Update the date separators to use "Today", "Yesterday" etc for messages in the past 7 days. (#4785)

* Update the date separators to use "Today", "Yesterday" etc for messages in the past 7 days.

* Fix the observation tests.

ElementX/Sources/Other/Extensions/Date.swift

@@ -34,6 +34,27 @@ extension Date {
         }
     }
     
+    /// Similar to ``formattedMinimal`` but returning "Today" instead of the time and
+    /// including the year when it the date is from a previous year (rather than over a year ago).
+    func formattedDateSeparator() -> String {
+        let calendar = Calendar.current
+        
+        if calendar.isDateInToday(self) || calendar.isDateInYesterday(self) {
+            // Simply "Today" or "Yesterday" if it was today or yesterday.
+            return DateFormatter.relative.string(from: self)
+        } else if let sixDaysAgo = calendar.date(byAdding: .day, value: -6, to: calendar.startOfDay(for: .now)),
+                  sixDaysAgo <= self {
+            // The named day if it was in the last 6 days.
+            return formatted(.dateTime.weekday(.wide))
+        } else if calendar.component(.year, from: self) == calendar.component(.year, from: .now) {
+            // The day and month if it was this year.
+            return formatted(.dateTime.weekday(.wide).day().month(.wide))
+        } else {
+            // The day, month and year if it is any older.
+            return formatted(.dateTime.weekday(.wide).day().month(.wide).year())
+        }
+    }
+    
     /// The date formatted as just the time, for use in timeline items specifically.
     func formattedTime() -> String {
         formatted(date: .omitted, time: .shortened)
@@ -44,3 +65,15 @@ extension Date {
         DateComponents(calendar: .current, year: 2007, month: 1, day: 9, hour: 9, minute: 41).date ?? .now
     }
 }
+
+private extension DateFormatter {
+    // There doesn't appear to be a way to get "Today" out of
+    // `Date.RelativeFormatStyle` so use the old way instead 😐
+    static let relative: DateFormatter = {
+        let formatter = DateFormatter()
+        formatter.doesRelativeDateFormatting = true
+        formatter.dateStyle = .long
+        formatter.timeStyle = .none
+        return formatter
+    }()
+}

ElementX/Sources/Screens/Timeline/View/TimelineItemViews/SeparatorRoomTimelineView.swift

@@ -12,7 +12,7 @@ struct SeparatorRoomTimelineView: View {
     let timelineItem: SeparatorRoomTimelineItem
     
     var body: some View {
-        Text(timelineItem.timestamp.formatted(date: .complete, time: .omitted))
+        Text(timelineItem.timestamp.formattedDateSeparator())
             .font(.compound.bodySMSemibold)
             .foregroundColor(.compound.textPrimary)
             .frame(maxWidth: .infinity)