<?php

namespace SilverStripe\MSSQL;

use InvalidArgumentException;
use SilverStripe\ORM\Queries\SQLSelect;
use SilverStripe\ORM\Connect\DBQueryBuilder;

/**
 * Builds a SQL query string from a SQLExpression object
 */
class MSSQLQueryBuilder extends DBQueryBuilder
{

    protected function buildSelectQuery(SQLSelect $query, array &$parameters)
    {
        list($limit, $offset) = $this->parseLimit($query);

        // If not using ofset then query generation is quite straightforward
        if (empty($offset)) {
            $sql = parent::buildSelectQuery($query, $parameters);
            // Inject limit into SELECT fragment
            if (!empty($limit)) {
                $sql = preg_replace('/^(SELECT (DISTINCT)?)/i', '${1} TOP '.$limit, $sql);
            }
            return $sql;
        }

        // When using offset we must use a subselect
        // @see http://stackoverflow.com/questions/2135418/equivalent-of-limit-and-offset-for-sql-server
        $orderby = $query->getOrderBy();

        // workaround for subselect not working with alias functions
        // just use the function directly in the order by instead of the alias
        $selects = $query->getSelect();
        foreach ($orderby as $field => $dir) {
            if (preg_match('/_SortColumn/', $field)) {
                unset($orderby[$field]);
                $orderby[$selects[str_replace('"', '', $field)]] = $dir;
            }
        }

        // Create order expression, using the first column if none explicitly specified
        if ($orderby) {
            // Simple implementation of buildOrderByFragment
            $statements = array();
            foreach ($orderby as $clause => $dir) {
                $statements[] = trim("$clause $dir");
            }
            $orderByClause = "ORDER BY " . implode(', ', $statements);
        } else {
            $selects = $query->getSelect();
            $firstCol = reset($selects);
            $orderByClause = "ORDER BY $firstCol";
        }

        // Build main query SQL
        $sql = parent::buildSelectQuery($query, $parameters);

        // Inject row number into selection
        $sql = preg_replace('/^(SELECT (DISTINCT)?)/i', '${1} ROW_NUMBER() OVER ('.$orderByClause.') AS Number, ', $sql);

        // Sub-query this SQL
        if (empty($limit)) {
            $limitCondition = "Number > ?";
            $parameters[] = $offset;
        } else {
            $limitCondition = "Number BETWEEN ? AND ?";
            $parameters[] = $offset + 1;
            $parameters[] = $offset + $limit;
        }
        return "SELECT * FROM ($sql) AS Numbered WHERE $limitCondition ORDER BY Number";
    }

    public function buildLimitFragment(SQLSelect $query, array &$parameters)
    {
        // Limit is handled at the buildSelectQuery level
        return '';
    }

    public function buildOrderByFragment(SQLSelect $query, array &$parameters)
    {
        // If doing a limit/offset at the same time then don't build the orde by fragment here
        list($offset, $limit) = $this->parseLimit($query);
        if (empty($offset) || empty($limit)) {
            return parent::buildOrderByFragment($query, $parameters);
        }
        return '';
    }

    /**
     * Extracts the limit and offset from the limit clause
     *
     * @param SQLSelect $query
     * @return array Two item array with $limit and $offset as values
     * @throws InvalidArgumentException
     */
    protected function parseLimit(SQLSelect $query)
    {
        $limit = '';
        $offset = '0';
        if (is_array($query->getLimit())) {
            $limitArr = $query->getLimit();
            if (isset($limitArr['limit'])) {
                $limit = $limitArr['limit'];
            }
            if (isset($limitArr['start'])) {
                $offset = $limitArr['start'];
            }
        } elseif (preg_match('/^([0-9]+) offset ([0-9]+)$/i', trim($query->getLimit()), $matches)) {
            $limit = $matches[1];
            $offset = $matches[2];
        } else {
            //could be a comma delimited string
            $bits = explode(',', $query->getLimit());
            if (sizeof($bits) > 1) {
                list($offset, $limit) = $bits;
            } else {
                $limit = $bits[0];
            }
        }
        return array($limit, $offset);
    }
}