/custom/modules/Project/gantt.php

<?php
/**
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU AFFERO GENERAL PUBLIC LICENSE as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU AFFERO GENERAL PUBLIC LICENSE
 * along with this program; if not, see http://www.gnu.org/licenses
 * or write to the Free Software Foundation,Inc., 51 Franklin Street,
 * Fifth Floor, Boston, MA 02110-1301  USA
 * @Package Gantt chart
 * @copyright Andrew Mclaughlan 2014
 * @author Andrew Mclaughlan <andrew@mclaughlan.info>
 */

class Gantt {

    private $start_date;
    private $end_date;
    private $tasks;

    public function __construct($start_date, $end_date, $tasks)
    {
        $this->start_date = $start_date;
        $this->end_date = $end_date;
        $this->tasks = $tasks;
        //draw the grid
        $this->draw($this->start_date, $this->end_date, $this->tasks);
    }

    public function draw($start_date, $end_date, $tasks){

        $time_span = $this->year_month($start_date, $end_date);
        $day_count = $this->count_days($start_date, $end_date);
       // $project_length = $this->time_range($start_date, $end_date);

        //Generate main table and the first row containing the months
        echo '<table class="main_table"><tr class="month_row">';

        foreach($time_span as $months) {

            foreach($months as $month => $days){
                echo '<td class="months">'.$month.'</td>';
            }
        }

        //end the month row and start the days row
        echo '</tr><tr class="day_row">';

        $month_count = 0;//start month count
        foreach($time_span as $months) {
            $m=0;
            foreach($months as $days){

                echo '<td class="inner_container">';
                //Generate a table containing the days in each month
                echo '<table class="table_inner"><tr>';

                foreach($days as $day => $d){
                    echo '<td class="inner_td"><div class="cell_width">'.$day.'</div></td>';//day number shown
                }
                echo '</tr><tr>';

                foreach($days as $d){
                    echo '<td class="inner_td"><div class="cell_width">'.$this->substr_unicode($d,0,1).'</div></td>';//First letter of the days name shown
                }
                echo '</tr></table></td>';//end table containing the days in each month
                $m++;
            }

            $month_count += $m; //total month count
        }
        //for each task generate a row of empty days
        $i=1;
        if(!is_null($tasks)){
            foreach($tasks as $task){

                echo '</tr><tr class="task_row">';
                echo '<td colspan="'.$month_count.'"><table id="task'.$i.'" class="table_inner"><tr>';

                $task_start_day = $this->count_days($start_date, $task->date_start);
                $task_end_day = $this->count_days($start_date, $task->date_finish);
                $task_duration = $this->count_days($task->date_start, $task->date_finish);
                $task->predecessors = $task->predecessors == '' ? 0 : $task->predecessors;


                for ($x=1; $x<= $day_count; $x++)
                {
                    if($x==1 && $x != $task_start_day){
                        echo '<td class="inner_td"><div class="cell_width day_block"></div></td>';
                    }

                    else if($x==1 && $x == $task_start_day){
                        if($task->milestone_flag == '1' && ($task_duration == 0 || $task_duration == 1)){
                            echo '<td class="task_td2"><div class="cell_width task_block1">
                                    <div class="task_block_inner">
                                        <div class="milestone link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                           <img src="custom/modules/Project/images/add_milestone.png" />
                                        </div>
                                    </div>
                                  </div></td><td class="inner_td"><div class="cell_width day_block"></div></td>';
                        }
                        else if($task_duration == 0 || $task_duration == 1){
                            echo '<td class="task_td2"><div class="cell_width task_block1">
                                    <div class="task_block_inner">
                                        <div class="task1 link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                            <div class="task_percent" rel="'.$task->percent_complete.'"></div>
                                        </div>
                                    </div>
                                  </div></td><td class="inner_td"><div class="cell_width day_block"></div></td>';
                        }
                        else {
                            echo '<td class="task_td" colspan="'.$task_duration.'"><div class="cell_width task_block">
                                    <div class="task_block_inner">
                                        <div class="task link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                            <div class="task_percent" rel="'.$task->percent_complete.'">'.$task->name.'</div>
                                        </div>
                                    </div>
                                  </div></td>';
                        }
                    }
                    else if($x == $task_start_day && $x == $day_count){
                        if($task->milestone_flag == '1' && ($task_duration == 0 || $task_duration == 1)){
                            echo '<td class="task_td2"><div class="cell_width task_block1">
                                    <div class="task_block_inner">
                                        <div class="milestone link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                            <img src="custom/modules/Project/images/add_milestone.png" />
                                        </div>
                                    </div>
                                  </div></td>';
                        }
                        else if($task_duration == 0 || $task_duration == 1){
                            echo '<td class="task_td2"><div class="cell_width task_block1">
                                <div class="task_block_inner">
                                     <div class="task1 link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                        <div class="task_percent" rel="'.$task->percent_complete.'"></div>
                                    </div>
                                </div>
                              </div></td>';
                        }
                        else {
                            echo '<td class="task_td" colspan="'.$task_duration.'"><div class="cell_width task_block">
                                    <div class="task_block_inner">
                                        <div class="task link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                            <div class="task_percent" rel="'.$task->percent_complete.'">'.$task->name.'</div>
                                        </div>
                                    </div>
                                  </div></td>';
                        }
                    }
                    else if($x == $task_start_day){

                        if($task->milestone_flag == '1' && ($task_duration == 0 || $task_duration == 1)){
                            echo '<td class="task_td2"><div class="cell_width task_block1">
                                    <div class="task_block_inner">
                                        <div class="milestone link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                            <img src="custom/modules/Project/images/add_milestone.png" />
                                        </div>
                                    </div>
                                  </div></td><td class="inner_td"><div class="cell_width day_block"></div></td>';
                        }
                        else if($task_duration == 0 || $task_duration == 1){
                            echo '<td class="task_td2"><div class="cell_width task_block1">
                                <div class="task_block_inner">
                                     <div class="task1 link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                        <div class="task_percent" rel="'.$task->percent_complete.'"></div>
                                    </div>
                                </div>
                              </div></td><td class="inner_td"><div class="cell_width day_block"></div></td>';
                        }
                        else {
                            echo '<td class="task_td" colspan="'.$task_duration.'"><div class="cell_width task_block">
                                <div class="task_block_inner">
                                     <div class="task link" id="'.$task->project_task_id.'" pre="'.$task->predecessors.'" link="'.$task->relationship_type.'" rel="'.$task->name.'">
                                        <div class="task_percent" rel="'.$task->percent_complete.'"></div>
                                    </div>
                                </div>
                              </div></td>';
                        }
                    }
                    else if($x == $day_count){

                    }
                    else if($x > $task_start_day && $x < $task_end_day){
                        //leave blank
                    }

                    else {
                          echo '<td class="inner_td"><div class="cell_width day_block"></div></td>';
                    }
                }

                echo '</tr></table ></td></tr>';
                $i++;
            }

        }
        echo '</table>';
    }


    //Returns an array containing the years, months and days between two dates
    public function year_month($start_date, $end_date)
    {
        $begin = new DateTime( $start_date );
        $end = new DateTime( $end_date);
        $end->add(new DateInterval('P1D')); //Add 1 day to include the end date as a day
        $interval = new DateInterval('P1D'); // 1 month interval
        $period = new DatePeriod($begin, $interval, $end);
        $aResult = array();

        foreach ( $period as $dt )
        {
            $aResult[$dt->format('Y')][strftime("%B", $dt->getTimestamp())][$dt->format('j')] = strftime("%a", $dt->getTimestamp());
        }

        return $aResult;
    }

    //Returns the total number of days between two dates
    public function count_days($start_date, $end_date){

        $d1 = new DateTime($start_date);
        $d2 = new DateTime($end_date);

        //If the task's end date is before chart's start date return 1 to make sure task starts on first day of the chart
        if($d2 < $d1){
            return 1;
        }

        $d2->add(new DateInterval('P1D')); //Add 1 day to include the end date as a day
        $difference = $d1->diff($d2);
        return $difference->days;

    }
    //Returns the time span between two dates in years  months and days
    public function time_range($start_date, $end_date){

        $datetime1 = new DateTime($start_date);
        $datetime2 = new DateTime($end_date);
        $datetime2->add(new DateInterval('P1D')); //Add 1 day to include the end date as a day
        $interval = $datetime1->diff($datetime2);
        return $interval->format('%y years %m months and %d days');
    }

    public function substr_unicode($str, $s, $l = null) {
        return join("", array_slice(
            preg_split("//u", $str, -1, PREG_SPLIT_NO_EMPTY), $s, $l));
    }

    // Function for basic field validation (present and neither empty nor only white space
    public function IsNullOrEmptyString($question){
        return (!isset($question) || trim($question)==='');
    }
}