<?php
/**
 * Pimcore
 *
 * This source file is available under two different licenses:
 * - GNU General Public License version 3 (GPLv3)
 * - Pimcore Enterprise License (PEL)
 * Full copyright and license information is available in
 * LICENSE.md which is distributed with this source code.
 *
 * @copyright  Copyright (c) Pimcore GmbH (http://www.pimcore.org)
 * @license    http://www.pimcore.org/license     GPLv3 and PEL
 */

/**
 * ----------------------------------------------------------------------------------
 * based on @author ZF1 Zend_Db_Select
 * ----------------------------------------------------------------------------------
 */

/**
 * Zend Framework
 *
 * LICENSE
 *
 * This source file is subject to the new BSD license that is bundled
 * with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://framework.zend.com/license/new-bsd
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@zend.com so we can send you a copy immediately.
 *
 * @copyright  Copyright (c) 2005-2015 Zend Technologies USA Inc. (http://www.zend.com)
 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 */

namespace Pimcore\Db\ZendCompatibility;

use Exception;
use Pimcore\Db\Connection;

class QueryBuilder
{
    const DISTINCT       = 'distinct';
    const COLUMNS        = 'columns';
    const FROM           = 'from';
    const UNION          = 'union';
    const WHERE          = 'where';
    const GROUP          = 'group';
    const HAVING         = 'having';
    const ORDER          = 'order';
    const LIMIT_COUNT    = 'limitcount';
    const LIMIT_OFFSET   = 'limitoffset';
    const FOR_UPDATE     = 'forupdate';

    const INNER_JOIN     = 'inner join';
    const LEFT_JOIN      = 'left join';
    const RIGHT_JOIN     = 'right join';
    const FULL_JOIN      = 'full join';
    const CROSS_JOIN     = 'cross join';
    const NATURAL_JOIN   = 'natural join';

    const SQL_WILDCARD   = '*';
    const SQL_SELECT     = 'SELECT';
    const SQL_UNION      = 'UNION';
    const SQL_UNION_ALL  = 'UNION ALL';
    const SQL_FROM       = 'FROM';
    const SQL_WHERE      = 'WHERE';
    const SQL_DISTINCT   = 'DISTINCT';
    const SQL_GROUP_BY   = 'GROUP BY';
    const SQL_ORDER_BY   = 'ORDER BY';
    const SQL_HAVING     = 'HAVING';
    const SQL_FOR_UPDATE = 'FOR UPDATE';
    const SQL_AND        = 'AND';
    const SQL_AS         = 'AS';
    const SQL_OR         = 'OR';
    const SQL_ON         = 'ON';
    const SQL_ASC        = 'ASC';
    const SQL_DESC       = 'DESC';

    const REGEX_COLUMN_EXPR       = '/^([\w]*\s*\(([^\(\)]|(?1))*\))$/';
    const REGEX_COLUMN_EXPR_ORDER = '/^([\w]+\s*\(([^\(\)]|(?1))*\))$/';
    const REGEX_COLUMN_EXPR_GROUP = '/^([\w]+\s*\(([^\(\)]|(?1))*\))$/';

    // @see http://stackoverflow.com/a/13823184/2028814
    const REGEX_SQL_COMMENTS      = '@
    (([\'"]).*?[^\\\]\2) # $1 : Skip single & double quoted expressions
    |(                   # $3 : Match comments
        (?:\#|--).*?$    # - Single line comments
        |                # - Multi line (nested) comments
         /\*             #   . comment open marker
            (?: [^/*]    #   . non comment-marker characters
                |/(?!\*) #   . ! not a comment open
                |\*(?!/) #   . ! not a comment close
                |(?R)    #   . recursive case
            )*           #   . repeat eventually
        \*\/             #   . comment close marker
    )\s*                 # Trim after comments
    |(?<=;)\s+           # Trim after semi-colon
    @msx';

    /**
     * \Doctrine\DBAL\Connection object.
     *
     * @var Connection
     */
    protected $_adapter;

    /**
     * The initial values for the $_parts array.
     * NOTE: It is important for the 'FOR_UPDATE' part to be last to ensure
     * meximum compatibility with database adapters.
     *
     * @var array
     */
    protected static $_partsInit = [
        self::DISTINCT     => false,
        self::COLUMNS      => [],
        self::UNION        => [],
        self::FROM         => [],
        self::WHERE        => [],
        self::GROUP        => [],
        self::HAVING       => [],
        self::ORDER        => [],
        self::LIMIT_COUNT  => null,
        self::LIMIT_OFFSET => null,
        self::FOR_UPDATE   => false
    ];

    /**
     * Specify legal join types.
     *
     * @var array
     */
    protected static $_joinTypes = [
        self::INNER_JOIN,
        self::LEFT_JOIN,
        self::RIGHT_JOIN,
        self::FULL_JOIN,
        self::CROSS_JOIN,
        self::NATURAL_JOIN,
    ];

    /**
     * Specify legal union types.
     *
     * @var array
     */
    protected static $_unionTypes = [
        self::SQL_UNION,
        self::SQL_UNION_ALL
    ];

    /**
     * The component parts of a SELECT statement.
     * Initialized to the $_partsInit array in the constructor.
     *
     * @var array
     */
    protected $_parts = [];

    /**
     * Tracks which columns are being select from each table and join.
     *
     * @var array
     */
    protected $_tableCols = [];

    /**
     * The query parameters.
     *
     * @var array
     */
    protected $params = [];

    /**
     * The parameter type map of this query.
     *
     * @var array
     */
    protected $paramTypes = [];

    /**
     * Class constructor
     *
     * @param \Doctrine\DBAL\Connection $adapter
     */
    public function __construct(\Doctrine\DBAL\Connection $adapter)
    {
        $this->_adapter = $adapter;
        $this->_parts = self::$_partsInit;
    }

    /**
     * Sets a query parameter for the query being constructed.
     *
     * <code>
     *     $qb = $conn->select()
     *         ->from(['u' => 'users'])
     *         ->columns('*')
     *         ->where('u.id = :user_id')
     *         ->setParameter(':user_id', 1);
     *
     *     $qb->execute()->fetchAll();
     * </code>
     *
     * @param string|int $key   The parameter position or name.
     * @param mixed          $value The parameter value.
     * @param string|null    $type  One of the PDO::PARAM_* constants.
     *
     * @return $this This QueryBuilder instance.
     */
    public function setParameter($key, $value, $type = null)
    {
        if ($type !== null) {
            $this->paramTypes[$key] = $type;
        }

        $this->params[$key] = $value;

        return $this;
    }

    /**
     * Sets a collection of query parameters for the query being constructed.
     *
     * <code>
     *     $qb = $conn->select()
     *         ->from(['u' => 'users'])
     *         ->columns('*')
     *         ->where('u.id = :user_id1 OR u.id = :user_id2')
     *         ->setParameters(array(
     *             ':user_id1' => 1,
     *             ':user_id2' => 2
     *         ));
     *
     *     $qb->execute()->fetchAll();
     * </code>
     *
     * @param array $params The query parameters to set.
     * @param array $types  The query parameters types to set.
     *
     * @return $this This QueryBuilder instance.
     */
    public function setParameters(array $params, array $types = [])
    {
        $this->paramTypes = $types;
        $this->params = $params;

        return $this;
    }

    /**
     * Gets all defined query parameters for the query being constructed indexed by parameter index or name.
     *
     * @return array The currently defined query parameters indexed by parameter index or name.
     */
    public function getParameters()
    {
        return $this->params;
    }

    /**
     * Gets a (previously set) query parameter of the query being constructed.
     *
     * @param mixed $key The key (index or name) of the bound parameter.
     *
     * @return mixed The value of the bound parameter.
     */
    public function getParameter($key)
    {
        return isset($this->params[$key]) ? $this->params[$key] : null;
    }

    /**
     * Gets all defined query parameter types for the query being constructed indexed by parameter index or name.
     *
     * @return array The currently defined query parameter types indexed by parameter index or name.
     */
    public function getParameterTypes()
    {
        return $this->paramTypes;
    }

    /**
     * Gets a (previously set) query parameter type of the query being constructed.
     *
     * @param mixed $key The key (index or name) of the bound parameter type.
     *
     * @return mixed The value of the bound parameter type.
     */
    public function getParameterType($key)
    {
        return isset($this->paramTypes[$key]) ? $this->paramTypes[$key] : null;
    }

    /**
     * Get bind variables
     *
     * @return array
     */
    public function getBind()
    {
        return $this->getParameters();
    }

    /**
     * Set bind variables
     *
     * @deprecated Use setParameters() instead
     *
     * @param mixed $bind
     *
     * @return self
     */
    public function bind($bind)
    {
        if (!is_array($bind)) {
            $bind = [$bind];
        }

        $this->setParameters($bind);

        return $this;
    }

    /**
     * Makes the query SELECT DISTINCT.
     *
     * @param bool $flag Whether or not the SELECT is DISTINCT (default true).
     *
     * @return self
     */
    public function distinct($flag = true)
    {
        $this->_parts[self::DISTINCT] = (bool) $flag;

        return $this;
    }

    /**
     * Adds a FROM table and optional columns to the query.
     *
     * The first parameter $name can be a simple string, in which case the
     * correlation name is generated automatically.  If you want to specify
     * the correlation name, the first parameter must be an associative
     * array in which the key is the correlation name, and the value is
     * the physical table name.  For example, array('alias' => 'table').
     * The correlation name is prepended to all columns fetched for this
     * table.
     *
     * The second parameter can be a single string or Expression object,
     * or else an array of strings or Expression objects.
     *
     * The first parameter can be null or an empty string, in which case
     * no correlation name is generated or prepended to the columns named
     * in the second parameter.
     *
     * @param  array|string|Expression $name The table name or an associative array
     *                                         relating correlation name to table name.
     * @param  array|string|Expression $cols The columns to select from this table.
     * @param  string $schema The schema name to specify, if any.
     *
     * @return self
     */
    public function from($name, $cols = '*', $schema = null)
    {
        return $this->_join(self::FROM, $name, null, $cols, $schema);
    }

    /**
     * Specifies the columns used in the FROM clause.
     *
     * The parameter can be a single string or Expression object,
     * or else an array of strings or Expression objects.
     *
     * @param  array|string|Expression $cols The columns to select from this table.
     * @param  string $correlationName Correlation name of target table. OPTIONAL
     *
     * @return self
     */
    public function columns($cols = '*', $correlationName = null)
    {
        if ($correlationName === null && count($this->_parts[self::FROM])) {
            $correlationNameKeys = array_keys($this->_parts[self::FROM]);
            $correlationName = current($correlationNameKeys);
        }

        if (!array_key_exists($correlationName, $this->_parts[self::FROM])) {
            throw new \Exception('No table has been specified for the FROM clause');
        }

        $this->_tableCols($correlationName, $cols);

        return $this;
    }

    /**
     * Adds a UNION clause to the query.
     *
     * The first parameter has to be an array of QueryBuilder or
     * sql query strings.
     *
     * <code>
     * $sql1 = $db->select();
     * $sql2 = "SELECT ...";
     * $select = $db->select()
     *      ->union(array($sql1, $sql2))
     *      ->order("id");
     * </code>
     *
     * @param  array $select Array of select clauses for the union.
     *
     * @return self
     */
    public function union($select = [], $type = self::SQL_UNION)
    {
        if (!is_array($select)) {
            throw new \Exception(
                'union() only accepts an array of QueryBuilder instances of sql query strings.'
            );
        }

        if (!in_array($type, self::$_unionTypes)) {
            throw new \Exception("Invalid union type '{$type}'");
        }

        foreach ($select as $target) {
            $this->_parts[self::UNION][] = [$target, $type];
        }

        return $this;
    }

    /**
     * Adds a JOIN table and columns to the query.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  array|string|Expression $name The table name.
     * @param  string $cond Join on this condition.
     * @param  array|string $cols The columns to select from the joined table.
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     */
    public function join($name, $cond, $cols = self::SQL_WILDCARD, $schema = null)
    {
        return $this->joinInner($name, $cond, $cols, $schema);
    }

    /**
     * Add an INNER JOIN table and colums to the query
     * Rows in both tables are matched according to the expression
     * in the $cond argument.  The result set is comprised
     * of all cases where rows from the left table match
     * rows from the right table.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  array|string|Expression $name The table name.
     * @param  string $cond Join on this condition.
     * @param  array|string $cols The columns to select from the joined table.
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     */
    public function joinInner($name, $cond, $cols = self::SQL_WILDCARD, $schema = null)
    {
        return $this->_join(self::INNER_JOIN, $name, $cond, $cols, $schema);
    }

    /**
     * Add a LEFT OUTER JOIN table and colums to the query
     * All rows from the left operand table are included,
     * matching rows from the right operand table included,
     * and the columns from the right operand table are filled
     * with NULLs if no row exists matching the left table.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  array|string|Expression $name The table name.
     * @param  string $cond Join on this condition.
     * @param  array|string $cols The columns to select from the joined table.
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     */
    public function joinLeft($name, $cond, $cols = self::SQL_WILDCARD, $schema = null)
    {
        return $this->_join(self::LEFT_JOIN, $name, $cond, $cols, $schema);
    }

    /**
     * Add a RIGHT OUTER JOIN table and colums to the query.
     * Right outer join is the complement of left outer join.
     * All rows from the right operand table are included,
     * matching rows from the left operand table included,
     * and the columns from the left operand table are filled
     * with NULLs if no row exists matching the right table.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  array|string|Expression $name The table name.
     * @param  string $cond Join on this condition.
     * @param  array|string $cols The columns to select from the joined table.
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     */
    public function joinRight($name, $cond, $cols = self::SQL_WILDCARD, $schema = null)
    {
        return $this->_join(self::RIGHT_JOIN, $name, $cond, $cols, $schema);
    }

    /**
     * Add a FULL OUTER JOIN table and colums to the query.
     * A full outer join is like combining a left outer join
     * and a right outer join.  All rows from both tables are
     * included, paired with each other on the same row of the
     * result set if they satisfy the join condition, and otherwise
     * paired with NULLs in place of columns from the other table.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  array|string|Expression $name The table name.
     * @param  string $cond Join on this condition.
     * @param  array|string $cols The columns to select from the joined table.
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     */
    public function joinFull($name, $cond, $cols = self::SQL_WILDCARD, $schema = null)
    {
        return $this->_join(self::FULL_JOIN, $name, $cond, $cols, $schema);
    }

    /**
     * Add a CROSS JOIN table and colums to the query.
     * A cross join is a cartesian product; there is no join condition.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  array|string|Expression $name The table name.
     * @param  array|string $cols The columns to select from the joined table.
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     */
    public function joinCross($name, $cols = self::SQL_WILDCARD, $schema = null)
    {
        return $this->_join(self::CROSS_JOIN, $name, null, $cols, $schema);
    }

    /**
     * Add a NATURAL JOIN table and colums to the query.
     * A natural join assumes an equi-join across any column(s)
     * that appear with the same name in both tables.
     * Only natural inner joins are supported by this API,
     * even though SQL permits natural outer joins as well.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  array|string|Expression $name The table name.
     * @param  array|string $cols The columns to select from the joined table.
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     */
    public function joinNatural($name, $cols = self::SQL_WILDCARD, $schema = null)
    {
        return $this->_join(self::NATURAL_JOIN, $name, null, $cols, $schema);
    }

    /**
     * Adds a WHERE condition to the query by AND.
     *
     * If a value is passed as the second param, it will be quoted
     * and replaced into the condition wherever a question-mark
     * appears. Array values are quoted and comma-separated.
     *
     * <code>
     * // simplest but non-secure
     * $select->where("id = $id");
     *
     * // secure (ID is quoted but matched anyway)
     * $select->where('id = ?', $id);
     *
     * // alternatively, with named binding
     * $select->where('id = :id');
     * </code>
     *
     * Note that it is more correct to use named bindings in your
     * queries for values other than strings. When you use named
     * bindings, don't forget to pass the values when actually
     * making a query:
     *
     * <code>
     * $db->fetchAll($select, array('id' => 5));
     * </code>
     *
     * @param string   $cond  The WHERE condition.
     * @param mixed    $value OPTIONAL The value to quote into the condition.
     * @param int      $type  OPTIONAL The type of the given value
     *
     * @return self
     */
    public function where($cond, $value = null, $type = null)
    {
        $this->_parts[self::WHERE][] = $this->_where($cond, $value, $type, true);

        return $this;
    }

    /**
     * Adds a WHERE condition to the query by OR.
     *
     * Otherwise identical to where().
     *
     * @param string   $cond  The WHERE condition.
     * @param mixed    $value OPTIONAL The value to quote into the condition.
     * @param int      $type  OPTIONAL The type of the given value
     *
     * @return self
     *
     * @see where()
     */
    public function orWhere($cond, $value = null, $type = null)
    {
        $this->_parts[self::WHERE][] = $this->_where($cond, $value, $type, false);

        return $this;
    }

    /**
     * Adds grouping to the query.
     *
     * @param  array|string $spec The column(s) to group by.
     *
     * @return self
     */
    public function group($spec)
    {
        if (!is_array($spec)) {
            $spec = [$spec];
        }

        foreach ($spec as $val) {
            // Remove comments from SQL statement
            $noComments = preg_replace(self::REGEX_SQL_COMMENTS, '$1', (string) $val);
            if (preg_match(self::REGEX_COLUMN_EXPR_GROUP, $noComments)) {
                $val = new Expression($val);
            }
            $this->_parts[self::GROUP][] = $val;
        }

        return $this;
    }

    /**
     * Adds a HAVING condition to the query by AND.
     *
     * If a value is passed as the second param, it will be quoted
     * and replaced into the condition wherever a question-mark
     * appears. See {@link where()} for an example
     *
     * @param string $cond The HAVING condition.
     * @param mixed    $value OPTIONAL The value to quote into the condition.
     * @param int      $type  OPTIONAL The type of the given value
     *
     * @return self
     */
    public function having($cond, $value = null, $type = null)
    {
        if ($value !== null) {
            $cond = $this->_adapter->quoteInto($cond, $value, $type);
        }

        if ($this->_parts[self::HAVING]) {
            $this->_parts[self::HAVING][] = self::SQL_AND . " ($cond)";
        } else {
            $this->_parts[self::HAVING][] = "($cond)";
        }

        return $this;
    }

    /**
     * Adds a HAVING condition to the query by OR.
     *
     * Otherwise identical to orHaving().
     *
     * @param string $cond The HAVING condition.
     * @param mixed    $value OPTIONAL The value to quote into the condition.
     * @param int      $type  OPTIONAL The type of the given value
     *
     * @return self
     *
     * @see having()
     */
    public function orHaving($cond, $value = null, $type = null)
    {
        if ($value !== null) {
            $cond = $this->_adapter->quoteInto($cond, $value, $type);
        }

        if ($this->_parts[self::HAVING]) {
            $this->_parts[self::HAVING][] = self::SQL_OR . " ($cond)";
        } else {
            $this->_parts[self::HAVING][] = "($cond)";
        }

        return $this;
    }

    /**
     * Adds a row order to the query.
     *
     * @param mixed $spec The column(s) and direction to order by.
     *
     * @return self
     */
    public function order($spec)
    {
        if (!is_array($spec)) {
            $spec = [$spec];
        }

        // force 'ASC' or 'DESC' on each order spec, default is ASC.
        foreach ($spec as $val) {
            if ($val instanceof Expression) {
                $expr = $val->__toString();
                if (empty($expr)) {
                    continue;
                }
                $this->_parts[self::ORDER][] = $val;
            } else {
                if (empty($val)) {
                    continue;
                }
                $direction = self::SQL_ASC;
                if (preg_match('/(.*\W)(' . self::SQL_ASC . '|' . self::SQL_DESC . ')\b/si', $val, $matches)) {
                    $val = trim($matches[1]);
                    $direction = $matches[2];
                }
                // Remove comments from SQL statement
                $noComments = preg_replace(self::REGEX_SQL_COMMENTS, '$1', (string) $val);
                if (preg_match(self::REGEX_COLUMN_EXPR_ORDER, $noComments)) {
                    $val = new Expression($val);
                }
                $this->_parts[self::ORDER][] = [$val, $direction];
            }
        }

        return $this;
    }

    /**
     * Sets a limit count and offset to the query.
     *
     * @param int $count OPTIONAL The number of rows to return.
     * @param int $offset OPTIONAL Start returning after this many rows.
     *
     * @return self
     */
    public function limit($count = null, $offset = null)
    {
        $this->_parts[self::LIMIT_COUNT]  = (int) $count;
        $this->_parts[self::LIMIT_OFFSET] = (int) $offset;

        return $this;
    }

    /**
     * Sets the limit and count by page number.
     *
     * @param int $page Limit results to this page number.
     * @param int $rowCount Use this many rows per page.
     *
     * @return self
     */
    public function limitPage($page, $rowCount)
    {
        $page     = ($page > 0) ? $page : 1;
        $rowCount = ($rowCount > 0) ? $rowCount : 1;
        $this->_parts[self::LIMIT_COUNT]  = (int) $rowCount;
        $this->_parts[self::LIMIT_OFFSET] = (int) $rowCount * ($page - 1);

        return $this;
    }

    /**
     * Makes the query SELECT FOR UPDATE.
     *
     * @param bool $flag Whether or not the SELECT is FOR UPDATE (default true).
     *
     * @return self
     */
    public function forUpdate($flag = true)
    {
        $this->_parts[self::FOR_UPDATE] = (bool) $flag;

        return $this;
    }

    /**
     * Get part of the structured information for the current query.
     *
     * @param string $part
     *
     * @return mixed
     *
     * @throws \Exception
     */
    public function getPart($part)
    {
        $part = strtolower($part);
        if (!array_key_exists($part, $this->_parts)) {
            throw new \Exception("Invalid Select part '$part'");
        }

        return $this->_parts[$part];
    }

    /**
     * Executes the current select object and returns the result
     *
     * @param int $fetchMode OPTIONAL
     * @param  mixed  $bind An array of data to bind to the placeholders.
     *
     * @return \Doctrine\DBAL\Driver\Statement
     */
    public function query($fetchMode = null, $bind = [])
    {
        if (!empty($bind)) {
            $this->bind($bind);
        }

        $stmt = $this->execute();
        if ($fetchMode == null) {
            $fetchMode = \PDO::FETCH_ASSOC;
        }

        $stmt->setFetchMode($fetchMode);

        return $stmt;
    }

    /**
     * Executes this query using the bound parameters and their types.
     *
     * Uses {@see Connection::executeQuery}
     *
     * @return \Doctrine\DBAL\Driver\Statement|int
     */
    public function execute()
    {
        return $this->_adapter->executeQuery($this->getSQL(), $this->params, $this->paramTypes);
    }

    /**
     * Converts this object to an SQL SELECT string.
     *
     * @return string|null This object as a SELECT string. (or null if a string cannot be produced.)
     */
    public function assemble()
    {
        $sql = self::SQL_SELECT;
        foreach (array_keys(self::$_partsInit) as $part) {
            $method = '_render' . ucfirst($part);
            if (method_exists($this, $method)) {
                $sql = $this->$method($sql);
            }
        }

        return $sql;
    }

    /**
     * Clear parts of the Select object, or an individual part.
     *
     * @param string $part OPTIONAL
     *
     * @return self
     */
    public function reset($part = null)
    {
        if ($part == null) {
            $this->_parts = self::$_partsInit;
        } elseif (array_key_exists($part, self::$_partsInit)) {
            $this->_parts[$part] = self::$_partsInit[$part];
        }

        return $this;
    }

    /**
     * Gets the \Doctrine\DBAL\Connection for this
     * particular QueryBuilder object.
     *
     * @return Connection|\Doctrine\DBAL\Connection
     */
    public function getAdapter()
    {
        return $this->_adapter;
    }

    /**
     * Populate the {@link $_parts} 'join' key
     *
     * Does the dirty work of populating the join key.
     *
     * The $name and $cols parameters follow the same logic
     * as described in the from() method.
     *
     * @param  null|string $type Type of join; inner, left, and null are currently supported
     * @param  array|string|Expression $name Table name
     * @param  string $cond Join on this condition
     * @param  array|string $cols The columns to select from the joined table
     * @param  string $schema The database name to specify, if any.
     *
     * @return self
     *
     * @throws \Exception
     */
    protected function _join($type, $name, $cond, $cols, $schema = null)
    {
        if (!in_array($type, self::$_joinTypes) && $type != self::FROM) {
            throw new \Exception("Invalid join type '$type'");
        }

        if (count($this->_parts[self::UNION])) {
            throw new \Exception('Invalid use of table with ' . self::SQL_UNION);
        }

        if (empty($name)) {
            $correlationName = $tableName = '';
        } elseif (is_array($name)) {
            // Must be array($correlationName => $tableName) or array($ident, ...)
            foreach ($name as $_correlationName => $_tableName) {
                if (is_string($_correlationName)) {
                    // We assume the key is the correlation name and value is the table name
                    $tableName = $_tableName;
                    $correlationName = $_correlationName;
                } else {
                    // We assume just an array of identifiers, with no correlation name
                    $tableName = $_tableName;
                    $correlationName = $this->_uniqueCorrelation($tableName);
                }
                break;
            }
        } elseif ($name instanceof Expression || $name instanceof self) {
            $tableName = $name;
            $correlationName = $this->_uniqueCorrelation('t');
        } elseif (preg_match('/^(.+)\s+AS\s+(.+)$/i', $name, $m)) {
            $tableName = $m[1];
            $correlationName = $m[2];
        } else {
            $tableName = $name;
            $correlationName = $this->_uniqueCorrelation($tableName);
        }

        // Schema from table name overrides schema argument
        if (!is_object($tableName) && false !== strpos($tableName, '.')) {
            list($schema, $tableName) = explode('.', $tableName);
        }

        $lastFromCorrelationName = null;
        if (!empty($correlationName)) {
            if (array_key_exists($correlationName, $this->_parts[self::FROM])) {
                throw new \Exception("You cannot define a correlation name '$correlationName' more than once");
            }

            if ($type == self::FROM) {
                // append this from after the last from joinType
                $tmpFromParts = $this->_parts[self::FROM];
                $this->_parts[self::FROM] = [];
                // move all the froms onto the stack
                while ($tmpFromParts) {
                    $currentCorrelationName = key($tmpFromParts);
                    if ($tmpFromParts[$currentCorrelationName]['joinType'] != self::FROM) {
                        break;
                    }
                    $lastFromCorrelationName = $currentCorrelationName;
                    $this->_parts[self::FROM][$currentCorrelationName] = array_shift($tmpFromParts);
                }
            } else {
                $tmpFromParts = [];
            }
            $this->_parts[self::FROM][$correlationName] = [
                'joinType'      => $type,
                'schema'        => $schema,
                'tableName'     => $tableName,
                'joinCondition' => $cond
            ];
            while ($tmpFromParts) {
                $currentCorrelationName = key($tmpFromParts);
                $this->_parts[self::FROM][$currentCorrelationName] = array_shift($tmpFromParts);
            }
        }

        // add to the columns from this joined table
        if ($type == self::FROM && $lastFromCorrelationName == null) {
            $lastFromCorrelationName = true;
        }
        $this->_tableCols($correlationName, $cols, $lastFromCorrelationName);

        return $this;
    }

    /**
     * Handle JOIN... USING... syntax
     *
     * This is functionality identical to the existing JOIN methods, however
     * the join condition can be passed as a single column name. This method
     * then completes the ON condition by using the same field for the FROM
     * table and the JOIN table.
     *
     * <code>
     * $select = $db->select()->from('table1')
     *                        ->joinUsing('table2', 'column1');
     *
     * // SELECT * FROM table1 JOIN table2 ON table1.column1 = table2.column2
     * </code>
     *
     * These joins are called by the developer simply by adding 'Using' to the
     * method name. E.g.
     * * joinUsing
     * * joinInnerUsing
     * * joinFullUsing
     * * joinRightUsing
     * * joinLeftUsing
     *
     * @return self
     */
    public function _joinUsing($type, $name, $cond, $cols = '*', $schema = null)
    {
        if (empty($this->_parts[self::FROM])) {
            throw new \Exception('You can only perform a joinUsing after specifying a FROM table');
        }

        $join  = $this->_adapter->quoteIdentifier(key($this->_parts[self::FROM]), true);
        $from  = $this->_adapter->quoteIdentifier($this->_uniqueCorrelation($name), true);

        $joinCond = [];
        foreach ((array)$cond as $fieldName) {
            $cond1 = $from . '.' . $fieldName;
            $cond2 = $join . '.' . $fieldName;
            $joinCond[]  = $cond1 . ' = ' . $cond2;
        }
        $cond = implode(' '.self::SQL_AND.' ', $joinCond);

        return $this->_join($type, $name, $cond, $cols, $schema);
    }

    /**
     * Generate a unique correlation name
     *
     * @param string|array $name A qualified identifier.
     *
     * @return string A unique correlation name.
     */
    private function _uniqueCorrelation($name)
    {
        if (is_array($name)) {
            $k = key($name);
            $c = is_string($k) ? $k : end($name);
        } else {
            // Extract just the last name of a qualified table name
            $dot = strrpos($name, '.');
            $c = ($dot === false) ? $name : substr($name, $dot + 1);
        }
        for ($i = 2; array_key_exists($c, $this->_parts[self::FROM]); ++$i) {
            $c = $name . '_' . (string) $i;
        }

        return $c;
    }

    /**
     * Adds to the internal table-to-column mapping array.
     *
     * @param  string $tbl The table/join the columns come from.
     * @param  array|string $cols The list of columns; preferably as
     * an array, but possibly as a string containing one column.
     * @param  bool|string True if it should be prepended, a correlation name if it should be inserted
     *
     * @return void
     */
    protected function _tableCols($correlationName, $cols, $afterCorrelationName = null)
    {
        if (!is_array($cols)) {
            $cols = [$cols];
        }

        if ($correlationName == null) {
            $correlationName = '';
        }

        $columnValues = [];

        foreach (array_filter($cols) as $alias => $col) {
            $currentCorrelationName = $correlationName;
            if (is_string($col)) {
                // Check for a column matching "<column> AS <alias>" and extract the alias name
                $col = trim(str_replace("\n", ' ', $col));
                if (preg_match('/^(.+)\s+' . self::SQL_AS . '\s+(.+)$/i', $col, $m)) {
                    $col = $m[1];
                    $alias = $m[2];
                }
                // Check for columns that look like functions and convert to Expression
                if (preg_match(self::REGEX_COLUMN_EXPR, (string) $col)) {
                    $col = new Expression($col);
                } elseif (preg_match('/(.+)\.(.+)/', $col, $m)) {
                    $currentCorrelationName = $m[1];
                    $col = $m[2];
                }
            }
            $columnValues[] = [$currentCorrelationName, $col, is_string($alias) ? $alias : null];
        }

        if ($columnValues) {

            // should we attempt to prepend or insert these values?
            if ($afterCorrelationName === true || is_string($afterCorrelationName)) {
                $tmpColumns = $this->_parts[self::COLUMNS];
                $this->_parts[self::COLUMNS] = [];
            } else {
                $tmpColumns = [];
            }

            // find the correlation name to insert after
            if (is_string($afterCorrelationName)) {
                while ($tmpColumns) {
                    $this->_parts[self::COLUMNS][] = $currentColumn = array_shift($tmpColumns);
                    if ($currentColumn[0] == $afterCorrelationName) {
                        break;
                    }
                }
            }

            // apply current values to current stack
            foreach ($columnValues as $columnValue) {
                array_push($this->_parts[self::COLUMNS], $columnValue);
            }

            // finish ensuring that all previous values are applied (if they exist)
            while ($tmpColumns) {
                array_push($this->_parts[self::COLUMNS], array_shift($tmpColumns));
            }
        }
    }

    /**
     * Internal function for creating the where clause
     *
     * @param string   $condition
     * @param mixed    $value  optional
     * @param string   $type   optional
     * @param bool  $bool  true = AND, false = OR
     *
     * @return string  clause
     */
    protected function _where($condition, $value = null, $type = null, $bool = true)
    {
        if (count($this->_parts[self::UNION])) {
            throw new \Exception('Invalid use of where clause with ' . self::SQL_UNION);
        }

        if ($value !== null) {
            $condition = $this->_adapter->quoteInto($condition, $value, $type);
        }

        $cond = '';
        if ($this->_parts[self::WHERE]) {
            if ($bool === true) {
                $cond = self::SQL_AND . ' ';
            } else {
                $cond = self::SQL_OR . ' ';
            }
        }

        return $cond . "($condition)";
    }

    /**
     * @return array
     */
    protected function _getDummyTable()
    {
        return [];
    }

    /**
     * Return a quoted schema name
     *
     * @param string   $schema  The schema name OPTIONAL
     *
     * @return string|null
     */
    protected function _getQuotedSchema($schema = null)
    {
        if ($schema === null) {
            return null;
        }

        return $this->_adapter->quoteIdentifier($schema, true) . '.';
    }

    /**
     * Return a quoted table name
     *
     * @param string   $tableName        The table name
     * @param string   $correlationName  The correlation name OPTIONAL
     *
     * @return string
     */
    protected function _getQuotedTable($tableName, $correlationName = null)
    {
        return $this->_adapter->quoteTableAs($tableName, $correlationName, true);
    }

    /**
     * Render DISTINCT clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderDistinct($sql)
    {
        if ($this->_parts[self::DISTINCT]) {
            $sql .= ' ' . self::SQL_DISTINCT;
        }

        return $sql;
    }

    /**
     * Render DISTINCT clause
     *
     * @param string   $sql SQL query
     *
     * @return string|null
     */
    protected function _renderColumns($sql)
    {
        if (!count($this->_parts[self::COLUMNS])) {
            return null;
        }

        $columns = [];
        foreach ($this->_parts[self::COLUMNS] as $columnEntry) {
            list($correlationName, $column, $alias) = $columnEntry;
            if ($column instanceof Expression) {
                $columns[] = $this->_adapter->quoteColumnAs($column, $alias, true);
            } else {
                if ($column == self::SQL_WILDCARD) {
                    $column = new Expression(self::SQL_WILDCARD);
                    $alias = null;
                }
                if (empty($correlationName)) {
                    $columns[] = $this->_adapter->quoteColumnAs($column, $alias, true);
                } else {
                    $columns[] = $this->_adapter->quoteColumnAs([$correlationName, $column], $alias, true);
                }
            }
        }

        return $sql . ' ' . implode(', ', $columns);
    }

    /**
     * Render FROM clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderFrom($sql)
    {
        /*
         * If no table specified, use RDBMS-dependent solution
         * for table-less query.  e.g. DUAL in Oracle.
         */
        if (empty($this->_parts[self::FROM])) {
            $this->_parts[self::FROM] = $this->_getDummyTable();
        }

        $from = [];

        foreach ($this->_parts[self::FROM] as $correlationName => $table) {
            $tmp = '';

            $joinType = ($table['joinType'] == self::FROM) ? self::INNER_JOIN : $table['joinType'];

            // Add join clause (if applicable)
            if (! empty($from)) {
                $tmp .= ' ' . strtoupper($joinType) . ' ';
            }

            $tmp .= $this->_getQuotedSchema($table['schema']);
            $tmp .= $this->_getQuotedTable($table['tableName'], $correlationName);

            // Add join conditions (if applicable)
            if (!empty($from) && ! empty($table['joinCondition'])) {
                $tmp .= ' ' . self::SQL_ON . ' ' . $table['joinCondition'];
            }

            // Add the table name and condition add to the list
            $from[] = $tmp;
        }

        // Add the list of all joins
        if (!empty($from)) {
            $sql .= ' ' . self::SQL_FROM . ' ' . implode("\n", $from);
        }

        return $sql;
    }

    /**
     * Render UNION query
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderUnion($sql)
    {
        if ($this->_parts[self::UNION]) {
            $parts = count($this->_parts[self::UNION]);
            foreach ($this->_parts[self::UNION] as $cnt => $union) {
                list($target, $type) = $union;
                if ($target instanceof self) {
                    $target = $target->assemble();
                }
                $sql .= $target;
                if ($cnt < $parts - 1) {
                    $sql .= ' ' . $type . ' ';
                }
            }
        }

        return $sql;
    }

    /**
     * Render WHERE clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderWhere($sql)
    {
        if ($this->_parts[self::FROM] && $this->_parts[self::WHERE]) {
            $sql .= ' ' . self::SQL_WHERE . ' ' .  implode(' ', $this->_parts[self::WHERE]);
        }

        return $sql;
    }

    /**
     * Render GROUP clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderGroup($sql)
    {
        if ($this->_parts[self::FROM] && $this->_parts[self::GROUP]) {
            $group = [];
            foreach ($this->_parts[self::GROUP] as $term) {
                $group[] = $this->_adapter->quoteIdentifier($term, true);
            }
            $sql .= ' ' . self::SQL_GROUP_BY . ' ' . implode(",\n\t", $group);
        }

        return $sql;
    }

    /**
     * Render HAVING clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderHaving($sql)
    {
        if ($this->_parts[self::FROM] && $this->_parts[self::HAVING]) {
            $sql .= ' ' . self::SQL_HAVING . ' ' . implode(' ', $this->_parts[self::HAVING]);
        }

        return $sql;
    }

    /**
     * Render ORDER clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderOrder($sql)
    {
        if ($this->_parts[self::ORDER]) {
            $order = [];
            foreach ($this->_parts[self::ORDER] as $term) {
                if (is_array($term)) {
                    if (is_numeric($term[0]) && strval(intval($term[0])) == $term[0]) {
                        $order[] = (int)trim($term[0]) . ' ' . $term[1];
                    } else {
                        $order[] = $this->_adapter->quoteIdentifier($term[0], true) . ' ' . $term[1];
                    }
                } elseif (is_numeric($term) && strval(intval($term)) == $term) {
                    $order[] = (int)trim($term);
                } else {
                    $order[] = $this->_adapter->quoteIdentifier($term, true);
                }
            }
            $sql .= ' ' . self::SQL_ORDER_BY . ' ' . implode(', ', $order);
        }

        return $sql;
    }

    /**
     * Render LIMIT OFFSET clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderLimitoffset($sql)
    {
        $count = 0;
        $offset = 0;

        if (!empty($this->_parts[self::LIMIT_OFFSET])) {
            $offset = (int) $this->_parts[self::LIMIT_OFFSET];
            $count = PHP_INT_MAX;
        }

        if (!empty($this->_parts[self::LIMIT_COUNT])) {
            $count = (int) $this->_parts[self::LIMIT_COUNT];
        }

        /*
         * Add limits clause
         */
        if ($count > 0) {
            $sql = trim($this->_adapter->limit($sql, $count, $offset));
        }

        return $sql;
    }

    /**
     * Render FOR UPDATE clause
     *
     * @param string   $sql SQL query
     *
     * @return string
     */
    protected function _renderForupdate($sql)
    {
        if ($this->_parts[self::FOR_UPDATE]) {
            $sql .= ' ' . self::SQL_FOR_UPDATE;
        }

        return $sql;
    }

    /**
     * Turn magic function calls into non-magic function calls
     * for joinUsing syntax
     *
     * @param string $method
     * @param array $args OPTIONAL query modifier
     *
     * @return self
     *
     * @throws \Exception If an invalid method is called.
     */
    public function __call($method, array $args)
    {
        $matches = [];

        /**
         * Recognize methods for Has-Many cases:
         * findParent<Class>()
         * findParent<Class>By<Rule>()
         * Use the non-greedy pattern repeat modifier e.g. \w+?
         */
        if (preg_match('/^join([a-zA-Z]*?)Using$/', $method, $matches)) {
            $type = strtolower($matches[1]);
            if ($type) {
                $type .= ' join';
                if (!in_array($type, self::$_joinTypes)) {
                    throw new \Exception("Unrecognized method '$method()'");
                }
                if (in_array($type, [self::CROSS_JOIN, self::NATURAL_JOIN])) {
                    throw new \Exception("Cannot perform a joinUsing with method '$method()'");
                }
            } else {
                $type = self::INNER_JOIN;
            }
            array_unshift($args, $type);

            return call_user_func_array([$this, '_joinUsing'], $args);
        }

        throw new \Exception("Unrecognized method '$method()'");
    }

    /**
     * Gets the complete SQL string formed by the current specifications of this QueryBuilder.
     *
     * <code>
     *     $qb = $conn->select()
     *         ->from(['u' => 'users'])
     *         ->columns('*')
     *         ->where('u.id = :user_id');
     *
     *     echo $qb->getSQL(); // SELECT u.* FROM users u WHERE u.id = :user_id
     * </code>
     *
     * @return string The SQL query string.
     */
    public function getSQL()
    {
        $sql = $this->assemble();

        return (string)$sql;
    }

    /**
     * Implements magic method.
     *
     * @return string This object as a SELECT string.
     */
    public function __toString()
    {
        try {
            $sql = $this->getSQL();
        } catch (Exception $e) {
            trigger_error($e->getMessage(), E_USER_WARNING);
            $sql = '';
        }

        return (string)$sql;
    }

    public function __sleep()
    {
        $vars      = get_object_vars($this);
        $blacklist = ['_adapter'];

        $result = [];
        foreach (array_keys($vars) as $var) {
            if (!in_array($var, $blacklist)) {
                $result[] = $var;
            }
        }

        return $result;
    }
}
