<?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/>.

/**
 * @copyright  1999 onwards Martin Dougiamas  {@link http://moodle.com}
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 * @package    core_group
 */

defined('MOODLE_INTERNAL') || die();

/**
 * Groups not used in course or activity
 */
define('NOGROUPS', 0);

/**
 * Groups used, users do not see other groups
 */
define('SEPARATEGROUPS', 1);

/**
 * Groups used, students see other groups
 */
define('VISIBLEGROUPS', 2);


/**
 * Determines if a group with a given groupid exists.
 *
 * @category group
 * @param int $groupid The groupid to check for
 * @return bool True if the group exists, false otherwise or if an error
 * occurred.
 */
function groups_group_exists($groupid) {
    global $DB;
    return $DB->record_exists('groups', array('id'=>$groupid));
}

/**
 * Gets the name of a group with a specified id
 *
 * @category group
 * @param int $groupid The id of the group
 * @return string The name of the group
 */
function groups_get_group_name($groupid) {
    global $DB;
    return $DB->get_field('groups', 'name', array('id'=>$groupid));
}

/**
 * Gets the name of a grouping with a specified id
 *
 * @category group
 * @param int $groupingid The id of the grouping
 * @return string The name of the grouping
 */
function groups_get_grouping_name($groupingid) {
    global $DB;
    return $DB->get_field('groupings', 'name', array('id'=>$groupingid));
}

/**
 * Returns the groupid of a group with the name specified for the course.
 * Group names should be unique in course
 *
 * @category group
 * @param int $courseid The id of the course
 * @param string $name name of group (without magic quotes)
 * @return int $groupid
 */
function groups_get_group_by_name($courseid, $name) {
    $data = groups_get_course_data($courseid);
    foreach ($data->groups as $group) {
        if ($group->name == $name) {
            return $group->id;
        }
    }
    return false;
}

/**
 * Returns the groupid of a group with the idnumber specified for the course.
 * Group idnumbers should be unique within course
 *
 * @category group
 * @param int $courseid The id of the course
 * @param string $idnumber idnumber of group
 * @return group object
 */
function groups_get_group_by_idnumber($courseid, $idnumber) {
    if (empty($idnumber)) {
        return false;
    }
    $data = groups_get_course_data($courseid);
    foreach ($data->groups as $group) {
        if ($group->idnumber == $idnumber) {
            return $group;
        }
    }
    return false;
}

/**
 * Returns the groupingid of a grouping with the name specified for the course.
 * Grouping names should be unique in course
 *
 * @category group
 * @param int $courseid The id of the course
 * @param string $name name of group (without magic quotes)
 * @return int $groupid
 */
function groups_get_grouping_by_name($courseid, $name) {
    $data = groups_get_course_data($courseid);
    foreach ($data->groupings as $grouping) {
        if ($grouping->name == $name) {
            return $grouping->id;
        }
    }
    return false;
}

/**
 * Returns the groupingid of a grouping with the idnumber specified for the course.
 * Grouping names should be unique within course
 *
 * @category group
 * @param int $courseid The id of the course
 * @param string $idnumber idnumber of the group
 * @return grouping object
 */
function groups_get_grouping_by_idnumber($courseid, $idnumber) {
    if (empty($idnumber)) {
        return false;
    }
    $data = groups_get_course_data($courseid);
    foreach ($data->groupings as $grouping) {
        if ($grouping->idnumber == $idnumber) {
            return $grouping;
        }
    }
    return false;
}

/**
 * Get the group object
 *
 * @category group
 * @param int $groupid ID of the group.
 * @param string $fields (default is all fields)
 * @param int $strictness (IGNORE_MISSING - default)
 * @return stdGlass group object
 */
function groups_get_group($groupid, $fields='*', $strictness=IGNORE_MISSING) {
    global $DB;
    return $DB->get_record('groups', array('id'=>$groupid), $fields, $strictness);
}

/**
 * Get the grouping object
 *
 * @category group
 * @param int $groupingid ID of the group.
 * @param string $fields
 * @param int $strictness (IGNORE_MISSING - default)
 * @return stdClass group object
 */
function groups_get_grouping($groupingid, $fields='*', $strictness=IGNORE_MISSING) {
    global $DB;
    return $DB->get_record('groupings', array('id'=>$groupingid), $fields, $strictness);
}

/**
 * Gets array of all groups in a specified course.
 *
 * @category group
 * @param int $courseid The id of the course.
 * @param mixed $userid optional user id or array of ids, returns only groups of the user.
 * @param int $groupingid optional returns only groups in the specified grouping.
 * @param string $fields
 * @return array Returns an array of the group objects (userid field returned if array in $userid)
 */
function groups_get_all_groups($courseid, $userid=0, $groupingid=0, $fields='g.*') {
    global $DB;

    // We need to check that we each field in the fields list belongs to the group table and that it has not being
    // aliased. If its something else we need to avoid the cache and run the query as who knows whats going on.
    $knownfields = true;
    if ($fields !== 'g.*') {
        // Quickly check if the first field is no longer g.id as using the
        // cache will return an array indexed differently than when expect
        if (strpos($fields, 'g.*') !== 0 && strpos($fields, 'g.id') !== 0) {
            $knownfields = false;
        } else {
            $fieldbits = explode(',', $fields);
            foreach ($fieldbits as $bit) {
                $bit = trim($bit);
                if (strpos($bit, 'g.') !== 0 or stripos($bit, ' AS ') !== false) {
                    $knownfields = false;
                    break;
                }
            }
        }
    }

    if (empty($userid) && $knownfields) {
        // We can use the cache.
        $data = groups_get_course_data($courseid);
        if (empty($groupingid)) {
            // All groups.. Easy!
            $groups = $data->groups;
        } else {
            $groups = array();
            foreach ($data->mappings as $mapping) {
                if ($mapping->groupingid != $groupingid) {
                    continue;
                }
                if (isset($data->groups[$mapping->groupid])) {
                    $groups[$mapping->groupid] = $data->groups[$mapping->groupid];
                }
            }
        }
        // Yay! We could use the cache. One more query saved.
        return $groups;
    }


    if (empty($userid)) {
        $userfrom  = "";
        $userwhere = "";
        $params = array();

    } else {
        list($usql, $params) = $DB->get_in_or_equal($userid);
        $userfrom  = ", {groups_members} gm";
        $userwhere = "AND g.id = gm.groupid AND gm.userid $usql";
    }

    if (!empty($groupingid)) {
        $groupingfrom  = ", {groupings_groups} gg";
        $groupingwhere = "AND g.id = gg.groupid AND gg.groupingid = ?";
        $params[] = $groupingid;
    } else {
        $groupingfrom  = "";
        $groupingwhere = "";
    }

    array_unshift($params, $courseid);

    return $DB->get_records_sql("SELECT $fields
                                   FROM {groups} g $userfrom $groupingfrom
                                  WHERE g.courseid = ? $userwhere $groupingwhere
                               ORDER BY name ASC", $params);
}


/**
 * Gets array of all groups in current user.
 *
 * @since Moodle 2.5
 * @category group
 * @return array Returns an array of the group objects.
 */
function groups_get_my_groups() {
    global $DB, $USER;
    return $DB->get_records_sql("SELECT *
                                   FROM {groups_members} gm
                                   JOIN {groups} g
                                    ON g.id = gm.groupid
                                  WHERE gm.userid = ?
                                   ORDER BY name ASC", array($USER->id));
}

/**
 * Returns info about user's groups in course.
 *
 * @category group
 * @param int $courseid
 * @param int $userid $USER if not specified
 * @return array Array[groupingid][groupid] including grouping id 0 which means all groups
 */
function groups_get_user_groups($courseid, $userid=0) {
    global $USER, $DB;

    if (empty($userid)) {
        $userid = $USER->id;
    }

    $sql = "SELECT g.id, gg.groupingid
              FROM {groups} g
                   JOIN {groups_members} gm   ON gm.groupid = g.id
              LEFT JOIN {groupings_groups} gg ON gg.groupid = g.id
             WHERE gm.userid = ? AND g.courseid = ?";
    $params = array($userid, $courseid);

    $rs = $DB->get_recordset_sql($sql, $params);

    if (!$rs->valid()) {
        $rs->close(); // Not going to iterate (but exit), close rs
        return array('0' => array());
    }

    $result    = array();
    $allgroups = array();

    foreach ($rs as $group) {
        $allgroups[$group->id] = $group->id;
        if (is_null($group->groupingid)) {
            continue;
        }
        if (!array_key_exists($group->groupingid, $result)) {
            $result[$group->groupingid] = array();
        }
        $result[$group->groupingid][$group->id] = $group->id;
    }
    $rs->close();

    $result['0'] = array_keys($allgroups); // all groups

    return $result;
}

/**
 * Gets an array of all groupings in a specified course. This value is cached
 * for a single course (so you can call it repeatedly for the same course
 * without a performance penalty).
 *
 * @category group
 * @param int $courseid return all groupings from course with this courseid
 * @return array Returns an array of the grouping objects (empty if none)
 */
function groups_get_all_groupings($courseid) {
    $data = groups_get_course_data($courseid);
    return $data->groupings;
}

/**
 * Determines if the user is a member of the given group.
 *
 * If $userid is null, use the global object.
 *
 * @category group
 * @param int $groupid The group to check for membership.
 * @param int $userid The user to check against the group.
 * @return bool True if the user is a member, false otherwise.
 */
function groups_is_member($groupid, $userid=null) {
    global $USER, $DB;

    if (!$userid) {
        $userid = $USER->id;
    }

    return $DB->record_exists('groups_members', array('groupid'=>$groupid, 'userid'=>$userid));
}

/**
 * Determines if current or specified is member of any active group in activity
 *
 * @category group
 * @staticvar array $cache
 * @param cm_info $cm course module object
 * @param int $userid id of user, null means $USER->id
 * @return bool true if user member of at least one group used in activity
 */
function groups_has_membership($cm, $userid=null) {
    global $CFG, $USER, $DB;

    static $cache = array();

    if (empty($userid)) {
        $userid = $USER->id;
    }

    $cachekey = $userid.'|'.$cm->course.'|'.$cm->groupingid;
    if (isset($cache[$cachekey])) {
        return($cache[$cachekey]);
    }

    if ($cm->groupingid) {
        // find out if member of any group in selected activity grouping
        $sql = "SELECT 'x'
                  FROM {groups_members} gm, {groupings_groups} gg
                 WHERE gm.userid = ? AND gm.groupid = gg.groupid AND gg.groupingid = ?";
        $params = array($userid, $cm->groupingid);

    } else {
        // no grouping used - check all groups in course
        $sql = "SELECT 'x'
                  FROM {groups_members} gm, {groups} g
                 WHERE gm.userid = ? AND gm.groupid = g.id AND g.courseid = ?";
        $params = array($userid, $cm->course);
    }

    $cache[$cachekey] = $DB->record_exists_sql($sql, $params);

    return $cache[$cachekey];
}

/**
 * Returns the users in the specified group.
 *
 * @category group
 * @param int $groupid The groupid to get the users for
 * @param int $fields The fields to return
 * @param int $sort optional sorting of returned users
 * @return array|bool Returns an array of the users for the specified
 * group or false if no users or an error returned.
 */
function groups_get_members($groupid, $fields='u.*', $sort='lastname ASC') {
    global $DB;

    return $DB->get_records_sql("SELECT $fields
                                   FROM {user} u, {groups_members} gm
                                  WHERE u.id = gm.userid AND gm.groupid = ?
                               ORDER BY $sort", array($groupid));
}


/**
 * Returns the users in the specified grouping.
 *
 * @category group
 * @param int $groupingid The groupingid to get the users for
 * @param string $fields The fields to return
 * @param string $sort optional sorting of returned users
 * @return array|bool Returns an array of the users for the specified
 * group or false if no users or an error returned.
 */
function groups_get_grouping_members($groupingid, $fields='u.*', $sort='lastname ASC') {
    global $DB;

    return $DB->get_records_sql("SELECT $fields
                                   FROM {user} u
                                     INNER JOIN {groups_members} gm ON u.id = gm.userid
                                     INNER JOIN {groupings_groups} gg ON gm.groupid = gg.groupid
                                  WHERE  gg.groupingid = ?
                               ORDER BY $sort", array($groupingid));
}

/**
 * Returns effective groupmode used in course
 *
 * @category group
 * @param stdClass $course course object.
 * @return int group mode
 */
function groups_get_course_groupmode($course) {
    return $course->groupmode;
}

/**
 * Returns effective groupmode used in activity, course setting
 * overrides activity setting if groupmodeforce enabled.
 *
 * @category group
 * @param cm_info $cm the course module object. Only the ->course and ->groupmode need to be set.
 * @param stdClass $course object optional course object to improve perf
 * @return int group mode
 */
function groups_get_activity_groupmode($cm, $course=null) {
    global $COURSE, $DB;

    // get course object (reuse COURSE if possible)
    if (isset($course->id) and $course->id == $cm->course) {
        //ok
    } else if ($cm->course == $COURSE->id) {
        $course = $COURSE;
    } else {
        if (!$course = $DB->get_record('course', array('id'=>$cm->course))) {
            print_error('invalidcourseid');
        }
    }

    return empty($course->groupmodeforce) ? $cm->groupmode : $course->groupmode;
}

/**
 * Print group menu selector for course level.
 *
 * @category group
 * @param stdClass $course course object
 * @param mixed $urlroot return address. Accepts either a string or a moodle_url
 * @param bool $return return as string instead of printing
 * @return mixed void or string depending on $return param
 */
function groups_print_course_menu($course, $urlroot, $return=false) {
    global $USER, $OUTPUT;

    if (!$groupmode = $course->groupmode) {
        if ($return) {
            return '';
        } else {
            return;
        }
    }

    $context = context_course::instance($course->id);
    $aag = has_capability('moodle/site:accessallgroups', $context);

    if ($groupmode == VISIBLEGROUPS or $aag) {
        $allowedgroups = groups_get_all_groups($course->id, 0, $course->defaultgroupingid);
    } else {
        $allowedgroups = groups_get_all_groups($course->id, $USER->id, $course->defaultgroupingid);
    }

    $activegroup = groups_get_course_group($course, true, $allowedgroups);

    $groupsmenu = array();
    if (!$allowedgroups or $groupmode == VISIBLEGROUPS or $aag) {
        $groupsmenu[0] = get_string('allparticipants');
    }

    if ($allowedgroups) {
        foreach ($allowedgroups as $group) {
            $groupsmenu[$group->id] = format_string($group->name);
        }
    }

    if ($groupmode == VISIBLEGROUPS) {
        $grouplabel = get_string('groupsvisible');
    } else {
        $grouplabel = get_string('groupsseparate');
    }

    if ($aag and $course->defaultgroupingid) {
        if ($grouping = groups_get_grouping($course->defaultgroupingid)) {
            $grouplabel = $grouplabel . ' (' . format_string($grouping->name) . ')';
        }
    }

    if (count($groupsmenu) == 1) {
        $groupname = reset($groupsmenu);
        $output = $grouplabel.': '.$groupname;
    } else {
        $select = new single_select(new moodle_url($urlroot), 'group', $groupsmenu, $activegroup, null, 'selectgroup');
        $select->label = $grouplabel;
        $output = $OUTPUT->render($select);
    }

    $output = '<div class="groupselector">'.$output.'</div>';

    if ($return) {
        return $output;
    } else {
        echo $output;
    }
}

/**
 * Print group menu selector for activity.
 *
 * @category group
 * @param stdClass $cm course module object
 * @param string|moodle_url $urlroot return address that users get to if they choose an option;
 *   should include any parameters needed, e.g. "$CFG->wwwroot/mod/forum/view.php?id=34"
 * @param bool $return return as string instead of printing
 * @param bool $hideallparticipants If true, this prevents the 'All participants'
 *   option from appearing in cases where it normally would. This is intended for
 *   use only by activities that cannot display all groups together. (Note that
 *   selecting this option does not prevent groups_get_activity_group from
 *   returning 0; it will still do that if the user has chosen 'all participants'
 *   in another activity, or not chosen anything.)
 * @return mixed void or string depending on $return param
 */
function groups_print_activity_menu($cm, $urlroot, $return=false, $hideallparticipants=false) {
    global $USER, $OUTPUT;

    if ($urlroot instanceof moodle_url) {
        // no changes necessary

    } else {
        if (strpos($urlroot, 'http') !== 0) { // Will also work for https
            // Display error if urlroot is not absolute (this causes the non-JS version to break)
            debugging('groups_print_activity_menu requires absolute URL for ' .
                      '$urlroot, not <tt>' . s($urlroot) . '</tt>. Example: ' .
                      'groups_print_activity_menu($cm, $CFG->wwwroot . \'/mod/mymodule/view.php?id=13\');',
                      DEBUG_DEVELOPER);
        }
        $urlroot = new moodle_url($urlroot);
    }

    if (!$groupmode = groups_get_activity_groupmode($cm)) {
        if ($return) {
            return '';
        } else {
            return;
        }
    }

    $context = context_module::instance($cm->id);
    $aag = has_capability('moodle/site:accessallgroups', $context);

    if ($groupmode == VISIBLEGROUPS or $aag) {
        $allowedgroups = groups_get_all_groups($cm->course, 0, $cm->groupingid); // any group in grouping
    } else {
        $allowedgroups = groups_get_all_groups($cm->course, $USER->id, $cm->groupingid); // only assigned groups
    }

    $activegroup = groups_get_activity_group($cm, true, $allowedgroups);

    $groupsmenu = array();
    if ((!$allowedgroups or $groupmode == VISIBLEGROUPS or $aag) and !$hideallparticipants) {
        $groupsmenu[0] = get_string('allparticipants');
    }

    if ($allowedgroups) {
        foreach ($allowedgroups as $group) {
            $groupsmenu[$group->id] = format_string($group->name);
        }
    }

    if ($groupmode == VISIBLEGROUPS) {
        $grouplabel = get_string('groupsvisible');
    } else {
        $grouplabel = get_string('groupsseparate');
    }

    if ($aag and $cm->groupingid) {
        if ($grouping = groups_get_grouping($cm->groupingid)) {
            $grouplabel = $grouplabel . ' (' . format_string($grouping->name) . ')';
        }
    }

    if (count($groupsmenu) == 1) {
        $groupname = reset($groupsmenu);
        $output = $grouplabel.': '.$groupname;
    } else {
        $select = new single_select($urlroot, 'group', $groupsmenu, $activegroup, null, 'selectgroup');
        $select->label = $grouplabel;
        $output = $OUTPUT->render($select);
    }

    $output = '<div class="groupselector">'.$output.'</div>';

    if ($return) {
        return $output;
    } else {
        echo $output;
    }
}

/**
 * Returns group active in course, changes the group by default if 'group' page param present
 *
 * @category group
 * @param stdClass $course course bject
 * @param bool $update change active group if group param submitted
 * @param array $allowedgroups list of groups user may access (INTERNAL, to be used only from groups_print_course_menu())
 * @return mixed false if groups not used, int if groups used, 0 means all groups (access must be verified in SEPARATE mode)
 */
function groups_get_course_group($course, $update=false, $allowedgroups=null) {
    global $USER, $SESSION;

    if (!$groupmode = $course->groupmode) {
        // NOGROUPS used
        return false;
    }

    $context = context_course::instance($course->id);
    if (has_capability('moodle/site:accessallgroups', $context)) {
        $groupmode = 'aag';
    }

    if (!is_array($allowedgroups)) {
        if ($groupmode == VISIBLEGROUPS or $groupmode === 'aag') {
            $allowedgroups = groups_get_all_groups($course->id, 0, $course->defaultgroupingid);
        } else {
            $allowedgroups = groups_get_all_groups($course->id, $USER->id, $course->defaultgroupingid);
        }
    }

    _group_verify_activegroup($course->id, $groupmode, $course->defaultgroupingid, $allowedgroups);

    // set new active group if requested
    $changegroup = optional_param('group', -1, PARAM_INT);
    if ($update and $changegroup != -1) {

        if ($changegroup == 0) {
            // do not allow changing to all groups without accessallgroups capability
            if ($groupmode == VISIBLEGROUPS or $groupmode === 'aag') {
                $SESSION->activegroup[$course->id][$groupmode][$course->defaultgroupingid] = 0;
            }

        } else {
            if ($allowedgroups and array_key_exists($changegroup, $allowedgroups)) {
                $SESSION->activegroup[$course->id][$groupmode][$course->defaultgroupingid] = $changegroup;
            }
        }
    }

    return $SESSION->activegroup[$course->id][$groupmode][$course->defaultgroupingid];
}

/**
 * Returns group active in activity, changes the group by default if 'group' page param present
 *
 * @category group
 * @param stdClass $cm course module object
 * @param bool $update change active group if group param submitted
 * @param array $allowedgroups list of groups user may access (INTERNAL, to be used only from groups_print_activity_menu())
 * @return mixed false if groups not used, int if groups used, 0 means all groups (access must be verified in SEPARATE mode)
 */
function groups_get_activity_group($cm, $update=false, $allowedgroups=null) {
    global $USER, $SESSION;

    if (!$groupmode = groups_get_activity_groupmode($cm)) {
        // NOGROUPS used
        return false;
    }

    $context = context_module::instance($cm->id);
    if (has_capability('moodle/site:accessallgroups', $context)) {
        $groupmode = 'aag';
    }

    if (!is_array($allowedgroups)) {
        if ($groupmode == VISIBLEGROUPS or $groupmode === 'aag') {
            $allowedgroups = groups_get_all_groups($cm->course, 0, $cm->groupingid);
        } else {
            $allowedgroups = groups_get_all_groups($cm->course, $USER->id, $cm->groupingid);
        }
    }

    _group_verify_activegroup($cm->course, $groupmode, $cm->groupingid, $allowedgroups);

    // set new active group if requested
    $changegroup = optional_param('group', -1, PARAM_INT);
    if ($update and $changegroup != -1) {

        if ($changegroup == 0) {
            // allgroups visible only in VISIBLEGROUPS or when accessallgroups
            if ($groupmode == VISIBLEGROUPS or $groupmode === 'aag') {
                $SESSION->activegroup[$cm->course][$groupmode][$cm->groupingid] = 0;
            }

        } else {
            if ($allowedgroups and array_key_exists($changegroup, $allowedgroups)) {
                $SESSION->activegroup[$cm->course][$groupmode][$cm->groupingid] = $changegroup;
            }
        }
    }

    return $SESSION->activegroup[$cm->course][$groupmode][$cm->groupingid];
}

/**
 * Gets a list of groups that the user is allowed to access within the
 * specified activity.
 *
 * @category group
 * @param stdClass $cm Course-module
 * @param int $userid User ID (defaults to current user)
 * @return array An array of group objects, or false if none
 */
function groups_get_activity_allowed_groups($cm,$userid=0) {
    // Use current user by default
    global $USER;
    if(!$userid) {
        $userid=$USER->id;
    }

    // Get groupmode for activity, taking into account course settings
    $groupmode=groups_get_activity_groupmode($cm);

    // If visible groups mode, or user has the accessallgroups capability,
    // then they can access all groups for the activity...
    $context = context_module::instance($cm->id);
    if ($groupmode == VISIBLEGROUPS or has_capability('moodle/site:accessallgroups', $context)) {
        return groups_get_all_groups($cm->course, 0, $cm->groupingid);
    } else {
        // ...otherwise they can only access groups they belong to
        return groups_get_all_groups($cm->course, $userid, $cm->groupingid);
    }
}

/**
 * Filter a user list and return only the users that can see the course module based on
 * groups/permissions etc. It is assumed that the users are pre-filtered to those who are enrolled in the course.
 *
 * @category group
 * @param stdClass $cm The course module
 * @param array $users An array of users, indexed by userid
 * @return array A filtered list of users that can see the module, indexed by userid.
 */
function groups_filter_users_by_course_module_visible($cm, $users) {
    global $CFG, $DB;

    if (empty($CFG->enablegroupmembersonly)) {
        return $users;
    }
    if (empty($cm->groupmembersonly)) {
        return $users;
    }
    list($usql, $uparams) = $DB->get_in_or_equal(array_keys($users), SQL_PARAMS_NAMED, 'userid', true);

    // Group membership sub-query.
    if ($cm->groupingid) {
        // Find out if member of any group in selected activity grouping.
        $igsql = "SELECT gm.userid
                  FROM {groups_members} gm
                  LEFT JOIN {groupings_groups} gg
                  ON gm.groupid = gg.groupid
                  WHERE gm.userid $usql AND gg.groupingid = :groupingid";
        $igparams = array_merge($uparams, array('groupingid' => $cm->groupingid));

    } else {
        // No grouping used - check all groups in course.
        $igsql = "SELECT gm.userid
                  FROM {groups_members} gm
                  LEFT JOIN {groups} g
                  ON gm.groupid = g.id
                  WHERE gm.userid $usql AND g.courseid = :courseid";
        $igparams = array_merge($uparams, array('courseid' => $cm->course));
    }

    $context = context_module::instance($cm->id);

    // Get the list of users in a valid group.
    $usersingroup = $DB->get_records_sql($igsql, $igparams);
    if (!$usersingroup) {
        $usersingroup = array();
    } else {
        $usersingroup = array_keys($usersingroup);
    }

    // Get the list of users who can access all groups.
    list($accessallgroupssql, $accessallgroupsparams) = get_enrolled_sql($context, 'moodle/site:accessallgroups');

    $userswithaccessallgroups = $DB->get_records_sql($accessallgroupssql, $accessallgroupsparams);
    if (!$userswithaccessallgroups) {
        $userswithaccessallgroups = array();
    } else {
        $userswithaccessallgroups = array_keys($userswithaccessallgroups);
    }

    // Explaining this array mangling:
    // $users is an array of $user[$userid] => stdClass etc
    // $userswithaccessallgroups is an array of $userswithaccessallgroups[random int] = $userid
    // $usersingroup is an array of $usersingroup[random int] = $userid
    // so - the inner array_merge combines the values of the 2 arrays disregarding the keys (because they are ints)
    // this is then flipped so the values become the keys (and the values are now nonsense)
    // this is then intersected with the users array only by looking at the keys - this
    // returns only the users from the original array that had a value in one of the two $usersxxx lists.
    return array_intersect_key($users, array_flip(array_merge($userswithaccessallgroups, $usersingroup)));
}

/**
 * Determine if a course module is currently visible to a user
 *
 * $USER If $userid is null, use the global object.
 *
 * @category group
 * @param stdClass $cm The course module
 * @param int $userid The user to check against the group.
 * @return bool True if the user can view the course module, false otherwise.
 */
function groups_course_module_visible($cm, $userid=null) {
    global $CFG, $USER;

    if (empty($userid)) {
        $userid = $USER->id;
    }
    if (empty($CFG->enablegroupmembersonly)) {
        return true;
    }
    if (empty($cm->groupmembersonly)) {
        return true;
    }
    if (has_capability('moodle/site:accessallgroups', context_module::instance($cm->id), $userid) or groups_has_membership($cm, $userid)) {
        return true;
    }
    return false;
}

/**
 * Internal method, sets up $SESSION->activegroup and verifies previous value
 *
 * @param int $courseid
 * @param int|string $groupmode SEPARATEGROUPS, VISIBLEGROUPS or 'aag' (access all groups)
 * @param int $groupingid 0 means all groups
 * @param array $allowedgroups list of groups user can see
 */
function _group_verify_activegroup($courseid, $groupmode, $groupingid, array $allowedgroups) {
    global $SESSION, $USER;

    // init activegroup array if necessary
    if (!isset($SESSION->activegroup)) {
        $SESSION->activegroup = array();
    }
    if (!array_key_exists($courseid, $SESSION->activegroup)) {
        $SESSION->activegroup[$courseid] = array(SEPARATEGROUPS=>array(), VISIBLEGROUPS=>array(), 'aag'=>array());
    }

    // make sure that the current group info is ok
    if (array_key_exists($groupingid, $SESSION->activegroup[$courseid][$groupmode]) and !array_key_exists($SESSION->activegroup[$courseid][$groupmode][$groupingid], $allowedgroups)) {
        // active group does not exist anymore or is 0
        if ($SESSION->activegroup[$courseid][$groupmode][$groupingid] > 0 or $groupmode == SEPARATEGROUPS) {
            // do not do this if all groups selected and groupmode is not separate
            unset($SESSION->activegroup[$courseid][$groupmode][$groupingid]);
        }
    }

    // set up defaults if necessary
    if (!array_key_exists($groupingid, $SESSION->activegroup[$courseid][$groupmode])) {
        if ($groupmode == 'aag') {
            $SESSION->activegroup[$courseid][$groupmode][$groupingid] = 0; // all groups by default if user has accessallgroups

        } else if ($allowedgroups) {
            if ($groupmode != SEPARATEGROUPS and $mygroups = groups_get_all_groups($courseid, $USER->id, $groupingid)) {
                $firstgroup = reset($mygroups);
            } else {
                $firstgroup = reset($allowedgroups);
            }
            $SESSION->activegroup[$courseid][$groupmode][$groupingid] = $firstgroup->id;

        } else {
            // this happen when user not assigned into group in SEPARATEGROUPS mode or groups do not exist yet
            // mod authors must add extra checks for this when SEPARATEGROUPS mode used (such as when posting to forum)
            $SESSION->activegroup[$courseid][$groupmode][$groupingid] = 0;
        }
    }
}

/**
 * Caches group data for a particular course to speed up subsequent requests.
 *
 * @param int $courseid The course id to cache data for.
 * @param cache $cache The cache if it has already been initialised. If not a new one will be created.
 * @return stdClass A data object containing groups, groupings, and mappings.
 */
function groups_cache_groupdata($courseid, cache $cache = null) {
    global $DB;

    if ($cache === null) {
        // Initialise a cache if we wern't given one.
        $cache = cache::make('core', 'groupdata');
    }

    // Get the groups that belong to the course.
    $groups = $DB->get_records('groups', array('courseid' => $courseid), 'name ASC');
    // Get the groupings that belong to the course.
    $groupings = $DB->get_records('groupings', array('courseid' => $courseid), 'name ASC');

    if (!is_array($groups)) {
        $groups = array();
    }

    if (!is_array($groupings)) {
        $groupings = array();
    }

    if (!empty($groupings)) {
        // Finally get the mappings between the two.
        list($insql, $params) = $DB->get_in_or_equal(array_keys($groupings));
        $mappings = $DB->get_records_sql("
                SELECT gg.id, gg.groupingid, gg.groupid
                  FROM {groupings_groups} gg
                  JOIN {groups} g ON g.id = gg.groupid
                 WHERE gg.groupingid $insql
              ORDER BY g.name ASC", $params);
    } else {
        $mappings = array();
    }

    // Prepare the data array.
    $data = new stdClass;
    $data->groups = $groups;
    $data->groupings = $groupings;
    $data->mappings = $mappings;
    // Cache the data.
    $cache->set($courseid, $data);
    // Finally return it so it can be used if desired.
    return $data;
}

/**
 * Gets group data for a course.
 *
 * This returns an object with the following properties:
 *   - groups : An array of all the groups in the course.
 *   - groupings : An array of all the groupings within the course.
 *   - mappings : An array of group to grouping mappings.
 *
 * @param int $courseid The course id to get data for.
 * @param cache $cache The cache if it has already been initialised. If not a new one will be created.
 * @return stdClass
 */
function groups_get_course_data($courseid, cache $cache = null) {
    if ($cache === null) {
        // Initialise a cache if we wern't given one.
        $cache = cache::make('core', 'groupdata');
    }
    // Try to retrieve it from the cache.
    $data = $cache->get($courseid);
    if ($data === false) {
        $data = groups_cache_groupdata($courseid, $cache);
    }
    return $data;
}
