Format date breaks to spec

// FREEBIE

Signal/src/ViewControllers/ConversationView/Cells/OWSMessageCell.m

@@ -253,26 +253,9 @@ NS_ASSUME_NONNULL_BEGIN
 {
     OWSAssert(self.conversationStyle);
 
-    static NSDateFormatter *dateHeaderDateFormatter = nil;
-    static NSDateFormatter *dateHeaderTimeFormatter = nil;
-    static dispatch_once_t onceToken;
-    dispatch_once(&onceToken, ^{
-        dateHeaderDateFormatter = [NSDateFormatter new];
-        [dateHeaderDateFormatter setLocale:[NSLocale currentLocale]];
-        [dateHeaderDateFormatter setDoesRelativeDateFormatting:YES];
-        [dateHeaderDateFormatter setDateStyle:NSDateFormatterMediumStyle];
-        [dateHeaderDateFormatter setTimeStyle:NSDateFormatterNoStyle];
-        
-        dateHeaderTimeFormatter = [NSDateFormatter new];
-        [dateHeaderTimeFormatter setLocale:[NSLocale currentLocale]];
-        [dateHeaderTimeFormatter setDoesRelativeDateFormatting:YES];
-        [dateHeaderTimeFormatter setDateStyle:NSDateFormatterNoStyle];
-        [dateHeaderTimeFormatter setTimeStyle:NSDateFormatterShortStyle];
-    });
-
     if (self.viewItem.shouldShowDate) {
         NSDate *date = self.viewItem.interaction.dateForSorting;
-        NSString *dateString = [dateHeaderDateFormatter stringFromDate:date];
+        NSString *dateString = [DateUtil formatDateForConversationDateBreaks:date];
 
         self.dateHeaderLabel.font = self.dateHeaderFont;
         self.dateHeaderLabel.textColor = UIColor.lightGrayColor;

Signal/src/util/DateUtil.h

@@ -34,6 +34,8 @@ NS_ASSUME_NONNULL_BEGIN
 + (NSString *)exemplaryNowTimeFormat;
 + (NSString *)exemplaryMinutesTimeFormat;
 
++ (NSString *)formatDateForConversationDateBreaks:(NSDate *)date;
+
 + (BOOL)isSameDayWithTimestamp:(uint64_t)timestamp1 timestamp:(uint64_t)timestamp2;
 + (BOOL)isSameDayWithDate:(NSDate *)date1 date:(NSDate *)date2;
 

Signal/src/util/DateUtil.m

@@ -25,6 +25,64 @@ static NSString *const DATE_FORMAT_WEEKDAY = @"EEEE";
     return formatter;
 }
 
++ (NSDateFormatter *)dateBreakRelativeDateFormatter
+{
+    static NSDateFormatter *formatter;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        formatter = [NSDateFormatter new];
+        formatter.locale = [NSLocale currentLocale];
+        formatter.dateStyle = NSDateFormatterShortStyle;
+        formatter.timeStyle = NSDateFormatterNoStyle;
+        formatter.doesRelativeDateFormatting = YES;
+    });
+
+    return formatter;
+}
+
++ (NSDateFormatter *)dateBreakThisWeekDateFormatter
+{
+    static NSDateFormatter *formatter;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        formatter = [NSDateFormatter new];
+        formatter.locale = [NSLocale currentLocale];
+        // "Monday", "Tuesday", etc.
+        formatter.dateFormat = @"EEEE";
+    });
+
+    return formatter;
+}
+
++ (NSDateFormatter *)dateBreakThisYearDateFormatter
+{
+    static NSDateFormatter *formatter;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        formatter = [NSDateFormatter new];
+        formatter.locale = [NSLocale currentLocale];
+        // Tue, Jun 6
+        formatter.dateFormat = @"EE, MMM d";
+    });
+
+    return formatter;
+}
+
++ (NSDateFormatter *)dateBreakOldDateFormatter
+{
+    static NSDateFormatter *formatter;
+    static dispatch_once_t onceToken;
+    dispatch_once(&onceToken, ^{
+        formatter = [NSDateFormatter new];
+        formatter.locale = [NSLocale currentLocale];
+        formatter.dateStyle = NSDateFormatterMediumStyle;
+        formatter.timeStyle = NSDateFormatterNoStyle;
+        formatter.doesRelativeDateFormatting = YES;
+    });
+
+    return formatter;
+}
+
 + (NSDateFormatter *)weekdayFormatter {
     static NSDateFormatter *formatter;
     static dispatch_once_t onceToken;
@@ -83,6 +141,17 @@ static NSString *const DATE_FORMAT_WEEKDAY = @"EEEE";
     return dayDifference > 0;
 }
 
++ (BOOL)dateIsOlderThanYesterday:(NSDate *)date
+{
+    return [self dateIsOlderThanYesterday:date now:[NSDate date]];
+}
+
++ (BOOL)dateIsOlderThanYesterday:(NSDate *)date now:(NSDate *)now
+{
+    NSInteger dayDifference = [self daysFromFirstDate:date toSecondDate:now];
+    return dayDifference > 1;
+}
+
 + (BOOL)dateIsOlderThanOneWeek:(NSDate *)date
 {
     return [self dateIsOlderThanOneWeek:date now:[NSDate date]];
@@ -206,6 +275,25 @@ static NSString *const DATE_FORMAT_WEEKDAY = @"EEEE";
     return dateTimeString.localizedUppercaseString;
 }
 
++ (NSString *)formatDateForConversationDateBreaks:(NSDate *)date
+{
+    OWSAssert(date);
+
+    if (![self dateIsThisYear:date]) {
+        // last year formatter: Nov 11, 2017
+        return [self.dateBreakOldDateFormatter stringFromDate:date];
+    } else if ([self dateIsOlderThanOneWeek:date]) {
+        // this year formatter: Tue, Jun 23
+        return [self.dateBreakThisYearDateFormatter stringFromDate:date];
+    } else if ([self dateIsOlderThanYesterday:date]) {
+        // day of week formatter: Thursday
+        return [self.dateBreakThisWeekDateFormatter stringFromDate:date];
+    } else {
+        // relative format: Today / Yesterday
+        return [self.dateBreakRelativeDateFormatter stringFromDate:date];
+    }
+}
+
 + (NSString *)formatTimestampAsTime:(uint64_t)timestamp
 {
     return [self formatDateAsTime:[NSDate ows_dateWithMillisecondsSince1970:timestamp]];