/**

 * Return the proper SQL to compare a field to multiple items

 *

 * By default it uses IN but can be negated (to NOT IN) using the 3rd argument

 *

 * The output from this is safe for Oracle, which has a limit of 1000 items in an

 * IN () call.

 *

 * @param string $field The field to compare against

 * @param array $items Array of items. If text they must already be quoted.

 * @param boolean $negate Return code for NOT IN () instead of IN ()

 *

 * @return array In the form array(sql, params) The SQL needed to compare $field to the items

 *              in $items and associated parameters

 */

function sql_sequence($field, $items, $type=SQL_PARAMS_QM, $negate = false) {

    global $DB;

    if (!is_array($items) || count($items) == 0) {

        return ($negate) ? array('1=1', array()) : array('1=0', array());

    }

    $not = $negate ? 'NOT' : '';

    if ($DB->get_dbfamily() != 'oracle' || $count($items) <= 1000) {

        list($sql, $params) = $DB->get_in_or_equal($items, $type, 'param', !$negate);

        return array(" $field " . $sql, $params);

    }

    $out = array();

    while ($some_items = totara_pop_n($items, 1000)) {

        list($sql, $params) = $DB->get_in_or_equal($items, $type, 'param', !$negate);

        $out[] =" $field " . $sql;

        $outparams = array_merge($outparams, $params);

    }

    $operator = $negate ? ' AND ' : ' OR ';

    return array('(' . implode($operator, $out) . ')', $outparams);

}

/**

 * Pop N items off the beginning of $items and return them as an array

 *

 * @param array &$items Array of items (passed by reference)

 * @param integer $number Number of items to remove from the start of $items

 *

 * @return array Array of $number items from $items, or false if $items is empty

 */

function totara_pop_n(&$items, $number) {

    if (count($items) == 0) {

        // none left, return false

        return false;

    } else if (count($items) < $number) {

        // return all remaining items

        $return = $items;

        $items = array();

        return $return;

    } else {

        // return the first N and shorten $items

        $return = array_slice($items, 0, $number, true);

        $items = array_slice($items, $number, null, true);

        return $return;

    }

}