redesigned payment page + a lot of fixes

frontend/pweb/lib/controllers/common/cooldown.dart

@@ -0,0 +1,85 @@
+import 'dart:async';
+
+
+class CooldownController {
+  CooldownController({void Function()? onTick}) : _onTick = onTick;
+
+  final void Function()? _onTick;
+  Timer? _timer;
+  DateTime? _until;
+  int _remainingSeconds = 0;
+
+  int get remainingSeconds => _remainingSeconds;
+  bool get isActive => _remainingSeconds > 0;
+  DateTime? get until => _until;
+
+  void start(Duration duration) {
+    startUntil(DateTime.now().add(duration));
+  }
+
+  void startUntil(DateTime until) {
+    _until = until;
+    _restartTimer();
+    _syncRemaining(notify: true);
+  }
+
+  void syncUntil(DateTime? until, {bool notify = true}) {
+    if (until == null) {
+      stop(notify: notify);
+      return;
+    }
+    _until = until;
+    _restartTimer();
+    _syncRemaining(notify: notify);
+  }
+
+  void stop({bool notify = false}) {
+    _timer?.cancel();
+    _timer = null;
+    _until = null;
+    final hadRemaining = _remainingSeconds != 0;
+    _remainingSeconds = 0;
+    if (notify && hadRemaining) {
+      _onTick?.call();
+    }
+  }
+
+  void dispose() {
+    _timer?.cancel();
+    _timer = null;
+  }
+
+  void _restartTimer() {
+    _timer?.cancel();
+    _timer = null;
+    if (_remaining() <= 0) return;
+
+    _timer = Timer.periodic(const Duration(seconds: 1), (_) {
+      final nextRemaining = _remaining();
+      if (nextRemaining <= 0) {
+        stop(notify: true);
+        return;
+      }
+      if (nextRemaining != _remainingSeconds) {
+        _remainingSeconds = nextRemaining;
+        _onTick?.call();
+      }
+    });
+  }
+
+  void _syncRemaining({required bool notify}) {
+    final nextRemaining = _remaining();
+    if (nextRemaining == _remainingSeconds) return;
+    _remainingSeconds = nextRemaining;
+    if (notify) {
+      _onTick?.call();
+    }
+  }
+
+  int _remaining() {
+    final until = _until;
+    if (until == null) return 0;
+    final remaining = until.difference(DateTime.now()).inSeconds;
+    return remaining < 0 ? 0 : remaining;
+  }
+}