<?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/>.

/**
 * The supplementary cache API.
 *
 * This file is part of Moodle's cache API, affectionately called MUC.
 * It contains elements of the API that are not required in order to use caching.
 * Things in here are more in line with administration and management of the cache setup and configuration.
 *
 * @package    core
 * @category   cache
 * @copyright  2012 Sam Hemelryk
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

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

/**
 * Cache configuration writer.
 *
 * This class should only be used when you need to write to the config, all read operations exist within the cache_config.
 *
 * @package    core
 * @category   cache
 * @copyright  2012 Sam Hemelryk
 * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class cache_config_writer extends cache_config {

    /**
     * Switch that gets set to true when ever a cache_config_writer instance is saving the cache configuration file.
     * If this is set to true when save is next called we must avoid the trying to save and instead return the
     * generated config so that is may be used instead of the file.
     * @var bool
     */
    protected static $creatingconfig = false;

    /**
     * Returns an instance of the configuration writer.
     *
     * @return cache_config_writer
     */
    public static function instance() {
        $factory = cache_factory::instance();
        return $factory->create_config_instance(true);
    }

    /**
     * Saves the current configuration.
     *
     * Exceptions within this function are tolerated but must be of type cache_exception.
     * They are caught during initialisation and written to the error log. This is required in order to avoid
     * infinite loop situations caused by the cache throwing exceptions during its initialisation.
     */
    protected function config_save() {
        global $CFG;
        static $confighash = '';
        $cachefile = static::get_config_file_path();
        $directory = dirname($cachefile);
        if ($directory !== $CFG->dataroot && !file_exists($directory)) {
            $result = make_writable_directory($directory, false);
            if (!$result) {
                throw new cache_exception('ex_configcannotsave', 'cache', '', null, 'Cannot create config directory. Check the permissions on your moodledata directory.');
            }
        }
        if (!file_exists($directory) || !is_writable($directory)) {
            throw new cache_exception('ex_configcannotsave', 'cache', '', null, 'Config directory is not writable. Check the permissions on the moodledata/muc directory.');
        }

        // Prepare a configuration array to store.
        $configuration = $this->generate_configuration_array();

        // Prepare the file content.
        $content = "<?php defined('MOODLE_INTERNAL') || die();\n \$configuration = ".var_export($configuration, true).";";

        // Do both file content and hash based detection because this might be called
        // many times within a single request.
        $hash = sha1($content);
        if (($hash === $confighash) || (file_exists($cachefile) && $content === file_get_contents($cachefile))) {
            // Config is unchanged so don't bother locking and writing.
            $confighash = $hash;
            return;
        }

        // We need to create a temporary cache lock instance for use here. Remember we are generating the config file
        // it doesn't exist and thus we can't use the normal API for this (it'll just try to use config).
        $lockconf = reset($this->configlocks);
        if ($lockconf === false) {
            debugging('Your cache configuration file is out of date and needs to be refreshed.', DEBUG_DEVELOPER);
            // Use the default
            $lockconf = array(
                'name' => 'cachelock_file_default',
                'type' => 'cachelock_file',
                'dir' => 'filelocks',
                'default' => true
            );
        }
        $factory = cache_factory::instance();
        $locking = $factory->create_lock_instance($lockconf);
        if ($locking->lock('configwrite', 'config', true)) {
            $tempcachefile = "{$cachefile}.tmp";
            // Its safe to use w mode here because we have already acquired the lock.
            $handle = fopen($tempcachefile, 'w');
            fwrite($handle, $content);
            fflush($handle);
            fclose($handle);
            $locking->unlock('configwrite', 'config');
            @chmod($tempcachefile, $CFG->filepermissions);
            rename($tempcachefile, $cachefile);
            // Tell PHP to recompile the script.
            core_component::invalidate_opcode_php_cache($cachefile);
        } else {
            throw new cache_exception('ex_configcannotsave', 'cache', '', null, 'Unable to open the cache config file.');
        }
    }

    /**
     * Generates a configuration array suitable to be written to the config file.
     * @return array
     */
    protected function generate_configuration_array() {
        $configuration = array();
        $configuration['siteidentifier'] = $this->siteidentifier;
        $configuration['stores'] = $this->configstores;
        $configuration['modemappings'] = $this->configmodemappings;
        $configuration['definitions'] = $this->configdefinitions;
        $configuration['definitionmappings'] = $this->configdefinitionmappings;
        $configuration['locks'] = $this->configlocks;
        return $configuration;
    }

    /**
     * Adds a plugin instance.
     *
     * This function also calls save so you should redirect immediately, or at least very shortly after
     * calling this method.
     *
     * @param string $name The name for the instance (must be unique)
     * @param string $plugin The name of the plugin.
     * @param array $configuration The configuration data for the plugin instance.
     * @return bool
     * @throws cache_exception
     */
    public function add_store_instance($name, $plugin, array $configuration = array()) {
        if (array_key_exists($name, $this->configstores)) {
            throw new cache_exception('Duplicate name specificed for cache plugin instance. You must provide a unique name.');
        }
        $class = 'cachestore_'.$plugin;
        if (!class_exists($class)) {
            $plugins = core_component::get_plugin_list_with_file('cachestore', 'lib.php');
            if (!array_key_exists($plugin, $plugins)) {
                throw new cache_exception('Invalid plugin name specified. The plugin does not exist or is not valid.');
            }
            $file = $plugins[$plugin];
            if (file_exists($file)) {
                require_once($file);
            }
            if (!class_exists($class)) {
                throw new cache_exception('Invalid cache plugin specified. The plugin does not contain the required class.');
            }
        }
        $reflection = new ReflectionClass($class);
        if (!$reflection->isSubclassOf('cache_store')) {
            throw new cache_exception('Invalid cache plugin specified. The plugin does not extend the required class.');
        }
        if (!$class::are_requirements_met()) {
            throw new cache_exception('Unable to add new cache plugin instance. The requested plugin type is not supported.');
        }
        $this->configstores[$name] = array(
            'name' => $name,
            'plugin' => $plugin,
            'configuration' => $configuration,
            'features' => $class::get_supported_features($configuration),
            'modes' => $class::get_supported_modes($configuration),
            'mappingsonly' => !empty($configuration['mappingsonly']),
            'class' => $class,
            'default' => false
        );
        if (array_key_exists('lock', $configuration)) {
            $this->configstores[$name]['lock'] = $configuration['lock'];
            unset($this->configstores[$name]['configuration']['lock']);
        }
        // Call instance_created()
        $store = new $class($name, $this->configstores[$name]['configuration']);
        $store->instance_created();

        $this->config_save();
        return true;
    }

    /**
     * Adds a new lock instance to the config file.
     *
     * @param string $name The name the user gave the instance. PARAM_ALHPANUMEXT
     * @param string $plugin The plugin we are creating an instance of.
     * @param string $configuration Configuration data from the config instance.
     * @throws cache_exception
     */
    public function add_lock_instance($name, $plugin, $configuration = array()) {
        if (array_key_exists($name, $this->configlocks)) {
            throw new cache_exception('Duplicate name specificed for cache lock instance. You must provide a unique name.');
        }
        $class = 'cachelock_'.$plugin;
        if (!class_exists($class)) {
            $plugins = core_component::get_plugin_list_with_file('cachelock', 'lib.php');
            if (!array_key_exists($plugin, $plugins)) {
                throw new cache_exception('Invalid lock name specified. The plugin does not exist or is not valid.');
            }
            $file = $plugins[$plugin];
            if (file_exists($file)) {
                require_once($file);
            }
            if (!class_exists($class)) {
                throw new cache_exception('Invalid lock plugin specified. The plugin does not contain the required class.');
            }
        }
        $reflection = new ReflectionClass($class);
        if (!$reflection->implementsInterface('cache_lock_interface')) {
            throw new cache_exception('Invalid lock plugin specified. The plugin does not implement the required interface.');
        }
        $this->configlocks[$name] = array_merge($configuration, array(
            'name' => $name,
            'type' => 'cachelock_'.$plugin,
            'default' => false
        ));
        $this->config_save();
    }

    /**
     * Deletes a lock instance given its name.
     *
     * @param string $name The name of the plugin, PARAM_ALPHANUMEXT.
     * @return bool
     * @throws cache_exception
     */
    public function delete_lock_instance($name) {
        if (!array_key_exists($name, $this->configlocks)) {
            throw new cache_exception('The requested store does not exist.');
        }
        if ($this->configlocks[$name]['default']) {
            throw new cache_exception('You can not delete the default lock.');
        }
        foreach ($this->configstores as $store) {
            if (isset($store['lock']) && $store['lock'] === $name) {
                throw new cache_exception('You cannot delete a cache lock that is being used by a store.');
            }
        }
        unset($this->configlocks[$name]);
        $this->config_save();
        return true;
    }

    /**
     * Sets the mode mappings.
     *
     * These determine the default caches for the different modes.
     * This function also calls save so you should redirect immediately, or at least very shortly after
     * calling this method.
     *
     * @param array $modemappings
     * @return bool
     * @throws cache_exception
     */
    public function set_mode_mappings(array $modemappings) {
        $mappings = array(
            cache_store::MODE_APPLICATION => array(),
            cache_store::MODE_SESSION => array(),
            cache_store::MODE_REQUEST => array(),
        );
        foreach ($modemappings as $mode => $stores) {
            if (!array_key_exists($mode, $mappings)) {
                throw new cache_exception('The cache mode for the new mapping does not exist');
            }
            $sort = 0;
            foreach ($stores as $store) {
                if (!array_key_exists($store, $this->configstores)) {
                    throw new cache_exception('The instance name for the new mapping does not exist');
                }
                if (array_key_exists($store, $mappings[$mode])) {
                    throw new cache_exception('This cache mapping already exists');
                }
                $mappings[$mode][] = array(
                    'store' => $store,
                    'mode' => $mode,
                    'sort' => $sort++
                );
            }
        }
        $this->configmodemappings = array_merge(
            $mappings[cache_store::MODE_APPLICATION],
            $mappings[cache_store::MODE_SESSION],
            $mappings[cache_store::MODE_REQUEST]
        );

        $this->config_save();
        return true;
    }

    /**
     * Edits a give plugin instance.
     *
     * The plugin instance is determined by its name, hence you cannot rename plugins.
     * This function also calls save so you should redirect immediately, or at least very shortly after
     * calling this method.
     *
     * @param string $name
     * @param string $plugin
     * @param array $configuration
     * @return bool
     * @throws cache_exception
     */
    public function edit_store_instance($name, $plugin, $configuration) {
        if (!array_key_exists($name, $this->configstores)) {
            throw new cache_exception('The requested instance does not exist.');
        }
        $plugins = core_component::get_plugin_list_with_file('cachestore', 'lib.php');
        if (!array_key_exists($plugin, $plugins)) {
            throw new cache_exception('Invalid plugin name specified. The plugin either does not exist or is not valid.');
        }
        $class = 'cachestore_'.$plugin;
        $file = $plugins[$plugin];
        if (!class_exists($class)) {
            if (file_exists($file)) {
                require_once($file);
            }
            if (!class_exists($class)) {
                throw new cache_exception('Invalid cache plugin specified. The plugin does not contain the required class.'.$class);
            }
        }
        $this->configstores[$name] = array(
            'name' => $name,
            'plugin' => $plugin,
            'configuration' => $configuration,
            'features' => $class::get_supported_features($configuration),
            'modes' => $class::get_supported_modes($configuration),
            'mappingsonly' => !empty($configuration['mappingsonly']),
            'class' => $class,
            'default' => $this->configstores[$name]['default'] // Can't change the default.
        );
        if (array_key_exists('lock', $configuration)) {
            $this->configstores[$name]['lock'] = $configuration['lock'];
            unset($this->configstores[$name]['configuration']['lock']);
        }
        $this->config_save();
        return true;
    }

    /**
     * Deletes a store instance.
     *
     * This function also calls save so you should redirect immediately, or at least very shortly after
     * calling this method.
     *
     * @param string $name The name of the instance to delete.
     * @return bool
     * @throws cache_exception
     */
    public function delete_store_instance($name) {
        if (!array_key_exists($name, $this->configstores)) {
            throw new cache_exception('The requested store does not exist.');
        }
        if ($this->configstores[$name]['default']) {
            throw new cache_exception('The can not delete the default stores.');
        }
        foreach ($this->configmodemappings as $mapping) {
            if ($mapping['store'] === $name) {
                throw new cache_exception('You cannot delete a cache store that has mode mappings.');
            }
        }
        foreach ($this->configdefinitionmappings as $mapping) {
            if ($mapping['store'] === $name) {
                throw new cache_exception('You cannot delete a cache store that has definition mappings.');
            }
        }

        // Call instance_deleted()
        $class = 'cachestore_'.$this->configstores[$name]['plugin'];
        $store = new $class($name, $this->configstores[$name]['configuration']);
        $store->instance_deleted();

        unset($this->configstores[$name]);
        $this->config_save();
        return true;
    }

    /**
     * Creates the default configuration and saves it.
     *
     * This function calls config_save, however it is safe to continue using it afterwards as this function should only ever
     * be called when there is no configuration file already.
     *
     * @param bool $forcesave If set to true then we will forcefully save the default configuration file.
     * @return true|array Returns true if the default configuration was successfully created.
     *     Returns a configuration array if it could not be saved. This is a bad situation. Check your error logs.
     */
    public static function create_default_configuration($forcesave = false) {
        // HACK ALERT.
        // We probably need to come up with a better way to create the default stores, or at least ensure 100% that the
        // default store plugins are protected from deletion.
        $writer = new self;
        $writer->configstores = self::get_default_stores();
        $writer->configdefinitions = self::locate_definitions();
        $writer->configmodemappings = array(
            array(
                'mode' => cache_store::MODE_APPLICATION,
                'store' => 'default_application',
                'sort' => -1
            ),
            array(
                'mode' => cache_store::MODE_SESSION,
                'store' => 'default_session',
                'sort' => -1
            ),
            array(
                'mode' => cache_store::MODE_REQUEST,
                'store' => 'default_request',
                'sort' => -1
            )
        );
        $writer->configlocks = array(
            'default_file_lock' => array(
                'name' => 'cachelock_file_default',
                'type' => 'cachelock_file',
                'dir' => 'filelocks',
                'default' => true
            )
        );

        $factory = cache_factory::instance();
        // We expect the cache to be initialising presently. If its not then something has gone wrong and likely
        // we are now in a loop.
        if (!$forcesave && $factory->get_state() !== cache_factory::STATE_INITIALISING) {
            return $writer->generate_configuration_array();
        }
        $factory->set_state(cache_factory::STATE_SAVING);
        $writer->config_save();
        return true;
    }

    /**
     * Returns an array of default stores for use.
     *
     * @return array
     */
    protected static function get_default_stores() {
        global $CFG;

        require_once($CFG->dirroot.'/cache/stores/file/lib.php');
        require_once($CFG->dirroot.'/cache/stores/session/lib.php');
        require_once($CFG->dirroot.'/cache/stores/static/lib.php');

        return array(
            'default_application' => array(
                'name' => 'default_application',
                'plugin' => 'file',
                'configuration' => array(),
                'features' => cachestore_file::get_supported_features(),
                'modes' => cachestore_file::get_supported_modes(),
                'default' => true,
            ),
            'default_session' => array(
                'name' => 'default_session',
                'plugin' => 'session',
                'configuration' => array(),
                'features' => cachestore_session::get_supported_features(),
                'modes' => cachestore_session::get_supported_modes(),
                'default' => true,
            ),
            'default_request' => array(
                'name' => 'default_request',
                'plugin' => 'static',
                'configuration' => array(),
                'features' => cachestore_static::get_supported_features(),
                'modes' => cachestore_static::get_supported_modes(),
                'default' => true,
            )
        );
    }

    /**
     * Updates the default stores within the MUC config file.
     */
    public static function update_default_config_stores() {
        $factory = cache_factory::instance();
        $factory->updating_started();
        $config = $factory->create_config_instance(true);
        $config->configstores = array_merge($config->configstores, self::get_default_stores());
        $config->config_save();
        $factory->updating_finished();
    }

    /**
     * Updates the definition in the configuration from those found in the cache files.
     *
     * Calls config_save further down, you should redirect immediately or asap after calling this method.
     *
     * @param bool $coreonly If set to true only core definitions will be updated.
     */
    public static function update_definitions($coreonly = false) {
        $factory = cache_factory::instance();
        $factory->updating_started();
        $config = $factory->create_config_instance(true);
        $config->write_definitions_to_cache(self::locate_definitions($coreonly));
        $factory->updating_finished();
    }

    /**
     * Locates all of the definition files.
     *
     * @param bool $coreonly If set to true only core definitions will be updated.
     * @return array
     */
    protected static function locate_definitions($coreonly = false) {
        global $CFG;

        $files = array();
        if (file_exists($CFG->dirroot.'/lib/db/caches.php')) {
            $files['core'] = $CFG->dirroot.'/lib/db/caches.php';
        }

        if (!$coreonly) {
            $plugintypes = core_component::get_plugin_types();
            foreach ($plugintypes as $type => $location) {
                $plugins = core_component::get_plugin_list_with_file($type, 'db/caches.php');
                foreach ($plugins as $plugin => $filepath) {
                    $component = clean_param($type.'_'.$plugin, PARAM_COMPONENT); // Standardised plugin name.
                    $files[$component] = $filepath;
                }
            }
        }

        $definitions = array();
        foreach ($files as $component => $file) {
            $filedefs = self::load_caches_file($file);
            foreach ($filedefs as $area => $definition) {
                $area = clean_param($area, PARAM_AREA);
                $id = $component.'/'.$area;
                $definition['component'] = $component;
                $definition['area'] = $area;
                if (array_key_exists($id, $definitions)) {
                    debugging('Error: duplicate cache definition found with id: '.$id, DEBUG_DEVELOPER);
                    continue;
                }
                $definitions[$id] = $definition;
            }
        }

        return $definitions;
    }

    /**
     * Writes the updated definitions for the config file.
     * @param array $definitions
     */
    private function write_definitions_to_cache(array $definitions) {

        // Preserve the selected sharing option when updating the definitions.
        // This is set by the user and should never come from caches.php.
        foreach ($definitions as $key => $definition) {
            unset($definitions[$key]['selectedsharingoption']);
            unset($definitions[$key]['userinputsharingkey']);
            if (isset($this->configdefinitions[$key]) && isset($this->configdefinitions[$key]['selectedsharingoption'])) {
                $definitions[$key]['selectedsharingoption'] = $this->configdefinitions[$key]['selectedsharingoption'];
            }
            if (isset($this->configdefinitions[$key]) && isset($this->configdefinitions[$key]['userinputsharingkey'])) {
                $definitions[$key]['userinputsharingkey'] = $this->configdefinitions[$key]['userinputsharingkey'];
            }
        }

        $this->configdefinitions = $definitions;
        foreach ($this->configdefinitionmappings as $key => $mapping) {
            if (!array_key_exists($mapping['definition'], $definitions)) {
                unset($this->configdefinitionmappings[$key]);
            }
        }
        $this->config_save();
    }

    /**
     * Loads the caches file if it exists.
     * @param string $file Absolute path to the file.
     * @return array
     */
    private static function load_caches_file($file) {
        if (!file_exists($file)) {
            return array();
        }
        $definitions = array();
        include($file);
        return $definitions;
    }

    /**
     * Sets the mappings for a given definition.
     *
     * @param string $definition
     * @param array $mappings
     * @throws coding_exception
     */
    public function set_definition_mappings($definition, $mappings) {
        if (!array_key_exists($definition, $this->configdefinitions)) {
            throw new coding_exception('Invalid definition name passed when updating mappings.');
        }
        foreach ($mappings as $store) {
            if (!array_key_exists($store, $this->configstores)) {
                throw new coding_exception('Invalid store name passed when updating definition mappings.');
            }
        }
        foreach ($this->configdefinitionmappings as $key => $mapping) {
            if ($mapping['definition'] == $definition) {
                unset($this->configdefinitionmappings[$key]);
            }
        }
        $sort = count($mappings);
        foreach ($mappings as $store) {
            $this->configdefinitionmappings[] = array(
                'store' => $store,
                'definition' => $definition,
                'sort' => $sort
            );
            $sort--;
        }

        $this->config_save();
    }

    /**
     * Update the site identifier stored by the cache API.
     *
     * @param string $siteidentifier
     * @return string The new site identifier.
     */
    public function update_site_identifier($siteidentifier) {
        $this->siteidentifier = md5((string)$siteidentifier);
        $this->config_save();
        return $this->siteidentifier;
    }

    /**
     * Sets the selected sharing options and key for a definition.
     *
     * @param string $definition The name of the definition to set for.
     * @param int $sharingoption The sharing option to set.
     * @param string|null $userinputsharingkey The user input key or null.
     * @throws coding_exception
     */
    public function set_definition_sharing($definition, $sharingoption, $userinputsharingkey = null) {
        if (!array_key_exists($definition, $this->configdefinitions)) {
            throw new coding_exception('Invalid definition name passed when updating sharing options.');
        }
        if (!($this->configdefinitions[$definition]['sharingoptions'] & $sharingoption)) {
            throw new coding_exception('Invalid sharing option passed when updating definition.');
        }
        $this->configdefinitions[$definition]['selectedsharingoption'] = (int)$sharingoption;
        if (!empty($userinputsharingkey)) {
            $this->configdefinitions[$definition]['userinputsharingkey'] = (string)$userinputsharingkey;
        }
        $this->config_save();
    }
}