/**
 * Check to see if a user's real email address should be used for the "From" field.
 *
 * @param  object $from The user object for the user we are sending the email from.
 * @param  object $user The user object that we are sending the email to.
 * @param  array $alloweddomains An array of allowed domains that we can send email from.
 * @return bool Returns true if we can use the from user's email adress in the "From" field.
 */
function can_send_from_real_email_address($from, $user, $alloweddomains)
{
    // Email is in the list of allowed domains for sending email,
    // and the senders email setting is either displayed to everyone, or display to only other users that are enrolled
    // in a course with the sender.
    if (\core\ip_utils::is_domain_in_allowed_list(substr($from->email, strpos($from->email, '@') + 1), $alloweddomains) && ($from->maildisplay == core_user::MAILDISPLAY_EVERYONE || $from->maildisplay == core_user::MAILDISPLAY_COURSE_MEMBERS_ONLY && enrol_get_shared_courses($user, $from, false, true))) {
        return true;
    }
    return false;
}

 // see.
 // In either case we need to decide whether we can show personal information
 // about the requested user to the current user so we will execute some checks
 // First check the obvious, its the current user, a specific course has been
 // provided (require_login has been called), or they have a course contact role.
 // True to any of those and the current user can see the details of the
 // requested user.
 $canviewuser = $iscurrentuser || $isspecificcourse || empty($CFG->forceloginforprofiles) || has_coursecontact_role($userid);
 // Next we'll check the caps, if the current user has the view details and a
 // specific course has been requested, or if they have the view all details
 $canviewuser = $canviewuser || ($isspecificcourse && has_capability('moodle/user:viewdetails', $coursecontext) || has_capability('moodle/user:viewalldetails', $usercontext));
 // If none of the above was true the next step is to check a shared relation
 // through some course
 if (!$canviewuser) {
     // Get all of the courses that the users have in common
     $sharedcourses = enrol_get_shared_courses($USER->id, $user->id, true);
     foreach ($sharedcourses as $sharedcourse) {
         // Check the view cap within the course context
         if (has_capability('moodle/user:viewdetails', get_context_instance(CONTEXT_COURSE, $sharedcourse->id))) {
             $canviewuser = true;
             break;
         }
     }
     unset($sharedcourses);
 }
 // Prepare the page title
 $pagetitle = get_string('noposts', 'mod_forum');
 // Get the page heading
 if ($isspecificcourse) {
     $pageheading = format_string($course->shortname, true, array('context' => $coursecontext));
 } else {

 public function test_enrol_get_shared_courses()
 {
     $this->resetAfterTest();
     $user1 = $this->getDataGenerator()->create_user();
     $user2 = $this->getDataGenerator()->create_user();
     $user3 = $this->getDataGenerator()->create_user();
     $course1 = $this->getDataGenerator()->create_course();
     $this->getDataGenerator()->enrol_user($user1->id, $course1->id);
     $this->getDataGenerator()->enrol_user($user2->id, $course1->id);
     $course2 = $this->getDataGenerator()->create_course();
     $this->getDataGenerator()->enrol_user($user1->id, $course2->id);
     // Test that user1 and user2 have courses in common.
     $this->assertTrue(enrol_get_shared_courses($user1, $user2, false, true));
     // Test that user1 and user3 have no courses in common.
     $this->assertFalse(enrol_get_shared_courses($user1, $user3, false, true));
     // Test retrieving the courses in common.
     $sharedcourses = enrol_get_shared_courses($user1, $user2, true);
     // Only should be one shared course.
     $this->assertCount(1, $sharedcourses);
     $sharedcourse = array_shift($sharedcourses);
     // It should be course 1.
     $this->assertEquals($sharedcourse->id, $course1->id);
 }

/**
 * Do these two students share any course?
 *
 * The courses has to be visible and enrolments has to be active,
 * timestart and timeend restrictions are ignored.
 *
 * This function calls {@see enrol_get_shared_courses()} setting checkexistsonly
 * to true.
 *
 * @param stdClass|int $user1
 * @param stdClass|int $user2
 * @return bool
 */
function enrol_sharing_course($user1, $user2)
{
    return enrol_get_shared_courses($user1, $user2, false, true);
}

/**
 * Check if a user has the permission to viewdetails in a shared course's context.
 *
 * @param object $user The other user's details.
 * @param object $course Use this course to see if we have permission to see this user's profile.
 * @param context $usercontext The user context if available.
 * @return bool true for ability to view this user, else false.
 */
function user_can_view_profile($user, $course = null, $usercontext = null)
{
    global $USER, $CFG;
    if ($user->deleted) {
        return false;
    }
    // If any of these four things, return true.
    // Number 1.
    if ($USER->id == $user->id) {
        return true;
    }
    // Number 2.
    if (empty($CFG->forceloginforprofiles)) {
        return true;
    }
    if (empty($usercontext)) {
        $usercontext = context_user::instance($user->id);
    }
    // Number 3.
    if (has_capability('moodle/user:viewdetails', $usercontext)) {
        return true;
    }
    // Number 4.
    if (has_coursecontact_role($user->id)) {
        return true;
    }
    if (isset($course)) {
        $sharedcourses = array($course);
    } else {
        $sharedcourses = enrol_get_shared_courses($USER->id, $user->id, true);
    }
    foreach ($sharedcourses as $sharedcourse) {
        $coursecontext = context_course::instance($sharedcourse->id);
        if (has_capability('moodle/user:viewdetails', $coursecontext)) {
            if (!groups_user_groups_visible($sharedcourse, $user->id)) {
                // Not a member of the same group.
                continue;
            }
            return true;
        }
    }
    return false;
}