Internationalize time ago since string

Switches to using standard date component formatting abbreviations and
enables it to be localized to non-English locales

Closes: #194
Changelog-Changed: Internationalize relative dates

damus/Util/TimeAgo.swift

@@ -11,36 +11,45 @@ public func time_ago_since(_ date: Date) -> String {
 
     let calendar = Calendar.current
     let now = Date()
-    let unitFlags: NSCalendar.Unit = [.second, .minute, .hour, .day, .weekOfYear, .month, .year]
+    let unitFlags: NSCalendar.Unit = [.second, .minute, .hour, .day, .weekOfMonth, .month, .year]
+
     let components = (calendar as NSCalendar).components(unitFlags, from: date, to: now, options: [])
 
+    let formatter = DateComponentsFormatter()
+    formatter.unitsStyle = .abbreviated
+    formatter.maximumUnitCount = 1
+    formatter.allowedUnits = unitFlags
+
+    // Manually format date component from only the most significant time unit because
+    // DateComponentsFormatter rounds up by default.
+
     if let year = components.year, year >= 1 {
-        return "\(year)yr"
+        return formatter.string(from: DateComponents(calendar: calendar, year: year))!
     }
 
     if let month = components.month, month >= 1 {
-        return "\(month)mth"
+        return formatter.string(from: DateComponents(calendar: calendar, month: month))!
     }
 
-    if let week = components.weekOfYear, week >= 1 {
-        return "\(week)wk"
+    if let week = components.weekOfMonth, week >= 1 {
+        return formatter.string(from: DateComponents(calendar: calendar, weekOfMonth: week))!
     }
 
     if let day = components.day, day >= 1 {
-        return "\(day)d"
+        return formatter.string(from: DateComponents(calendar: calendar, day: day))!
     }
 
     if let hour = components.hour, hour >= 1 {
-        return "\(hour)h"
+        return formatter.string(from: DateComponents(calendar: calendar, hour: hour))!
     }
 
     if let minute = components.minute, minute >= 1 {
-        return "\(minute)m"
+        return formatter.string(from: DateComponents(calendar: calendar, minute: minute))!
     }
 
     if let second = components.second, second >= 3 {
-        return "\(second)s"
+        return formatter.string(from: DateComponents(calendar: calendar, second: second))!
     }
 
-    return "now"
+    return NSLocalizedString("now", comment: "String indicating that a given timestamp just occurred")
 }