/**
 * Returns an array of category ids of all the subcategories for a given
 * category.
 *
 * @global object
 * @param int $catid - The id of the category whose subcategories we want to find.
 * @return array of category ids.
 */
function get_all_subcategories($catid)
{
    global $DB;
    $subcats = array();
    if ($categories = $DB->get_records('course_categories', array('parent' => $catid))) {
        foreach ($categories as $cat) {
            array_push($subcats, $cat->id);
            $subcats = array_merge($subcats, get_all_subcategories($cat->id));
        }
    }
    return $subcats;
}

/**
 * Returns an array of category ids of all the subcategories for a given
 * category.
 * @param $catid - The id of the category whose subcategories we want to find.
 * @return array of category ids.
 */
function get_all_subcategories($catid)
{
    $subcats = array();
    if ($categories = get_records('course_categories', 'parent', $catid)) {
        foreach ($categories as $cat) {
            array_push($subcats, $cat->id);
            $subcats = array_merge($subcats, get_all_subcategories($cat->id));
        }
    }
    return $subcats;
}

/**
 * Returns an array of category ids of all the subcategories for a given
 * category.
 *
 * This function is deprecated.
 *
 * To get visible children categories of the given category use:
 * coursecat::get($categoryid)->get_children();
 * This function will return the array or coursecat objects, on each of them
 * you can call get_children() again
 *
 * @see coursecat::get()
 * @see coursecat::get_children()
 *
 * @deprecated since 2.5
 *
 * @global object
 * @param int $catid - The id of the category whose subcategories we want to find.
 * @return array of category ids.
 */
function get_all_subcategories($catid)
{
    global $DB;
    debugging('Function get_all_subcategories() is deprecated. Please use appropriate methods() of coursecat class. See phpdocs for more details', DEBUG_DEVELOPER);
    $subcats = array();
    if ($categories = $DB->get_records('course_categories', array('parent' => $catid))) {
        foreach ($categories as $cat) {
            array_push($subcats, $cat->id);
            $subcats = array_merge($subcats, get_all_subcategories($cat->id));
        }
    }
    return $subcats;
}

/**
 * Recursive function which, given a context, find all its children context ids.
 * @param object $context.
 * @return array of children context ids.
 */
function get_child_contexts($context)
{
    global $CFG;
    $children = array();
    switch ($context->contextlevel) {
        case CONTEXT_BLOCK:
            // No children.
            return array();
            break;
        case CONTEXT_MODULE:
            // No children.
            return array();
            break;
        case CONTEXT_GROUP:
            // No children.
            return array();
            break;
        case CONTEXT_COURSE:
            // Find all block instances for the course.
            $page = new page_course();
            $page->id = $context->instanceid;
            $page->type = 'course-view';
            if ($blocks = blocks_get_by_page_pinned($page)) {
                foreach ($blocks['l'] as $leftblock) {
                    if ($child = get_context_instance(CONTEXT_BLOCK, $leftblock->id)) {
                        array_push($children, $child->id);
                    }
                }
                foreach ($blocks['r'] as $rightblock) {
                    if ($child = get_context_instance(CONTEXT_BLOCK, $rightblock->id)) {
                        array_push($children, $child->id);
                    }
                }
            }
            // Find all module instances for the course.
            if ($modules = get_records('course_modules', 'course', $context->instanceid)) {
                foreach ($modules as $module) {
                    if ($child = get_context_instance(CONTEXT_MODULE, $module->id)) {
                        array_push($children, $child->id);
                    }
                }
            }
            // Find all group instances for the course.
            if ($groupids = groups_get_groups($context->instanceid)) {
                foreach ($groupids as $groupid) {
                    if ($child = get_context_instance(CONTEXT_GROUP, $groupid)) {
                        array_push($children, $child->id);
                    }
                }
            }
            return $children;
            break;
        case CONTEXT_COURSECAT:
            // We need to get the contexts for:
            //   1) The subcategories of the given category
            //   2) The courses in the given category and all its subcategories
            //   3) All the child contexts for these courses
            $categories = get_all_subcategories($context->instanceid);
            // Add the contexts for all the subcategories.
            foreach ($categories as $catid) {
                if ($catci = get_context_instance(CONTEXT_COURSECAT, $catid)) {
                    array_push($children, $catci->id);
                }
            }
            // Add the parent category as well so we can find the contexts
            // for its courses.
            array_unshift($categories, $context->instanceid);
            foreach ($categories as $catid) {
                // Find all courses for the category.
                if ($courses = get_records('course', 'category', $catid)) {
                    foreach ($courses as $course) {
                        if ($courseci = get_context_instance(CONTEXT_COURSE, $course->id)) {
                            array_push($children, $courseci->id);
                            $children = array_merge($children, get_child_contexts($courseci));
                        }
                    }
                }
            }
            return $children;
            break;
        case CONTEXT_USER:
            // No children.
            return array();
            break;
        case CONTEXT_PERSONAL:
            // No children.
            return array();
            break;
        case CONTEXT_SYSTEM:
            // Just get all the contexts except for CONTEXT_SYSTEM level.
            $sql = 'SELECT c.id ' . 'FROM ' . $CFG->prefix . 'context AS c ' . 'WHERE contextlevel != ' . CONTEXT_SYSTEM;
            $contexts = get_records_sql($sql);
            foreach ($contexts as $cid) {
                array_push($children, $cid->id);
            }
//.........这里部分代码省略.........