<?php

if (!defined('ABSPATH')) {
    exit;
}

if (!class_exists('AIEO_Schema_Lock', false)) {

final class AIEO_Schema_Lock {

    
    private static $held = array();

    
    public static function acquire($option, $timeout = 5) {
        global $wpdb;
        $option = (string) $option;
        if (isset(self::$held[$option])) {
            return true;
        }
        $seen = get_option($option, null);
        $lock = self::name($option);
        if (1 !== (int) $wpdb->get_var($wpdb->prepare('SELECT GET_LOCK(%s, %d)', $lock, (int) $timeout))) {
            return false;
        }
        $stored = $wpdb->get_var($wpdb->prepare("SELECT option_value FROM {$wpdb->options} WHERE option_name = %s LIMIT 1", $option));
        if (self::differs($seen, $stored)) {
            $wpdb->query($wpdb->prepare('SELECT RELEASE_LOCK(%s)', $lock));
            wp_cache_delete($option, 'options');
            wp_cache_delete('notoptions', 'options');
            return false;
        }
        self::$held[$option] = $lock;
        add_action("update_option_{$option}", array(__CLASS__, 'on_update'), 10, 3);
        add_action("add_option_{$option}", array(__CLASS__, 'on_add'), 10, 1);
        if (!has_action('shutdown', array(__CLASS__, 'release_all'))) {
            add_action('shutdown', array(__CLASS__, 'release_all'));
        }
        return true;
    }

    
    public static function release($option) {
        global $wpdb;
        $option = (string) $option;
        if (!isset(self::$held[$option])) {
            return;
        }
        $lock = self::$held[$option];
        unset(self::$held[$option]);
        remove_action("update_option_{$option}", array(__CLASS__, 'on_update'), 10);
        remove_action("add_option_{$option}", array(__CLASS__, 'on_add'), 10);
        $wpdb->query($wpdb->prepare('SELECT RELEASE_LOCK(%s)', $lock));
    }

    
    public static function release_all() {
        foreach (array_keys(self::$held) as $option) {
            self::release($option);
        }
    }

    
    public static function on_update($old_value, $value, $option) {
        self::release($option);
    }

    
    public static function on_add($option) {
        self::release($option);
    }

    
    public static function held($option) {
        return isset(self::$held[(string) $option]);
    }

    
    public static function name($option) {
        global $wpdb;
        return 'aieo_schema_' . md5((defined('DB_NAME') ? DB_NAME : '') . '.' . $wpdb->options . '.' . $option);
    }

    
    private static function differs($seen, $stored) {
        if (null === $seen || null === $stored) {
            return (null === $seen) !== (null === $stored);
        }
        return (string) $stored !== (string) maybe_serialize($seen);
    }
}

}