Setting up basic API Structure

ac_web/lib/Api/ApiException.dart

@@ -0,0 +1,46 @@
+/// Base class for every error the Rest API layer can produce.
+sealed class ApiException implements Exception {
+  const ApiException(this.message, {this.uri});
+
+  final String message;
+  final Uri? uri;
+
+  @override
+  String toString() => '$runtimeType: $message${uri != null ? ' ($uri)' : ''}';
+}
+
+/// The server answered with a non success status code.
+class ApiHttpException extends ApiException {
+  const ApiHttpException({
+    required this.statusCode,
+    required String message,
+    this.body,
+    super.uri,
+  }) : super(message);
+
+  final int statusCode;
+  final String? body;
+
+  bool get isClientError => statusCode >= 400 && statusCode < 500;
+  bool get isServerError => statusCode >= 500;
+
+  @override
+  String toString() => 'ApiHttpException($statusCode): $message${uri != null ? ' ($uri)' : ''}';
+}
+
+/// The server could not be reached at all (no route, refused, offline, ...).
+class ApiNetworkException extends ApiException {
+  const ApiNetworkException(super.message, {super.uri});
+}
+
+/// The request ran longer than the configured timeout.
+class ApiTimeoutException extends ApiException {
+  const ApiTimeoutException(super.message, {super.uri});
+}
+
+/// The response body could not be parsed into the expected shape.
+class ApiParsingException extends ApiException {
+  const ApiParsingException(super.message, {super.uri, this.body});
+
+  final String? body;
+}