DSShortNumberFormatter.m

#import "DSShortNumberFormatter.h"

@implementation DSShortNumberFormatter

- (instancetype)init {
    self = [super init];
    if (self) {
        NSURL *pattern_plist_url = [NSBundle.mainBundle URLForResource:@"patterns" withExtension:@"plist"];
        pattern_dict = [[NSDictionary alloc] initWithContentsOfURL:pattern_plist_url];
    }
    return self;
}

- (void)dealloc {
    [pattern_dict release];
    [super dealloc];
}

- (NSArray<NSDictionary<NSString *, NSString *> *> *)patternsForLocale:(NSLocale *)locale {
    NSString *identifier = locale.localeIdentifier;
    if (pattern_dict[identifier])
        return pattern_dict[identifier];
    
    NSArray<NSString *> *components = [identifier componentsSeparatedByString:@"_"];
    if (components.firstObject && pattern_dict[components.firstObject])
        return pattern_dict[components.firstObject];
    
    return pattern_dict[@"root"];
}

- (NSString *)stringFromNumber:(NSNumber *)number {
    if (self.numberStyle == NSNumberFormatterPercentStyle ||
        self.numberStyle == NSNumberFormatterScientificStyle)
        return [super stringFromNumber:number];
    
    double num_val = number.doubleValue;
    NSArray<NSDictionary<NSString *, NSString *> *> *patterns = [self patternsForLocale:self.locale];
    
    NSString *orig_positive_format = self.positiveFormat;
    NSString *orig_negative_format = self.negativeFormat;
        
    for (NSDictionary<NSString *, NSString *> *patternInfo in patterns) {
        NSString *pattern = patternInfo[@"pattern"];
        NSString *count = patternInfo[@"count"];
        NSString *type = patternInfo[@"type"];
        
        /* I don't think non-other patterns are different
         * for the short patterns. If this ever supports
         * the long pattern it will be necessary to
         * distinguish "one", "two", "few", and "many"
         */
        if (![count isEqualToString:@"other"])
            continue;
        
        if (fabs(num_val) >= [type doubleValue]) {
            NSInteger type_zeroes = type.length - 1;
            NSInteger pattern_zeroes = 0;
            NSInteger first_zero = -1;
            for (int i=0; i<pattern.length; i++) {
                if ([pattern characterAtIndex:i] == '0') {
                    if (first_zero == -1)
                        first_zero = i;
                    pattern_zeroes++;
                }
            }
            self.multiplier = @(__exp10(-(type_zeroes - pattern_zeroes + 1)));
            self.positiveFormat = [pattern stringByReplacingCharactersInRange:NSMakeRange(first_zero, pattern_zeroes)
                                                                   withString:orig_positive_format];
            self.negativeFormat = [pattern stringByReplacingCharactersInRange:NSMakeRange(first_zero, pattern_zeroes)
                                                                   withString:orig_negative_format];
        }
    }
    
    NSString *result = [super stringFromNumber:number];
    self.positiveFormat = orig_positive_format;
    self.negativeFormat = orig_negative_format;
    return result;
}

@end