feat: add more methods to the timeline interface

packages/flutter_timeline_firebase/lib/src/service/firebase_timeline_service.dart

@@ -122,6 +122,50 @@ class FirebaseTimelineService with ChangeNotifier implements TimelineService {
     return posts;
   }
 
+  @override
+  Future<List<TimelinePost>> fetchPostsPaginated(
+    String? category,
+    int limit,
+  ) async {
+    // only take posts that are in our category
+    var oldestPost = _posts
+        .where(
+          (element) => category == null || element.category == category,
+        )
+        .fold(
+          _posts.first,
+          (previousValue, element) =>
+              (previousValue.createdAt.isBefore(element.createdAt))
+                  ? previousValue
+                  : element,
+        );
+    var snapshot = (category != null)
+        ? await _db
+            .collection(_options.timelineCollectionName)
+            .where('category', isEqualTo: category)
+            .orderBy('created_at', descending: true)
+            .startAfter([oldestPost])
+            .limit(limit)
+            .get()
+        : await _db
+            .collection(_options.timelineCollectionName)
+            .orderBy('created_at', descending: true)
+            .startAfter([oldestPost.createdAt])
+            .limit(limit)
+            .get();
+    // add the new posts to the list
+    var posts = <TimelinePost>[];
+    for (var doc in snapshot.docs) {
+      var data = doc.data();
+      var user = await _userService.getUser(data['creator_id']);
+      var post = TimelinePost.fromJson(doc.id, data).copyWith(creator: user);
+      posts.add(post);
+    }
+    _posts = [..._posts, ...posts];
+    notifyListeners();
+    return posts;
+  }
+
   @override
   Future<TimelinePost> fetchPost(TimelinePost post) async {
     var doc = await _db
@@ -139,6 +183,43 @@ class FirebaseTimelineService with ChangeNotifier implements TimelineService {
     return updatedPost;
   }
 
+  @override
+  Future<List<TimelinePost>> refreshPosts(String? category) async {
+    // fetch all posts between now and the newest posts we have
+    var newestPostWeHave = _posts
+        .where(
+          (element) => category == null || element.category == category,
+        )
+        .fold(
+          _posts.first,
+          (previousValue, element) =>
+              (previousValue.createdAt.isAfter(element.createdAt))
+                  ? previousValue
+                  : element,
+        );
+    var snapshot = (category != null)
+        ? await _db
+            .collection(_options.timelineCollectionName)
+            .where('category', isEqualTo: category)
+            .orderBy('created_at', descending: true)
+            .endBefore([newestPostWeHave.createdAt]).get()
+        : await _db
+            .collection(_options.timelineCollectionName)
+            .orderBy('created_at', descending: true)
+            .endBefore([newestPostWeHave.createdAt]).get();
+    // add the new posts to the list
+    var posts = <TimelinePost>[];
+    for (var doc in snapshot.docs) {
+      var data = doc.data();
+      var user = await _userService.getUser(data['creator_id']);
+      var post = TimelinePost.fromJson(doc.id, data).copyWith(creator: user);
+      posts.add(post);
+    }
+    _posts = [...posts, ..._posts];
+    notifyListeners();
+    return posts;
+  }
+
   @override
   TimelinePost? getPost(String postId) =>
       (_posts.any((element) => element.id == postId))

packages/flutter_timeline_interface/lib/src/services/timeline_service.dart

@@ -14,8 +14,10 @@ abstract class TimelineService with ChangeNotifier {
   Future<TimelinePost> createPost(TimelinePost post);
   Future<List<TimelinePost>> fetchPosts(String? category);
   Future<TimelinePost> fetchPost(TimelinePost post);
+  Future<List<TimelinePost>> fetchPostsPaginated(String? category, int limit);
   TimelinePost? getPost(String postId);
   List<TimelinePost> getPosts(String? category);
+  Future<List<TimelinePost>> refreshPosts(String? category);
   Future<TimelinePost> fetchPostDetails(TimelinePost post);
   Future<TimelinePost> reactToPost(
     TimelinePost post,