<?php //$id: $
/* For licensing terms, see /license.txt */
/**
* This is the session library for Chamilo.
* All main sessions functions should be placed here.
* @package chamilo.library
*/
/**
 * Code
 */
/* LIBRARIES */


/**
*	This class provides methods for sessions management.
*	Include/require it in your code to use its features.
*
*	@package chamilo.library
*/
class SessionManager {    
	private function __construct() {
	}
    
    /**
     * Fetches a session from the database
     * @param   int     Session ID
     * @return  array   Session details (id, id_coach, name, nbr_courses, nbr_users, nbr_classes, date_start, date_end, nb_days_access_before_beginning,nb_days_access_after_end, session_admin_id)
     */
    public static function fetch($id) {
    	$t = Database::get_main_table(TABLE_MAIN_SESSION);
        if ($id != strval(intval($id))) { return array(); }
        $s = "SELECT * FROM $t WHERE id = $id";
        $r = Database::query($s);
        if (Database::num_rows($r) != 1) { return array(); }
        return Database::fetch_array($r,'ASSOC');
    }
    
	 /**
	  * Create a session
	  * @author Carlos Vargas from existing code
	  * @param	string 		name
	  * @param 	integer		Start year (yyyy)
	  * @param 	integer		Start month (mm)
	  * @param 	integer		Start day (dd)
	  * @param 	integer		End year (yyyy)
	  * @param 	integer		End month (mm)
	  * @param 	integer		End day (dd)
	  * @param 	integer		Number of days that the coach can access the session before the start date
	  * @param 	integer		Number of days that the coach can access the session after the end date
	  * @param 	integer		If 1, means there are no date limits
	  * @param 	mixed		If integer, this is the session coach id, if string, the coach ID will be looked for from the user table
	  * @param 	integer		ID of the session category in which this session is registered
      * @param  integer     Visibility after end date (0 = read-only, 1 = invisible, 2 = accessible)
      * @param  string      Start limit = true if the start date has to be considered
      * @param  string      End limit = true if the end date has to be considered
      * @todo use an array to replace all this parameters or use the model.lib.php ...
	  * @return mixed       Session ID on success, error message otherwise
      **/
	public static function create_session($sname,$syear_start,$smonth_start,$sday_start,$syear_end,$smonth_end,$sday_end,$snb_days_acess_before,$snb_days_acess_after, $nolimit,$coach_username, $id_session_category,$id_visibility, $start_limit = true, $end_limit = true, $fix_name = false) {		
		global $_configuration;
        
		//Check portal limits
        $access_url_id = 1;
        if (api_get_multiple_access_url()) {
            $access_url_id = api_get_current_access_url_id();
        }
        if (is_array($_configuration[$access_url_id]) && isset($_configuration[$access_url_id]['hosting_limit_sessions']) && $_configuration[$access_url_id]['hosting_limit_sessions'] > 0) {
            $num = self::count_sessions();
            if ($num >= $_configuration[$access_url_id]['hosting_limit_sessions']) {
                return get_lang('PortalSessionsLimitReached');
            }
        }

		$name                 = Database::escape_string(trim($sname));
		$year_start           = intval($syear_start);
		$month_start          = intval($smonth_start);
		$day_start            = intval($sday_start);
		$year_end             = intval($syear_end);
		$month_end            = intval($smonth_end);
		$day_end              = intval($sday_end);
		$nb_days_acess_before = intval($snb_days_acess_before);
		$nb_days_acess_after  = intval($snb_days_acess_after);
		$id_session_category  = intval($id_session_category);
		$id_visibility        = intval($id_visibility);
		$tbl_user		      = Database::get_main_table(TABLE_MAIN_USER);
		$tbl_session	      = Database::get_main_table(TABLE_MAIN_SESSION);        
    
		if (is_int($coach_username)) {
			$id_coach = $coach_username;
		} else {
			$sql = 'SELECT user_id FROM '.$tbl_user.' WHERE username="'.Database::escape_string($coach_username).'"';
			$rs = Database::query($sql);
			$id_coach = Database::result($rs,0,'user_id');
		}

		if (empty($nolimit)) {
			$date_start  ="$year_start-".(($month_start < 10)?"0$month_start":$month_start)."-".(($day_start < 10)?"0$day_start":$day_start);
			$date_end    ="$year_end-".(($month_end < 10)?"0$month_end":$month_end)."-".(($day_end < 10)?"0$day_end":$day_end);
		} else {
			$id_visibility   = 1; // by default session visibility is read only
			$date_start      ="0000-00-00";
			$date_end        ="0000-00-00";
		}
        
        if (empty($end_limit)) {
            $date_end ="0000-00-00";
            $id_visibility   = 1; // by default session visibility is read only
        }
              
        if (empty($start_limit)) {
            $date_start ="0000-00-00";
        }            
         
		if (empty($name)) {
			$msg=get_lang('SessionNameIsRequired');
			return $msg;
		} elseif (empty($coach_username))   {
			$msg=get_lang('CoachIsRequired');
			return $msg;
		} elseif (!empty($start_limit)  && empty($nolimit) && (!$month_start || !$day_start || !$year_start || !checkdate($month_start,$day_start,$year_start))) {
			$msg=get_lang('InvalidStartDate');
			return $msg;
		} elseif (!empty($end_limit)  &&  empty($nolimit) && (!$month_end || !$day_end || !$year_end || !checkdate($month_end,$day_end,$year_end))) {
			$msg=get_lang('InvalidEndDate');
			return $msg;
		} elseif(!empty($start_limit) && !empty($end_limit)  && empty($nolimit) && $date_start >= $date_end) {
			$msg=get_lang('StartDateShouldBeBeforeEndDate');
			return $msg;
		} else {
		    $ready_to_create = false;
		    if ($fix_name) {
		        $name = self::generate_nice_next_session_name($name);		    
		        if ($name) {
		            $ready_to_create = true;
		        } else {
		            $msg=get_lang('SessionNameAlreadyExists');
    				return $msg;
		        }	        
		    } else {
    		    $rs = Database::query("SELECT 1 FROM $tbl_session WHERE name='".$name."'");
    			if (Database::num_rows($rs)) {
    				$msg=get_lang('SessionNameAlreadyExists');
    				return $msg;
    			} 
    			$ready_to_create = true;
		    }
			
			if ($ready_to_create) {
				$sql_insert = "INSERT INTO $tbl_session(name,date_start,date_end,id_coach,session_admin_id, nb_days_access_before_beginning, nb_days_access_after_end, session_category_id,visibility)
							   VALUES('".$name."','$date_start','$date_end','$id_coach',".api_get_user_id().",".$nb_days_acess_before.", ".$nb_days_acess_after.", ".$id_session_category.", ".$id_visibility.")";
				Database::query($sql_insert);
				$session_id = Database::insert_id();
                
                if (!empty($session_id)) {     	
    				//Adding to the correct URL                    
                    $access_url_id = api_get_current_access_url_id();
                    UrlManager::add_session_to_url($session_id,$access_url_id);            
    
    				// add event to system log				
    				$user_id = api_get_user_id();
    				event_system(LOG_SESSION_CREATE, LOG_SESSION_ID, $session_id, api_get_utc_datetime(), $user_id);
    		    }
				return $session_id;
			}
		}
	}
	
	function session_name_exists($session_name) {
	    $session_name = Database::escape_string($session_name);
        $result = Database::fetch_array(Database::query("SELECT COUNT(*) as count FROM ".Database::get_main_table(TABLE_MAIN_SESSION)." WHERE name = '$session_name' "));
        return $result['count'] > 0;
	}
    
    function get_count_admin() {
        $tbl_session            = Database::get_main_table(TABLE_MAIN_SESSION);
        $tbl_session_category   = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);        
        $tbl_user               = Database::get_main_table(TABLE_MAIN_USER);

        $where = 'WHERE 1=1 ';
        $user_id = api_get_user_id();
		
        if (api_is_session_admin() && api_get_setting('allow_session_admins_to_see_all_sessions') == 'false') {
            $where.=" WHERE s.session_admin_id = $user_id ";
        }
        
        $query_rows = "SELECT count(*) as total_rows
         FROM $tbl_session s
            LEFT JOIN  $tbl_session_category sc ON s.session_category_id = sc.id
            INNER JOIN $tbl_user u ON s.id_coach = u.user_id
         $where ";
         
        global $_configuration;
        if ($_configuration['multiple_access_urls']) {
            $table_access_url_rel_session= Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_SESSION);
            $access_url_id = api_get_current_access_url_id();
            if ($access_url_id != -1) {
				$where.= " AND ar.access_url_id = $access_url_id ";
				
                $query_rows = "SELECT count(*) as total_rows
                 FROM $tbl_session s
                    LEFT JOIN  $tbl_session_category sc ON s.session_category_id = sc.id
                    INNER JOIN $tbl_user u ON s.id_coach = u.user_id
                    INNER JOIN $table_access_url_rel_session ar ON ar.session_id = s.id
                 $where ";
            }
        }
        $result_rows = Database::query($query_rows);
        $recorset = Database::fetch_array($result_rows);
        $num = $recorset['total_rows'];
        return $num;    
    }
    
    /**
     * Gets the admin session list callback of the admin/session_list.php page
     * @param array order and limit keys
     */
	public function get_sessions_admin($options) {
		$tbl_session            = Database::get_main_table(TABLE_MAIN_SESSION);
		$tbl_session_category   = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);        
		$tbl_user               = Database::get_main_table(TABLE_MAIN_USER);        

		$where = 'WHERE 1=1 ';
		$user_id = api_get_user_id();
        
		if (api_is_session_admin() && api_get_setting('allow_session_admins_to_see_all_sessions') == 'false') {
			$where.=" AND s.session_admin_id = $user_id ";
		}        

		$coach_name = " CONCAT (u.lastname , ' ', u.firstname) as coach_name ";

		if (api_is_western_name_order()) {            
			$coach_name = " CONCAT (u.firstname, ' ', u.lastname) as coach_name ";
		}        

		$today = api_get_utc_datetime();
		$today = api_strtotime($today, 'UTC');
		$today = date('Y-m-d', $today);

		$select = "SELECT * FROM (SELECT 
				IF ( 
					(s.date_start <= '$today' AND '$today' < s.date_end) OR 
					(s.date_start  = '0000-00-00' AND s.date_end  = '0000-00-00' ) OR
					(s.date_start <= '$today' AND '0000-00-00' = s.date_end) OR
					('$today' < s.date_end AND '0000-00-00' = s.date_start)
				, 1, 0) 
				as session_active, 
				s.name, nbr_courses, nbr_users, s.date_start, s.date_end, $coach_name, sc.name as category_name, s.visibility, u.user_id, s.id";

		$query = "$select FROM $tbl_session s 
				LEFT JOIN  $tbl_session_category sc ON s.session_category_id = sc.id 
				INNER JOIN $tbl_user u ON s.id_coach = u.user_id ".
			 $where;
		global $_configuration;
		if ($_configuration['multiple_access_urls']) {
			$table_access_url_rel_session= Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_SESSION);
			$access_url_id = api_get_current_access_url_id();
			if ($access_url_id != -1) {
				$where.= " AND ar.access_url_id = $access_url_id ";
				$query = "$select
				 FROM $tbl_session s
					LEFT JOIN  $tbl_session_category sc ON s.session_category_id = sc.id
					INNER JOIN $tbl_user u ON s.id_coach = u.user_id
					INNER JOIN $table_access_url_rel_session ar ON ar.session_id = s.id
				 $where";
			}
		}  
		$query .= ") AS session_table";   


		if (!empty($options['where'])) {
		   $query .= ' WHERE '.$options['where']; 
		}

		$query .= " ORDER BY ".$options['order']." LIMIT ".$options['limit'];

		$result = Database::query($query);
		$formatted_sessions = array();
		if (Database::num_rows($result)) {
			$sessions   = Database::store_result($result);
			foreach ($sessions as $session) {
				$session['name'] = Display::url($session['name'], "resume_session.php?id_session=".$session['id']);

				$session['coach_name'] = Display::url($session['coach_name'], "user_information.php?user_id=".$session['user_id']);

				if ($session['date_start'] == '0000-00-00' && $session['date_end'] == '0000-00-00') {
				//    $session['session_active'] = 1;
				}

				if ($session['session_active'] == 1) {
					$session['session_active'] = Display::return_icon('accept.png', get_lang('Active'), array(), ICON_SIZE_SMALL);
				} else {
					$session['session_active'] = Display::return_icon('error.png', get_lang('Inactive'), array(), ICON_SIZE_SMALL);
				}


				if ($session['date_start'] == '0000-00-00') {
					$session['date_start'] = '';
				}
				if ($session['date_end'] == '0000-00-00') {
					$session['date_end'] = '';
				}
                
				switch ($session['visibility']) {
					case SESSION_VISIBLE_READ_ONLY: //1
						$session['visibility'] =  get_lang('ReadOnly');
					break;
					case SESSION_VISIBLE:           //2
						$session['visibility'] =  get_lang('Visible');
					break;
					case SESSION_INVISIBLE:         //3
						$session['visibility'] =  api_ucfirst(get_lang('Invisible'));
					break;
			  }
			  $formatted_sessions[] = $session;
			}
		}
		
		return $formatted_sessions;
	}    
    	
    /**
     * Creates a new course code based in given code
     * 
     * @param string	wanted code
     * <code>
     * $wanted_code = 'curse' if there are in the DB codes like curse1 curse2 the function will return: course3
     * if the course code doest not exist in the DB the same course code will be returned
     * </code>
     * @return string	wanted unused code
     */
	function generate_nice_next_session_name($session_name) {        
        $session_name_ok = !self::session_name_exists($session_name);        
        if (!$session_name_ok) {           
           $table = Database::get_main_table(TABLE_MAIN_SESSION);
           $session_name = Database::escape_string($session_name);
           $sql = "SELECT count(*) as count FROM $table WHERE name LIKE '$session_name%'";           
           $result = Database::query($sql);
           if (Database::num_rows($result) > 0 ) {
		       $row = Database::fetch_array($result);
		       $count = $row['count'] + 1;
		       $session_name = $session_name.'_'.$count;
		       $result = self::session_name_exists($session_name);
		       if (!$result) {
		           return $session_name;
		       }		    
           }
           return false;     
        }     
        return $session_name;
    }
    
	/**
	 * Edit a session
	 * @author Carlos Vargas from existing code
	 * @param	integer		id
	 * @param	string 		name
	 * @param 	integer		year_start
	 * @param 	integer		month_start
	 * @param 	integer		day_start
	 * @param 	integer		year_end
	 * @param 	integer		month_end
	 * @param 	integer		day_end
	 * @param 	integer		nb_days_acess_before
	 * @param 	integer		nb_days_acess_after
	 * @param 	integer		nolimit
	 * @param 	integer		id_coach
	 * @param 	integer		id_session_category
	 * @return $id;
	 * The parameter id is a primary key
	**/
	public static function edit_session ($id,$name,$year_start,$month_start,$day_start,$year_end,$month_end,$day_end,$nb_days_acess_before,$nb_days_acess_after,$nolimit,$id_coach, $id_session_category, $id_visibility, $start_limit = true, $end_limit = true) {
		global $_user;
		$name=trim(stripslashes($name));
		$year_start=intval($year_start);
		$month_start=intval($month_start);
		$day_start=intval($day_start);
		$year_end=intval($year_end);
		$month_end=intval($month_end);
		$day_end=intval($day_end);
		$id_coach= intval($id_coach);
		$nb_days_acess_before= intval($nb_days_acess_before);
		$nb_days_acess_after = intval($nb_days_acess_after);
		$id_session_category = intval($id_session_category);
		$id_visibility = intval($id_visibility);

		$tbl_user		= Database::get_main_table(TABLE_MAIN_USER);
		$tbl_session	= Database::get_main_table(TABLE_MAIN_SESSION);
		$tbl_session_rel_course = Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
              
		if (empty($nolimit)) {
			$date_start  = "$year_start-".(($month_start < 10)?"0$month_start":$month_start)."-".(($day_start < 10)?"0$day_start":$day_start);
			$date_end    = "$year_end-".(($month_end < 10)?"0$month_end":$month_end)."-".(($day_end < 10)?"0$day_end":$day_end);
		} else {
			$date_start  = "0000-00-00";
			$date_end    = "0000-00-00";
			$id_visibility = 1;//force read only
		}
        
        if (!empty($no_end_limit)) {
        	$date_end   = "0000-00-00";
        }
        
        if (empty($end_limit)) {
            $date_end ="0000-00-00";
            $id_visibility = 1;//force read only
        }
              
        if (empty($start_limit)) {
            $date_start ="0000-00-00";
        }
               
		if (empty($name)) {
			$msg=get_lang('SessionNameIsRequired');
			return $msg;
		} elseif (empty($id_coach))   {
			$msg=get_lang('CoachIsRequired');
			return $msg;
		} elseif (!empty($start_limit) && empty($nolimit) && (!$month_start || !$day_start || !$year_start || !checkdate($month_start,$day_start,$year_start))) {
			$msg=get_lang('InvalidStartDate');
			return $msg;
		} elseif (!empty($end_limit) && empty($nolimit) && (!$month_end || !$day_end || !$year_end || !checkdate($month_end,$day_end,$year_end))) {
			$msg=get_lang('InvalidEndDate');
			return $msg;
		} elseif (!empty($start_limit) && !empty($end_limit) && empty($nolimit) && $date_start >= $date_end) {
			$msg=get_lang('StartDateShouldBeBeforeEndDate');
			return $msg;
		} else {
			$rs = Database::query("SELECT id FROM $tbl_session WHERE name='".Database::escape_string($name)."'");
			$exists = false;
			while ($row = Database::fetch_array($rs)) {
				if($row['id']!=$id)
					$exists = true;
			}
			if ($exists) {
				$msg=get_lang('SessionNameAlreadyExists');
				return $msg;
			} else {
				$sql="UPDATE $tbl_session " .
					"SET name='".Database::escape_string($name)."',
						date_start='".$date_start."',
						date_end='".$date_end."',
						id_coach='".$id_coach."',
						nb_days_access_before_beginning = ".$nb_days_acess_before.",
						nb_days_access_after_end = ".$nb_days_acess_after.",
						session_category_id = ".$id_session_category." ,
						visibility= ".$id_visibility."
					  WHERE id='$id'";
				Database::query($sql);
				return $id;
			}
		}
	}
	/**
	 * Delete session
	 * @author Carlos Vargas  from existing code
	 * @param	array	id_checked
	 * @param   boolean  optional, true if the function is called by a webservice, false otherwise.
     * @return	void	Nothing, or false on error
	 * The parameters is a array to delete sessions
	 **/
	public static function delete_session ($id_checked,$from_ws = false) {
		$tbl_session=						Database::get_main_table(TABLE_MAIN_SESSION);
		$tbl_session_rel_course=			Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
		$tbl_session_rel_course_rel_user=	Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
		$tbl_session_rel_user=				Database::get_main_table(TABLE_MAIN_SESSION_USER);
		$tbl_user = 						Database::get_main_table(TABLE_MAIN_USER);
		$tbl_url_session                  = Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_SESSION);
		
		global $_user;
		if(is_array($id_checked)) {
			$id_checked = Database::escape_string(implode(',',$id_checked));
		} else {
			$id_checked = intval($id_checked);
		}

		if (!api_is_platform_admin() && !$from_ws) {
			$sql = 'SELECT session_admin_id FROM '.Database :: get_main_table(TABLE_MAIN_SESSION).' WHERE id='.$id_checked;
			$rs  = Database::query($sql);
			if (Database::result($rs,0,0)!=$_user['user_id']) {
				api_not_allowed(true);
			}
		}
		Database::query("DELETE FROM $tbl_session WHERE id IN($id_checked)");
		Database::query("DELETE FROM $tbl_session_rel_course WHERE id_session IN($id_checked)");
		Database::query("DELETE FROM $tbl_session_rel_course_rel_user WHERE id_session IN($id_checked)");
		Database::query("DELETE FROM $tbl_session_rel_user WHERE id_session IN($id_checked)");
		Database::query("DELETE FROM $tbl_url_session WHERE session_id IN($id_checked)");

		// delete extra session fields
		$t_sf 		= Database::get_main_table(TABLE_MAIN_SESSION_FIELD);
		$t_sfv 		= Database::get_main_table(TABLE_MAIN_SESSION_FIELD_VALUES);

		// Delete extra fields from session where field variable is "SECCION"
		$sql = "SELECT t_sfv.field_id FROM $t_sfv t_sfv, $t_sf t_sf  WHERE t_sfv.session_id = '$id_checked' AND t_sf.field_variable = 'SECCION' ";
		$rs_field = Database::query($sql);

		$field_id = 0;
		if (Database::num_rows($rs_field) == 1) {
			$row_field = Database::fetch_row($rs_field);
			$field_id = $row_field[0];

			$sql_delete_sfv = "DELETE FROM $t_sfv WHERE session_id = '$id_checked' AND field_id = '$field_id'";
			$rs_delete_sfv = Database::query($sql_delete_sfv);
		}

		$sql = "SELECT * FROM $t_sfv WHERE field_id = '$field_id' ";
		$rs_field_id = Database::query($sql);

		if (Database::num_rows($rs_field_id) == 0) {
			$sql_delete_sf = "DELETE FROM $t_sf WHERE id = '$field_id'";
			$rs_delete_sf = Database::query($sql_delete_sf);
		}

		/*
		$sql = "SELECT distinct field_id FROM $t_sfv  WHERE session_id = '$id_checked'";
		$res_field_ids = @Database::query($sql);

		if (Database::num_rows($res_field_ids) > 0) {
			while($row_field_id = Database::fetch_row($res_field_ids)){
				$field_ids[] = $row_field_id[0];
			}
		}

		//delete from table_session_field_value from a given session id

		$sql_session_field_value = "DELETE FROM $t_sfv WHERE session_id = '$id_checked'";
		@Database::query($sql_session_field_value);

		$sql = "SELECT distinct field_id FROM $t_sfv";
		$res_field_all_ids = @Database::query($sql);

		if (Database::num_rows($res_field_all_ids) > 0) {
			while($row_field_all_id = Database::fetch_row($res_field_all_ids)){
				$field_all_ids[] = $row_field_all_id[0];
			}
		}

		if (count($field_ids) > 0 && count($field_all_ids) > 0) {
			foreach($field_ids as $field_id) {
				// check if field id is used into table field value
				if (in_array($field_id,$field_all_ids)) {
					continue;
				} else {
					$sql_session_field = "DELETE FROM $t_sf WHERE id = '$field_id'";
					Database::query($sql_session_field);
				}
			}
		}
		*/
		// Add event to system log		
		$user_id = api_get_user_id();
		event_system(LOG_SESSION_DELETE, LOG_SESSION_ID, $id_checked, api_get_utc_datetime(), $user_id);
	}


	 /**
	  * Subscribes users to the given session and optionally (default) unsubscribes previous users
	  * @author Carlos Vargas from existing code
	  * @param	integer		Session ID
	  * @param	array		List of user IDs
	  * @param	bool		Whether to unsubscribe existing users (true, default) or not (false)
	  * @return	void		Nothing, or false on error
	  **/
	public static function suscribe_users_to_session($id_session, $user_list, $session_visibility = SESSION_VISIBLE_READ_ONLY, $empty_users=true, $send_email=false) {

	  	if ($id_session!= strval(intval($id_session))) return false;
	   	foreach($user_list as $intUser){
	   		if ($intUser!= strval(intval($intUser))) return false;
	   	}
	   	$tbl_session_rel_course				= Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
		$tbl_session_rel_course_rel_user	= Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
	   	$tbl_session_rel_user 				= Database::get_main_table(TABLE_MAIN_SESSION_USER);
	   	$tbl_session						= Database::get_main_table(TABLE_MAIN_SESSION);

		$session_info 		= api_get_session_info($id_session);
		$session_name 		= $session_info['name'];

		//from function parameter		
	   	if (empty($session_visibility)) {
	   		$session_visibility	= $session_info['visibility']; //loaded from DB
	   		//default status loaded if empty
			if (empty($session_visibility))
				$session_visibility = SESSION_VISIBLE_READ_ONLY; // by default readonly 1
	   	} else {
	   	    if (!in_array($session_visibility, array(SESSION_VISIBLE_READ_ONLY, SESSION_VISIBLE, SESSION_INVISIBLE))) {
	   	        $session_visibility = SESSION_VISIBLE_READ_ONLY;
	   	    }
	   	}

        $sql = "SELECT id_user FROM $tbl_session_rel_course_rel_user WHERE id_session = '$id_session' ";
        
		$result = Database::query($sql);
		$existingUsers = array();
		while($row = Database::fetch_array($result)) {
			$existingUsers[] = $row['id_user'];
		}
		$sql = "SELECT course_code FROM $tbl_session_rel_course WHERE id_session = '$id_session'";
		$result = Database::query($sql);
		$course_list = array();

		while($row = Database::fetch_array($result)) {
			$course_list[]=$row['course_code'];
		}


		if ($send_email) {
		    //global $_configuration;
			//sending emails only
			if (is_array($user_list) && count($user_list)>0) {
				foreach($user_list as $enreg_user) {
				    if (!in_array($enreg_user,$existingUsers )) {
					    //send email
					    $emailbody 	= '';
					    $emailheaders = '';

					    $user_info 	= UserManager::get_user_info_by_id($enreg_user);
					    $firstname 	= $user_info['firstname'];
					    $lastname 	= $user_info['lastname'];
					    $email 		= $user_info['email'];

					    $emailto = '"'.$firstname.' '.$lastname.'" <'.$email.'>';
					    $emailsubject = '['.get_setting('siteName').'] '.get_lang('YourReg').' '.get_setting('siteName');
					    $emailheaders = 'From: '.get_setting('administratorName').' '.get_setting('administratorSurname').' <'.get_setting('emailAdministrator').">\n";
					    $emailheaders .= 'Reply-To: '.get_setting('emailAdministrator');
		
					    $emailbody	= get_lang('Dear')." ".stripslashes(api_get_person_name($firstname, $lastname)).",\n\n".sprintf(get_lang('YouAreRegisterToSessionX'), $session_name) ." \n\n" .get_lang('Address') ." ". get_setting('siteName') ." ". get_lang('Is') ." : ". api_get_path(WEB_PATH) ."\n\n". get_lang('Problem'). "\n\n". get_lang('Formula').",\n\n".get_setting('administratorName')." ".get_setting('administratorSurname')."\n". get_lang('Manager'). " ".get_setting('siteName')."\nT. ".get_setting('administratorTelephone')."\n" .get_lang('Email') ." : ".get_setting('emailAdministrator');
			
					    @api_send_mail($emailto, $emailsubject, $emailbody, $emailheaders);

					}
				}
			}
		}

		foreach ($course_list as $enreg_course) {
			// for each course in the session
			$nbr_users=0;
	        $enreg_course = Database::escape_string($enreg_course);
		    // delete existing users
			if ($empty_users) {
				foreach ($existingUsers as $existing_user) {
					if (!in_array($existing_user, $user_list)) {
						$sql = "DELETE FROM $tbl_session_rel_course_rel_user WHERE id_session='$id_session' AND course_code='$enreg_course' AND id_user='$existing_user' ";
						Database::query($sql);
						if (Database::affected_rows()) {
							$nbr_users--;
						}
					}
				}
			}
            
			//Replace with this new function
            //
			// insert new users into session_rel_course_rel_user and ignore if they already exist
			foreach ($user_list as $enreg_user) {
				if(!in_array($enreg_user, $existingUsers)) {
	                $enreg_user = Database::escape_string($enreg_user);
					$insert_sql = "INSERT IGNORE INTO $tbl_session_rel_course_rel_user(id_session,course_code,id_user,visibility) VALUES('$id_session','$enreg_course','$enreg_user','$session_visibility')";
					Database::query($insert_sql);
					if(Database::affected_rows()) {
						$nbr_users++;
					}
				}
			}
			// count users in this session-course relation
			$sql = "SELECT COUNT(id_user) as nbUsers FROM $tbl_session_rel_course_rel_user WHERE id_session='$id_session' AND course_code='$enreg_course' AND status<>2";
			$rs = Database::query($sql);
			list($nbr_users) = Database::fetch_array($rs);
			// update the session-course relation to add the users total
			$update_sql = "UPDATE $tbl_session_rel_course SET nbr_users=$nbr_users WHERE id_session='$id_session' AND course_code='$enreg_course'";
			Database::query($update_sql);
		}

		// Delete users from the session
		if ($empty_users===true) {
			Database::query("DELETE FROM $tbl_session_rel_user WHERE id_session = $id_session AND relation_type<>".SESSION_RELATION_TYPE_RRHH."");
		}
		
		// Insert missing users into session
		$nbr_users = 0;		
		foreach ($user_list as $enreg_user) {
	        $enreg_user = Database::escape_string($enreg_user);
			$nbr_users++;
			$insert_sql = "INSERT IGNORE INTO $tbl_session_rel_user (id_session, id_user) VALUES ('$id_session','$enreg_user')";
			Database::query($insert_sql);
		}

		// update number of users in the session
		$nbr_users = count($user_list);		
        if ($empty_users) {
            // update number of users in the session            
            $update_sql = "UPDATE $tbl_session SET nbr_users= $nbr_users WHERE id='$id_session' ";
            Database::query($update_sql);
        } else {
            $update_sql = "UPDATE $tbl_session SET nbr_users= nbr_users + $nbr_users WHERE id='$id_session' ";
            Database::query($update_sql);           
        }
	}
    
    function subscribe_users_to_session_course($user_list, $session_id, $course_code, $session_visibility = SESSION_VISIBLE_READ_ONLY ) {
           	$tbl_session_rel_course				= Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
            $tbl_session_rel_course_rel_user	= Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
            
            if (empty($user_list) || empty($session_id) || empty($course_code)) {
                return false;                
            }
            
            $session_id = intval($session_id);
            $course_code = Database::escape_string($course_code);
            $session_visibility = intval($session_visibility);                      
    
            $nbr_users = 0;
			foreach ($user_list as $enreg_user) {
				//if (!in_array($enreg_user, $existingUsers)) {
	                $enreg_user = intval($enreg_user);
					$insert_sql = "INSERT IGNORE INTO $tbl_session_rel_course_rel_user(id_session,course_code,id_user,visibility) 
                                   VALUES ('$session_id','$course_code','$enreg_user','$session_visibility')";
					Database::query($insert_sql);
					if (Database::affected_rows()) {
						$nbr_users++;
					}
				//}
			}
			// count users in this session-course relation
			$sql = "SELECT COUNT(id_user) as nbUsers FROM $tbl_session_rel_course_rel_user WHERE id_session='$id_session' AND course_code='$enreg_course' AND status<>2";
			$rs = Database::query($sql);
			list($nbr_users) = Database::fetch_array($rs);
			// update the session-course relation to add the users total
			$update_sql = "UPDATE $tbl_session_rel_course SET nbr_users=$nbr_users WHERE id_session='$id_session' AND course_code='$enreg_course'";
			Database::query($update_sql);
    }

	/**
	 * Unsubscribe user from session
	 *
	 * @param int Session id
	 * @param int User id
	 * @return bool True in case of success, false in case of error
	 */
	public static function unsubscribe_user_from_session($session_id, $user_id) {
		$session_id = (int)$session_id;
		$user_id = (int)$user_id;

		$tbl_session_rel_course_rel_user = Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
		$tbl_session_rel_course	= Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
		$tbl_session_rel_user = Database::get_main_table(TABLE_MAIN_SESSION_USER);
		$tbl_session = Database::get_main_table(TABLE_MAIN_SESSION);

		$delete_sql = "DELETE FROM $tbl_session_rel_user WHERE id_session = '$session_id' AND id_user ='$user_id' AND relation_type<>".SESSION_RELATION_TYPE_RRHH."";
		Database::query($delete_sql);
		$return = Database::affected_rows();

		// Update number of users
		$update_sql = "UPDATE $tbl_session SET nbr_users= nbr_users - $return WHERE id='$session_id' ";
		Database::query($update_sql);

		// Get the list of courses related to this session
		$course_list = SessionManager::get_course_list_by_session_id($session_id);
		if(!empty($course_list)) {
			foreach($course_list as $course) {
				$course_code = $course['code'];
				// Delete user from course
				Database::query("DELETE FROM $tbl_session_rel_course_rel_user WHERE id_session='$session_id' AND course_code='$course_code' AND id_user='$user_id'");
				if(Database::affected_rows()) {
					// Update number of users in this relation
					Database::query("UPDATE $tbl_session_rel_course SET nbr_users=nbr_users - 1 WHERE id_session='$session_id' AND course_code='$course_code'");
				}
			}
		}

		return true;

	}

	 /** Subscribes courses to the given session and optionally (default) unsubscribes previous users
	 * @author Carlos Vargas from existing code
     * @param	int		Session ID
     * @param	array	List of courses IDs
     * @param	bool	Whether to unsubscribe existing users (true, default) or not (false)
     * @return	void	Nothing, or false on error
     **/
     public static function add_courses_to_session ($id_session, $course_list, $empty_courses=true) {
     	// security checks
     	if ($id_session!= strval(intval($id_session))) { return false; }
	   	//foreach($course_list as $intCourse){
	   	//	if ($intCourse!= strval(intval($intCourse))) { return false; }
	   	//}
	   	// initialisation
		$tbl_session_rel_course_rel_user	= Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
		$tbl_session						= Database::get_main_table(TABLE_MAIN_SESSION);
		$tbl_session_rel_user				= Database::get_main_table(TABLE_MAIN_SESSION_USER);
		$tbl_session_rel_course				= Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
		$tbl_course							= Database::get_main_table(TABLE_MAIN_COURSE);
     	// get general coach ID
		$id_coach = Database::query("SELECT id_coach FROM $tbl_session WHERE id=$id_session");
		$id_coach = Database::fetch_array($id_coach);
		$id_coach = $id_coach[0];
		// get list of courses subscribed to this session
		$rs = Database::query("SELECT course_code FROM $tbl_session_rel_course WHERE id_session=$id_session");
		$existingCourses = Database::store_result($rs);
		$nbr_courses=count($existingCourses);
		// get list of users subscribed to this session
		$sql="SELECT id_user
			FROM $tbl_session_rel_user
			WHERE id_session = $id_session AND relation_type<>".SESSION_RELATION_TYPE_RRHH."";
		$result=Database::query($sql);
		$user_list=Database::store_result($result);

		// remove existing courses from the session
		if ($empty_courses===true) {
			foreach ($existingCourses as $existingCourse) {
				if (!in_array($existingCourse['course_code'], $course_list)){
					Database::query("DELETE FROM $tbl_session_rel_course WHERE course_code='".$existingCourse['course_code']."' AND id_session=$id_session");
					Database::query("DELETE FROM $tbl_session_rel_course_rel_user WHERE course_code='".$existingCourse['course_code']."' AND id_session=$id_session");

				}
			}
			$nbr_courses=0;
		}

		// Pass through the courses list we want to add to the session
		foreach ($course_list as $enreg_course) {
			$enreg_course = Database::escape_string($enreg_course);
			$exists = false;
			// check if the course we want to add is already subscribed
			foreach ($existingCourses as $existingCourse) {
				if ($enreg_course == $existingCourse['course_code']) {
					$exists=true;
				}
			}
			if (!$exists) {
				//if the course isn't subscribed yet
				$sql_insert_rel_course= "INSERT INTO $tbl_session_rel_course (id_session,course_code) VALUES ('$id_session','$enreg_course')";
				Database::query($sql_insert_rel_course);
				//We add the current course in the existing courses array, to avoid adding another time the current course
				$existingCourses[]=array('course_code'=>$enreg_course);
				$nbr_courses++;

				// subscribe all the users from the session to this course inside the session
				$nbr_users=0;
				foreach ($user_list as $enreg_user) {
					$enreg_user_id = Database::escape_string($enreg_user['id_user']);
					$sql_insert = "INSERT IGNORE INTO $tbl_session_rel_course_rel_user (id_session,course_code,id_user) VALUES ('$id_session','$enreg_course','$enreg_user_id')";
					Database::query($sql_insert);
					if (Database::affected_rows()) {
						$nbr_users++;
					}
				}
				Database::query("UPDATE $tbl_session_rel_course SET nbr_users=$nbr_users WHERE id_session='$id_session' AND course_code='$enreg_course'");
			}
		}
		Database::query("UPDATE $tbl_session SET nbr_courses=$nbr_courses WHERE id='$id_session'");
     }

	/**
	 * Unsubscribe course from a session
	 *
	 * @param int Session id
	 * @param int Course id
	 * @return bool True in case of success, false otherwise
	 */
	public static function unsubscribe_course_from_session($session_id, $course_id) {
		$session_id = (int)$session_id;
		$course_id = (int)$course_id;

		$tbl_session_rel_course = Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
		$tbl_session_rel_course_rel_user	= Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
		$tbl_session = Database::get_main_table(TABLE_MAIN_SESSION);

		// Get course code
		$course_code = CourseManager::get_course_code_from_course_id($course_id);
		if($course_code == 0) {
			return false;
		}

		// Unsubscribe course
	    Database::query("DELETE FROM $tbl_session_rel_course WHERE course_code='$course_code' AND id_session='$session_id'");
	    $nb_affected = Database::affected_rows();

	    Database::query("DELETE FROM $tbl_session_rel_course_rel_user WHERE course_code='$course_code' AND id_session='$session_id'");
	    if($nb_affected > 0) {
			// Update number of courses in the session
			Database::query("UPDATE $tbl_session SET nbr_courses= nbr_courses + $nb_affected WHERE id='$session_id' ");
			return true;
		} else {
			return false;
		}
	}


  /**
  * Creates a new extra field for a given session
  * @param	string	Field's internal variable name
  * @param	int		Field's type
  * @param	string	Field's language var name
  * @return int     new extra field id
  */
	public static function create_session_extra_field ($fieldvarname, $fieldtype, $fieldtitle) {
		// database table definition
		$t_sf 			= Database::get_main_table(TABLE_MAIN_SESSION_FIELD);
		$fieldvarname 	= Database::escape_string($fieldvarname);
		$fieldtitle 	= Database::escape_string($fieldtitle);
		$fieldtype = (int)$fieldtype;
		$time = time();
		$sql_field = "SELECT id FROM $t_sf WHERE field_variable = '$fieldvarname'";
		$res_field = Database::query($sql_field);

		$r_field = Database::fetch_row($res_field);

		if (Database::num_rows($res_field)>0) {
			$field_id = $r_field[0];
		} else {
			// save new fieldlabel into course_field table
			$sql = "SELECT MAX(field_order) FROM $t_sf";
			$res = Database::query($sql);

			$order = 0;
			if (Database::num_rows($res)>0) {
				$row = Database::fetch_row($res);
				$order = $row[0]+1;
			}

			$sql = "INSERT INTO $t_sf
						                SET field_type = '$fieldtype',
						                field_variable = '$fieldvarname',
						                field_display_text = '$fieldtitle',
						                field_order = '$order',
						                tms = FROM_UNIXTIME($time)";
			$result = Database::query($sql);

			$field_id=Database::insert_id();
		}
		return $field_id;
	}

/**
 * Update an extra field value for a given session
 * @param	integer	Course ID
 * @param	string	Field variable name
 * @param	string	Field value
 * @return	boolean	true if field updated, false otherwise
 */
	public static function update_session_extra_field_value ($session_id,$fname,$fvalue='') {

		$t_sf 			= Database::get_main_table(TABLE_MAIN_SESSION_FIELD);
		$t_sfv 			= Database::get_main_table(TABLE_MAIN_SESSION_FIELD_VALUES);
		$fname = Database::escape_string($fname);
		$session_id = (int)$session_id;
		$fvalues = '';
		if(is_array($fvalue))
		{
			foreach($fvalue as $val)
			{
				$fvalues .= Database::escape_string($val).';';
			}
			if(!empty($fvalues))
			{
				$fvalues = substr($fvalues,0,-1);
			}
		}
		else
		{
			$fvalues = Database::escape_string($fvalue);
		}

		$sqlsf = "SELECT * FROM $t_sf WHERE field_variable='$fname'";
		$ressf = Database::query($sqlsf);
		if(Database::num_rows($ressf)==1)
		{ //ok, the field exists
			//	Check if enumerated field, if the option is available
			$rowsf = Database::fetch_array($ressf);

			$tms = time();
			$sqlsfv = "SELECT * FROM $t_sfv WHERE session_id = '$session_id' AND field_id = '".$rowsf['id']."' ORDER BY id";
			$ressfv = Database::query($sqlsfv);
			$n = Database::num_rows($ressfv);
			if ($n>1) {
				//problem, we already have to values for this field and user combination - keep last one
				while($rowsfv = Database::fetch_array($ressfv))
				{
					if($n > 1)
					{
						$sqld = "DELETE FROM $t_sfv WHERE id = ".$rowsfv['id'];
						$resd = Database::query($sqld);
						$n--;
					}
					$rowsfv = Database::fetch_array($ressfv);
					if($rowsfv['field_value'] != $fvalues)
					{
						$sqlu = "UPDATE $t_sfv SET field_value = '$fvalues', tms = FROM_UNIXTIME($tms) WHERE id = ".$rowsfv['id'];
						$resu = Database::query($sqlu);
						return($resu?true:false);
					}
					return true;
				}
			} else if ($n==1) {
				//we need to update the current record
				$rowsfv = Database::fetch_array($ressfv);
				if($rowsfv['field_value'] != $fvalues)
				{
					$sqlu = "UPDATE $t_sfv SET field_value = '$fvalues', tms = FROM_UNIXTIME($tms) WHERE id = ".$rowsfv['id'];
					//error_log('UM::update_extra_field_value: '.$sqlu);
					$resu = Database::query($sqlu);
					return($resu?true:false);
				}
				return true;
			} else {
				$sqli = "INSERT INTO $t_sfv (session_id,field_id,field_value,tms) " .
					"VALUES ('$session_id',".$rowsf['id'].",'$fvalues',FROM_UNIXTIME($tms))";
				//error_log('UM::update_extra_field_value: '.$sqli);
				$resi = Database::query($sqli);
				return($resi?true:false);
			}
		} else {
			return false; //field not found
		}
	}

	/**
	* Checks the relationship between a session and a course.
	* @param int $session_id
	* @param int $course_id
	* @return bool				Returns TRUE if the session and the course are related, FALSE otherwise.
	* */
	public static function relation_session_course_exist ($session_id, $course_id) {
		$tbl_session_course	= Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
		$return_value = false;
		$sql= "SELECT course_code FROM $tbl_session_course WHERE id_session = ".Database::escape_string($session_id)." AND course_code = '".Database::escape_string($course_id)."'";
		$result = Database::query($sql);
		$num = Database::num_rows($result);
		if ($num>0) {
			$return_value = true;
		}
		return $return_value;
	}

	/**
	* Get the session information by name
	* @param string session name
	* @return mixed false if the session does not exist, array if the session exist
	* */
	public static function get_session_by_name ($session_name) {
		$tbl_session = Database::get_main_table(TABLE_MAIN_SESSION);
		$sql = 'SELECT id, id_coach, date_start, date_end FROM '.$tbl_session.' WHERE name="'.Database::escape_string($session_name).'"';
		$result = Database::query($sql);
		$num = Database::num_rows($result);
		if ($num>0){
			return Database::fetch_array($result);
		} else {
			return false;
		}
	}

	/**
	  * Create a session category
	  * @author Jhon Hinojosa <jhon.hinojosa@dokeos.com>, from existing code
	  * @param	string 		name
	  * @param 	integer		year_start
	  * @param 	integer		month_start
	  * @param 	integer		day_start
	  * @param 	integer		year_end
	  * @param 	integer		month_end
	  * @param 	integer		day_end
	  * @return $id_session;
	  **/
	public static function create_category_session($sname,$syear_start,$smonth_start,$sday_start,$syear_end,$smonth_end, $sday_end){
		$tbl_session_category = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);
		$name= trim($sname);
		$year_start= intval($syear_start);
		$month_start=intval($smonth_start);
		$day_start=intval($sday_start);
		$year_end=intval($syear_end);
		$month_end=intval($smonth_end);
		$day_end=intval($sday_end);

    $date_start = "$year_start-".(($month_start < 10)?"0$month_start":$month_start)."-".(($day_start < 10)?"0$day_start":$day_start);
    $date_end = "$year_end-".(($month_end < 10)?"0$month_end":$month_end)."-".(($day_end < 10)?"0$day_end":$day_end);

		if (empty($name)) {
			$msg=get_lang('SessionCategoryNameIsRequired');
			return $msg;
		} elseif (!$month_start || !$day_start || !$year_start || !checkdate($month_start,$day_start,$year_start)) {
			$msg=get_lang('InvalidStartDate');
			return $msg;
        } elseif (!$month_end && !$day_end && !$year_end) {
            $date_end = "null";
		} elseif (!$month_end || !$day_end || !$year_end || !checkdate($month_end,$day_end,$year_end)) {
			$msg=get_lang('InvalidEndDate');
			return $msg;
		} elseif($date_start >= $date_end) {
			$msg=get_lang('StartDateShouldBeBeforeEndDate');
			return $msg;
		}
		$access_url_id = api_get_current_access_url_id();
        $sql = "INSERT INTO $tbl_session_category (name, date_start, date_end, access_url_id)
        		VALUES('".Database::escape_string($name)."','$date_start','$date_end', '$access_url_id')";
        Database::query($sql);
        $id_session = Database::insert_id();
        // Add event to system log        
        $user_id = api_get_user_id();
        event_system(LOG_SESSION_CATEGORY_CREATE, LOG_SESSION_CATEGORY_ID, $id_session, api_get_utc_datetime(), $user_id);
        return $id_session;
	}

	/**
	 * Edit a sessions categories
	 * @author Jhon Hinojosa <jhon.hinojosa@dokeos.com>,from existing code
	 * @param	integer		id
	 * @param	string 		name
	 * @param 	integer		year_start
	 * @param 	integer		month_start
	 * @param 	integer		day_start
	 * @param 	integer		year_end
	 * @param 	integer		month_end
	 * @param 	integer		day_end
	 * @return $id;
	 * The parameter id is a primary key
	**/
	public static function edit_category_session($id, $sname,$syear_start,$smonth_start,$sday_start,$syear_end,$smonth_end, $sday_end){
		$tbl_session_category = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);
		$name= trim($sname);
		$year_start= intval($syear_start);
		$month_start=intval($smonth_start);
		$day_start=intval($sday_start);
		$year_end=intval($syear_end);
		$month_end=intval($smonth_end);
		$day_end=intval($sday_end);
		$id=intval($id);
		$date_start = "$year_start-".(($month_start < 10)?"0$month_start":$month_start)."-".(($day_start < 10)?"0$day_start":$day_start);
		$date_end = "$year_end-".(($month_end < 10)?"0$month_end":$month_end)."-".(($day_end < 10)?"0$day_end":$day_end);

		if (empty($name)) {
			$msg=get_lang('SessionCategoryNameIsRequired');
			return $msg;
		} elseif (!$month_start || !$day_start || !$year_start || !checkdate($month_start,$day_start,$year_start)) {
			$msg=get_lang('InvalidStartDate');
			return $msg;
		} elseif (!$month_end && !$day_end && !$year_end) {
            $date_end = null;
		} elseif (!$month_end || !$day_end || !$year_end || !checkdate($month_end,$day_end,$year_end)) {
			$msg=get_lang('InvalidEndDate');
			return $msg;
		} elseif($date_start >= $date_end) {
			$msg=get_lang('StartDateShouldBeBeforeEndDate');
			return $msg;
		}
        if ( $date_end <> null ) {
	        $sql = "UPDATE $tbl_session_category SET name = '".Database::escape_string($name)."', date_start = '$date_start' ".
                ", date_end = '$date_end' WHERE id= '".$id."' ";
        } else {
            $sql = "UPDATE $tbl_session_category SET name = '".Database::escape_string($name)."', date_start = '$date_start' ".
                ", date_end = NULL WHERE id= '".$id."' ";
        }
		$result = Database::query($sql);
		return ($result? true:false);

	}

	/**
	 * Delete sessions categories
	 * @author Jhon Hinojosa <jhon.hinojosa@dokeos.com>, from existing code
	 * @param	array	id_checked
	 * @param	bool	include delete session
	 * @param	bool	optional, true if the function is called by a webservice, false otherwise.
     * @return	void	Nothing, or false on error
	 * The parameters is a array to delete sessions
	 **/
	public static function delete_session_category($id_checked, $delete_session = false,$from_ws = false){
		$tbl_session_category = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);
		$tbl_session = Database::get_main_table(TABLE_MAIN_SESSION);
		if (is_array($id_checked)) {
			$id_checked = Database::escape_string(implode(',',$id_checked));
		} else {
			$id_checked = intval($id_checked);
		}
		
		//Setting session_category_id to 0
		$sql = "UPDATE $tbl_session SET session_category_id = 0 WHERE session_category_id IN (".$id_checked.")";
        $result = Database::query($sql);
        
		$sql = "SELECT id FROM $tbl_session WHERE session_category_id IN (".$id_checked.")";
		$result = @Database::query($sql);
		while ($rows = Database::fetch_array($result)) {
			$session_id = $rows['id'];
			if ($delete_session) {
				if ($from_ws) {
					SessionManager::delete_session($session_id,true);
				} else {
					SessionManager::delete_session($session_id);
				}
			}
		}
		$sql = "DELETE FROM $tbl_session_category WHERE id IN (".$id_checked.")";
		$rs = @Database::query($sql);
		$result = Database::affected_rows();

		// Add event to system log		
		$user_id = api_get_user_id();
        
		event_system(LOG_SESSION_CATEGORY_DELETE, LOG_SESSION_CATEGORY_ID, $id_checked, api_get_utc_datetime(), $user_id);


		// delete extra session fields where field variable is "PERIODO"
		$t_sf 		= Database::get_main_table(TABLE_MAIN_SESSION_FIELD);
		$t_sfv 		= Database::get_main_table(TABLE_MAIN_SESSION_FIELD_VALUES);

		$sql = "SELECT t_sfv.field_id FROM $t_sfv t_sfv, $t_sf t_sf  WHERE t_sfv.session_id = '$id_checked' AND t_sf.field_variable = 'PERIODO' ";
		$rs_field = Database::query($sql);

		$field_id = 0;
		if (Database::num_rows($rs_field) > 0) {
			$row_field = Database::fetch_row($rs_field);
			$field_id = $row_field[0];
			$sql_delete_sfv = "DELETE FROM $t_sfv WHERE session_id = '$id_checked' AND field_id = '$field_id'";
			$rs_delete_sfv = Database::query($sql_delete_sfv);
		}

		$sql = "SELECT * FROM $t_sfv WHERE field_id = '$field_id' ";
		$rs_field_id = Database::query($sql);

		if (Database::num_rows($rs_field_id) == 0) {
			$sql_delete_sf = "DELETE FROM $t_sf WHERE id = '$field_id'";
			$rs_delete_sf = Database::query($sql_delete_sf);
		}

		return true;
	}

	/**
     * Get a list of sessions of which the given conditions match with an = 'cond'
	 * @param  array $conditions a list of condition (exemple : array('status =' =>STUDENT) or array('s.name LIKE' => "%$needle%")
	 * @param  array $order_by a list of fields on which sort
	 * @return array An array with all sessions of the platform.
	 * @todo   optional course code parameter, optional sorting parameters...
	*/
	public static function get_sessions_list($conditions = array(), $order_by = array()) {

		$session_table                = Database::get_main_table(TABLE_MAIN_SESSION);
		$session_category_table       = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);
		$user_table                   = Database::get_main_table(TABLE_MAIN_USER);
		$table_access_url_rel_session = Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_SESSION);
		
		$access_url_id = api_get_current_access_url_id();
		  
        $return_array = array();

		$sql_query = " SELECT s.id, s.name, s.nbr_courses, s.date_start, s.date_end, u.firstname, u.lastname, sc.name as category_name, s.promotion_id
				FROM $session_table s
				INNER JOIN $user_table u ON s.id_coach = u.user_id
				INNER JOIN $table_access_url_rel_session ar ON ar.session_id = s.id
				LEFT JOIN  $session_category_table sc ON s.session_category_id = sc.id
				WHERE ar.access_url_id = $access_url_id ";
        
		if (count($conditions)>0) {
			$sql_query .= ' AND ';
			foreach ($conditions as $field=>$value) {
                $field = Database::escape_string($field);
                $value = Database::escape_string($value);
				$sql_query .= $field." '".$value."'";
			}
		}
		if (count($order_by)>0) {
			$sql_query .= ' ORDER BY '.Database::escape_string(implode(',',$order_by));
		}
        //echo $sql_query;
		$sql_result = Database::query($sql_query);
        if (Database::num_rows($sql_result)>0) {
    		while ($result = Database::fetch_array($sql_result)) {
    			$return_array[$result['id']] = $result;
    		}
        }
		return $return_array;
	}
	
	/**
	 * Get the session category information by id
	 * @param string session category ID
	 * @return mixed false if the session category does not exist, array if the session category exists
	 */
	public static function get_session_category ($id) {
		$id = intval($id);
		$tbl_session_category = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);
		$sql = "SELECT id, name, date_start, date_end FROM $tbl_session_category WHERE id= $id";
		$result = Database::query($sql);
		$num = Database::num_rows($result);
		if ($num>0){
			return Database::fetch_array($result);
		} else {
			return false;
		}
	}
	
	/**
	 * Get all session categories (filter by access_url_id)
	 * @return mixed false if the session category does not exist, array if the session category exists
	 */
	public static function get_all_session_category() {		
		$tbl_session_category = Database::get_main_table(TABLE_MAIN_SESSION_CATEGORY);
		$id = api_get_current_access_url_id();
		$sql = 'SELECT * FROM '.$tbl_session_category.' WHERE access_url_id ="'.$id.'" ORDER BY name ASC';
		$result = Database::query($sql);		
		if (Database::num_rows($result) > 0 ){
		    $data = Database::store_result($result,'ASSOC');
		    return $data;
		} else {
			return false;
		}
	}

	/**
	 * Assign a coach to course in session with status = 2
	 * @param int  		- user id
	 * @param int  		- session id
	 * @param string  	- course code
	 * @param bool  	- optional, if is true the user don't be a coach now, otherwise it'll assign a coach
	 * @return bool true if there are affected rows, otherwise false
	 */
	public static function set_coach_to_course_session($user_id, $session_id = 0, $course_code = '',$nocoach = false) {

		// Definition of variables
		$user_id = intval($user_id);

		if (!empty($session_id)) {
			$session_id = intval($session_id);
		} else {
			$session_id = api_get_session_id();
		}

		if (!empty($course_code)) {
			$course_code = Database::escape_string($course_code);
		} else {
			$course_code = api_get_course_id();
		}

		// definitios of tables
		$tbl_session_rel_course_rel_user = Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
		$tbl_session_rel_user = Database::get_main_table(TABLE_MAIN_SESSION_USER);
		$tbl_user	= Database::get_main_table(TABLE_MAIN_USER);

		// check if user is a teacher
		$sql= "SELECT * FROM $tbl_user WHERE status='1' AND user_id = '$user_id'";

		$rs_check_user = Database::query($sql);

		if (Database::num_rows($rs_check_user) > 0) {

			if ($nocoach) {

				// check if user_id exits int session_rel_user
				$sql = "SELECT id_user FROM $tbl_session_rel_user WHERE id_session = '$session_id' AND id_user = '$user_id'";
				$res = Database::query($sql);

				if (Database::num_rows($res) > 0) {
					// The user don't be a coach now
					$sql = "UPDATE $tbl_session_rel_course_rel_user SET status = 0 WHERE id_session = '$session_id' AND course_code = '$course_code' AND id_user = '$user_id' ";
					$rs_update = Database::query($sql);
					if (Database::affected_rows() > 0) return true;
					else return false;
				} else {
					// The user don't be a coach now
					$sql = "DELETE FROM $tbl_session_rel_course_rel_user WHERE id_session = '$session_id' AND course_code = '$course_code' AND id_user = '$user_id' ";
					$rs_delete = Database::query($sql);
					if (Database::affected_rows() > 0) return true;
					else return false;
				}

			} else {
				// Assign user like a coach to course
				// First check if the user is registered in the course
				$sql = "SELECT id_user FROM $tbl_session_rel_course_rel_user WHERE id_session = '$session_id' AND course_code = '$course_code' AND id_user = '$user_id'";
				$rs_check = Database::query($sql);

				//Then update or insert
				if (Database::num_rows($rs_check) > 0) {
					$sql = "UPDATE $tbl_session_rel_course_rel_user SET status = 2 WHERE id_session = '$session_id' AND course_code = '$course_code' AND id_user = '$user_id' ";
					$rs_update = Database::query($sql);
					if (Database::affected_rows() > 0) return true;
					else return false;
				} else {
					$sql = " INSERT INTO $tbl_session_rel_course_rel_user(id_session, course_code, id_user, status) VALUES('$session_id', '$course_code', '$user_id', 2)";
					$rs_insert = Database::query($sql);
					if (Database::affected_rows() > 0) return true;
					else return false;
				}
			}
		} else {
			return false;
		}
	}

	/**
	  * Subscribes sessions to human resource manager (Dashboard feature)
	  *	@param	int 		Human Resource Manager id
	  * @param	array 		Sessions id
	  * @param	int			Relation type
	  **/
	public static function suscribe_sessions_to_hr_manager($hr_manager_id,$sessions_list) {
        global $_configuration;
        // Database Table Definitions
        $tbl_session                    =   Database::get_main_table(TABLE_MAIN_SESSION);
        $tbl_session_rel_user           =   Database::get_main_table(TABLE_MAIN_SESSION_USER);
        $tbl_session_rel_course_user    =   Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);        
        $tbl_session_rel_access_url     =   Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_SESSION);        

        $hr_manager_id = intval($hr_manager_id);
        $affected_rows = 0;

        //Deleting assigned sessions to hrm_id
        if ($_configuration['multiple_access_urls']) {  
            $sql = "SELECT id_session FROM $tbl_session_rel_user s INNER JOIN $tbl_session_rel_access_url a ON (a.session_id = s.id_session) WHERE id_user = $hr_manager_id AND relation_type=".SESSION_RELATION_TYPE_RRHH." AND access_url_id = ".api_get_current_access_url_id()."";
        } else {
            $sql = "SELECT id_session FROM $tbl_session_rel_user s WHERE id_user = $hr_manager_id AND relation_type=".SESSION_RELATION_TYPE_RRHH."";
        }
        $result = Database::query($sql);  

        if (Database::num_rows($result) > 0) {
            while ($row = Database::fetch_array($result))   {
                 $sql = "DELETE FROM $tbl_session_rel_user WHERE id_session = {$row['id_session']} AND id_user = $hr_manager_id AND relation_type=".SESSION_RELATION_TYPE_RRHH." ";
                 Database::query($sql);
            }
        }

		/*
		//Deleting assigned courses in sessions to hrm_id
	   	$sql = "SELECT * FROM $tbl_session_rel_course_user WHERE id_user = $hr_manager_id ";
		$result = Database::query($sql);

		if (Database::num_rows($result) > 0) {
			$sql = "DELETE FROM $tbl_session_rel_course_user WHERE id_user = $hr_manager_id ";
			Database::query($sql);
		}
		*/

		// inserting new sessions list
		if (is_array($sessions_list)) {
			foreach ($sessions_list as $session_id) {
				$session_id = intval($session_id);
				$insert_sql = "INSERT IGNORE INTO $tbl_session_rel_user(id_session, id_user, relation_type) VALUES($session_id, $hr_manager_id, '".SESSION_RELATION_TYPE_RRHH."')";
				Database::query($insert_sql);
				$affected_rows = Database::affected_rows();
			}
		}
		return $affected_rows;

	}

	/**
	 * Get sessions followed by human resources manager
	 * @param int		Human resources manager or Session admin id
	 * @return array 	sessions
	 */
	public static function get_sessions_followed_by_drh($hr_manager_id) {
        global $_configuration;
		// Database Table Definitions
		$tbl_session 			= 	Database::get_main_table(TABLE_MAIN_SESSION);
		$tbl_session_rel_user 	= 	Database::get_main_table(TABLE_MAIN_SESSION_USER);
        $tbl_session_rel_access_url =   Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_SESSION);

		$hr_manager_id = intval($hr_manager_id);
		$assigned_sessions_to_hrm = array();

		if ($_configuration['multiple_access_urls']) {   
           $sql = "SELECT * FROM $tbl_session s INNER JOIN $tbl_session_rel_user sru ON (sru.id_session = s.id) LEFT JOIN $tbl_session_rel_access_url a  ON (s.id = a.session_id)
                   WHERE sru.id_user = '$hr_manager_id' AND sru.relation_type = '".SESSION_RELATION_TYPE_RRHH."' AND access_url_id = ".api_get_current_access_url_id()."";
        } else {
            $sql = "SELECT * FROM $tbl_session s
                     INNER JOIN $tbl_session_rel_user sru ON sru.id_session = s.id AND sru.id_user = '$hr_manager_id' AND sru.relation_type = '".SESSION_RELATION_TYPE_RRHH."' ";   
        }
		$rs_assigned_sessions = Database::query($sql);
		if (Database::num_rows($rs_assigned_sessions) > 0) {
			while ($row_assigned_sessions = Database::fetch_array($rs_assigned_sessions))	{
				$assigned_sessions_to_hrm[$row_assigned_sessions['id']] = $row_assigned_sessions;
			}
		}
		return $assigned_sessions_to_hrm;
	}

	
	/**
	 * Gets the list of courses by session filtered by access_url
	 * @param int session id
	 * @return array list of courses
	 */
	public static function get_course_list_by_session_id ($session_id) {
		$tbl_course				= Database::get_main_table(TABLE_MAIN_COURSE);
		$tbl_session_rel_course	= Database::get_main_table(TABLE_MAIN_SESSION_COURSE);
        
		// select the courses
		$sql = "SELECT * FROM $tbl_course c INNER JOIN $tbl_session_rel_course src ON c.code = src.course_code 
		        WHERE src.id_session = '$session_id' ORDER BY title;";
		$result 	= Database::query($sql);
		$num_rows 	= Database::num_rows($result);
		$courses = array();
		if ($num_rows > 0) {
			while ($row = Database::fetch_array($result,'ASSOC'))	{
				$courses[$row['id']] = $row;
			}
		}
		return $courses;
	}

	/**
	 * Get the session id based on the original id and field name in the extra fields. Returns 0 if session was not found
	 *
	 * @param string Original session id
	 * @param string Original field name
	 * @return int Session id
	 */
	public static function get_session_id_from_original_id($original_session_id_value, $original_session_id_name) {
		$t_sfv = Database::get_main_table(TABLE_MAIN_SESSION_FIELD_VALUES);
		$table_field = Database::get_main_table(TABLE_MAIN_SESSION_FIELD);
		$sql_session = "SELECT session_id FROM $table_field sf INNER JOIN $t_sfv sfv ON sfv.field_id=sf.id WHERE field_variable='$original_session_id_name' AND field_value='$original_session_id_value'";
		$res_session = Database::query($sql_session);
		$row = Database::fetch_object($res_session);
		if ($row) {
			return $row->session_id;
		} else {
			return 0;
		}
	}
    
    /**
     * Get users by session
     * @param   int sesssion id
     * @param	int	filter by status 
     * @return  array a list with an user list
     */
    public static function get_users_by_session($id, $with_status = false) {
        if (empty($id)) {
            return array();
        }
        $id = intval($id);
        $tbl_user                           = Database::get_main_table(TABLE_MAIN_USER);
        $tbl_session_rel_user               = Database::get_main_table(TABLE_MAIN_SESSION_USER);

        $sql = 'SELECT '.$tbl_user.'.user_id, lastname, firstname, username
                FROM '.$tbl_user.'
                INNER JOIN '.$tbl_session_rel_user.'
                    ON '.$tbl_user.'.user_id = '.$tbl_session_rel_user.'.id_user 
                    AND '.$tbl_session_rel_user.'.id_session = '.$id;
        if ($with_status !== false) {
        	$with_status = intval($with_status);
        	$sql .= " WHERE relation_type = $with_status ";
        }        
        $result = Database::query($sql);
        while ($row = Database::fetch_array($result,'ASSOC')) {
            $return_array[] = $row;
        }
        
        return $return_array;
    }
    
    public static function get_sessions_by_coach($user_id) {
        $session_table = Database::get_main_table(TABLE_MAIN_SESSION);
        return Database::select('*', $session_table, array('where'=>array('id_coach = ?'=>$user_id)));    	
    }
    
    /*
    public static function get_coaches_by_session($session_id, $course_code) {
        $tbl_session_rel_course_rel_user    = Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
        $tbl_user                           = Database::get_main_table(TABLE_MAIN_USER);
        
        $sql = "SELECT user.user_id
                FROM $tbl_session_rel_course_rel_user session_rcru, $tbl_user user
                WHERE session_rcru.id_user = user.user_id AND 
                session_rcru.id_session = '".intval($session_id)."' AND 
                session_rcru.course_code ='".Database::escape_string($course_code)."' AND 
                session_rcru.status = 2 ";
        $result = Database::query($sql);
        while ($row = Database::fetch_array($result,'ASSOC')) {
            $return_array[] = $row;
        }
        return $return_array;
    }*/
    
    /**
     * Gets user status within a session 
     * @param $user_id
     * @param $course_code
     * @param $session_id
     * @return unknown_type
     */
    public function get_user_status_in_session($user_id, $course_code, $session_id) {
        $tbl_session_rel_course_rel_user    = Database::get_main_table(TABLE_MAIN_SESSION_COURSE_USER);
        $tbl_user                           = Database::get_main_table(TABLE_MAIN_USER);        
        $sql = "SELECT session_rcru.status
                FROM $tbl_session_rel_course_rel_user session_rcru, $tbl_user user
                WHERE session_rcru.id_user = user.user_id AND 
                session_rcru.id_session = '".intval($session_id)."' AND 
                session_rcru.course_code ='".Database::escape_string($course_code)."' AND 
                user.user_id = ".intval($user_id);        
        $result = Database::query($sql);
        $status = false;
        if (Database::num_rows($result)) {
            $status = Database::fetch_row($result);
            $status = $status['0'];
        }
        return $status;
    }
        
    
    public static function get_session_by_user($coach_id, $user_id) {
    	
    }
    
    function get_all_sessions_by_promotion($id) {
        $t = Database::get_main_table(TABLE_MAIN_SESSION);
        return Database::select('*', $t, array('where'=>array('promotion_id = ?'=>$id)));
    }
    
    function suscribe_sessions_to_promotion($promotion_id, $list) {
        $t = Database::get_main_table(TABLE_MAIN_SESSION);
        $params = array();
        $params['promotion_id'] = 0;             
        Database::update($t, $params, array('promotion_id = ?'=>$promotion_id));
        
        $params['promotion_id'] = $promotion_id;
        if (!empty($list)) {
            foreach ($list as $session_id) {
                $session_id= intval($session_id);
                Database::update($t, $params, array('id = ?'=>$session_id));
            }                
        }
    }
    
    /**
    * Updates a session status
    * @param	int 	session id
    * @param	int 	status
    */
    public function set_session_status($session_id, $status) {
        $t = Database::get_main_table(TABLE_MAIN_SESSION);
        $params['visibility'] = $status;
    	Database::update($t, $params, array('id = ?'=>$session_id));
    }
    
    /**
     * Copies a session with the same data to a new session. 
     * The new copy is not assigned to the same promotion. @see suscribe_sessions_to_promotions() for that
     * @param   int     Session ID
     * @param   bool    Whether to copy the relationship with courses
     * @param   bool    Whether to copy the relationship with users
     * @param	bool	New courses will be created
     * @return  int     The new session ID on success, 0 otherwise
     * @todo make sure the extra session fields are copied too
     */
    /**
     * @param $id
     * @param $copy_courses
     * @param $copy_users
     * @param $create_new_courses
     * @param $set_exercises_lp_invisible
     * @return unknown_type
     */
    public function copy_session($id, $copy_courses = true, $copy_users = true, $create_new_courses = false, $set_exercises_lp_invisible = false) {
        $id = intval($id);
        $s = self::fetch($id);
        $s['year_start']    = substr($s['date_start'],0,4);
        $s['month_start']   = substr($s['date_start'],5,2);
        $s['day_start']     = substr($s['date_start'],8,2);
        $s['year_end']      = substr($s['date_end'],0,4);
        $s['month_end']     = substr($s['date_end'],5,2);
        $s['day_end']       = substr($s['date_end'],8,2);        
        $consider_start = true;
        if ($s['year_start'].'-'.$s['month_start'].'-'.$s['day_start'] == '0000-00-00') {
            $consider_start = false;
        }
        $consider_end = true;
        if ($s['year_end'].'-'.$s['month_end'].'-'.$s['day_end'] == '0000-00-00') {
            $consider_end = false;
        }
        
        $sid = self::create_session($s['name'].' '.get_lang('Copy'),
             $s['year_start'], $s['month_start'], $s['day_start'],
             $s['year_end'],$s['month_end'],$s['day_end'],
             $s['nb_days_acess_before_beginning'],$s['nb_days_acess_after_end'],
             false,(int)$s['id_coach'], $s['session_category_id'],
             (int)$s['visibility'],$consider_start, $consider_end, true);
        
        if (!is_numeric($sid) || empty($sid)) {
        	return false;
        }
        
        if ($copy_courses) {
            // Register courses from the original session to the new session
            $courses = self::get_course_list_by_session_id($id);
            
            $short_courses = $new_short_courses = array();
            if (is_array($courses) && count($courses)>0) {
            	foreach ($courses as $course) {
            		$short_courses[] = $course;
            	}
            }
            $courses = null;
            
            //We will copy the current courses of the session to new courses
            if (!empty($short_courses)) {
                if ($create_new_courses) {
                    //Just in case
                    if (function_exists('ini_set')) {
                    	ini_set('memory_limit','256M');
                    	ini_set('max_execution_time',0);
                    }      
                    $params = array();                    
                    $params['skip_lp_dates'] = true;                    
                    
                    foreach ($short_courses as $course_data) {
                        $course_info = CourseManager::copy_course_simple($course_data['title'].' '.get_lang('Copy'), $course_data['course_code'], $id, $sid, $params);
                        if ($course_info) {
                            //By default new elements are invisible
                            if ($set_exercises_lp_invisible) {    
                                require_once api_get_path(SYS_CODE_PATH).'newscorm/learnpathList.class.php';
                                $list       = new LearnpathList('', $course_info['code'], $sid);
                                $flat_list  = $list->get_flat_list(); 
                                if (!empty($flat_list)) {                               
                                    foreach($flat_list as $lp_id => $data) { 
                                        api_item_property_update($course_info, TOOL_LEARNPATH, $lp_id, 'invisible', api_get_user_id(), 0 ,0, 0, 0, $sid);
                                        api_item_property_update($course_info, TOOL_LEARNPATH, $lp_id, 'invisible', api_get_user_id(), 0 ,0, 0, 0);
                                    }
                                }
                                $quiz_table   = Database::get_course_table(TABLE_QUIZ_TEST);
                                $course_id	 = $course_info['real_id'];
                                //@todo check this query
                                $sql = "UPDATE $quiz_table SET active = 0 WHERE c_id = $course_id ";
                                $result=Database::query($sql);                                
                            }
                            $new_short_courses[] = $course_info['code'];
                        }                             
                    }                    
                } else {
                    foreach($short_courses as $course_data) {
                         $new_short_courses[] = $course_data['code'];
                    }
                }
                $short_courses = $new_short_courses;
                $res = self::add_courses_to_session($sid, $short_courses, true);
                $short_courses = null;
            }
        }
        if ($copy_users) {
            // Register users from the original session to the new session
            $users = self::get_users_by_session($id);
            $short_users = array();
            if (is_array($users) && count($users)>0) {
                foreach ($users as $user) {
                    $short_users[] = $user['user_id'];
                }
            }
            $users = null;
            //Subscribing in read only mode
            $res = self::suscribe_users_to_session($sid, $short_users, SESSION_VISIBLE_READ_ONLY, true, false);
            $short_users = null;
        }
    	return $sid;
    }
    
    function user_is_general_coach($user_id, $session_id) {
    	$session_id = intval($session_id);
    	$user_id = intval($user_id);
    	$session_table = Database::get_main_table(TABLE_MAIN_SESSION);    	
    	$sql = "SELECT DISTINCT id
	         	FROM $session_table
	         	WHERE session.id_coach =  '".$user_id."' AND id = '$session_id'";
    	$result = Database::query($sql);	
    	if ($result && Database::num_rows($result)) {
    		return true;
    	}
    	return false;
    }
    /**
     * Get the number of sessions
     * @param  int ID of the URL we want to filter on (optional)
     * @return int Number of sessions
     */
    public function count_sessions($access_url_id=null) {
        $session_table = Database::get_main_table(TABLE_MAIN_SESSION);
        $access_url_rel_session_table = Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_SESSION);
        $sql = "SELECT count(id) FROM $session_table s";
        if (!empty($access_url_id) && $access_url_id == intval($access_url_id)) {
            $sql .= ", $access_url_rel_session_table u ".
                    " WHERE s.id = u.session_id AND u.access_url_id = $access_url_id";
        }
        $res = Database::query($sql);
        $row = Database::fetch_row($res);
        return $row[0];
    }
}