refactor: share low-risk UI and tracker helpers

lib/services/trackers/anilist/anilist_session.dart

@@ -1,6 +1,5 @@
-import 'dart:convert';
-
 import '../oauth_proxy_client.dart';
+import '../tracker_session_utils.dart';
 
 /// Immutable AniList OAuth session.
 ///
@@ -14,7 +13,7 @@ class AnilistSession {
 
   const AnilistSession({required this.accessToken, required this.expiresAt, required this.createdAt, this.username});
 
-  bool get isExpired => DateTime.now().millisecondsSinceEpoch ~/ 1000 >= expiresAt;
+  bool get isExpired => isTrackerTokenExpired(expiresAt);
 
   AnilistSession copyWith({String? accessToken, int? expiresAt, String? username, int? createdAt}) {
     return AnilistSession(
@@ -43,11 +42,11 @@ class AnilistSession {
   /// and have no refresh; when the proxy doesn't echo an explicit expiry we
   /// default to the documented year.
   factory AnilistSession.fromProxyResult(OAuthProxyResult r) {
-    final createdAt = DateTime.now().millisecondsSinceEpoch ~/ 1000;
+    final createdAt = trackerSessionNowEpochSeconds();
     final expiresIn = r.expiresIn ?? 365 * 24 * 60 * 60;
     return AnilistSession(accessToken: r.accessToken, expiresAt: createdAt + expiresIn, createdAt: createdAt);
   }
 
-  String encode() => json.encode(toJson());
-  static AnilistSession decode(String raw) => AnilistSession.fromJson(json.decode(raw) as Map<String, dynamic>);
+  String encode() => encodeTrackerSessionJson(toJson());
+  static AnilistSession decode(String raw) => decodeTrackerSessionJson(raw, AnilistSession.fromJson);
 }

lib/services/trackers/mal/mal_session.dart

@@ -1,6 +1,5 @@
-import 'dart:convert';
-
 import '../oauth_proxy_client.dart';
+import '../tracker_session_utils.dart';
 
 /// Immutable MyAnimeList OAuth session.
 ///
@@ -21,8 +20,8 @@ class MalSession {
     this.username,
   });
 
-  bool get isExpired => DateTime.now().millisecondsSinceEpoch ~/ 1000 >= expiresAt;
-  bool get needsRefresh => DateTime.now().millisecondsSinceEpoch ~/ 1000 >= expiresAt - 300;
+  bool get isExpired => isTrackerTokenExpired(expiresAt);
+  bool get needsRefresh => trackerTokenNeedsRefresh(expiresAt);
 
   MalSession copyWith({String? accessToken, String? refreshToken, int? expiresAt, String? username, int? createdAt}) {
     return MalSession(
@@ -52,7 +51,7 @@ class MalSession {
 
   /// Build a session from MAL's `/oauth2/token` response.
   factory MalSession.fromTokenResponse(Map<String, dynamic> json) {
-    final createdAt = DateTime.now().millisecondsSinceEpoch ~/ 1000;
+    final createdAt = trackerSessionNowEpochSeconds();
     final expiresIn = (json['expires_in'] as num).toInt();
     return MalSession(
       accessToken: json['access_token'] as String,
@@ -65,7 +64,7 @@ class MalSession {
   /// Build a session from an OAuth-proxy result. MAL's refresh_token is
   /// required for the 31-day refresh loop.
   factory MalSession.fromProxyResult(OAuthProxyResult r) {
-    final createdAt = DateTime.now().millisecondsSinceEpoch ~/ 1000;
+    final createdAt = trackerSessionNowEpochSeconds();
     final expiresIn = r.expiresIn ?? 31 * 24 * 60 * 60;
     return MalSession(
       accessToken: r.accessToken,
@@ -75,6 +74,6 @@ class MalSession {
     );
   }
 
-  String encode() => json.encode(toJson());
-  static MalSession decode(String raw) => MalSession.fromJson(json.decode(raw) as Map<String, dynamic>);
+  String encode() => encodeTrackerSessionJson(toJson());
+  static MalSession decode(String raw) => decodeTrackerSessionJson(raw, MalSession.fromJson);
 }

lib/services/trackers/simkl/simkl_session.dart

@@ -1,4 +1,4 @@
-import 'dart:convert';
+import '../tracker_session_utils.dart';
 
 /// Immutable Simkl OAuth session.
 ///
@@ -27,11 +27,9 @@ class SimklSession {
 
   /// Build a session from Simkl's device-code `/oauth/pin/<code>` response.
   /// Simkl doesn't expose a creation timestamp so we stamp "now".
-  factory SimklSession.fromTokenResponse(Map<String, dynamic> json) => SimklSession(
-    accessToken: json['access_token'] as String,
-    createdAt: DateTime.now().millisecondsSinceEpoch ~/ 1000,
-  );
+  factory SimklSession.fromTokenResponse(Map<String, dynamic> json) =>
+      SimklSession(accessToken: json['access_token'] as String, createdAt: trackerSessionNowEpochSeconds());
 
-  String encode() => json.encode(toJson());
-  static SimklSession decode(String raw) => SimklSession.fromJson(json.decode(raw) as Map<String, dynamic>);
+  String encode() => encodeTrackerSessionJson(toJson());
+  static SimklSession decode(String raw) => decodeTrackerSessionJson(raw, SimklSession.fromJson);
 }

lib/services/trackers/tracker_session_utils.dart

@@ -0,0 +1,16 @@
+import 'dart:convert' as convert;
+
+/// Current epoch time in seconds, matching tracker OAuth expiry fields.
+int trackerSessionNowEpochSeconds() => DateTime.now().millisecondsSinceEpoch ~/ 1000;
+
+bool isTrackerTokenExpired(int expiresAt, {int? nowSeconds}) =>
+    (nowSeconds ?? trackerSessionNowEpochSeconds()) >= expiresAt;
+
+bool trackerTokenNeedsRefresh(int expiresAt, {int refreshWindowSeconds = 300, int? nowSeconds}) =>
+    (nowSeconds ?? trackerSessionNowEpochSeconds()) >= expiresAt - refreshWindowSeconds;
+
+String encodeTrackerSessionJson(Map<String, dynamic> value) => convert.json.encode(value);
+
+T decodeTrackerSessionJson<T>(String raw, T Function(Map<String, dynamic> json) fromJson) {
+  return fromJson(convert.json.decode(raw) as Map<String, dynamic>);
+}