<!-- Collection of code snippets by Arne Vajhøj -->
<!-- posted to eksperten.dk, usenet and other places (2002-now) -->
<?php
/**
 * Class AnniversaryPolicyItem hold information about a single anniversary item:
 *    - textual description
 *    - interval that triggers anniversary
 */
class AnniversaryPolicyItem {
    public $descrip;
    public $interval;
    /**
     * Constrcut instance.
     * @param string $descrip textual description
     * @param DateInterval $interval interval that triggers anniversary
     */
    public function __construct($descrip, $interval) {
        $this->descrip = $descrip;
        $this->interval = $interval;
    }
}

/**
 * Class AnniversaryPolicy holds multiple instances of AnniversaryPolicyItem
 * and can test if a given start date has any anniversaries.
 * @author arne
 *
 */
class AnniversaryPolicy {
    private $before;
    private $after;
    private $format;
    private $annlist;
    /**
     * Construct instance.
     * @param integer $daysbefore number of days before actual anniversary to start triggering
     * @param integer $daysafter number of days after actual anniversary to start triggering
     * @param string $format dormat to use to displayt date
     */
    public function __construct($daysbefore, $daysafter, $format = 'd/m/Y') {
        $this->before = new DateInterval('P' . $daysbefore . 'D');
        $this->after = new DateInterval('P' . $daysafter . 'D');
        $this->format = $format;
        $this->annlist = array();
    }
    /**
     * Add interval that triggers anniversary.
     * @param string $descrip textual description
     * @param DateInterval $interval interval that triggers anniversary
     */
    public function add($descrip, $interval) {
        $this->annlist[] = new AnniversaryPolicyItem($descrip, new DateInterval($interval));
    }
    /**
     * Get any anniversary for the specified start date
     * @param integer $ts start date as Unix timestamp (seconds since 1/1/1970)
     * @return string|NULL anniversary information if any, null of no anniversary
     */
    public function getAnniversary($ts) {
        // construct range $t1 .. $t2 where actual anniversay has to be in to trigger anniversary display, basically:
        // $t1 = now - before days, adjusted to start of day
        // $t2 = now - after days, adjusted to end of day
        $now = new DateTime();
        $t1 = $now->sub($this->before);
        $t1->setTime(0, 0, 0);
        $now = new DateTime();
        $t2 = $now->add($this->after);
        $t2->setTime(23, 59, 59);
        // loop through all anniversary items
        foreach($this->annlist as $annitem) {
            // calculate actual anniversary time
            // $tsdt = start date + interval from anniversary item
            $tsdt = new DateTime();
            $tsdt->setTimestamp($ts);
            $anntim = $tsdt->add($annitem->interval);
            // test if $tsdt is in range $t1 .. $t2 and if so return anniversary description and date
            if($t1->getTimestamp() <= $anntim->getTimestamp() && $anntim->getTimestamp() <= $t2->getTimestamp()) {
                return $annitem->descrip . ' ' . $anntim->format($this->format);
            }
        }
        // no anniversaries found so return null
        return null;
    }
}

// demo code:

function test($annpol, $ts) {
    $ann = $annpol->getAnniversary($ts);
    if($ann != null) {
        echo "$ann\r\n";
    } else {
        echo "No anniversary\r\n";
    }
}

$annpol = new AnniversaryPolicy(2, 2);
$annpol->add('1 year anniversay', 'P1Y');
$annpol->add('3 months anniversary', 'P3M');
$annpol->add('1 month anniversary', 'P1M');

test($annpol, time() - 28*24*60*60);
test($annpol, time() - 31*24*60*60);
test($annpol, time() - 34*24*60*60);
test($annpol, time() - 82*24*60*60);
test($annpol, time() - 92*24*60*60);
test($annpol, time() - 102*24*60*60);
test($annpol, time() - 255*24*60*60);
test($annpol, time() - 365*24*60*60);
test($annpol, time() - 375*24*60*60);

?>