How to build a web calendar in PHP

<?php

/**

*@author  Xu Ding

*@email   thedilab@gmail.com

*@website http://www.StarTutorial.com

**/

class Calendar {  

     

    /**

     * Constructor

     */

    public function __construct(){     

        $this->naviHref = htmlentities($_SERVER['PHP_SELF']);

    }

     

    /********************* PROPERTY ********************/  

    private $dayLabels = array("Mon","Tue","Wed","Thu","Fri","Sat","Sun");

     

    private $currentYear=0;

     

    private $currentMonth=0;

     

    private $currentDay=0;

     

    private $currentDate=null;

     

    private $daysInMonth=0;

     

    private $naviHref= null;

     

    /********************* PUBLIC **********************/  

        

    /**

    * print out the calendar

    */

    public function show() {

        $year  == null;

         

        $month == null;

         

        if(null==$year&&isset($_GET['year'])){

            $year = $_GET['year'];

         

        }else if(null==$year){

            $year = date("Y",time());  

         

        }          

         

        if(null==$month&&isset($_GET['month'])){

            $month = $_GET['month'];

         

        }else if(null==$month){

            $month = date("m",time());

         

        }                  

         

        $this->currentYear=$year;

         

        $this->currentMonth=$month;

         

        $this->daysInMonth=$this->_daysInMonth($month,$year);  

         

        $content='<div id="calendar">'.

                        '<div class="box">'.

                        $this->_createNavi().

                        '</div>'.

                        '<div class="box-content">'.

                                '<ul class="label">'.$this->_createLabels().'</ul>';   

                                $content.='<div class="clear"></div>';     

                                $content.='<ul class="dates">';    

                                 

                                $weeksInMonth = $this->_weeksInMonth($month,$year);

                                // Create weeks in a month

                                for( $i=0; $i<$weeksInMonth; $i++ ){

                                     

                                    //Create days in a week

                                    for($j=1;$j<=7;$j++){

                                        $content.=$this->_showDay($i*7+$j);

                                    }

                                }

                                 

                                $content.='</ul>';

                                 

                                $content.='<div class="clear"></div>';     

             

                        $content.='</div>';

                 

        $content.='</div>';

        return $content;   

    }

     

    /********************* PRIVATE **********************/ 

    /**

    * create the li element for ul

    */

    private function _showDay($cellNumber){

         

        if($this->currentDay==0){

             

            $firstDayOfTheWeek = date('N',strtotime($this->currentYear.'-'.$this->currentMonth.'-01'));

                     

            if(intval($cellNumber) == intval($firstDayOfTheWeek)){

                 

                $this->currentDay=1;

                 

            }

        }

         

        if( ($this->currentDay!=0)&&($this->currentDay<=$this->daysInMonth) ){

             

            $this->currentDate = date('Y-m-d',strtotime($this->currentYear.'-'.$this->currentMonth.'-'.($this->currentDay)));

             

            $cellContent = $this->currentDay;

             

            $this->currentDay++;   

             

        }else{

             

            $this->currentDate =null;

            $cellContent=null;

        }

             

         

        return '<li id="li-'.$this->currentDate.'" class="'.($cellNumber%7==1?' start ':($cellNumber%7==0?' end ':' ')).

                ($cellContent==null?'mask':'').'">'.$cellContent.'</li>';

    }

     

    /**

    * create navigation

    */

    private function _createNavi(){

         

        $nextMonth = $this->currentMonth==12?1:intval($this->currentMonth)+1;

         

        $nextYear = $this->currentMonth==12?intval($this->currentYear)+1:$this->currentYear;

         

        $preMonth = $this->currentMonth==1?12:intval($this->currentMonth)-1;

         

        $preYear = $this->currentMonth==1?intval($this->currentYear)-1:$this->currentYear;

         

        return

            '<div class="header">'.

                '<a class="prev" href="'.$this->naviHref.'?month='.sprintf('%02d',$preMonth).'&year='.$preYear.'">Prev</a>'.

                    '<span class="title">'.date('Y M',strtotime($this->currentYear.'-'.$this->currentMonth.'-1')).'</span>'.

                '<a class="next" href="'.$this->naviHref.'?month='.sprintf("%02d", $nextMonth).'&year='.$nextYear.'">Next</a>'.

            '</div>';

    }

         

    /**

    * create calendar week labels

    */

    private function _createLabels(){  

                 

        $content='';

         

        foreach($this->dayLabels as $index=>$label){

             

            $content.='<li class="'.($label==6?'end title':'start title').' title">'.$label.'</li>';

        }

         

        return $content;

    }

     

     

     

    /**

    * calculate number of weeks in a particular month

    */

    private function _weeksInMonth($month=null,$year=null){

         

        if( null==($year) ) {

            $year =  date("Y",time()); 

        }

         

        if(null==($month)) {

            $month = date("m",time());

        }

         

        // find number of days in this month

        $daysInMonths = $this->_daysInMonth($month,$year);

         

        $numOfweeks = ($daysInMonths%7==0?0:1) + intval($daysInMonths/7);

         

        $monthEndingDay= date('N',strtotime($year.'-'.$month.'-'.$daysInMonths));

         

        $monthStartDay = date('N',strtotime($year.'-'.$month.'-01'));

         

        if($monthEndingDay<$monthStartDay){

             

            $numOfweeks++;

         

        }

         

        return $numOfweeks;

    }

    /**

    * calculate number of days in a particular month

    */

    private function _daysInMonth($month=null,$year=null){

         

        if(null==($year))

            $year =  date("Y",time()); 

        if(null==($month))

            $month = date("m",time());

             

        return date('t',strtotime($year.'-'.$month.'-01'));

    }

     

}

?>