Properly handle timezones

This should (hopefully 🤞) take care of problems saving entries with timezone
information.

Author: rolandgeider

lib/helpers/date.dart

@@ -16,11 +16,6 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-/// Returns a timezone aware DateTime object from a date and time string.
-DateTime getDateTimeFromDateAndTime(String date, String time) {
-  return DateTime.parse('$date $time');
-}
-
 /// Returns a list of [DateTime] objects from [first] to [last], inclusive.
 List<DateTime> daysInRange(DateTime first, DateTime last) {
   final dayCount = last.difference(first).inDays + 1;

lib/helpers/json.dart

@@ -62,6 +62,14 @@ String dateToUtcIso8601(DateTime dateTime) {
   return dateTime.toUtc().toIso8601String();
 }
 
+/// Converts an ISO8601 datetime string in UTC to a local DateTime object.
+///
+/// Needs to be used in conjunction with [dateToUtcIso8601] in the models to
+/// correctly handle timezones.
+DateTime utcIso8601ToLocalDate(String dateTime) {
+  return DateTime.parse(dateTime).toLocal();
+}
+
 /*
  * Converts a time to a date object.
  * Needed e.g. when the wger api only sends a time but no date information.

lib/models/body_weight/weight_entry.dart

@@ -29,7 +29,7 @@ class WeightEntry {
   @JsonKey(required: true, fromJson: stringToNum, toJson: numToString)
   late num weight = 0;
 
-  @JsonKey(required: true)
+  @JsonKey(required: true, fromJson: utcIso8601ToLocalDate, toJson: dateToUtcIso8601)
   late DateTime date;
 
   WeightEntry({this.id, weight, DateTime? date}) {

lib/models/body_weight/weight_entry.g.dart

@@ -26,7 +26,7 @@ class Image {
   @JsonKey(required: true)
   int? id;
 
-  @JsonKey(required: true, toJson: dateToYYYYMMDD)
+  @JsonKey(required: true, fromJson: utcIso8601ToLocalDate, toJson: dateToUtcIso8601)
   late DateTime date;
 
   @JsonKey(required: true, name: 'image')

lib/models/gallery/image.dart

@@ -36,7 +36,7 @@ class Log {
   @JsonKey(required: true, name: 'plan')
   int planId;
 
-  @JsonKey(required: true, toJson: dateToUtcIso8601)
+  @JsonKey(required: true, fromJson: utcIso8601ToLocalDate, toJson: dateToUtcIso8601)
   late DateTime datetime;
 
   String? comment;

lib/models/gallery/image.g.dart

@@ -41,7 +41,12 @@ class NutritionalPlan {
   @JsonKey(required: true)
   late String description;
 
-  @JsonKey(required: true, name: 'creation_date', toJson: dateToUtcIso8601)
+  @JsonKey(
+    required: true,
+    name: 'creation_date',
+    fromJson: utcIso8601ToLocalDate,
+    toJson: dateToUtcIso8601,
+  )
   late DateTime creationDate;
 
   @JsonKey(required: true, name: 'start', toJson: dateToYYYYMMDD)