/**
 	 * This method return a graph containing information about evaluations
     * inside courses in sessions, it's used inside get_block method for
     * showing it inside dashboard interface
 	 * @return string  img html
 	 */
    public function get_evaluations_courses_in_sessions_graph()
    {
		$graphs = array();
		if (!empty($this->sessions)) {
			$session_ids = array_keys($this->sessions);
			foreach ($session_ids as $session_id) {
				$courses_code = array_keys(Tracking::get_courses_list_from_session($session_id));
				$courses_graph = array();
				foreach ($courses_code as $course_code) {
					$cats = Category::load(null, null, $course_code, null, null, $session_id);
					if (isset($cats) && isset($cats[0])) {
						$alleval = $cats[0]->get_evaluations(null, true, $course_code);
						$alllinks = $cats[0]->get_links(null, true);
						$users = get_all_users($alleval, $alllinks);
						$datagen = new FlatViewDataGenerator ($users, $alleval, $alllinks);
						$evaluation_sumary = $datagen->get_evaluation_sumary_results();
						if (!empty($evaluation_sumary)) {
							$items = array_keys($evaluation_sumary);
							$max = $min = $avg = array();
							foreach ($evaluation_sumary as $evaluation) {
								$max[] = $evaluation['max'];
								$min[] = $evaluation['min'];
								$avg[] = $evaluation['avg'];
							}
							// Dataset definition
						    $data_set = new pData;
						    $data_set->AddPoint($max, "Max");
						    $data_set->AddPoint($avg, "Avg");
						    $data_set->AddPoint($min, "Min");
						    $data_set->AddPoint($items, "Items");
						    $data_set->SetXAxisName(get_lang('EvaluationName'));
							$data_set->SetYAxisName(get_lang('Percentage'));
							$data_set->AddAllSeries();
						   	$data_set->RemoveSerie("Items");
						   	$data_set->SetAbsciseLabelSerie("Items");
						    $graph_id = $this->user_id.'StudentEvaluationGraph';
							$cache = new pCache();
							// the graph id
							$data = $data_set->GetData();
							if ($cache->IsInCache($graph_id, $data)) {
								//if we already created the img
								$img_file = $cache->GetHash($graph_id, $data);
							} else {
								// Initialise the graph
                                $angle = -30;
							    $test = new pChart($this->bg_width, $this->bg_height);
							    $test->setFontProperties(api_get_path(LIBRARY_PATH) . 'pchart/fonts/tahoma.ttf', 8);
                                $test->fixHeightByRotation(
                                    $data_set->GetData(),
                                    $data_set->GetDataDescription(),
                                    $angle
                                );
                                $test->setGraphArea(50, 30, $this->bg_width - 75, $this->bg_height - 75);
                                $test->drawFilledRoundedRectangle(
                                    7,
                                    7,
                                    $this->bg_width - 20,
                                    $test->YSize - 20,
                                    5,
                                    240,
                                    240,
                                    240
                                );
                                $test->drawRoundedRectangle(
                                    5,
                                    5,
                                    $this->bg_width - 18,
                                    $test->YSize - 18,
                                    5,
                                    230,
                                    230,
                                    230
                                );
							    $test->drawGraphArea(255,255,255,TRUE);
							    $test->setFixedScale(0,100,5);
                                $test->drawScale(
                                    $data_set->GetData(),
                                    $data_set->GetDataDescription(),
                                    SCALE_ADDALL,
                                    150,
                                    150,
                                    150,
                                    TRUE,
                                    $angle,
                                    2,
                                    TRUE
                                );
							    $test->setColorPalette(0,105,221,34);
								$test->setColorPalette(1,255,135,30);
								$test->setColorPalette(2,255,0,0);
							    $test->drawGrid(4,TRUE,230,230,230,50);
							    // Draw the 0 line
							    $test->setFontProperties(api_get_path(LIBRARY_PATH).'pchart/fonts/tahoma.ttf',6);
							    $test->drawTreshold(0,143,55,72,TRUE,TRUE);
							    // Draw the bar graph
							    $test->drawOverlayBarGraph($data_set->GetData(),$data_set->GetDataDescription(), 100);
							    // Finish the graph
							    $test->setFontProperties(api_get_path(LIBRARY_PATH).'pchart/fonts/tahoma.ttf',8);
							    $test->drawLegend($this->bg_width-80,20,$data_set->GetDataDescription(),255,255,255);
							    $test->setFontProperties(api_get_path(LIBRARY_PATH).'pchart/fonts/tahoma.ttf',10);
							    $test->setColorPalette(0,50,50,50);
								$test->setColorPalette(1,50,50,50);
								$test->setColorPalette(2,50,50,50);
							    $test->writeValues($data_set->GetData(),$data_set->GetDataDescription(),array("Min", "Max", "Avg"));
							    $cache->WriteToCache($graph_id, $data_set->GetData(), $test);
								ob_start();
								$test->Stroke();
								ob_end_clean();
								$img_file = $cache->GetHash($graph_id, $data_set->GetData());
							}
							if (!empty($img_file)) {
								$courses_graph[$course_code] = '<img src="'.api_get_path(WEB_ARCHIVE_PATH).$img_file.'">';
							}
						}
					}
				}
				if (!empty($courses_graph)) {
					$graphs[$session_id] = $courses_graph;
				}
			}
		}
    	return $graphs;
 	}