<?php

class Qs_Paginator_Adapter_DbSelect extends Zend_Paginator_Adapter_DbSelect
{
    /**
     * Get the COUNT select object for the provided query
     *
     * TODO: Have a look at queries that have both GROUP BY and DISTINCT specified.
     * In that use-case I'm expecting problems when either GROUP BY or DISTINCT
     * has one column.
     *
     * @return Zend_Db_Select
     */
    public function getCountSelect()
    {
        /**
         * We only need to generate a COUNT query once. It will not change for
         * this instance.
         */
        if ($this->_countSelect !== null) {
            return $this->_countSelect;
        }

        $rowCount = clone $this->_select;
        $rowCount->__toString(); // Workaround for ZF-3719 and related

        $db = $rowCount->getAdapter();

        $countColumn = $db->quoteIdentifier($db->foldCase(self::ROW_COUNT_COLUMN));
        $countPart   = 'COUNT(1) AS ';
        $groupPart   = null;
        $unionParts  = $rowCount->getPart(Zend_Db_Select::UNION);

        /**
         * If we're dealing with a UNION query, execute the UNION as a subquery
         * to the COUNT query.
         */
        if (!empty($unionParts)) {
            $expression = new Zend_Db_Expr($countPart . $countColumn);

            /**
             * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
             * !! UNION FIX START
             * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
             */
            $rowCount->reset(Zend_Db_Select::LIMIT_COUNT);
            $rowCount->reset(Zend_Db_Select::LIMIT_OFFSET);
            $rowCount->reset(Zend_Db_Select::ORDER);
            /**
             * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
             * !! UNION FIX FINISH
             * !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
             */

            $rowCount = $db
                            ->select()
                            ->bind($rowCount->getBind())
                            ->from($rowCount, $expression);
        } else {
            $columnParts = $rowCount->getPart(Zend_Db_Select::COLUMNS);
            $groupParts  = $rowCount->getPart(Zend_Db_Select::GROUP);
            $havingParts = $rowCount->getPart(Zend_Db_Select::HAVING);
            $isDistinct  = $rowCount->getPart(Zend_Db_Select::DISTINCT);

            /**
             * If there is more than one column AND it's a DISTINCT query, more
             * than one group, or if the query has a HAVING clause, then take
             * the original query and use it as a subquery os the COUNT query.
             */
            if (($isDistinct && ((count($columnParts) == 1 && $columnParts[0][1] == Zend_Db_Select::SQL_WILDCARD)
                 || count($columnParts) > 1)) || count($groupParts) > 1 || !empty($havingParts)) {
                $rowCount->reset(Zend_Db_Select::ORDER);
                $rowCount = $db
                               ->select()
                               ->bind($rowCount->getBind())
                               ->from($rowCount);
            } else if ($isDistinct) {
                $part = $columnParts[0];

                if ($part[1] !== Zend_Db_Select::SQL_WILDCARD && !($part[1] instanceof Zend_Db_Expr)) {
                    $column = $db->quoteIdentifier($part[1], true);

                    if (!empty($part[0])) {
                        $column = $db->quoteIdentifier($part[0], true) . '.' . $column;
                    }

                    $groupPart = $column;
                }
            } else if (!empty($groupParts)) {
                $groupPart = $db->quoteIdentifier($groupParts[0], true);
            }

            /**
             * If the original query had a GROUP BY or a DISTINCT part and only
             * one column was specified, create a COUNT(DISTINCT ) query instead
             * of a regular COUNT query.
             */
            if (!empty($groupPart)) {
                $countPart = 'COUNT(DISTINCT ' . $groupPart . ') AS ';
            }

            /**
             * Create the COUNT part of the query
             */
            $expression = new Zend_Db_Expr($countPart . $countColumn);

            $rowCount->reset(Zend_Db_Select::COLUMNS)
                     ->reset(Zend_Db_Select::ORDER)
                     ->reset(Zend_Db_Select::LIMIT_OFFSET)
                     ->reset(Zend_Db_Select::GROUP)
                     ->reset(Zend_Db_Select::DISTINCT)
                     ->reset(Zend_Db_Select::HAVING)
                     ->columns($expression);
        }

        $this->_countSelect = $rowCount;

        return $rowCount;
    }
}