Convert a NSTimeInterval into a human-readable string. Used to convert EKAlerts to text

timeIntervalToStringWithInterval

+ (NSString *)timeIntervalToStringWithInterval:(NSTimeInterval)interval
{
    NSString *retVal = @"At time of event";
    if (interval == 0) return retVal;
    
    int second = 1;
    int minute = second*60;
    int hour = minute*60;
    int day = hour*24;
    // interval can be before (negative) or after (positive)
    int num = abs(interval);
    
    NSString *beforeOrAfter = @"before";
    NSString *unit = @"day";
    if (interval > 0) {
        beforeOrAfter = @"after";
    }
        
    if (num >= day) {
        num /= day;
        if (num > 1) unit = @"days";
    } else if (num >= hour) {
        num /= hour;
        unit = (num > 1) ? @"hours" : @"hour";
    } else if (num >= minute) {
        num /= minute;
        unit = (num > 1) ? @"minutes" : @"minute";
    } else if (num >= second) {
        num /= second;
        unit = (num > 1) ? @"seconds" : @"second";

    }
    
    return [NSString stringWithFormat:@"%d %@ %@", num, unit, beforeOrAfter];
}