+          .doc(leafRef)
+          .collection("diseases")
+          .where('id', isEqualTo: id)
+          .get();
+    } on FirebaseException catch (e) {
+      ErrorModel.errorMessage = e.message!;
+    } on Exception catch (e) {
+      ErrorModel.errorMessage = e.toString();
+    }
+    return documentSnapshot;
+  }
+}