<?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/>.
/**
* Class core_tag_index_builder
*
* @package core_tag
* @copyright 2016 Marina Glancy
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
defined('MOODLE_INTERNAL') || die();
/**
* Helper to build tag index
*
* This can be used by components to implement tag area callbacks. This is especially
* useful for in-course content when we need to check and cache user's access to
* multiple courses. Course access and accessible items are stored in session cache
* with 15 minutes expiry time.
*
* Example of usage:
*
* $builder = new core_tag_index_builder($component, $itemtype, $sql, $params, $from, $limit);
* while ($item = $builder->has_item_that_needs_access_check()) {
* if (!$builder->can_access_course($item->courseid)) {
* $builder->set_accessible($item, false);
* } else {
* $accessible = true; // Check access and set $accessible respectively.
* $builder->set_accessible($item, $accessible);
* }
* }
* $items = $builder->get_items();
*
* @package core_tag
* @copyright 2016 Marina Glancy
* @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
*/
class core_tag_index_builder {
/** @var string component specified in the constructor */
protected $component;
/** @var string itemtype specified in the constructor */
protected $itemtype;
/** @var string SQL statement */
protected $sql;
/** @var array parameters for SQL statement */
protected $params;
/** @var int index from which to return records */
protected $from;
/** @var int maximum number of records to return */
protected $limit;
/** @var array result of SQL query */
protected $items;
/** @var array list of item ids ( array_keys($this->items) ) */
protected $itemkeys;
/** @var string alias of the item id in the SQL result */
protected $idfield = 'id';
/** @var array cache of items accessibility (id => bool) */
protected $accessibleitems;
/** @var array cache of courses accessibility (courseid => bool) */
protected $courseaccess;
/** @var bool indicates that items cache was changed in this class and needs pushing to MUC */
protected $cachechangedaccessible = false;
/** @var bool indicates that course accessibiity cache was changed in this class and needs pushing to MUC */
protected $cachechangedcourse = false;
/** @var array cached courses (not pushed to MUC) */
protected $courses;
/**
* Constructor.
*
* Specify the SQL query for retrieving the tagged items, SQL query must:
* - return the item id as the first field and make sure that it is unique in the result
* - provide ORDER BY that exclude any possibility of random results, if $fromctx was specified when searching
* for tagged items it is the best practice to make sure that items from this context are returned first.
*
* This query may also contain placeholders %COURSEFILTER% or %ITEMFILTER% that will be substituted with
* expressions excluding courses and/or filters that are already known as inaccessible.
*
* Example: "WHERE c.id %COURSEFILTER% AND cm.id %ITEMFILTER%"
*
* This query may contain fields to preload context if context is needed for formatting values.
*
* It is recommended to sort by course sortorder first, this way the items from the same course will be next to
* each other and the sequence of courses will the same in different tag areas.
*
* @param string $component component responsible for tagging
* @param string $itemtype type of item that is being tagged
* @param string $sql SQL query that would retrieve all relevant items without permission check
* @param array $params parameters for the query (must be named)
* @param int $from return a subset of records, starting at this point
* @param int $limit return a subset comprising this many records in total (this field is NOT optional)
*/
public function __construct($component, $itemtype, $sql, $params, $from, $limit) {
$this->component = preg_replace('/[^A-Za-z0-9_]/i', '', $component);
$this->itemtype = preg_replace('/[^A-Za-z0-9_]/i', '', $itemtype);
$this->sql = $sql;
$this->params = $params;
$this->from = $from;
$this->limit = $limit;
$this->courses = array();
}
/**
* Substitute %COURSEFILTER% with an expression filtering out courses where current user does not have access
*/
protected function prepare_sql_courses() {
global $DB;
if (!preg_match('/\\%COURSEFILTER\\%/', $this->sql)) {
return;
}
$this->init_course_access();
$unaccessiblecourses = array_filter($this->courseaccess, function($item) {
return !$item;
});
$idx = 0;
while (preg_match('/^([^\\0]*?)\\%COURSEFILTER\\%([^\\0]*)$/', $this->sql, $matches)) {
list($sql, $params) = $DB->get_in_or_equal(array_keys($unaccessiblecourses),
SQL_PARAMS_NAMED, 'ca_'.($idx++).'_', false, 0);
$this->sql = $matches[1].' '.$sql.' '.$matches[2];
$this->params += $params;
}
}
/**
* Substitute %ITEMFILTER% with an expression filtering out items where current user does not have access
*/
protected function prepare_sql_items() {
global $DB;
if (!preg_match('/\\%ITEMFILTER\\%/', $this->sql)) {
return;
}
$this->init_items_access();
$unaccessibleitems = array_filter($this->accessibleitems, function($item) {
return !$item;
});
$idx = 0;
while (preg_match('/^([^\\0]*?)\\%ITEMFILTER\\%([^\\0]*)$/', $this->sql, $matches)) {
list($sql, $params) = $DB->get_in_or_equal(array_keys($unaccessibleitems),
SQL_PARAMS_NAMED, 'ia_'.($idx++).'_', false, 0);
$this->sql = $matches[1].' '.$sql.' '.$matches[2];
$this->params += $params;
}
}
/**
* Ensures that SQL query was executed and $this->items is filled
*/
protected function retrieve_items() {
global $DB;
if ($this->items !== null) {
return;
}
$this->prepare_sql_courses();
$this->prepare_sql_items();
$this->items = $DB->get_records_sql($this->sql, $this->params);
$this->itemkeys = array_keys($this->items);
if ($this->items) {
// Find the name of the first key of the item - usually 'id' but can be something different.
// This must be a unique identifier of the item.
$firstitem = reset($this->items);
$firstitemarray = (array)$firstitem;
$this->idfield = key($firstitemarray);
}
}
/**
* Returns the filtered records from SQL query result.
*
* This function can only be executed after $builder->has_item_that_needs_access_check() returns null
*
*
* @return array
*/
public function get_items() {
global $DB, $CFG;
if (is_siteadmin()) {
$this->sql = preg_replace('/\\%COURSEFILTER\\%/', '<>0', $this->sql);
$this->sql = preg_replace('/\\%ITEMFILTER\\%/', '<>0', $this->sql);
return $DB->get_records_sql($this->sql, $this->params, $this->from, $this->limit);
}
if ($CFG->debugdeveloper && $this->has_item_that_needs_access_check()) {
debugging('Caller must ensure that has_item_that_needs_access_check() does not return anything '
. 'before calling get_items(). The item list may be incomplete', DEBUG_DEVELOPER);
}
$this->retrieve_items();
$this->save_caches();
$idx = 0;
$items = array();
foreach ($this->itemkeys as $id) {
if (!array_key_exists($id, $this->accessibleitems) || !$this->accessibleitems[$id]) {
continue;
}
if ($idx >= $this->from) {
$items[$id] = $this->items[$id];
}
$idx++;
if ($idx >= $this->from + $this->limit) {
break;
}
}
return $items;
}
/**
* Returns the first row from the SQL result that we don't know whether it is accessible by user or not.
*
* This will return null when we have necessary number of accessible items to return in {@link get_items()}
*
* After analyzing you may decide to mark not only this record but all similar as accessible or not accessible.
* For example, if you already call get_fast_modinfo() to check this item's accessibility, why not mark all
* items in the same course as accessible or not accessible.
*
* Helpful methods: {@link set_accessible()} and {@link walk()}
*
* @return null|object
*/
public function has_item_that_needs_access_check() {
if (is_siteadmin()) {
return null;
}
$this->retrieve_items();
$counter = 0; // Counter for accessible items.
foreach ($this->itemkeys as $id) {
if (!array_key_exists($id, $this->accessibleitems)) {
return (object)(array)$this->items[$id];
}
$counter += $this->accessibleitems[$id] ? 1 : 0;
if ($counter >= $this->from + $this->limit) {
// We found enough accessible items fot get_items() method, do not look any further.
return null;
}
}
return null;
}
/**
* Walk through the array of items and call $callable for each of them
* @param callable $callable
*/
public function walk($callable) {
$this->retrieve_items();
array_walk($this->items, $callable);
}
/**
* Marks record or group of records as accessible (or not accessible)
*
* @param int|std_Class $identifier either record id of the item that needs to be set accessible
* @param bool $accessible whether to mark as accessible or not accessible (default true)
*/
public function set_accessible($identifier, $accessible = true) {
if (is_object($identifier)) {
$identifier = (int)($identifier->{$this->idfield});
}
$this->init_items_access();
if (is_int($identifier)) {
$accessible = (int)(bool)$accessible;
if (!array_key_exists($identifier, $this->accessibleitems) ||
$this->accessibleitems[$identifier] != $accessible) {
$this->accessibleitems[$identifier] = $accessible;
$this->cachechangedaccessible;
}
} else {
throw new coding_exception('Argument $identifier must be either int or object');
}
}
/**
* Retrieves a course record (only fields id,visible,fullname,shortname,cacherev).
*
* This method is useful because it also caches results and preloads course context.
*
* @param int $courseid
*/
public function get_course($courseid) {
global $DB;
if (!array_key_exists($courseid, $this->courses)) {
$ctxquery = context_helper::get_preload_record_columns_sql('ctx');
$sql = "SELECT c.id,c.visible,c.fullname,c.shortname,c.cacherev, $ctxquery
FROM {course} c JOIN {context} ctx ON ctx.contextlevel = ? AND ctx.instanceid=c.id
WHERE c.id = ?";
$params = array(CONTEXT_COURSE, $courseid);
$this->courses[$courseid] = $DB->get_record_sql($sql, $params);
context_helper::preload_from_record($this->courses[$courseid]);
}
return $this->courses[$courseid];
}
/**
* Ensures that we read the course access from the cache.
*/
protected function init_course_access() {
if ($this->courseaccess === null) {
$this->courseaccess = cache::make('core', 'tagindexbuilder')->get('courseaccess') ?: [];
}
}
/**
* Ensures that we read the items access from the cache.
*/
protected function init_items_access() {
if ($this->accessibleitems === null) {
$this->accessibleitems = cache::make('core', 'tagindexbuilder')->get($this->component.'__'.$this->itemtype) ?: [];
}
}
/**
* Checks if current user has access to the course
*
* This method calls global function {@link can_access_course} and caches results
*
* @param int $courseid
* @return bool
*/
public function can_access_course($courseid) {
$this->init_course_access();
if (!array_key_exists($courseid, $this->courseaccess)) {
$this->courseaccess[$courseid] = can_access_course($this->get_course($courseid)) ? 1 : 0;
$this->cachechangedcourse = true;
}
return $this->courseaccess[$courseid];
}
/**
* Saves course/items caches if needed
*/
protected function save_caches() {
if ($this->cachechangedcourse) {
cache::make('core', 'tagindexbuilder')->set('courseaccess', $this->courseaccess);
$this->cachechangedcourse = false;
}
if ($this->cachechangedaccessible) {
cache::make('core', 'tagindexbuilder')->set($this->component.'__'.$this->itemtype,
$this->accessibleitems);
$this->cachechangedaccessible = false;
}
}
/**
* Resets all course/items session caches - useful in unittests when we change users and enrolments.
*/
public static function reset_caches() {
cache_helper::purge_by_event('resettagindexbuilder');
}
}