Add DateTime extension

lib/utils/date_time_extension.dart

@@ -0,0 +1,101 @@
+import 'package:flutter/material.dart';
+
+/// Provides extra functionality for formatting the time.
+extension DateTimeExtension on DateTime {
+  @Deprecated('Use [millisecondsSinceEpoch] instead.')
+  num toTimeStamp() => this.millisecondsSinceEpoch;
+
+  @deprecated
+  String toTimeString() => localizedTimeOfDay(null);
+  @deprecated
+  String toEventTimeString() => localizedTime(null);
+
+  operator <(DateTime other) {
+    return this.millisecondsSinceEpoch < other.millisecondsSinceEpoch;
+  }
+
+  operator >(DateTime other) {
+    return this.millisecondsSinceEpoch > other.millisecondsSinceEpoch;
+  }
+
+  operator >=(DateTime other) {
+    return this.millisecondsSinceEpoch >= other.millisecondsSinceEpoch;
+  }
+
+  operator <=(DateTime other) {
+    return this.millisecondsSinceEpoch <= other.millisecondsSinceEpoch;
+  }
+
+  /// Two message events can belong to the same environment. That means that they
+  /// don't need to display the time they were sent because they are close
+  /// enaugh.
+  static final minutesBetweenEnvironments = 5;
+
+  /// Checks if two DateTimes are close enough to belong to the same
+  /// environment.
+  bool sameEnvironment(DateTime prevTime) {
+    return millisecondsSinceEpoch - prevTime.millisecondsSinceEpoch <
+        1000 * 60 * minutesBetweenEnvironments;
+  }
+
+  /// Returns a simple time String.
+  /// TODO: Add localization
+  String localizedTimeOfDay(BuildContext context) {
+    return "${_z(this.hour % 12)}:${_z(this.minute)} ${this.hour > 11 ? 'pm' : 'am'}";
+  }
+
+  /// Returns [localizedTimeOfDay()] if the ChatTime is today, the name of the week
+  /// day if the ChatTime is this week and a date string else.
+  String localizedTimeShort(BuildContext context) {
+    DateTime now = DateTime.now();
+
+    bool sameYear = now.year == this.year;
+
+    bool sameDay = sameYear && now.month == this.month && now.day == this.day;
+
+    bool sameWeek = sameYear &&
+        !sameDay &&
+        now.millisecondsSinceEpoch - this.millisecondsSinceEpoch <
+            1000 * 60 * 60 * 24 * 7;
+
+    if (sameDay) {
+      return localizedTimeOfDay(context);
+    } else if (sameWeek) {
+      switch (this.weekday) {
+        case 1:
+          return "Monday";
+        case 2:
+          return "Tuesday";
+        case 3:
+          return "Wednesday";
+        case 4:
+          return "Thursday";
+        case 5:
+          return "Friday";
+        case 6:
+          return "Saturday";
+        case 7:
+          return "Sunday";
+      }
+    } else if (sameYear) {
+      return "${this.month.toString().padLeft(2, '0')}-${this.day.toString().padLeft(2, '0')}";
+    }
+    return "${this.year.toString()}-${this.month.toString().padLeft(2, '0')}-${this.day.toString().padLeft(2, '0')}";
+  }
+
+  /// If the DateTime is today, this returns [localizedTimeOfDay()], if not it also
+  /// shows the date.
+  /// TODO: Add localization
+  String localizedTime(BuildContext context) {
+    DateTime now = DateTime.now();
+
+    bool sameYear = now.year == this.year;
+
+    bool sameDay = sameYear && now.month == this.month && now.day == this.day;
+
+    if (sameDay) return localizedTimeOfDay(context);
+    return "${localizedTimeShort(context)}, ${localizedTimeOfDay(context)}";
+  }
+
+  static String _z(int i) => i < 10 ? "0${i.toString()}" : i.toString();
+}