Don't pop an error when there is no logs file (#245)

lib/screens/SiteLogsScreen.dart

@@ -5,6 +5,8 @@ import 'package:flutter/material.dart';
 import 'package:flutter_platform_widgets/flutter_platform_widgets.dart';
 import 'package:mobile_nebula/components/SimplePage.dart';
 import 'package:mobile_nebula/models/Site.dart';
+import 'package:mobile_nebula/services/logs.dart';
+import 'package:mobile_nebula/services/result.dart';
 import 'package:mobile_nebula/services/settings.dart';
 import 'package:mobile_nebula/services/share.dart';
 import 'package:mobile_nebula/services/utils.dart';
@@ -22,14 +24,14 @@ class SiteLogsScreen extends StatefulWidget {
 }
 
 class _SiteLogsScreenState extends State<SiteLogsScreen> {
-  String logs = '';
+  final ScrollController controller = ScrollController();
-  ScrollController controller = ScrollController();
+  final RefreshController refreshController = RefreshController(initialRefresh: false);
-  RefreshController refreshController = RefreshController(initialRefresh: false);
+  final LogsNotifier logsNotifier = LogsNotifier();
 
   var settings = Settings();
   @override
   void initState() {
-    loadLogs();
+    logsNotifier.loadLogs(logFile: widget.site.logFile);
     super.initState();
   }
 
@@ -49,18 +51,29 @@ class _SiteLogsScreenState extends State<SiteLogsScreen> {
       scrollable: SimpleScrollable.both,
       scrollController: controller,
       onRefresh: () async {
-        await loadLogs();
+        await logsNotifier.loadLogs(logFile: widget.site.logFile);
         refreshController.refreshCompleted();
       },
       onLoading: () async {
-        await loadLogs();
+        await logsNotifier.loadLogs(logFile: widget.site.logFile);
         refreshController.loadComplete();
       },
       refreshController: refreshController,
       child: Container(
           padding: EdgeInsets.all(5),
           constraints: logBoxConstraints(context),
-          child: SelectableText(logs.trim(), style: TextStyle(fontFamily: 'RobotoMono', fontSize: 14))),
+          child: ListenableBuilder(
+            listenable: logsNotifier,
+            builder: (context, child) => SelectableText(
+                switch (logsNotifier.logsResult) {
+                  Ok<String>(:var value) => value.trim(),
+                  Error<String>(:var error) => error is LogsNotFoundException
+                      ? error.error()
+                      : Utils.popError(context, "Error while reading logs.", error.toString()),
+                  null => "",
+                },
+                style: TextStyle(fontFamily: 'RobotoMono', fontSize: 14)),
+          )),
       bottomBar: _buildBottomBar(),
     );
   }
@@ -143,27 +156,6 @@ class _SiteLogsScreenState extends State<SiteLogsScreen> {
         material: (context, child, platform) => BottomAppBar(child: child));
   }
 
-  loadLogs() async {
-    var file = File(widget.site.logFile);
-    try {
-      final v = await file.readAsString();
-
-      setState(() {
-        logs = v;
-      });
-    } on FileSystemException {
-      Utils.popError(context, 'Error while reading logs', 'No log file was present');
-    } catch (err) {
-      Utils.popError(context, 'Error while reading logs', err.toString());
-    }
-  }
-
-  deleteLogs() async {
-    var file = File(widget.site.logFile);
-    await file.writeAsBytes([]);
-    await loadLogs();
-  }
-
   logBoxConstraints(BuildContext context) {
     if (settings.logWrap) {
       return BoxConstraints(maxWidth: MediaQuery.of(context).size.width);

lib/services/logs.dart

@@ -0,0 +1,31 @@
+import 'dart:io';
+
+import 'package:flutter/widgets.dart';
+import 'package:mobile_nebula/services/result.dart';
+
+class LogsNotFoundException implements Exception {
+  String error() => 'No logs found. Logs will be available after starting the site for the first time.';
+}
+
+class LogsNotifier extends ChangeNotifier {
+  Result<String>? logsResult;
+
+  LogsNotifier();
+
+  loadLogs({required String logFile}) async {
+    final file = File(logFile);
+    try {
+      logsResult = Result.ok(await file.readAsString());
+      notifyListeners();
+    } on FileSystemException {
+      logsResult = Result.error(LogsNotFoundException());
+      notifyListeners();
+    } on Exception catch (err) {
+      logsResult = Result.error(err);
+      notifyListeners();
+    } catch (err) {
+      logsResult = Result.error(Exception(err));
+      notifyListeners();
+    }
+  }
+}

lib/services/result.dart

@@ -0,0 +1,52 @@
+/// Utility class that simplifies handling errors.
+///
+/// Return a [Result] from a function to indicate success or failure.
+///
+/// A [Result] is either an [Ok] with a value of type [T]
+/// or an [Error] with an [Exception].
+///
+/// Use [Result.ok] to create a successful result with a value of type [T].
+/// Use [Result.error] to create an error result with an [Exception].
+///
+/// Evaluate the result using a switch statement:
+/// ```dart
+/// switch (result) {
+///   case Ok(): {
+///     print(result.value);
+///   }
+///   case Error(): {
+///     print(result.error);
+///   }
+/// }
+/// ```
+sealed class Result<T> {
+  const Result();
+
+  /// Creates a successful [Result], completed with the specified [value].
+  const factory Result.ok(T value) = Ok._;
+
+  /// Creates an error [Result], completed with the specified [error].
+  const factory Result.error(Exception error) = Error._;
+}
+
+/// A successful [Result] with a returned [value].
+final class Ok<T> extends Result<T> {
+  const Ok._(this.value);
+
+  /// The returned value of this result.
+  final T value;
+
+  @override
+  String toString() => 'Result<$T>.ok($value)';
+}
+
+/// An error [Result] with a resulting [error].
+final class Error<T> extends Result<T> {
+  const Error._(this.error);
+
+  /// The resulting error of this result.
+  final Exception error;
+
+  @override
+  String toString() => 'Result<$T>.error($error)';
+}