class SelectQueryExtender

class SelectQueryExtender implements SelectQueryInterface {
    
    /**
     * The SelectQuery object we are extending/decorating.
     *
     * @var SelectQueryInterface
     */
    protected $query;
    
    /**
     * The connection object on which to run this query.
     *
     * @var DatabaseConnection
     */
    protected $connection;
    
    /**
     * A unique identifier for this query object.
     */
    protected $uniqueIdentifier;
    
    /**
     * The placeholder counter.
     */
    protected $placeholder = 0;
    public function __construct(SelectQueryInterface $query, DatabaseConnection $connection) {
        $this->uniqueIdentifier = uniqid('', TRUE);
        $this->query = $query;
        $this->connection = $connection;
    }
    
    /**
     * Implements QueryPlaceholderInterface::uniqueIdentifier().
     */
    public function uniqueIdentifier() {
        return $this->uniqueIdentifier;
    }
    
    /**
     * Implements QueryPlaceholderInterface::nextPlaceholder().
     */
    public function nextPlaceholder() {
        return $this->placeholder++;
    }
    
    /* Implementations of QueryAlterableInterface. */
    public function addTag($tag) {
        $this->query
            ->addTag($tag);
        return $this;
    }
    public function hasTag($tag) {
        return $this->query
            ->hasTag($tag);
    }
    public function hasAllTags() {
        $args = func_get_args();
        return call_user_func_array(array(
            $this->query,
            'hasAllTags',
        ), $args);
    }
    public function hasAnyTag() {
        $args = func_get_args();
        return call_user_func_array(array(
            $this->query,
            'hasAnyTag',
        ), $args);
    }
    public function addMetaData($key, $object) {
        $this->query
            ->addMetaData($key, $object);
        return $this;
    }
    public function getMetaData($key) {
        return $this->query
            ->getMetaData($key);
    }
    
    /* Implementations of QueryConditionInterface for the WHERE clause. */
    public function condition($field, $value = NULL, $operator = NULL) {
        $this->query
            ->condition($field, $value, $operator);
        return $this;
    }
    public function &conditions() {
        return $this->query
            ->conditions();
    }
    public function arguments() {
        return $this->query
            ->arguments();
    }
    public function where($snippet, $args = array()) {
        $this->query
            ->where($snippet, $args);
        return $this;
    }
    public function compile(DatabaseConnection $connection, QueryPlaceholderInterface $queryPlaceholder) {
        return $this->query
            ->compile($connection, $queryPlaceholder);
    }
    public function compiled() {
        return $this->query
            ->compiled();
    }
    
    /* Implementations of QueryConditionInterface for the HAVING clause. */
    public function havingCondition($field, $value = NULL, $operator = '=') {
        $this->query
            ->havingCondition($field, $value, $operator);
        return $this;
    }
    public function &havingConditions() {
        return $this->query
            ->havingConditions();
    }
    public function havingArguments() {
        return $this->query
            ->havingArguments();
    }
    public function having($snippet, $args = array()) {
        $this->query
            ->having($snippet, $args);
        return $this;
    }
    public function havingCompile(DatabaseConnection $connection) {
        return $this->query
            ->havingCompile($connection);
    }
    
    /* Implementations of QueryExtendableInterface. */
    public function extend($extender_name) {
        // The extender can be anywhere so this needs to go to the registry, which
        // is surely loaded by now.
        $class = $this->connection
            ->getDriverClass($extender_name, array(), TRUE);
        return new $class($this, $this->connection);
    }
    
    /* Alter accessors to expose the query data to alter hooks. */
    public function &getFields() {
        return $this->query
            ->getFields();
    }
    public function &getExpressions() {
        return $this->query
            ->getExpressions();
    }
    public function &getOrderBy() {
        return $this->query
            ->getOrderBy();
    }
    public function &getGroupBy() {
        return $this->query
            ->getGroupBy();
    }
    public function &getTables() {
        return $this->query
            ->getTables();
    }
    public function &getUnion() {
        return $this->query
            ->getUnion();
    }
    public function getArguments(QueryPlaceholderInterface $queryPlaceholder = NULL) {
        return $this->query
            ->getArguments($queryPlaceholder);
    }
    public function isPrepared() {
        return $this->query
            ->isPrepared();
    }
    public function preExecute(SelectQueryInterface $query = NULL) {
        // If no query object is passed in, use $this.
        if (!isset($query)) {
            $query = $this;
        }
        return $this->query
            ->preExecute($query);
    }
    public function execute() {
        // By calling preExecute() here, we force it to preprocess the extender
        // object rather than just the base query object.  That means
        // hook_query_alter() gets access to the extended object.
        if (!$this->preExecute($this)) {
            return NULL;
        }
        return $this->query
            ->execute();
    }
    public function distinct($distinct = TRUE) {
        $this->query
            ->distinct($distinct);
        return $this;
    }
    public function addField($table_alias, $field, $alias = NULL) {
        return $this->query
            ->addField($table_alias, $field, $alias);
    }
    public function fields($table_alias, array $fields = array()) {
        $this->query
            ->fields($table_alias, $fields);
        return $this;
    }
    public function addExpression($expression, $alias = NULL, $arguments = array()) {
        return $this->query
            ->addExpression($expression, $alias, $arguments);
    }
    public function join($table, $alias = NULL, $condition = NULL, $arguments = array()) {
        return $this->query
            ->join($table, $alias, $condition, $arguments);
    }
    public function innerJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
        return $this->query
            ->innerJoin($table, $alias, $condition, $arguments);
    }
    public function leftJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
        return $this->query
            ->leftJoin($table, $alias, $condition, $arguments);
    }
    public function rightJoin($table, $alias = NULL, $condition = NULL, $arguments = array()) {
        return $this->query
            ->rightJoin($table, $alias, $condition, $arguments);
    }
    public function addJoin($type, $table, $alias = NULL, $condition = NULL, $arguments = array()) {
        return $this->query
            ->addJoin($type, $table, $alias, $condition, $arguments);
    }
    public function orderBy($field, $direction = 'ASC') {
        $this->query
            ->orderBy($field, $direction);
        return $this;
    }
    public function orderRandom() {
        $this->query
            ->orderRandom();
        return $this;
    }
    public function range($start = NULL, $length = NULL) {
        $this->query
            ->range($start, $length);
        return $this;
    }
    public function union(SelectQueryInterface $query, $type = '') {
        $this->query
            ->union($query, $type);
        return $this;
    }
    public function groupBy($field) {
        $this->query
            ->groupBy($field);
        return $this;
    }
    public function forUpdate($set = TRUE) {
        $this->query
            ->forUpdate($set);
        return $this;
    }
    public function countQuery() {
        return $this->query
            ->countQuery();
    }
    function isNull($field) {
        $this->query
            ->isNull($field);
        return $this;
    }
    function isNotNull($field) {
        $this->query
            ->isNotNull($field);
        return $this;
    }
    public function exists(SelectQueryInterface $select) {
        $this->query
            ->exists($select);
        return $this;
    }
    public function notExists(SelectQueryInterface $select) {
        $this->query
            ->notExists($select);
        return $this;
    }
    public function __toString() {
        return (string) $this->query;
    }
    public function __clone() {
        $this->uniqueIdentifier = uniqid('', TRUE);
        // We need to deep-clone the query we're wrapping, which in turn may
        // deep-clone other objects.  Exciting!
        $this->query = clone $this->query;
    }
    
    /**
     * Magic override for undefined methods.
     *
     * If one extender extends another extender, then methods in the inner extender
     * will not be exposed on the outer extender.  That's because we cannot know
     * in advance what those methods will be, so we cannot provide wrapping
     * implementations as we do above.  Instead, we use this slower catch-all method
     * to handle any additional methods.
     */
    public function __call($method, $args) {
        $return = call_user_func_array(array(
            $this->query,
            $method,
        ), $args);
        // Some methods will return the called object as part of a fluent interface.
        // Others will return some useful value.  If it's a value, then the caller
        // probably wants that value.  If it's the called object, then we instead
        // return this object.  That way we don't "lose" an extender layer when
        // chaining methods together.
        if ($return instanceof SelectQueryInterface) {
            return $this;
        }
        else {
            return $return;
        }
    }

}