<?php

namespace SilverStripe\PostgreSQL;

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

class PostgreSQLQueryBuilder extends DBQueryBuilder
{
    /**
     * Return the LIMIT clause ready for inserting into a query.
     *
     * @param SQLSelect $query The expression object to build from
     * @param array $parameters Out parameter for the resulting query parameters
     * @return string The finalised limit SQL fragment
     */
    public function buildLimitFragment(SQLSelect $query, array &$parameters)
    {
        $nl = $this->getSeparator();

        // Ensure limit is given
        $limit = $query->getLimit();
        if (empty($limit)) {
            return '';
        }

        // For literal values return this as the limit SQL
        if (! is_array($limit)) {
            return "{$nl}LIMIT $limit";
        }

        // Assert that the array version provides the 'limit' key
        if (! array_key_exists('limit', $limit) || ($limit['limit'] !== null && ! is_numeric($limit['limit']))) {
            throw new InvalidArgumentException(
                'DBQueryBuilder::buildLimitSQL(): Wrong format for $limit: '. var_export($limit, true)
            );
        }

        if ($limit['limit'] === null) {
            $limit['limit'] = 'ALL';
        }

        $clause = "{$nl}LIMIT {$limit['limit']}";
        if (isset($limit['start']) && is_numeric($limit['start']) && $limit['start'] !== 0) {
            $clause .= " OFFSET {$limit['start']}";
        }
        return $clause;
    }
}