<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * Code for ajax user selectors.
 *
 * @package   core_user
 * @copyright 1999 onwards Martin Dougiamas  http://dougiamas.com
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

/**
 * The default size of a user selector.
 */
define('USER_SELECTOR_DEFAULT_ROWS', 20);

/**
 * Base class for user selectors.
 *
 * In your theme, you must give each user-selector a defined width. If the
 * user selector has name="myid", then the div myid_wrapper must have a width
 * specified.
 *
 * @copyright 1999 onwards Martin Dougiamas  http://dougiamas.com
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
abstract class user_selector_base {
    /** @var string The control name (and id) in the HTML. */
    protected $name;
    /** @var array Extra fields to search on and return in addition to firstname and lastname. */
    protected $extrafields;
    /** @var object Context used for capability checks regarding this selector (does
     * not necessarily restrict user list) */
    protected $accesscontext;
    /** @var boolean Whether the conrol should allow selection of many users, or just one. */
    protected $multiselect = true;
    /** @var int The height this control should have, in rows. */
    protected $rows = USER_SELECTOR_DEFAULT_ROWS;
    /** @var array A list of userids that should not be returned by this control. */
    protected $exclude = array();
    /** @var array|null A list of the users who are selected. */
    protected $selected = null;
    /** @var boolean When the search changes, do we keep previously selected options that do
     * not match the new search term? */
    protected $preserveselected = false;
    /** @var boolean If only one user matches the search, should we select them automatically. */
    protected $autoselectunique = false;
    /** @var boolean When searching, do we only match the starts of fields (better performance)
     * or do we match occurrences anywhere? */
    protected $searchanywhere = false;
    /** @var mixed This is used by get selected users */
    protected $validatinguserids = null;

    /**  @var boolean Used to ensure we only output the search options for one user selector on
     * each page. */
    private static $searchoptionsoutput = false;

    /** @var array JavaScript YUI3 Module definition */
    protected static $jsmodule = array(
                'name' => 'user_selector',
                'fullpath' => '/user/selector/module.js',
                'requires'  => array('node', 'event-custom', 'datasource', 'json', 'moodle-core-notification'),
                'strings' => array(
                    array('previouslyselectedusers', 'moodle', '%%SEARCHTERM%%'),
                    array('nomatchingusers', 'moodle', '%%SEARCHTERM%%'),
                    array('none', 'moodle')
                ));

    /** @var int this is used to define maximum number of users visible in list */
    public $maxusersperpage = 100;

    /** @var boolean Whether to override fullname() */
    public $viewfullnames = false;

    /**
     * Constructor. Each subclass must have a constructor with this signature.
     *
     * @param string $name the control name/id for use in the HTML.
     * @param array $options other options needed to construct this selector.
     * You must be able to clone a userselector by doing new get_class($us)($us->get_name(), $us->get_options());
     */
    public function __construct($name, $options = array()) {
        global $CFG, $PAGE;

        // Initialise member variables from constructor arguments.
        $this->name = $name;

        // Use specified context for permission checks, system context if not specified.
        if (isset($options['accesscontext'])) {
            $this->accesscontext = $options['accesscontext'];
        } else {
            $this->accesscontext = context_system::instance();
        }

        // Check if some legacy code tries to override $CFG->showuseridentity.
        if (isset($options['extrafields'])) {
            debugging('The user_selector classes do not support custom list of extra identity fields any more. '.
                'Instead, the user identity fields defined by the site administrator will be used to respect '.
                'the configured privacy setting.', DEBUG_DEVELOPER);
            unset($options['extrafields']);
        }

        // Populate the list of additional user identifiers to display.
        $this->extrafields = get_extra_user_fields($this->accesscontext);

        if (isset($options['exclude']) && is_array($options['exclude'])) {
            $this->exclude = $options['exclude'];
        }
        if (isset($options['multiselect'])) {
            $this->multiselect = $options['multiselect'];
        }

        // Read the user prefs / optional_params that we use.
        $this->preserveselected = $this->initialise_option('userselector_preserveselected', $this->preserveselected);
        $this->autoselectunique = $this->initialise_option('userselector_autoselectunique', $this->autoselectunique);
        $this->searchanywhere = $this->initialise_option('userselector_searchanywhere', $this->searchanywhere);

        if (!empty($CFG->maxusersperpage)) {
            $this->maxusersperpage = $CFG->maxusersperpage;
        }
    }

    /**
     * All to the list of user ids that this control will not select.
     *
     * For example, on the role assign page, we do not list the users who already have the role in question.
     *
     * @param array $arrayofuserids the user ids to exclude.
     */
    public function exclude($arrayofuserids) {
        $this->exclude = array_unique(array_merge($this->exclude, $arrayofuserids));
    }

    /**
     * Clear the list of excluded user ids.
     */
    public function clear_exclusions() {
        $this->exclude = array();
    }

    /**
     * Returns the list of user ids that this control will not select.
     *
     * @return array the list of user ids that this control will not select.
     */
    public function get_exclusions() {
        return clone($this->exclude);
    }

    /**
     * The users that were selected.
     *
     * This is a more sophisticated version of optional_param($this->name, array(), PARAM_INT) that validates the
     * returned list of ids against the rules for this user selector.
     *
     * @return array of user objects.
     */
    public function get_selected_users() {
        // Do a lazy load.
        if (is_null($this->selected)) {
            $this->selected = $this->load_selected_users();
        }
        return $this->selected;
    }

    /**
     * Convenience method for when multiselect is false (throws an exception if not).
     *
     * @throws moodle_exception
     * @return object the selected user object, or null if none.
     */
    public function get_selected_user() {
        if ($this->multiselect) {
            throw new moodle_exception('cannotcallusgetselecteduser');
        }
        $users = $this->get_selected_users();
        if (count($users) == 1) {
            return reset($users);
        } else if (count($users) == 0) {
            return null;
        } else {
            throw new moodle_exception('userselectortoomany');
        }
    }

    /**
     * Invalidates the list of selected users.
     *
     * If you update the database in such a way that it is likely to change the
     * list of users that this component is allowed to select from, then you
     * must call this method. For example, on the role assign page, after you have
     * assigned some roles to some users, you should call this.
     */
    public function invalidate_selected_users() {
        $this->selected = null;
    }

    /**
     * Output this user_selector as HTML.
     *
     * @param boolean $return if true, return the HTML as a string instead of outputting it.
     * @return mixed if $return is true, returns the HTML as a string, otherwise returns nothing.
     */
    public function display($return = false) {
        global $PAGE;

        // Get the list of requested users.
        $search = optional_param($this->name . '_searchtext', '', PARAM_RAW);
        if (optional_param($this->name . '_clearbutton', false, PARAM_BOOL)) {
            $search = '';
        }
        $groupedusers = $this->find_users($search);

        // Output the select.
        $name = $this->name;
        $multiselect = '';
        if ($this->multiselect) {
            $name .= '[]';
            $multiselect = 'multiple="multiple" ';
        }
        $output = '<div class="userselector" id="' . $this->name . '_wrapper">' . "\n" .
                '<select name="' . $name . '" id="' . $this->name . '" ' .
                $multiselect . 'size="' . $this->rows . '" class="form-control no-overflow">' . "\n";

        // Populate the select.
        $output .= $this->output_options($groupedusers, $search);

        // Output the search controls.
        $output .= "</select>\n<div class=\"form-inline\">\n";
        $output .= '<input type="text" name="' . $this->name . '_searchtext" id="' .
                $this->name . '_searchtext" size="15" value="' . s($search) . '" class="form-control"/>';
        $output .= '<input type="submit" name="' . $this->name . '_searchbutton" id="' .
                $this->name . '_searchbutton" value="' . $this->search_button_caption() . '" class="btn btn-secondary"/>';
        $output .= '<input type="submit" name="' . $this->name . '_clearbutton" id="' .
                $this->name . '_clearbutton" value="' . get_string('clear') . '" class="btn btn-secondary"/>';

        // And the search options.
        $optionsoutput = false;
        if (!user_selector_base::$searchoptionsoutput) {
            $output .= print_collapsible_region_start('', 'userselector_options',
                get_string('searchoptions'), 'userselector_optionscollapsed', true, true);
            $output .= $this->option_checkbox('preserveselected', $this->preserveselected,
                get_string('userselectorpreserveselected'));
            $output .= $this->option_checkbox('autoselectunique', $this->autoselectunique,
                get_string('userselectorautoselectunique'));
            $output .= $this->option_checkbox('searchanywhere', $this->searchanywhere,
                get_string('userselectorsearchanywhere'));
            $output .= print_collapsible_region_end(true);

            $PAGE->requires->js_init_call('M.core_user.init_user_selector_options_tracker', array(), false, self::$jsmodule);
            user_selector_base::$searchoptionsoutput = true;
        }
        $output .= "</div>\n</div>\n\n";

        // Initialise the ajax functionality.
        $output .= $this->initialise_javascript($search);

        // Return or output it.
        if ($return) {
            return $output;
        } else {
            echo $output;
        }
    }

    /**
     * The height this control will be displayed, in rows.
     *
     * @param integer $numrows the desired height.
     */
    public function set_rows($numrows) {
        $this->rows = $numrows;
    }

    /**
     * Returns the number of rows to display in this control.
     *
     * @return integer the height this control will be displayed, in rows.
     */
    public function get_rows() {
        return $this->rows;
    }

    /**
     * Whether this control will allow selection of many, or just one user.
     *
     * @param boolean $multiselect true = allow multiple selection.
     */
    public function set_multiselect($multiselect) {
        $this->multiselect = $multiselect;
    }

    /**
     * Returns true is multiselect should be allowed.
     *
     * @return boolean whether this control will allow selection of more than one user.
     */
    public function is_multiselect() {
        return $this->multiselect;
    }

    /**
     * Returns the id/name of this control.
     *
     * @return string the id/name that this control will have in the HTML.
     */
    public function get_name() {
        return $this->name;
    }

    /**
     * Set the user fields that are displayed in the selector in addition to the user's name.
     *
     * @param array $fields a list of field names that exist in the user table.
     */
    public function set_extra_fields($fields) {
        $this->extrafields = $fields;
    }

    /**
     * Search the database for users matching the $search string, and any other
     * conditions that apply. The SQL for testing whether a user matches the
     * search string should be obtained by calling the search_sql method.
     *
     * This method is used both when getting the list of choices to display to
     * the user, and also when validating a list of users that was selected.
     *
     * When preparing a list of users to choose from ($this->is_validating()
     * return false) you should probably have an maximum number of users you will
     * return, and if more users than this match your search, you should instead
     * return a message generated by the too_many_results() method. However, you
     * should not do this when validating.
     *
     * If you are writing a new user_selector subclass, I strongly recommend you
     * look at some of the subclasses later in this file and in admin/roles/lib.php.
     * They should help you see exactly what you have to do.
     *
     * @param string $search the search string.
     * @return array An array of arrays of users. The array keys of the outer
     *      array should be the string names of optgroups. The keys of the inner
     *      arrays should be userids, and the values should be user objects
     *      containing at least the list of fields returned by the method
     *      required_fields_sql(). If a user object has a ->disabled property
     *      that is true, then that option will be displayed greyed out, and
     *      will not be returned by get_selected_users.
     */
    public abstract function find_users($search);

    /**
     *
     * Note: this function must be implemented if you use the search ajax field
     *       (e.g. set $options['file'] = '/admin/filecontainingyourclass.php';)
     * @return array the options needed to recreate this user_selector.
     */
    protected function get_options() {
        return array(
            'class' => get_class($this),
            'name' => $this->name,
            'exclude' => $this->exclude,
            'extrafields' => $this->extrafields,
            'multiselect' => $this->multiselect,
            'accesscontext' => $this->accesscontext,
        );
    }

    /**
     * Returns true if this control is validating a list of users.
     *
     * @return boolean if true, we are validating a list of selected users,
     *      rather than preparing a list of uesrs to choose from.
     */
    protected function is_validating() {
        return !is_null($this->validatinguserids);
    }

    /**
     * Get the list of users that were selected by doing optional_param then validating the result.
     *
     * @return array of user objects.
     */
    protected function load_selected_users() {
        // See if we got anything.
        if ($this->multiselect) {
            $userids = optional_param_array($this->name, array(), PARAM_INT);
        } else if ($userid = optional_param($this->name, 0, PARAM_INT)) {
            $userids = array($userid);
        }
        // If there are no users there is nobody to load.
        if (empty($userids)) {
            return array();
        }

        // If we did, use the find_users method to validate the ids.
        $this->validatinguserids = $userids;
        $groupedusers = $this->find_users('');
        $this->validatinguserids = null;

        // Aggregate the resulting list back into a single one.
        $users = array();
        foreach ($groupedusers as $group) {
            foreach ($group as $user) {
                if (!isset($users[$user->id]) && empty($user->disabled) && in_array($user->id, $userids)) {
                    $users[$user->id] = $user;
                }
            }
        }

        // If we are only supposed to be selecting a single user, make sure we do.
        if (!$this->multiselect && count($users) > 1) {
            $users = array_slice($users, 0, 1);
        }

        return $users;
    }

    /**
     * Returns SQL to select required fields.
     *
     * @param string $u the table alias for the user table in the query being
     *      built. May be ''.
     * @return string fragment of SQL to go in the select list of the query.
     */
    protected function required_fields_sql($u) {
        // Raw list of fields.
        $fields = array('id');
        // Add additional name fields.
        $fields = array_merge($fields, get_all_user_name_fields(), $this->extrafields);

        // Prepend the table alias.
        if ($u) {
            foreach ($fields as &$field) {
                $field = $u . '.' . $field;
            }
        }
        return implode(',', $fields);
    }

    /**
     * Returns an array with SQL to perform a search and the params that go into it.
     *
     * @param string $search the text to search for.
     * @param string $u the table alias for the user table in the query being
     *      built. May be ''.
     * @return array an array with two elements, a fragment of SQL to go in the
     *      where clause the query, and an array containing any required parameters.
     *      this uses ? style placeholders.
     */
    protected function search_sql($search, $u) {
        return users_search_sql($search, $u, $this->searchanywhere, $this->extrafields,
                $this->exclude, $this->validatinguserids);
    }

    /**
     * Used to generate a nice message when there are too many users to show.
     *
     * The message includes the number of users that currently match, and the
     * text of the message depends on whether the search term is non-blank.
     *
     * @param string $search the search term, as passed in to the find users method.
     * @param int $count the number of users that currently match.
     * @return array in the right format to return from the find_users method.
     */
    protected function too_many_results($search, $count) {
        if ($search) {
            $a = new stdClass;
            $a->count = $count;
            $a->search = $search;
            return array(get_string('toomanyusersmatchsearch', '', $a) => array(),
                    get_string('pleasesearchmore') => array());
        } else {
            return array(get_string('toomanyuserstoshow', '', $count) => array(),
                    get_string('pleaseusesearch') => array());
        }
    }

    /**
     * Output the list of <optgroup>s and <options>s that go inside the select.
     *
     * This method should do the same as the JavaScript method
     * user_selector.prototype.handle_response.
     *
     * @param array $groupedusers an array, as returned by find_users.
     * @param string $search
     * @return string HTML code.
     */
    protected function output_options($groupedusers, $search) {
        $output = '';

        // Ensure that the list of previously selected users is up to date.
        $this->get_selected_users();

        // If $groupedusers is empty, make a 'no matching users' group. If there is
        // only one selected user, set a flag to select them if that option is turned on.
        $select = false;
        if (empty($groupedusers)) {
            if (!empty($search)) {
                $groupedusers = array(get_string('nomatchingusers', '', $search) => array());
            } else {
                $groupedusers = array(get_string('none') => array());
            }
        } else if ($this->autoselectunique && count($groupedusers) == 1 &&
                count(reset($groupedusers)) == 1) {
            $select = true;
            if (!$this->multiselect) {
                $this->selected = array();
            }
        }

        // Output each optgroup.
        foreach ($groupedusers as $groupname => $users) {
            $output .= $this->output_optgroup($groupname, $users, $select);
        }

        // If there were previously selected users who do not match the search, show them too.
        if ($this->preserveselected && !empty($this->selected)) {
            $output .= $this->output_optgroup(get_string('previouslyselectedusers', '', $search), $this->selected, true);
        }

        // This method trashes $this->selected, so clear the cache so it is rebuilt before anyone tried to use it again.
        $this->selected = null;

        return $output;
    }

    /**
     * Output one particular optgroup. Used by the preceding function output_options.
     *
     * @param string $groupname the label for this optgroup.
     * @param array $users the users to put in this optgroup.
     * @param boolean $select if true, select the users in this group.
     * @return string HTML code.
     */
    protected function output_optgroup($groupname, $users, $select) {
        if (!empty($users)) {
            $output = '  <optgroup label="' . htmlspecialchars($groupname) . ' (' . count($users) . ')">' . "\n";
            foreach ($users as $user) {
                $attributes = '';
                if (!empty($user->disabled)) {
                    $attributes .= ' disabled="disabled"';
                } else if ($select || isset($this->selected[$user->id])) {
                    $attributes .= ' selected="selected"';
                }
                unset($this->selected[$user->id]);
                $output .= '    <option' . $attributes . ' value="' . $user->id . '">' .
                        $this->output_user($user) . "</option>\n";
                if (!empty($user->infobelow)) {
                    // Poor man's indent  here is because CSS styles do not work in select options, except in Firefox.
                    $output .= '    <option disabled="disabled" class="userselector-infobelow">' .
                            '&nbsp;&nbsp;&nbsp;&nbsp;' . s($user->infobelow) . '</option>';
                }
            }
        } else {
            $output = '  <optgroup label="' . htmlspecialchars($groupname) . '">' . "\n";
            $output .= '    <option disabled="disabled">&nbsp;</option>' . "\n";
        }
        $output .= "  </optgroup>\n";
        return $output;
    }

    /**
     * Convert a user object to a string suitable for displaying as an option in the list box.
     *
     * @param object $user the user to display.
     * @return string a string representation of the user.
     */
    public function output_user($user) {
        $out = fullname($user, $this->viewfullnames);
        if ($this->extrafields) {
            $displayfields = array();
            foreach ($this->extrafields as $field) {
                $displayfields[] = $user->{$field};
            }
            $out .= ' (' . implode(', ', $displayfields) . ')';
        }
        return $out;
    }

    /**
     * Returns the string to use for the search button caption.
     *
     * @return string the caption for the search button.
     */
    protected function search_button_caption() {
        return get_string('search');
    }

    /**
     * Initialise one of the option checkboxes, either from  the request, or failing that from the
     * user_preferences table, or finally from the given default.
     *
     * @param string $name
     * @param mixed $default
     * @return mixed|null|string
     */
    private function initialise_option($name, $default) {
        $param = optional_param($name, null, PARAM_BOOL);
        if (is_null($param)) {
            return get_user_preferences($name, $default);
        } else {
            set_user_preference($name, $param);
            return $param;
        }
    }

    /**
     * Output one of the options checkboxes.
     *
     * @param string $name
     * @param string $on
     * @param string $label
     * @return string
     */
    private function option_checkbox($name, $on, $label) {
        if ($on) {
            $checked = ' checked="checked"';
        } else {
            $checked = '';
        }
        $name = 'userselector_' . $name;
        // For the benefit of brain-dead IE, the id must be different from the name of the hidden form field above.
        // It seems that document.getElementById('frog') in IE will return and element with name="frog".
        $output = '<div class="form-check"><input type="hidden" name="' . $name . '" value="0" />' .
                    '<label class="form-check-label" for="' . $name . 'id">' .
                        '<input class="form-check-input" type="checkbox" id="' . $name . 'id" name="' . $name .
                            '" value="1"' . $checked . ' /> ' . $label .
                    "</label>
                   </div>\n";
        user_preference_allow_ajax_update($name, PARAM_BOOL);
        return $output;
    }

    /**
     * Initialises JS for this control.
     *
     * @param string $search
     * @return string any HTML needed here.
     */
    protected function initialise_javascript($search) {
        global $USER, $PAGE, $OUTPUT;
        $output = '';

        // Put the options into the session, to allow search.php to respond to the ajax requests.
        $options = $this->get_options();
        $hash = md5(serialize($options));
        $USER->userselectors[$hash] = $options;

        // Initialise the selector.
        $PAGE->requires->js_init_call(
            'M.core_user.init_user_selector',
            array($this->name, $hash, $this->extrafields, $search),
            false,
            self::$jsmodule
        );
        return $output;
    }
}

/**
 * Base class to avoid duplicating code.
 *
 * @copyright 1999 onwards Martin Dougiamas  http://dougiamas.com
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
abstract class groups_user_selector_base extends user_selector_base {
    /** @var int */
    protected $groupid;
    /** @var  int */
    protected $courseid;

    /**
     * Constructor.
     *
     * @param string $name control name
     * @param array $options should have two elements with keys groupid and courseid.
     */
    public function __construct($name, $options) {
        global $CFG;
        $options['accesscontext'] = context_course::instance($options['courseid']);
        parent::__construct($name, $options);
        $this->groupid = $options['groupid'];
        $this->courseid = $options['courseid'];
        require_once($CFG->dirroot . '/group/lib.php');
    }

    /**
     * Returns options for this selector.
     * @return array
     */
    protected function get_options() {
        $options = parent::get_options();
        $options['groupid'] = $this->groupid;
        $options['courseid'] = $this->courseid;
        return $options;
    }

    /**
     * Creates an organised array from given data.
     *
     * @param array $roles array in the format returned by groups_calculate_role_people.
     * @param string $search
     * @return array array in the format find_users is supposed to return.
     */
    protected function convert_array_format($roles, $search) {
        if (empty($roles)) {
            $roles = array();
        }
        $groupedusers = array();
        foreach ($roles as $role) {
            if ($search) {
                $a = new stdClass;
                $a->role = $role->name;
                $a->search = $search;
                $groupname = get_string('matchingsearchandrole', '', $a);
            } else {
                $groupname = $role->name;
            }
            $groupedusers[$groupname] = $role->users;
            foreach ($groupedusers[$groupname] as &$user) {
                unset($user->roles);
                $user->fullname = fullname($user);
                if (!empty($user->component)) {
                    $user->infobelow = get_string('addedby', 'group',
                        get_string('pluginname', $user->component));
                }
            }
        }
        return $groupedusers;
    }
}

/**
 * User selector subclass for the list of users who are in a certain group.
 *
 * Used on the add group memebers page.
 *
 * @copyright 1999 onwards Martin Dougiamas  http://dougiamas.com
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class group_members_selector extends groups_user_selector_base {

    /**
     * Finds users to display in this control.
     * @param string $search
     * @return array
     */
    public function find_users($search) {
        list($wherecondition, $params) = $this->search_sql($search, 'u');

        list($sort, $sortparams) = users_order_by_sql('u', $search, $this->accesscontext);

        $roles = groups_get_members_by_role($this->groupid, $this->courseid,
                $this->required_fields_sql('u') . ', gm.component',
                $sort, $wherecondition, array_merge($params, $sortparams));

        return $this->convert_array_format($roles, $search);
    }
}

/**
 * User selector subclass for the list of users who are not in a certain group.
 *
 * Used on the add group members page.
 *
 * @copyright 1999 onwards Martin Dougiamas  http://dougiamas.com
 * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class group_non_members_selector extends groups_user_selector_base {
    /**
     * An array of user ids populated by find_users() used in print_user_summaries()
     * @var array
     */
    private $potentialmembersids = array();

    /**
     * Output user.
     *
     * @param stdClass $user
     * @return string
     */
    public function output_user($user) {
        return parent::output_user($user) . ' (' . $user->numgroups . ')';
    }

    /**
     * Returns the user selector JavaScript module
     * @return array
     */
    public function get_js_module() {
        return self::$jsmodule;
    }

    /**
     * Creates a global JS variable (userSummaries) that is used by the group selector
     * to print related information when the user clicks on a user in the groups UI.
     *
     * Used by /group/clientlib.js
     *
     * @global moodle_page $PAGE
     * @param int $courseid
     */
    public function print_user_summaries($courseid) {
        global $PAGE;
        $usersummaries = $this->get_user_summaries($courseid);
        $PAGE->requires->data_for_js('userSummaries', $usersummaries);
    }

    /**
     * Construct HTML lists of group-memberships of the current set of users.
     *
     * Used in user/selector/search.php to repopulate the userSummaries JS global
     * that is created in self::print_user_summaries() above.
     *
     * @param int $courseid The course
     * @return string[] Array of HTML lists of groups.
     */
    public function get_user_summaries($courseid) {
        global $DB;

        $usersummaries = array();

        // Get other groups user already belongs to.
        $usergroups = array();
        $potentialmembersids = $this->potentialmembersids;
        if (empty($potentialmembersids) == false) {
            list($membersidsclause, $params) = $DB->get_in_or_equal($potentialmembersids, SQL_PARAMS_NAMED, 'pm');
            $sql = "SELECT u.id AS userid, g.*
                    FROM {user} u
                    JOIN {groups_members} gm ON u.id = gm.userid
                    JOIN {groups} g ON gm.groupid = g.id
                    WHERE u.id $membersidsclause AND g.courseid = :courseid ";
            $params['courseid'] = $courseid;
            $rs = $DB->get_recordset_sql($sql, $params);
            foreach ($rs as $usergroup) {
                $usergroups[$usergroup->userid][$usergroup->id] = $usergroup;
            }
            $rs->close();

            foreach ($potentialmembersids as $userid) {
                if (isset($usergroups[$userid])) {
                    $usergrouplist = html_writer::start_tag('ul');
                    foreach ($usergroups[$userid] as $groupitem) {
                        $usergrouplist .= html_writer::tag('li', format_string($groupitem->name));
                    }
                    $usergrouplist .= html_writer::end_tag('ul');
                } else {
                    $usergrouplist = '';
                }
                $usersummaries[] = $usergrouplist;
            }
        }
        return $usersummaries;
    }

    /**
     * Finds users to display in this control.
     *
     * @param string $search
     * @return array
     */
    public function find_users($search) {
        global $DB;

        // Get list of allowed roles.
        $context = context_course::instance($this->courseid);
        if ($validroleids = groups_get_possible_roles($context)) {
            list($roleids, $roleparams) = $DB->get_in_or_equal($validroleids, SQL_PARAMS_NAMED, 'r');
        } else {
            $roleids = " = -1";
            $roleparams = array();
        }

        // We want to query both the current context and parent contexts.
        list($relatedctxsql, $relatedctxparams) =
            $DB->get_in_or_equal($context->get_parent_context_ids(true), SQL_PARAMS_NAMED, 'relatedctx');

        // Get the search condition.
        list($searchcondition, $searchparams) = $this->search_sql($search, 'u');

        // Build the SQL.
        $enrolledjoin = get_enrolled_join($context, 'u.id');

        $wheres = [];
        $wheres[] = $enrolledjoin->wheres;
        $wheres[] = 'u.deleted = 0';
        $wheres[] = 'gm.id IS NULL';
        $wheres = implode(' AND ', $wheres);
        $wheres .= ' AND ' . $searchcondition;

        $fields = "SELECT r.id AS roleid, u.id AS userid,
                          " . $this->required_fields_sql('u') . ",
                          (SELECT count(igm.groupid)
                             FROM {groups_members} igm
                             JOIN {groups} ig ON igm.groupid = ig.id
                            WHERE igm.userid = u.id AND ig.courseid = :courseid) AS numgroups";
        $sql = "   FROM {user} u
                   $enrolledjoin->joins
              LEFT JOIN {role_assignments} ra ON (ra.userid = u.id AND ra.contextid $relatedctxsql AND ra.roleid $roleids)
              LEFT JOIN {role} r ON r.id = ra.roleid
              LEFT JOIN {groups_members} gm ON (gm.userid = u.id AND gm.groupid = :groupid)
                  WHERE $wheres";

        list($sort, $sortparams) = users_order_by_sql('u', $search, $this->accesscontext);
        $orderby = ' ORDER BY ' . $sort;

        $params = array_merge($searchparams, $roleparams, $relatedctxparams, $enrolledjoin->params);
        $params['courseid'] = $this->courseid;
        $params['groupid']  = $this->groupid;

        if (!$this->is_validating()) {
            $potentialmemberscount = $DB->count_records_sql("SELECT COUNT(DISTINCT u.id) $sql", $params);
            if ($potentialmemberscount > $this->maxusersperpage) {
                return $this->too_many_results($search, $potentialmemberscount);
            }
        }

        $rs = $DB->get_recordset_sql("$fields $sql $orderby", array_merge($params, $sortparams));
        $roles = groups_calculate_role_people($rs, $context);

        // Don't hold onto user IDs if we're doing validation.
        if (empty($this->validatinguserids) ) {
            if ($roles) {
                foreach ($roles as $k => $v) {
                    if ($v) {
                        foreach ($v->users as $uid => $userobject) {
                            $this->potentialmembersids[] = $uid;
                        }
                    }
                }
            }
        }

        return $this->convert_array_format($roles, $search);
    }
}
