Fuzzy Date algorithm in Objective-C

Question

I would like to write a fuzzy date method for calculating dates in Objective-C for iPhone. There is a popular explanation here:

Calculate relative time in C#

However it contains missing arguments. How could this be used in Objective-C?. Thanks.

const int SECOND = 1;
const int MINUTE = 60 * SECOND;
const int HOUR = 60 * MINUTE;
const int DAY = 24 * HOUR;
const int MONTH = 30 * DAY;

if (delta < 1 * MINUTE)
{
  return ts.Seconds == 1 ? "one second ago" : ts.Seconds + " seconds ago";
}
if (delta < 2 * MINUTE)
{
  return "a minute ago";
}
if (delta < 45 * MINUTE)
{
  return ts.Minutes + " minutes ago";
}
if (delta < 90 * MINUTE)
{
  return "an hour ago";
}
if (delta < 24 * HOUR)
{
  return ts.Hours + " hours ago";
}
if (delta < 48 * HOUR)
{
  return "yesterday";
}
if (delta < 30 * DAY)
{
  return ts.Days + " days ago";
}
if (delta < 12 * MONTH)
{
  int months = Convert.ToInt32(Math.Floor((double)ts.Days / 30));
  return months <= 1 ? "one month ago" : months + " months ago";
}
else
{
  int years = Convert.ToInt32(Math.Floor((double)ts.Days / 365));
  return years <= 1 ? "one year ago" : years + " years ago";
}

Answer 1

Dates are represented in Cocoa using the NSDate class. There is a convenient method implemented in NSDate to obtain the delta in seconds between two date instances, timeIntervalSinceDate:. This is called upon an NSDate instance, taking another NSDate object as an argument. It returns an NSTimeInterval (which is a typedef for a double), which is representative of the number of seconds between the two dates.

Given this, it would be fairly simple to adapt the code you have given above to an Objective-C/Cocoa context. Since the delta calculated by NSDate is given in seconds, given two dates, you could easily adapt the code above:

//Constants
#define SECOND 1
#define MINUTE (60 * SECOND)
#define HOUR (60 * MINUTE)
#define DAY (24 * HOUR)
#define MONTH (30 * DAY)

- (NSString*)timeIntervalWithStartDate:(NSDate*)d1 withEndDate:(NSDate*)d2
{
    //Calculate the delta in seconds between the two dates
    NSTimeInterval delta = [d2 timeIntervalSinceDate:d1];

    if (delta < 1 * MINUTE)
    {
        return delta == 1 ? @"one second ago" : [NSString stringWithFormat:@"%d seconds ago", (int)delta];
    }
    if (delta < 2 * MINUTE)
    {
        return @"a minute ago";
    }
    if (delta < 45 * MINUTE)
    {
        int minutes = floor((double)delta/MINUTE);
        return [NSString stringWithFormat:@"%d minutes ago", minutes];
    }
    if (delta < 90 * MINUTE)
    {
        return @"an hour ago";
    }
    if (delta < 24 * HOUR)
    {
        int hours = floor((double)delta/HOUR);
        return [NSString stringWithFormat:@"%d hours ago", hours];
    }
    if (delta < 48 * HOUR)
    {
        return @"yesterday";
    }
    if (delta < 30 * DAY)
    {
        int days = floor((double)delta/DAY);
        return [NSString stringWithFormat:@"%d days ago", days];
    }
    if (delta < 12 * MONTH)
    {
        int months = floor((double)delta/MONTH);
        return months <= 1 ? @"one month ago" : [NSString stringWithFormat:@"%d months ago", months];
    }
    else
    {
        int years = floor((double)delta/MONTH/12.0);
        return years <= 1 ? @"one year ago" : [NSString stringWithFormat:@"%d years ago", years];
    }
}

This would then be called, passing the start and end NSDate objects as arguments, and would return an NSString with the time interval.

Answer 2

You can get the delta between two NSDate objects by using the timeIntervalSinceDate: method. That'll give you the delta in seconds.

From that you can figure out minutes/hours/days/moths/years by dividing by the appropriate amount.