<?php

/**
 * allows for easy manipulation and fetching of dates/times.
 */
class Date {
	private
		$timestamp,
		$valid;

	// parameter is optional timestamp; if not provided, defaults to current time
	public function __construct ($time = null) {
		if ($time === null)
			$time = time();

		if (preg_match('/\D/', $time))
			$time = strtotime($time);

		$this->timestamp = $time;
		$this->valid = $time !== false;
	}

	// read the object's timestamp in one of a variety of formats
	public function __get ($prop) {
		switch ($prop) {
			// unix timestamp (ie: 10000001)
			case 'timestamp':
			case 'valid':
				return $this->$prop;

			// date in mysql '2007-12-25' format
			case 'mysql_date':
				return $this->valid ? date('Y-m-d', $this->timestamp) : false;

			// time in mysql '13:14:15' format
			case 'mysql_time':
				return $this->valid ? date('H:i:s', $this->timestamp) : false;

			// date/time in mysql '2007-12-25 13:14:15' format
			case 'mysql_datetime':
				return $this->valid ? date('Y-m-d H:i:s', $this->timestamp) : false;

			default:
				return false;
		}
	}

	// modify the timestamp using a delta
	// ie: $date->modify('+12 hours')
	public function modify ($delta) {
		// if delta starts with "now"/"today", force delta to be from NOW, not the existing timestamp
		if (preg_match('/^now|today/', $delta))
			$this->timestamp = strtotime($delta, time());

		// otherwise, delta applies to the existing timestamp
		else
			$this->timestamp = strtotime($delta, $this->timestamp);

		$this->valid = $this->timestamp !== false;
	}

	// diff this object with another Date object
	public function diff (Date $time) {
		return new DateDiff($this, $time);
	}
}


/**
 * diff's two timestamps, providing access to the diff info
 */
class DateDiff {
	private
		$yrs = 0,
		$mnths = 0,
		$days = 0,
		$hrs = 0,
		$mins = 0,
		$secs = 0;

	// pass in 2 Date objects to run the diff; object properties populated with diff values
	public function __construct (Date $t1, Date $t2) {
		if (! $t1->valid || ! $t2->valid)
			return;

		$t1 = $t1->timestamp;
		$t2 = $t2->timestamp;

		// make sure that $t2 > $t1
		if ($t1 > $t2)
			list($t1, $t2) = array($t2, $t1);

		// secs
		$s2 = (int)date('s', $t2);
		while ( ($s1 = (int)date('s', $t1)) !== $s2 ) {
			$t1 = strtotime('+1 second', $t1);
			$this->secs++;
		}

		// mins
		$s2 = (int)date('i', $t2);
		while ( ($s1 = (int)date('i', $t1)) !== $s2) {
			$t1 = strtotime('+1 minute', $t1);
			$this->mins++;
		}

		// hrs
		$s2 = date('G', $t2);
		while ( ($s1 = date('G', $t1)) !== $s2 ) {
			$t1 = strtotime('+1 hour', $t1);
			$this->hrs++;
		}

		// days
		$s2 = date('j', $t2);
		while ( ($s1 = date('j', $t1)) !== $s2 ) {
			$t1 = strtotime('+1 day', $t1);
			$this->days++;
		}

		// mnths
		$s2 = date('n', $t2);
		while ( ($s1 = date('n', $t1)) !== $s2 ) {
			$t1 = strtotime('+1 month', $t1);
			$this->mnths++;
		}

		// yrs
		$s2 = date('Y', $t2);
		while ( ($s1 = date('Y', $t1)) < $s2 ) {
			$t1 = strtotime('+1 year', $t1);
			$this->yrs++;
		}
	}

	/**
	 * format the diff according to preference; returns a string like "4 hrs, 3 mins, 2 secs"
	 *
	 * precision is number of time pieces to display (ie: 2 = yrs, mnths or mins, secs)
	 * when abbr=true, identifiers are short (yrs/hrs) rather than full (years/hours)
	 */
    public function format_diff ($precision = 6, $abbr = false) {
        $stack = array(
            array($this->yrs, ($abbr ? 'yr' : 'year') . ($this->yrs == 1 ? '' : 's')),
            array($this->mnths, ($abbr ? 'mnth' : 'month') . ($this->mnths == 1 ? '' : 's')),
            array($this->days, 'day' . ($this->days == 1 ? '' : 's')),
            array($this->hrs, ($abbr ? 'hr' : 'hour') . ($this->hrs == 1 ? '' : 's')),
            array($this->mins, ($abbr ? 'min' : 'minute') . ($this->mins == 1 ? '' : 's')),
            array($this->secs, ($abbr ? 'sec' : 'second') . ($this->secs == 1 ? '' : 's'))
        );

        while (count($stack) > 0 && $stack[0][0] == 0)
            array_splice($stack, 0, 1);

        array_splice($stack, $precision);

        $ret = array();
        foreach ($stack as $item)
            $ret[] = "{$item[0]} {$item[1]}";

        return implode(', ', $ret);
    }
}

$t1 = new Date('2008-01-29 18:09:06');
$t2 = new Date();
$diff = $t1->diff($t2);

echo $diff->format_diff(3), "\n";

?>