Initial Support

packages/fl_query/lib/query.dart

@@ -0,0 +1,108 @@
+import 'dart:async';
+
+import 'package:flutter/widgets.dart';
+
+enum QueryStatus {
+  failed,
+  succeed,
+  pending,
+  refetching;
+}
+
+typedef QueryTaskFunction<T> = FutureOr<T> Function(String);
+
+typedef QueryListener<T> = FutureOr<void> Function(T);
+
+typedef ListenerUnsubscriber = void Function();
+
+class Query<T> extends ChangeNotifier {
+  // all params
+  final String queryKey;
+  QueryTaskFunction<T> task;
+  final int retries;
+  final Duration retryDelay;
+
+  // all properties
+  T? data;
+  dynamic error;
+  QueryStatus status;
+  int retryAttempts = 0;
+  late DateTime updatedAt;
+  int refetchCount = 0;
+
+  @protected
+  bool fetched = false;
+
+  final QueryListener<T>? _onData;
+  final QueryListener<dynamic>? _onError;
+
+  Query({
+    required this.queryKey,
+    required this.task,
+    this.retries = 3,
+    this.retryDelay = const Duration(milliseconds: 200),
+    T? initialData,
+    QueryListener<T>? onData,
+    QueryListener<dynamic>? onError,
+  })  : status = QueryStatus.pending,
+        data = initialData,
+        _onData = onData,
+        _onError = onError;
+
+  // all getters & setters
+  bool get hasData => data != null && error == null;
+  bool get hasError =>
+      status == QueryStatus.failed && error != null && data == null;
+  bool get isLoading =>
+      status == QueryStatus.pending && data == null && error == null;
+  bool get isRefetching =>
+      status == QueryStatus.refetching && data == null && error == null;
+  bool get isSucceeded => status == QueryStatus.succeed && data != null;
+
+  // all methods
+  Future<void> _execute({bool isFetch = true}) async {
+    try {
+      retryAttempts = 0;
+      status = isFetch ? QueryStatus.pending : QueryStatus.refetching;
+      data = await task(queryKey);
+      updatedAt = DateTime.now();
+      status = QueryStatus.succeed;
+      _onData?.call(data!);
+      notifyListeners();
+    } catch (e) {
+      status = QueryStatus.failed;
+      error = e;
+      _onError?.call(e);
+      notifyListeners();
+      // retrying for retry count if failed for the first time
+      while (retryAttempts <= retries) {
+        await Future.delayed(retryDelay);
+        try {
+          data = await task(queryKey);
+          status = QueryStatus.succeed;
+          _onData?.call(data!);
+          notifyListeners();
+          break;
+        } catch (e) {
+          status = QueryStatus.failed;
+          error = e;
+          retryAttempts++;
+          _onError?.call(e);
+          notifyListeners();
+        }
+      }
+    }
+  }
+
+  Future<T?> fetch() async {
+    return _execute().then((_) {
+      fetched = true;
+      return data;
+    });
+  }
+
+  Future<T?> refetch() {
+    refetchCount++;
+    return _execute(isFetch: false).then((_) => data);
+  }
+}