Calculate the time that has passed since a specified Unix formatted date and time, and show it in a human readable format, all in a PHP function.

function TimeSince($original) // $original should be the original date and time in Unix format
{
    // Common time periods as an array of arrays
    $periods = array(
        array(60 * 60 * 24 * 365 , 'year'),
        array(60 * 60 * 24 * 30 , 'month'),
        array(60 * 60 * 24 * 7, 'week'),
        array(60 * 60 * 24 , 'day'),
        array(60 * 60 , 'hour'),
        array(60 , 'minute'),
    );
   
    $today = time();
    $since = $today - $original; // Find the difference of time between now and the past
   
    // Loop around the periods, starting with the biggest
    for ($i = 0, $j = count($periods); $i < $j; $i++)
        {    
        $seconds = $periods[$i][0];
        $name = $periods[$i][1];
       
        // Find the biggest whole period
        if (($count = floor($since / $seconds)) != 0)
                {
            break;
        }
    }
   
    $output = ($count == 1) ? '1 '.$name : "$count {$name}s";
   
    if ($i + 1 < $j)
        {
        // Retrieving the second relevant period
        $seconds2 = $periods[$i + 1][0];
        $name2 = $periods[$i + 1][1];
       
        // Only show it if it's greater than 0
        if (($count2 = floor(($since - ($seconds * $count)) / $seconds2)) != 0)
                {
            $output .= ($count2 == 1) ? ', 1 '.$name2 : ", $count2 {$name2}s";
        }
    }
    return $output;
}
 
echo TimeSince(1249091056);

The provided code is a PHP function named TimeSince designed to calculate the time elapsed since a given date and time, specified in Unix format (Unix timestamp). It returns a human-readable string representing this time difference. Here’s an explanation:

1. Function Definition: function TimeSince($original) takes one argument, $original, which is the date and time in Unix timestamp format.
2. Time Periods Array: The $periods array defines various time periods in seconds (years, months, weeks, days, hours, minutes) along with their textual representation.
3. Current Time Calculation: $today = time(); gets the current time in Unix timestamp format. $since = $today - $original; calculates the difference in seconds between the current time and the provided timestamp.
4. Calculating the Largest Time Period: The for loop iterates through the $periods array, starting from the largest time unit (year). It calculates how many of each unit fits into the $since time difference. Once it finds a time unit that fits (floor($since / $seconds) != 0), it breaks out of the loop.
5. Formatting the Output: $output is formatted to show the elapsed time in the largest fitting time unit found. If the count is 1, it uses the singular form of the unit; otherwise, it uses the plural.
6. Adding a Second Time Period: The code then checks if there’s a smaller time unit that can also be used to describe the remaining time. If so, it appends this information to the $output.
7. Returning the Result: The function returns the formatted string $output, which describes the time elapsed since the original timestamp in a human-readable format.
8. Example Usage: echo TimeSince(1249091056); This line would output the time elapsed since the Unix timestamp 1249091056.