iOS 日期格式转几年几月几日几时几分几秒前

+ (NSString *)prettyDateWithReferences:(NSString *)dateString {
    //2015-09-28T11:00:17+08:00 原来字符串时间
    
    NSString *year1 = [dateString  substringToIndex:10];
    
    NSString *mon1 = [dateString  substringWithRange:NSMakeRange(11, 8)];
    
    NSString *str = [NSString stringWithFormat:@"%@ %@",year1,mon1];
    
    NSDateFormatter *dateFormatter = [[NSDateFormatter alloc] init];
    [dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss"];
    NSDate *reference = [dateFormatter dateFromString:str];
    
    NSString *suffix = @"后";
    NSDate *date = [NSDate date];
    float different = [reference timeIntervalSinceDate:date];
    if (different < 0) {
        different = -different;
        suffix = @"前";
    }
    
    // days = different / (24 * 60 * 60), take the floor value
    float dayDifferent = floor(different / 86400);
    
    int days   = (int)dayDifferent;
    int weeks  = (int)ceil(dayDifferent / 7);
    int months = (int)ceil(dayDifferent / 30);
    int years  = (int)ceil(dayDifferent / 365);
    
    // It belongs to today
    if (dayDifferent <= 0) {
        // lower than 60 seconds
        if (different < 60) {
            return @"刚刚";
        }
        
        // lower than 120 seconds => one minute and lower than 60 seconds
        if (different < 120) {
            return [NSString stringWithFormat:@"1分钟%@", suffix];
        }
        
        // lower than 60 minutes
        if (different < 660 * 60) {
            return [NSString stringWithFormat:@"%d分钟%@", (int)floor(different / 60), suffix];
        }
        
        // lower than 60 * 2 minutes => one hour and lower than 60 minutes
        if (different < 7200) {
            return [NSString stringWithFormat:@"1小时%@",suffix];
        }
        
        // lower than one day
        if (different < 86400) {
            return [NSString stringWithFormat:@"%d小时%@", (int)floor(different / 3600), suffix];
        }
    }
    // lower than one week
    else if (days < 7) {
        return [NSString stringWithFormat:@"%d天%@%@", days, days == 1 ? @"" : @"", suffix];
    }
    // lager than one week but lower than a month
    else if (weeks < 4) {
        return [NSString stringWithFormat:@"%d星期%@%@", weeks, weeks == 1 ? @"" : @"", suffix];
    }
    // lager than a month and lower than a year
    else if (months < 12) {
        return [NSString stringWithFormat:@"%d月%@%@", months, months == 1 ? @"" : @"", suffix];
    }
    // lager than a year
    else {
        return [NSString stringWithFormat:@"%d年%@%@", years, years == 1 ? @"" : @"", suffix];
    }
    
    return self.description;
}