<?php

/**
 * DNS Library for handling lookups and updates. 
 *
 * Copyright (c) 2020, Mike Pultz <mike@mikepultz.com>. All rights reserved.
 *
 * See LICENSE for more details.
 *
 * @category  Networking
 * @package   Net_DNS2
 * @author    Mike Pultz <mike@mikepultz.com>
 * @copyright 2020 Mike Pultz <mike@mikepultz.com>
 * @license   http://www.opensource.org/licenses/bsd-license.php  BSD License
 * @link      https://netdns2.com/
 * @since     File available since Release 1.1.0
 *
 */

/**
 * Shared Memory-based caching for the Net_DNS2_Cache class
 *
 */
class Net_DNS2_Cache_Shm extends Net_DNS2_Cache
{
    /*
     * resource id of the shared memory cache
     */
    private $_cache_id = false;

    /*
     * the IPC key
     */
    private $_cache_file_tok = -1;

    /**
     * open a cache object
     *
     * @param string  $cache_file path to a file to use for cache storage
     * @param integer $size       the size of the shared memory segment to create
     * @param string  $serializer the name of the cache serialize to use
     *
     * @throws Net_DNS2_Exception
     * @access public
     * @return void
     *
     */
    public function open($cache_file, $size, $serializer)
    {
        $this->cache_size       = $size;
        $this->cache_file       = $cache_file;
        $this->cache_serializer = $serializer;

        //
        // if we've already loaded the cache data, then just return right away
        //
        if ($this->cache_opened == true)
        {
            return;
        }

        //
        // make sure the file exists first
        //
        if (!file_exists($cache_file)) {

            if (file_put_contents($cache_file, '') === false) {
        
                throw new Net_DNS2_Exception(
                    'failed to create empty SHM file: ' . $cache_file,
                    Net_DNS2_Lookups::E_CACHE_SHM_FILE
                );
            }
        }

        //
        // convert the filename to a IPC key
        //
        $this->_cache_file_tok = ftok($cache_file, 't');
        if ($this->_cache_file_tok == -1) {

            throw new Net_DNS2_Exception(
                'failed on ftok() file: ' . $this->_cache_file_tok,
                Net_DNS2_Lookups::E_CACHE_SHM_FILE
            );
        }

        //
        // try to open an existing cache; if it doesn't exist, then there's no
        // cache, and nothing to do.
        //
        $this->_cache_id = @shmop_open($this->_cache_file_tok, 'w', 0, 0);
        if ($this->_cache_id !== false) {

            //
            // this returns the size allocated, and not the size used, but it's
            // still a good check to make sure there's space allocated.
            //
            $allocated = shmop_size($this->_cache_id);
            if ($allocated > 0) {
            
                //
                // read the data from the shared memory segment
                //
                $data = trim(shmop_read($this->_cache_id, 0, $allocated));
                if ( ($data !== false) && (strlen($data) > 0) ) {

                    //
                    // unserialize and store the data
                    //
                    $decoded = null;

                    if ($this->cache_serializer == 'json') {

                        $decoded = json_decode($data, true);
                    } else {

                        $decoded = unserialize($data);
                    }

                    if (is_array($decoded) == true) {

                        $this->cache_data = $decoded;
                    } else {

                        $this->cache_data = [];
                    }

                    //
                    // call clean to clean up old entries
                    //
                    $this->clean();

                    //
                    // mark the cache as loaded, so we don't load it more than once
                    //
                    $this->cache_opened = true;
                }
            }
        }
    }

    /**
     * Destructor
     *
     * @access public
     *
     */
    public function __destruct()
    {
        //
        // if there's no cache file set, then there's nothing to do
        //
        if (strlen($this->cache_file) == 0) {
            return;
        }

        $fp = fopen($this->cache_file, 'r');
        if ($fp !== false) {

            //
            // lock the file
            //
            flock($fp, LOCK_EX);

            //
            // check to see if we have an open shm segment
            //
            if ($this->_cache_id === false) {

                //
                // try opening it again, incase it was created by another
                // process in the mean time
                //
                $this->_cache_id = @shmop_open(
                    $this->_cache_file_tok, 'w', 0, 0
                );
                if ($this->_cache_id === false) {

                    //
                    // otherwise, create it.
                    //
                    $this->_cache_id = @shmop_open(
                        $this->_cache_file_tok, 'c', 0, $this->cache_size
                    );
                }
            }

            //
            // get the size allocated to the segment
            //
            $allocated = shmop_size($this->_cache_id);

            //
            // read the contents
            //
            $data = trim(shmop_read($this->_cache_id, 0, $allocated));

            //
            // if there was some data
            //    
            if ( ($data !== false) && (strlen($data) > 0) ) {

                //
                // unserialize and store the data
                //
                $c = $this->cache_data;

                $decoded = null;
  
                if ($this->cache_serializer == 'json') {
                
                    $decoded = json_decode($data, true);
                } else {
                        
                    $decoded = unserialize($data);
                }   
                         
                if (is_array($decoded) == true) {
                
                    $this->cache_data = array_merge($c, $decoded);
                }
            }

            //
            // delete the segment
            //
            shmop_delete($this->_cache_id);

            //
            // clean the data
            //
            $this->clean();

            //
            // clean up and write the data
            //
            $data = $this->resize();
            if (!is_null($data)) {

                //
                // re-create segment
                //
                $this->_cache_id = @shmop_open(
                    $this->_cache_file_tok, 'c', 0644, $this->cache_size
                );
                if ($this->_cache_id === false) {
                    return;
                }

                $o = shmop_write($this->_cache_id, $data, 0);
            }

            //
            // close the segment
            //
            shmop_close($this->_cache_id);

            //
            // unlock
            //
            flock($fp, LOCK_UN);

            //
            // close the file
            //
            fclose($fp);
        }
    }
}