Support startAfter for firebase query

Author: lejard-h

crossfire/lib/src/crossfire_base.dart

@@ -46,6 +46,10 @@ abstract class FirebaseCollection {
     bool isNull,
   });
   FirebaseQuery orderBy(String field, {bool descending: false});
+  FirebaseQuery startAfter({
+    FirebaseDocument snapshot,
+    List fieldValues,
+  });
 }
 
 abstract class FirebaseQuerySnapshot {
@@ -89,6 +93,10 @@ abstract class FirebaseQuery {
   });
   FirebaseQuery orderBy(String field, {bool descending: false});
   FirebaseQuery limit(int length);
+  FirebaseQuery startAfter({
+    FirebaseDocument snapshot,
+    List fieldValues,
+  });
 }
 
 enum FireDocumentChangeType {

crossfire_flutter/lib/crossfire_flutter.dart

@@ -196,6 +196,12 @@ class FlutterFirebaseCollection implements FirebaseCollection {
     var q = collection.orderBy(field, descending: descending);
     return new FlutterFirebaseQuery(q);
   }
+
+   @override
+  FirebaseQuery startAfter({FirebaseDocument snapshot, List fieldValues}) {
+    final q = collection.startAfter(fieldValues);
+    return FlutterFirebaseQuery(q);
+  }
 }
 
 class FlutterFirebaseQuery implements FirebaseQuery {
@@ -237,6 +243,12 @@ class FlutterFirebaseQuery implements FirebaseQuery {
     var snapshot = await _ref.getDocuments();
     return new FlutterFirebaseQuerySnapshot(snapshot);
   }
+
+  @override
+  FirebaseQuery startAfter({FirebaseDocument snapshot, List fieldValues}) {
+    final q = _ref.startAfter(fieldValues);
+    return FlutterFirebaseQuery(q);
+  }
 }
 
 class FlutterFirebaseQuerySnapshot implements FirebaseQuerySnapshot {

crossfire_web/lib/crossfire_web.dart

@@ -37,13 +37,12 @@ class FirebaseWeb implements Firebase {
     if (usePersistence != null && usePersistence) {
       try {
         _store.enablePersistence();
-      } catch(e) {
+      } catch (e) {
         // Support re-initializing with a different app. Enabling persistence
         // can throw an error if it has already been enabled once on the page.
       }
     }
     _storage = fb.storage(app);
-
   }
 
   @override
@@ -180,6 +179,25 @@ class BrowserFirebaseCollection implements FirebaseCollection {
     var q = _collection.where(field, op, value);
     return new BrowserFirebaseQuery(q);
   }
+
+  @override
+  FirebaseQuery startAfter({
+    FirebaseDocument snapshot,
+    List fieldValues,
+  }) {
+    DocumentSnapshot snap;
+
+    if (snapshot != null) {
+      final doc = snapshot as BrowserDocumentSnapshot;
+      snap = doc._snapshot;
+    }
+
+    final q = _collection.startAfter(
+      snapshot: snap,
+      fieldValues: fieldValues,
+    );
+    return BrowserFirebaseQuery(q);
+  }
 }
 
 class BrowserDocumentSnapshot implements FirebaseDocument {
@@ -321,4 +339,22 @@ class BrowserFirebaseQuery extends FirebaseQuery {
     var q = _ref.where(field, op, value);
     return new BrowserFirebaseQuery(q);
   }
+
+  @override
+  FirebaseQuery startAfter({
+    FirebaseDocument snapshot,
+    List fieldValues,
+  }) {
+    DocumentSnapshot snap;
+    if (snapshot != null) {
+      final doc = snapshot as BrowserDocumentSnapshot;
+      snap = doc._snapshot;
+    }
+
+    final q = _ref.startAfter(
+      snapshot: snap,
+      fieldValues: fieldValues,
+    );
+    return BrowserFirebaseQuery(q);
+  }
 }