weightValues.m

- (NSArray <NSDictionary <NSString *, NSNumber *>*>*)weightValues:(int)numberOfValues 
fromData:(NSArray <NSDictionary <NSString *, NSNumber *>*>*)healthKitData 
usingDates:(NSArray <NSDate *>*)dates {
    
    // Make a dictionary with a date string key
    // (e.g. "2017-01-04") and a value of zero for each date
    NSMutableDictionary *datesAndValues = [[NSMutableDictionary alloc] initWithCapacity:dates.count];
    // Make an array of date strings to use when looping and comparing dates
    NSMutableArray *dateStrings = [[NSMutableArray alloc] initWithCapacity:dates.count];
    
    for (NSDate *date in dates) {
        NSString *key = [BCDateHelper stringFromDate:date withFormat:ISO_DATE];
        NSNumber *value = @0;
        [datesAndValues setObject:value forKey:key];
        [dateStrings addObject:key];
    }
    
    // This is the value we'll update each time we find a real weight
    // And we'll use this to set real weight values for future dates that don't have a weight value
    NSNumber *lastWeight = 0;

    // Use string dates to compare to those returned in healthkit data
    // Any healthkit data dictionaries with a date string matching one we're looping on
    // gets its datesAndValues value updated to the real healthkit value
    for (NSString *dateString in dateStrings) {
        for (NSDictionary *dict in healthKitData) {
            if ([[dict valueForKey:@"date"] isEqualToString:dateString]) {
                [datesAndValues setValue:[dict valueForKey:@"value"] forKey:dateString];
                // Set lastWeight to this real healthkit value
                // to be used for future dates with no weight values
                lastWeight = [dict valueForKey:@"value"];
            
                // If there's no real healthkit value for this date,
                // use lastWeight if it's not zero
            } else if (lastWeight != 0) {
                [datesAndValues setValue:lastWeight forKey:dateString];
            }
        }
    }
    
    // Return only as many date and value dictionaries as requested
    // in the method parameters
    // The index range starts at the number of total dictionaries we have to return,
    // minus how many are requested
    // (e.g. 30 total, 4 requested, would be a starting index of 26)
    // The index range ends with one less than the number of possible dictionaries to return
    // because indexes start at zero
    // (e.g. 30 total, minus one = 29, since the indexes for 30 objects are 0-29)
    // So this range would include objects at indexes 26, 27, 28, and 29,
    // returning 4 values as requested
    NSIndexSet *indexSet = [NSIndexSet indexSetWithIndexesInRange:NSMakeRange(dates.count - numberOfValues, dates.count - 1)];
    NSMutableArray *returnDictionaries = [[NSMutableArray alloc] initWithCapacity:indexSet.count];
    // Reverse dates so we can work from back to front (most recent to least recent dates)
    NSArray *reversedDates = [[dateStrings reverseObjectEnumerator] allObjects];
    for (int i = 0; i < indexSet.count; i++) {
        NSString *dateString = reversedDates[i];
        if ([[datesAndValues valueForKey:dateString] isEqual:@0]) {
            // don't include zero values
            continue;
        }
        NSDictionary *jsonDict = [self makeJSONAttributeDict:@"weight" 
        withData:@{dateString: [datesAndValues valueForKey:dateString]}];
        [returnDictionaries addObject:jsonDict];
    }
    
    return [returnDictionaries copy];
}