<?php
/* For licensing terms, see /license.txt */

/**
 * Class ClassManager
 */
class ClassManager
{
    /**
     * Get class information
     * note: This function can't be named get_class() because that's a standard
     * php-function.
     */
    public static function get_class_info($class_id) {
        $class_id = intval($class_id);
        $table_class = Database :: get_main_table(TABLE_MAIN_CLASS);
        $sql = "SELECT * FROM $table_class WHERE id='".$class_id."'";
        $res = Database::query($sql);
        return Database::fetch_array($res, 'ASSOC');
    }
    /**
     * Change the name of a class
     * @param string $name The new name
     * @param int $class_id The class id
     */
    public static function set_name($name, $class_id) {
        $class_id = intval($class_id);
        $table_class = Database :: get_main_table(TABLE_MAIN_CLASS);
        $sql = "UPDATE $table_class SET name='".Database::escape_string($name)."' WHERE id='".$class_id."'";
        $res = Database::query($sql);
    }
    /**
     * Create a class
     * @param string $name
     */
    public static function create_class($name)
    {
        $table_class = Database :: get_main_table(TABLE_MAIN_CLASS);
        $sql = "INSERT INTO $table_class SET name='".Database::escape_string($name)."'";
        $result = Database::query($sql);
        return Database::affected_rows($result) == 1;
    }

    /**
     * Check if a classname is allready in use
     * @param string $name
     */
    public static function class_name_exists($name) {
        $table_class = Database :: get_main_table(TABLE_MAIN_CLASS);
        $sql = "SELECT * FROM $table_class WHERE name='".Database::escape_string($name)."'";
        $res = Database::query($sql);
        return Database::num_rows($res) != 0;
    }
    /**
     * Delete a class
     * @param int $class_id
     * @todo Add option to unsubscribe class-members from the courses where the
     * class was subscibed to
     */
    public static function delete_class($class_id) {
        $class_id = intval($class_id);
        $table_class = Database :: get_main_table(TABLE_MAIN_CLASS);
        $table_class_course = Database :: get_main_table(TABLE_MAIN_COURSE_CLASS);
        $table_class_user = Database :: get_main_table(TABLE_MAIN_CLASS_USER);
        $sql = "DELETE FROM $table_class_user WHERE class_id = '".$class_id."'";
        Database::query($sql);
        $sql = "DELETE FROM $table_class_course WHERE class_id = '".$class_id."'";
        Database::query($sql);
        $sql = "DELETE FROM $table_class WHERE id = '".$class_id."'";
        Database::query($sql);
    }
    /**
     * Get all users from a class
     * @param int $class_id
     * @return array
     */
    public static function get_users($class_id) {
        $class_id = intval($class_id);
        $table_class_user = Database :: get_main_table(TABLE_MAIN_CLASS_USER);
        $table_user = Database :: get_main_table(TABLE_MAIN_USER);
        $sql = "SELECT * FROM $table_class_user cu, $table_user u WHERE cu.class_id = '".$class_id."' AND cu.user_id = u.user_id";
        $res = Database::query($sql);
        $users = array ();
        while ($user = Database::fetch_array($res, 'ASSOC')) {
            $users[] = $user;
        }
        return $users;
    }
    /**
     * Add a user to a class. If the class is subscribed to a course, the new
     * user will also be subscribed to that course.
     * @param int $user_id The user id
     * @param int $class_id The class id
     */
    public static function add_user($user_id, $class_id) {
        $table_class_user = Database :: get_main_table(TABLE_MAIN_CLASS_USER);
        $user_id  = intval($user_id);
        $class_id = intval($class_id);
        $sql = "INSERT IGNORE INTO $table_class_user SET user_id = '".$user_id."', class_id='".$class_id."'";
        Database::query($sql);
        $courses = ClassManager :: get_courses($class_id);
        foreach ($courses as $index => $course) {
            CourseManager :: subscribe_user($user_id, $course['course_code']);
        }
    }
    /**
     * Unsubscribe a user from a class. If the class is also subscribed in a
     * course, the user will be unsubscribed from that course
     * @param int $user_id The user id
     * @param int $class_id The class id
     */
    public static function unsubscribe_user($user_id, $class_id) {
        $class_id = intval($class_id);
        $user_id  = intval($user_id);

        $table_class_user = Database :: get_main_table(TABLE_MAIN_CLASS_USER);
        $table_course_class = Database :: get_main_table(TABLE_MAIN_COURSE_CLASS);
        $courses = ClassManager :: get_courses($class_id);
        if (count($courses) != 0) {
            $course_codes = array ();
            foreach ($courses as $index => $course) {
                $course_codes[] = $course['course_code'];
                $sql = "SELECT DISTINCT user_id FROM $table_class_user t1, $table_course_class t2 WHERE t1.class_id=t2.class_id AND course_code = '".$course['course_code']."' AND user_id = $user_id AND t2.class_id<>'$class_id'";
                $res = Database::query($sql);
                if (Database::num_rows($res) == 0 && CourseManager :: get_user_in_course_status($user_id, $course['course_code']) == STUDENT)
                {
                    CourseManager :: unsubscribe_user($user_id, $course['course_code']);
                }
            }
        }
        $sql = "DELETE FROM $table_class_user WHERE user_id='".$user_id."' AND class_id = '".$class_id."'";
        Database::query($sql);
    }
    /**
     * Get all courses in which a class is subscribed
     * @param int $class_id
     * @return array
     */
    public static function get_courses($class_id) {
        $class_id = intval($class_id);
        $table_class_course = Database :: get_main_table(TABLE_MAIN_COURSE_CLASS);
        $table_course = Database :: get_main_table(TABLE_MAIN_COURSE);
        $sql = "SELECT * FROM $table_class_course cc, $table_course c WHERE cc.class_id = '".$class_id."' AND cc.course_code = c.code";
        $res = Database::query($sql);
        $courses = array ();
        while ($course = Database::fetch_array($res, 'ASSOC')) {
            $courses[] = $course;
        }
        return $courses;
    }
    /**
     * Subscribe all members of a class to a course
     * @param  int $class_id The class id
     * @param string $course_code The course code
     */
    public static function subscribe_to_course($class_id, $course_code)
    {
        $tbl_course_class = Database :: get_main_table(TABLE_MAIN_COURSE_CLASS);
        $tbl_class_user = Database :: get_main_table(TABLE_MAIN_CLASS_USER);
        $sql = "INSERT IGNORE INTO $tbl_course_class SET course_code = '".Database::escape_string($course_code)."', class_id = '".Database::escape_string($class_id)."'";
        Database::query($sql);
        $sql = "SELECT user_id FROM $tbl_class_user WHERE class_id = '".intval($class_id)."'";
        $res = Database::query($sql);
        while ($user = Database::fetch_object($res)) {
            CourseManager :: subscribe_user($user->user_id, $course_code);
        }
    }
    /**
     * Unsubscribe a class from a course.
     * Only students are unsubscribed. If a user is member of 2 classes which
     * are both subscribed to the course, the user stays in the course.
     * @param int $class_id The class id
     * @param string $course_code The course code
     */
    public static function unsubscribe_from_course($class_id, $course_code)
    {
        $tbl_course_class = Database :: get_main_table(TABLE_MAIN_COURSE_CLASS);
        $tbl_class_user = Database :: get_main_table(TABLE_MAIN_CLASS_USER);
        $sql = "SELECT cu.user_id,COUNT(cc.class_id) FROM $tbl_course_class cc, $tbl_class_user cu WHERE  cc.class_id = cu.class_id AND cc.course_code = '".Database::escape_string($course_code)."' GROUP BY cu.user_id HAVING COUNT(cc.class_id) = 1";
        $single_class_users = Database::query($sql);
        while ($single_class_user = Database::fetch_object($single_class_users))
        {
            $sql = "SELECT * FROM $tbl_class_user WHERE class_id = '".intval($class_id)."' AND user_id = '".Database::escape_string($single_class_user->user_id)."'";
            $res = Database::query($sql);
            if (Database::num_rows($res) > 0)
            {
                if (CourseManager :: get_user_in_course_status($single_class_user->user_id, $course_code) == STUDENT)
                {
                    CourseManager :: unsubscribe_user($single_class_user->user_id, $course_code);
                }
            }
        }
        $sql = "DELETE FROM $tbl_course_class WHERE course_code = '".Database::escape_string($course_code)."' AND class_id = '".Database::escape_string($class_id)."'";
        Database::query($sql);
    }

    /**
     * Get the class-id
     * @param string $name The class name
     * @return int the ID of the class
     */
    public static function get_class_id($name) {
        $name = Database::escape_string($name);
        $table_class = Database :: get_main_table(TABLE_MAIN_CLASS);
        $sql = "SELECT * FROM $table_class WHERE name='".$name."'";
        $res = Database::query($sql);
        $obj = Database::fetch_object($res);
        return $obj->id;
    }
    /**
     * Get all classes subscribed in a course
     * @param string $course_code
     * @return array An array with all classes (keys: 'id','code','name')
     */
    public static function get_classes_in_course($course_code) {
        $table_class = Database :: get_main_table(TABLE_MAIN_CLASS);
        $table_course_class = Database :: get_main_table(TABLE_MAIN_COURSE_CLASS);
        $sql = "SELECT cl.* FROM $table_class cl, $table_course_class cc WHERE cc.course_code = '".Database::escape_string($course_code)."' AND cc.class_id = cl.id";
        $res = Database::query($sql);
        $classes = array ();
        while ($class = Database::fetch_array($res, 'ASSOC')) {
            $classes[] = $class;
        }
        return $classes;
    }
}