a simple php database connection manager

connection_manager.php

<?php

abstract class ConnectionManager {
    
    static $configurations = array();
    static $connections = array();
    
    static function &connection($name) {
        if (!isset(self::$connections[$name])) self::establish_connection($name);
        return self::$connections[$name];
    }
    
    protected static function establish_connection($name) {
        if (isset(self::$configurations[$name])) {
            $configuration = self::$configurations[$name];
            if (!isset($configuration['dbname'])) $configuration['dbname'] = array_delete('database', $configuration);
            $adapter = array_delete('adapter', $configuration);
            $username = array_delete('username', $configuration);
            $password = array_delete('password', $configuration);
            $connection_string = $adapter.':';
            $connection_string .= ($adapter == 'sqlite') ? $configuration['dbname'] : array_join_assoc('=', ';', $configuration);
            self::$connections[$name] = new PDO($connection_string, $username, $password);
        } else {
            throw new InvalidArgumentException('Database configuration "'.$name.'" does not exist');
        }
    }
    
}

functions.php

<?php

function array_delete($key, &$array) {
    $value = null;
    if (isset($array[$key])) {
        $value = $array[$key];
        unset($array[$key]);
    }
    return $value;
}

function array_join_assoc($assoc_glue, $glue, $array) {
    $assoc_joins = array();
    foreach ($array as $key => $value) {
        $assoc_joins[] = $key.$assoc_glue.$value;
    }
    return implode($glue, $assoc_joins);
}