diff --git a/main/inc/lib/CourseChatUtils.php b/main/inc/lib/CourseChatUtils.php
index 35a58dc0bf..a9358a3ff3 100644
--- a/main/inc/lib/CourseChatUtils.php
+++ b/main/inc/lib/CourseChatUtils.php
@@ -90,6 +90,8 @@ class CourseChatUtils
         if (empty($message)) {
             return false;
         }
+        $friendId = (int) $friendId;
+
         $user = api_get_user_entity($this->userId);
         $courseInfo = api_get_course_info_by_id($this->courseId);
         $isMaster = api_is_course_admin();
diff --git a/main/inc/lib/course_category.lib.php b/main/inc/lib/course_category.lib.php
index 2c785c4a48..6e5374f1a8 100755
--- a/main/inc/lib/course_category.lib.php
+++ b/main/inc/lib/course_category.lib.php
@@ -482,8 +482,8 @@ class CourseCategory
      */
     public static function listCategories($categorySource)
     {
-        $categorySource = isset($categorySource) ? $categorySource : null;
         $categories = self::getCategories($categorySource);
+        $categorySource = Security::remove_XSS($categorySource);
 
         if (count($categories) > 0) {
             $table = new HTML_Table(['class' => 'data_table']);
@@ -676,51 +676,6 @@ class CourseCategory
         return (int) $row['count'];
     }
 
-    /**
-     * create recursively all categories as option of the select passed in parameter.
-     *
-     * @param HTML_QuickForm_Element $element
-     * @param string                 $defaultCode the option value to select by default (used mainly for edition of courses)
-     * @param string                 $parentCode  the parent category of the categories added (default=null for root category)
-     * @param string                 $padding     the indent param (you shouldn't indicate something here)
-     */
-    public static function setCategoriesInForm(
-        $element,
-        $defaultCode = null,
-        $parentCode = null,
-        $padding = null
-    ) {
-        $tbl_category = Database::get_main_table(TABLE_MAIN_CATEGORY);
-
-        $table = Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_COURSE_CATEGORY);
-        $conditions = " INNER JOIN $table a ON (c.id = a.course_category_id)";
-        $whereCondition = " AND a.access_url_id = ".api_get_current_access_url_id();
-
-        $sql = "SELECT code, name, auth_course_child, auth_cat_child
-                FROM $tbl_category c
-                $conditions
-                WHERE parent_id ".(empty($parentCode) ? "IS NULL" : "='".Database::escape_string($parentCode)."'")."
-                $whereCondition
-                ORDER BY name,  code";
-        $res = Database::query($sql);
-
-        while ($cat = Database::fetch_array($res, 'ASSOC')) {
-            $params = $cat['auth_course_child'] == 'TRUE' ? '' : 'disabled';
-            $params .= ($cat['code'] == $defaultCode) ? ' selected' : '';
-            $option = $padding.' '.$cat['name'].' ('.$cat['code'].')';
-
-            $element->addOption($option, $cat['code'], $params);
-            if ($cat['auth_cat_child'] == 'TRUE') {
-                self::setCategoriesInForm(
-                    $element,
-                    $defaultCode,
-                    $cat['code'],
-                    $padding.' - '
-                );
-            }
-        }
-    }
-
     /**
      * @param array $list
      *
@@ -778,33 +733,6 @@ class CourseCategory
         return Database::store_result($result, 'ASSOC');
     }
 
-    /**
-     * @param array $list
-     *
-     * @return array
-     */
-    public static function searchCategoryById($list)
-    {
-        if (empty($list)) {
-            return [];
-        } else {
-            $list = array_map('intval', $list);
-            $list = implode("','", $list);
-        }
-
-        $tableCategory = Database::get_main_table(TABLE_MAIN_CATEGORY);
-
-        $table = Database::get_main_table(TABLE_MAIN_ACCESS_URL_REL_COURSE_CATEGORY);
-        $conditions = " INNER JOIN $table a ON (c.id = a.course_category_id)";
-        $whereCondition = " AND a.access_url_id = ".api_get_current_access_url_id();
-
-        $sql = "SELECT c.*, c.name as text FROM $tableCategory c $conditions
-                WHERE c.id IN $list $whereCondition";
-        $result = Database::query($sql);
-
-        return Database::store_result($result, 'ASSOC');
-    }
-
     /**
      * Get Pagination HTML div.
      *
diff --git a/main/inc/lib/course_description.lib.php b/main/inc/lib/course_description.lib.php
index 896500fd38..f0190fd0b8 100755
--- a/main/inc/lib/course_description.lib.php
+++ b/main/inc/lib/course_description.lib.php
@@ -248,44 +248,6 @@ class CourseDescription
         return $last_id > 0 ? 1 : 0;
     }
 
-    /**
-     * Insert a row like history inside track_e_item_property table
-     * first you must set description_type, title, content, progress and
-     * session_id properties with the object CourseDescription.
-     *
-     * @param int $description_type
-     *
-     * @return int affected rows
-     */
-    public function insert_stats($description_type)
-    {
-        $table = Database::get_main_table(TABLE_STATISTIC_TRACK_E_ITEM_PROPERTY);
-        $description_id = $this->get_id_by_description_type($description_type);
-        $course_id = api_get_course_int_id();
-        $course_code = api_get_course_id();
-        $item_property_id = api_get_item_property_id(
-            $course_code,
-            TOOL_COURSE_DESCRIPTION,
-            $description_id
-        );
-
-        $params = [
-            'c_id' => api_get_course_int_id(),
-            'course_id' => $course_id,
-            'item_property_id' => $item_property_id,
-            'title' => $this->title,
-            'content' => $this->content,
-            'progress' => $this->progress,
-            'lastedit_date' => api_get_utc_datetime(),
-            'lastedit_user_id' => api_get_user_id(),
-            'session_id' => $this->session_id,
-        ];
-
-        $result = Database::insert($table, $params);
-
-        return $result ? 1 : 0;
-    }
-
     /**
      * Update a description, first you must set description_type, title, content, progress
      * and session_id properties with the object CourseDescription.
@@ -358,29 +320,6 @@ class CourseDescription
         return $affected_rows;
     }
 
-    /**
-     * Get description id by description type.
-     *
-     * @param int $description_type
-     *
-     * @return int description id
-     */
-    public function get_id_by_description_type($description_type)
-    {
-        $table = Database::get_course_table(TABLE_COURSE_DESCRIPTION);
-        $course_id = api_get_course_int_id();
-
-        $sql = "SELECT id FROM $table
-		        WHERE 
-		            c_id = $course_id AND 
-		            description_type = '".intval($description_type)."'";
-        $rs = Database::query($sql);
-        $row = Database::fetch_array($rs);
-        $description_id = $row['id'];
-
-        return $description_id;
-    }
-
     /**
      * Get description titles by default.
      *
diff --git a/main/inc/lib/groupmanager.lib.php b/main/inc/lib/groupmanager.lib.php
index b9579be174..9b8b4a9549 100755
--- a/main/inc/lib/groupmanager.lib.php
+++ b/main/inc/lib/groupmanager.lib.php
@@ -2052,32 +2052,6 @@ class GroupManager
         return $groups;
     }
 
-    /**
-     * Remove all users that are not students and all users who have tutor status
-     * from  the list.
-     *
-     * @param array $user_array_in
-     *
-     * @return array
-     */
-    public static function filter_only_students($user_array_in)
-    {
-        $user_array_out = [];
-        foreach ($user_array_in as $this_user) {
-            if (api_get_session_id()) {
-                if ($this_user['status_session'] == 0) {
-                    $user_array_out[] = $this_user;
-                }
-            } else {
-                if ($this_user['status_rel'] == STUDENT) {
-                    $user_array_out[] = $this_user;
-                }
-            }
-        }
-
-        return $user_array_out;
-    }
-
     /**
      * Check if a user has access to a certain group tool.
      *
@@ -2278,45 +2252,6 @@ class GroupManager
         return $groups;
     }
 
-    /**
-     * @param array $userList
-     * @param array $groupInfo
-     *
-     * @return mixed
-     */
-    public static function getNumberLeftFromGroupFromUserList($userList, $groupInfo)
-    {
-        $groupIid = (int) $groupInfo['iid'];
-        $category = self::get_category_from_group($groupIid);
-        $number_groups_per_user = $groupInfo['maximum_number_of_students'];
-        $categoryId = 0;
-        if ($category) {
-            $groups_per_user = $category['groups_per_user'];
-            $number_groups_per_user = $groups_per_user == self::GROUP_PER_MEMBER_NO_LIMIT ? self::INFINITE : $groups_per_user;
-            $categoryId = $category['id'];
-        }
-
-        $usersAdded = [];
-        foreach ($userList as &$userInfo) {
-            // find # of groups the user is enrolled in
-            $numberOfGroups = self::user_in_number_of_groups(
-                $userInfo['user_id'],
-                $categoryId
-            );
-
-            if (in_array($userInfo['user_id'], $usersAdded)) {
-                continue;
-            }
-
-            $usersAdded[] = $userInfo['user_id'];
-
-            // add # of groups to user list
-            $userInfo['number_groups_left'] = $number_groups_per_user - $numberOfGroups;
-        }
-
-        return $userList;
-    }
-
     /**
      * @param array $group_list
      * @param int   $category_id
diff --git a/main/inc/lib/link.lib.php b/main/inc/lib/link.lib.php
index d2a1254d44..7dc9ae447f 100755
--- a/main/inc/lib/link.lib.php
+++ b/main/inc/lib/link.lib.php
@@ -579,7 +579,6 @@ class Link extends Model
             'display_order' => $max_display_order,
             'on_homepage' => $values['on_homepage'],
             'target' => $values['target'],
-            'category_id' => $values['category_id'],
         ];
 
         Database::update(
@@ -861,7 +860,6 @@ class Link extends Model
                     'LinkCategoryAdded',
                     api_get_user_id()
                 );
-                //api_set_default_visibility($category['id'], TOOL_LINK_CATEGORY);
             }
         }
 
@@ -1433,81 +1431,6 @@ class Link extends Model
         return $rv;
     }
 
-    /**
-     * CSV file import functions.
-     *
-     * @author René Haentjens , Ghent University
-     */
-    public static function import_link($linkdata)
-    {
-        // url, category_id, title, description, ...
-        // Field names used in the uploaded file
-        $known_fields = [
-            'url',
-            'category',
-            'title',
-            'description',
-            'on_homepage',
-            'hidden',
-        ];
-
-        $hide_fields = [
-            'kw',
-            'kwd',
-            'kwds',
-            'keyword',
-            'keywords',
-        ];
-
-        // All other fields are added to description, as "name:value".
-        // Only one hide_field is assumed to be present, <> is removed from value.
-        if (!($url = trim($linkdata['url'])) || !($title = trim($linkdata['title']))) {
-            return 0; // 0 = fail
-        }
-
-        $cat = ($catname = trim($linkdata['category'])) ? self::get_cat($catname) : 0;
-
-        $regs = []; // Will be passed to ereg()
-        $d = '';
-        foreach ($linkdata as $key => $value) {
-            if (!in_array($key, $known_fields)) {
-                if (in_array($key, $hide_fields) && ereg(
-                        '^<?([^>]*)>?$',
-                        $value,
-                        $regs
-                    )
-                ) { // possibly in <...>
-                    if (($kwlist = trim($regs[1])) != '') {
-                        $kw = '<i kw="'.htmlspecialchars($kwlist).'">';
-                    } else {
-                        $kw = '';
-                    }
-                    // i.e. assume only one of the $hide_fields will be present
-                    // and if found, hide the value as expando property of an <i> tag
-                } elseif (trim($value)) {
-                    $d .= ', '.$key.':'.$value;
-                }
-            }
-        }
-        if (!empty($d)) {
-            $d = substr($d, 2).' - ';
-        }
-
-        return self::put_link(
-            $url,
-            $cat,
-            $title,
-            $kw.ereg_replace(
-                '\[((/?(b|big|i|small|sub|sup|u))|br/)\]',
-                '<\\1>',
-                htmlspecialchars($d.$linkdata['description'])
-            ).($kw ? '</i>' : ''),
-            $linkdata['on_homepage'] ? '1' : '0',
-            $linkdata['hidden'] ? '1' : '0'
-        );
-        // i.e. allow some BBcode tags, e.g. [b]...[/b]
-    }
-
     /**
      * This function checks if the url is a vimeo link.
      *
@@ -1517,7 +1440,7 @@ class Link extends Model
      */
     public static function isVimeoLink($url)
     {
-        $isLink = strrpos($url, "vimeo.com");
+        $isLink = strrpos($url, 'vimeo.com');
 
         return $isLink;
     }
@@ -1556,9 +1479,9 @@ class Link extends Model
      */
     public static function is_youtube_link($url)
     {
-        $is_youtube_link = strrpos($url, "youtube") || strrpos(
+        $is_youtube_link = strrpos($url, 'youtube') || strrpos(
             $url,
-            "youtu.be"
+            'youtu.be'
         );
 
         return $is_youtube_link;
@@ -1643,9 +1566,7 @@ class Link extends Model
         $show = 'none',
         $token = null
     ) {
-        $tbl_link = Database::get_course_table(TABLE_LINK);
-        $tblCIP = Database::get_course_table(TABLE_ITEM_PROPERTY);
-        $categoryId = intval($categoryId);
+        $categoryId = (int) $categoryId;
 
         /*	Action Links */
         echo '<div class="actions">';
@@ -1870,6 +1791,9 @@ class Link extends Model
      */
     public static function getCategoryForm($id, $action)
     {
+        $id = (int) $id;
+        $action = Security::remove_XSS($action);
+
         $form = new FormValidator(
             'category',
             'post',
@@ -1902,7 +1826,7 @@ class Link extends Model
     public static function getCategory($id)
     {
         $table = Database::get_course_table(TABLE_LINK_CATEGORY);
-        $id = intval($id);
+        $id = (int) $id;
         $courseId = api_get_course_int_id();
 
         if (empty($id) || empty($courseId)) {
diff --git a/main/inc/lib/message.lib.php b/main/inc/lib/message.lib.php
index d39de3fa62..be561dc9d8 100755
--- a/main/inc/lib/message.lib.php
+++ b/main/inc/lib/message.lib.php
@@ -971,35 +971,6 @@ class MessageManager
         }
     }
 
-    /**
-     * update messages by user id and message id.
-     *
-     * @param int $user_id
-     * @param int $message_id
-     *
-     * @return bool
-     */
-    public static function update_message($user_id, $message_id)
-    {
-        $user_id = (int) $user_id;
-        $message_id = (int) $message_id;
-
-        if (empty($user_id) || empty($message_id)) {
-            return false;
-        }
-
-        $table = Database::get_main_table(TABLE_MESSAGE);
-        $sql = "UPDATE $table SET 
-                    msg_status = '".MESSAGE_STATUS_NEW."'
-                WHERE
-                    msg_status <> ".MESSAGE_STATUS_OUTBOX." AND
-                    user_receiver_id = ".$user_id." AND
-                    id = '".$message_id."'";
-        Database::query($sql);
-
-        return true;
-    }
-
     /**
      * @param int $user_id
      * @param int $message_id
@@ -1026,31 +997,6 @@ class MessageManager
         Database::query($sql);
     }
 
-    /**
-     * get messages by user id and message id.
-     *
-     * @param int $user_id
-     * @param int $message_id
-     *
-     * @return array
-     */
-    public static function get_message_by_user($user_id, $message_id)
-    {
-        $user_id = (int) $user_id;
-        $message_id = (int) $message_id;
-
-        if (empty($user_id) || empty($message_id)) {
-            return false;
-        }
-
-        $table = Database::get_main_table(TABLE_MESSAGE);
-        $query = "SELECT * FROM $table
-                  WHERE user_receiver_id=".$user_id." AND id='".$message_id."'";
-        $result = Database::query($query);
-
-        return $row = Database::fetch_array($result);
-    }
-
     /**
      * get messages by group id.
      *
@@ -1988,19 +1934,6 @@ class MessageManager
         }
     }
 
-    /**
-     * Sort date by desc from a multi-dimensional array.
-     *
-     * @param array $array1 first array to compare
-     * @param array $array2 second array to compare
-     *
-     * @return bool
-     */
-    public function order_desc_date($array1, $array2)
-    {
-        return strcmp($array2['send_date'], $array1['send_date']);
-    }
-
     /**
      * @param int $messageId
      *
@@ -2299,44 +2232,6 @@ class MessageManager
         return $html;
     }
 
-    /**
-     * Get the count of the last received messages for a user.
-     *
-     * @param int $userId The user id
-     * @param int $lastId The id of the last received message
-     *
-     * @return int The count of new messages
-     */
-    public static function countMessagesFromLastReceivedMessage($userId, $lastId = 0)
-    {
-        $userId = intval($userId);
-        $lastId = intval($lastId);
-
-        if (empty($userId)) {
-            return 0;
-        }
-
-        $messagesTable = Database::get_main_table(TABLE_MESSAGE);
-
-        $conditions = [
-            'where' => [
-                'user_receiver_id = ?' => $userId,
-                'AND msg_status = ?' => MESSAGE_STATUS_UNREAD,
-                'AND id > ?' => $lastId,
-            ],
-        ];
-
-        $result = Database::select('COUNT(1) AS qty', $messagesTable, $conditions);
-
-        if (!empty($result)) {
-            $row = current($result);
-
-            return $row['qty'];
-        }
-
-        return 0;
-    }
-
     /**
      * Get the data of the last received messages for a user.
      *
diff --git a/main/inc/lib/notification.lib.php b/main/inc/lib/notification.lib.php
index a2f870f544..5d5e384d41 100644
--- a/main/inc/lib/notification.lib.php
+++ b/main/inc/lib/notification.lib.php
@@ -450,25 +450,6 @@ class Notification extends Model
             $content = $content.'<br /><br />'.$linkToNewMessage;
         }
 
-        /*$courseInfo = api_get_course_info();
-        // Add course info
-        if (!empty($courseInfo)) {
-            $sessionId = api_get_session_id();
-            if (empty($sessionId)) {
-                $courseNotification = sprintf(get_lang('ThisEmailWasSentViaCourseX'), $courseInfo['title']);
-            } else {
-                $sessionInfo = api_get_session_info($sessionId);
-                if (!empty($sessionInfo)) {
-                    $courseNotification = sprintf(
-                        get_lang('ThisEmailWasSentViaCourseXInSessionX'),
-                        $courseInfo['title'],
-                        $sessionInfo['title']
-                    );
-                }
-            }
-            $content = $content.'<br /><br />'.$courseNotification;
-        }*/
-
         // You have received this message because you are subscribed text
         $content = $content.'<br /><hr><i>'.
             sprintf(