Express difference between two timestamps in various English time units

time_delta.php

	/*
	time_delta() returns the difference between two times
	expressed in many ways.

	(mixed) $start:		The initial time to calculate from
	(mixed) $target:	The time in the past or future to calculate the difference between
	(int) $precision:
		0: Generic 	- ex. "About 7 hours ago"
		1: Approximate 	- ex. "7 hours, 15 minutes ago"
		2: Exact	- ex. "7 hours, 15 minutes and 6 seconds ago"
		s: seconds
		m: minutes
		h: hours
		d: days
		w: weeks
		mo: months
		y: years
	(int) $labels:
		0: No labels	- ex. "7 15 6 ago"
		1: Short	- ex. "7h 15m 6s ago"
		2: Long		- ex. "7 hours, 15 minutes and 6 seconds ago"
	(bool) $suffix:		Whether or not to add "ago" or "from now"
	*/

function time_delta($start='now', $target='', $precision=0, $labels=2, $suffix=true)
{
	date_default_timezone_set('America/Los_Angeles'); // PHP complains if this isn't set, for some reason
	
	// Define all time units in terms of seconds
	$units = array(
			'y'  => array('year', 31556926), // Source: Google calculator
			'mo' => array('month', 2629744), // Source: Google calculator
			'w'  => array('week', 604800),
			'd'  => array('day', 86400),
			'h'  => array('hour', 3600),
			'm'  => array('minute', 60),
			's'  => array('second', 1)
			);

	// Some basic sanity checking
	if (empty($target)) return "No target time specified.\n";
	if ($start < 0) return "Invalid start time.\n";
	if (!array_key_exists($precision, $units) AND $precision > 2) return "Improper value for precision.\n";
	if (!is_int($labels) OR !is_bool($suffix)) return "Improper values for labels and/or suffix.\n";
	if (!is_int($target) AND !strtotime($target)) return "Could not understand your target time.\n";
	if (!is_int($start) AND !strtotime($start)) return "Could not understand your start time.\n";

	// Set some sensible defaults
	$fuzz_factor = 0.8; // How close to the next value will we call it "about" something?
	if ($precision < 0 OR $precision > 2) $precision = 2;
	if ($labels < 0 OR $labels > 2) $labels = 2;
	if (!is_int($start)) $start = strtotime($start);
	if (!is_int($target)) $target = strtotime($target);

	// Are we past or future?
	$ending = ($target > $start) ? " from now" : " ago";

	// Calculate time difference & initialize output string
	$delta = abs($target - $start);
	$out = '';

	// Calculate for single-unit precision
	if (is_string($precision))
	{
		if ($delta < $units[$precision][1])
		{
			$out .= "Less than one {$units[$precision][0]}";
			return ($suffix === true) ? $out.$ending : $out;
		}
		else
		{
			$out .= intval(($delta / $units[$precision][1]));
			if ($labels == 0) return $out;
			$out .= ($labels == 1) ? $precision : ' '.$units[$precision][0]
			     .  (($out > 1 AND $labels >= 2) ? 's' : '');
			return ($suffix === true) ? $out.$ending : $out;
		}
	}

	/* Calculate fuzzy precision
	   -------------------------
	  Fuzzy precision should output only one unit of precision
	  and use the modifier "about" if the remainder is > $fuzz_factor.
	*/
	if ($precision == 0)
	{
		foreach ($units as $unit => $type)
		{
			if ($delta >= $type[1] * $fuzz_factor)
			{
				$fuzzy = (fmod(($delta / $type[1]), 1) > $fuzz_factor) ? true : false;
				if ($labels > 0 AND $labels >= 2) $out .= ($fuzzy === true) ? 'About ' : '';
				$diff = ($fuzzy === true) ? ceil($delta / $type[1]) : intval($delta / $type[1]);
				if ($diff == 1 AND $fuzzy === true) $out .= ($unit == 'h') ? 'an ' : 'a ';
				else $out .= $diff;
				if ($labels == 0) return $diff;
				$out .= ($labels > 1 OR $fuzzy === false) ? ' ' : ''; 
				$out .= ($labels == 1) ? $unit : $type[0];
				$out .= ($diff > 1 AND $labels > 1) ? 's' : '';
				return ($suffix === true) ? $out.$ending : $out;
			}
		}
	}
		
	/* Calculate approximate and exact precision
	   -----------------------------------------
	  Approximate precision outputs up to 2 units of measure, exact prints
	  as many as we have.
	*/
	else
	{
		$max = ($precision == 1) ? 2 : count($units); // Iterate twice if approximate precision
		$i = 0;
		foreach ($units as $unit => $type)
		{
			if ($delta >= $type[1] AND $i < $max)
			{
				$diff = intval($delta / $type[1]);
				$out .= $diff.(($labels > 1) ? (' '.$type[0]) : (($labels == 0) ? ' ' : $unit)).(($diff > 1 AND $labels > 1) ? ('s') : (''));
				$delta -= intval($delta / $type[1]) * $type[1];
				$out .= ($i == 0 AND $precision == 1 AND $labels > 0 AND !empty($diff)) ? ' and ' : '';
				$next_index = array_search($unit,array_keys($units)) + 1;
				$units_numeric = array_values($units);
				if (array_key_exists($next_index, $units_numeric)) $next = $units_numeric[$next_index][1];
				$and = ($precision == 2 AND $labels > 0 AND ($delta % $next == 0) AND $unit != 's');
				$out .= $and ? ' and ' : (($labels > 0 AND $unit != 's' AND $precision != 1) ? ', ' : '' );
				$i++;
			}
		}
		return ($suffix === true) ? $out.$ending : $out;
	}
}