Introduced auto refresh for API Data

ac_web/lib/Widgets/AgentAvailabilityColumn.dart

@@ -3,6 +3,7 @@ import 'package:ac_web/Api/Dtos/AgentDto.dart';
 import 'package:ac_web/Pages/AgentDetails.dart';
 import 'package:ac_web/Widgets/AgentStatusIndicator.dart';
 import 'package:ac_web/Widgets/AgentTypeIcons.dart';
+import 'package:ac_web/Widgets/AutoRefreshState.dart';
 import 'package:flutter/material.dart';
 
 /// Fetches all agents from the AgentsController and lists them with a colored
@@ -14,7 +15,8 @@ class AgentAvailabilityColumn extends StatefulWidget{
   State<AgentAvailabilityColumn> createState() => _AgentAvailabilityColumnState();
 }
 
-class _AgentAvailabilityColumnState extends State<AgentAvailabilityColumn>{
+class _AgentAvailabilityColumnState extends State<AgentAvailabilityColumn>
+    with AutoRefreshState<AgentAvailabilityColumn> {
 
   late Future<List<AgentDto>> mAgentsFuture;
 
@@ -24,23 +26,44 @@ class _AgentAvailabilityColumnState extends State<AgentAvailabilityColumn>{
     mAgentsFuture = AcApi.instance.agents.getAgents();
   }
 
+  /// Reload triggered by the user. Shows the loading indicator again because
+  /// the user asked for the request and should see that it is running.
   void ReloadAgents(){
     setState(() {
       mAgentsFuture = AcApi.instance.agents.getAgents();
     });
   }
 
+  /// Automatic reload. The agents that are already on screen stay visible
+  /// while the request runs, the future is only replaced once it succeeded.
+  @override
+  Future<void> RefreshData() async {
+
+    final List<AgentDto> agents = await AcApi.instance.agents.getAgents();
+
+    if (!mounted) {
+      return;
+    }
+
+    setState(() {
+      mAgentsFuture = Future<List<AgentDto>>.value(agents);
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return FutureBuilder<List<AgentDto>>(
       future: mAgentsFuture,
       builder: (context, snapshot) {
 
-        if (snapshot.connectionState != ConnectionState.done) {
+        // Not `connectionState`: a refresh puts the builder back into the
+        // waiting state although the previous agents are still available, and
+        // those should stay on screen instead of flashing a spinner.
+        if (!snapshot.hasData && !snapshot.hasError) {
           return const Center(child: CircularProgressIndicator());
         }
 
-        if (snapshot.hasError) {
+        if (snapshot.hasError && !snapshot.hasData) {
           return Center(child: Text('Could not load agents: ${snapshot.error}'));
         }
 

ac_web/lib/Widgets/AutoRefreshState.dart

@@ -0,0 +1,68 @@
+import 'dart:async';
+
+import 'package:flutter/material.dart';
+
+/// Keeps the data of a widget up to date by reloading it every
+/// [refreshInterval].
+///
+/// Mix this into the [State] of every widget that shows data of the backend and
+/// implement [RefreshData]. The mixin only owns the timer, fetching the data and
+/// putting it on screen stays in the widget itself.
+///
+/// The backend has no push channel, so the only way to notice new agents,
+/// tasks or reports is polling. The interval is therefore a compromise between
+/// fresh data and load on the api.
+///
+/// A refresh happens quietly: implementations are expected to keep the data
+/// that is already on screen while the request runs, so that the user neither
+/// sees a spinner nor loses the scroll position every half minute. Failures of
+/// a refresh are swallowed on purpose - the data on screen simply stays as it
+/// is and the next tick tries again.
+mixin AutoRefreshState<TWidget extends StatefulWidget> on State<TWidget> {
+
+  /// Interval in which the api data of the whole app is refreshed.
+  static const Duration refreshInterval = Duration(seconds: 30);
+
+  Timer? _refreshTimer;
+
+  /// True while a refresh triggered by the timer is running. A slow api must
+  /// not pile up requests.
+  bool mIsAutoRefreshing = false;
+
+  @override
+  void initState() {
+    super.initState();
+    _refreshTimer = Timer.periodic(refreshInterval, (_) => _onTick());
+  }
+
+  @override
+  void dispose() {
+    _refreshTimer?.cancel();
+    _refreshTimer = null;
+    super.dispose();
+  }
+
+  /// Fetches the data of this widget again. Called every [refreshInterval] as
+  /// long as the widget is mounted.
+  ///
+  /// Implementations may let api errors escape, [_onTick] catches them.
+  Future<void> RefreshData();
+
+  Future<void> _onTick() async {
+
+    if (mIsAutoRefreshing || !mounted) {
+      return;
+    }
+
+    mIsAutoRefreshing = true;
+
+    try {
+      await RefreshData();
+    } catch (error) {
+      // An automatic refresh must never replace data that is already on screen
+      // with an error message, so a failed tick is ignored.
+    } finally {
+      mIsAutoRefreshing = false;
+    }
+  }
+}

ac_web/lib/Widgets/LatestReportColumn.dart

@@ -2,6 +2,7 @@ import 'package:ac_web/Api/AcApi.dart';
 import 'package:ac_web/Api/Dtos/EReportType.dart';
 import 'package:ac_web/Api/Dtos/ReportDto.dart';
 import 'package:ac_web/Pages/ReportDetails.dart';
+import 'package:ac_web/Widgets/AutoRefreshState.dart';
 import 'package:ac_web/Widgets/LatestReportEntry.dart';
 import 'package:ac_web/Widgets/LatestReportHeader.dart';
 import 'package:ac_web/Widgets/ReportTypeIcons.dart';
@@ -20,7 +21,8 @@ class LatestReportColumn extends StatefulWidget{
   State<LatestReportColumn> createState() => _LatestReportColumnState();
 }
 
-class _LatestReportColumnState extends State<LatestReportColumn>{
+class _LatestReportColumnState extends State<LatestReportColumn>
+    with AutoRefreshState<LatestReportColumn> {
 
   late Future<List<ReportDto>> mReportsFuture;
 
@@ -30,17 +32,36 @@ class _LatestReportColumnState extends State<LatestReportColumn>{
     mReportsFuture = AcApi.instance.reports.getReports();
   }
 
+  /// Automatic reload. The reports that are already on screen stay visible
+  /// while the request runs, the future is only replaced once it succeeded.
+  @override
+  Future<void> RefreshData() async {
+
+    final List<ReportDto> reports = await AcApi.instance.reports.getReports();
+
+    if (!mounted) {
+      return;
+    }
+
+    setState(() {
+      mReportsFuture = Future<List<ReportDto>>.value(reports);
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return FutureBuilder<List<ReportDto>>(
       future: mReportsFuture,
       builder: (context, snapshot) {
 
-        if (snapshot.connectionState != ConnectionState.done) {
+        // Not `connectionState`: a refresh puts the builder back into the
+        // waiting state although the previous reports are still available, and
+        // those should stay on screen instead of flashing a spinner.
+        if (!snapshot.hasData && !snapshot.hasError) {
           return const Center(child: CircularProgressIndicator());
         }
 
-        if (snapshot.hasError) {
+        if (snapshot.hasError && !snapshot.hasData) {
           return Center(child: Text('Could not load reports: ${snapshot.error}'));
         }