<?php
#BEGIN_LICENSE
#-------------------------------------------------------------------------
# Module: \CMSMS\Database\DataDictionary (c) 2015 by Robert Campbell
#         (calguy1000@cmsmadesimple.org)
#  A class to define methods of interacting with database tables.
#
#-------------------------------------------------------------------------
# CMS - CMS Made Simple is (c) 2005 by Ted Kulp (wishy@cmsmadesimple.org)
# Visit our homepage at: http://www.cmsmadesimple.org
#
#-------------------------------------------------------------------------
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# However, as a special exception to the GPL, this software is distributed
# as an addon module to CMS Made Simple.  You may not use this software
# in any Non GPL version of CMS Made simple, or in any version of CMS
# Made simple that does not indicate clearly and obviously in its admin
# section that the site was built with CMS Made simple.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
# Or read it online: http://www.gnu.org/licenses/licenses.html#GPL
#
#-------------------------------------------------------------------------
#END_LICENSE

/**
 * This file defines the DataDictionary class.
 *
 * This file is based on the DataDictionary base class from the adodb_lite library
 * which was in turn a fork of the adodb library at approximately 2004.
 *
 * Credits and kudos to the authors of those packages.
 *
 * @package CMS
 */

namespace CMSMS\Database;

// shouldn't need this.
if (!function_exists('ctype_alnum')) {
    /**
     * @ignore
     */
    function ctype_alnum($text) {
        return preg_match('/^[a-z0-9]*$/i', $text);
    }
}

/**
 * @ignore
 */
function _array_change_key_case($an_array)
{
    if (is_array($an_array)) {
        $new_array = array();
        foreach($an_array as $key=>$value)
            $new_array[strtoupper($key)] = $value;

        return $new_array;
    }

    return $an_array;
}

/**
 * @ignore
 */
function Lens_ParseArgs($args,$endstmtchar=',',$tokenchars='_.-')
{
    $pos = 0;
    $intoken = false;
    $stmtno = 0;
    $endquote = false;
    $tokens = array();
    $tokens[$stmtno] = array();
    $max = strlen($args);
    $quoted = false;

    while ($pos < $max) {
        $ch = substr($args,$pos,1);
        switch($ch) {
            case ' ':
            case "\t":
            case "\n":
            case "\r":
                if (!$quoted) {
                    if ($intoken) {
                        $intoken = false;
                        $tokens[$stmtno][] = implode('',$tokarr);
                    }
                    break;
                }
                $tokarr[] = $ch;
                break;
            case '`':
                if ($intoken) $tokarr[] = $ch;
                // fall through
            case '(':
            case ')':
            case '"':
            case "'":
                if ($intoken) {
                    if (empty($endquote)) {
                        $tokens[$stmtno][] = implode('',$tokarr);
                        if ($ch == '(') $endquote = ')';
                        else $endquote = $ch;
                        $quoted = true;
                        $intoken = true;
                        $tokarr = array();
                    } else if ($endquote == $ch) {
                        $ch2 = substr($args,$pos+1,1);
                        if ($ch2 == $endquote) {
                            $pos += 1;
                            $tokarr[] = $ch2;
                        } else {
                            $quoted = false;
                            $intoken = false;
                            $tokens[$stmtno][] = implode('',$tokarr);
                            $endquote = '';
                        }
                    } else
                    $tokarr[] = $ch;
                }
                else {
                    if ($ch == '(') $endquote = ')';
                    else $endquote = $ch;
                    $quoted = true;
                    $intoken = true;
                    $tokarr = array();
                    if ($ch == '`') $tokarr[] = '`';
                }
                break;
            default:
                if (!$intoken) {
                    if ($ch == $endstmtchar) {
                        $stmtno += 1;
                        $tokens[$stmtno] = array();
                        break;
                    }
                    $intoken = true;
                    $quoted = false;
                    $endquote = false;
                    $tokarr = array();
                }
                if ($quoted) $tokarr[] = $ch;
                else if (ctype_alnum($ch) || strpos($tokenchars,$ch) !== false) $tokarr[] = $ch;
                else {
                    if ($ch == $endstmtchar) {
                        $tokens[$stmtno][] = implode('',$tokarr);
                        $stmtno += 1;
                        $tokens[$stmtno] = array();
                        $intoken = false;
                        $tokarr = array();
                        break;
                    }
                    $tokens[$stmtno][] = implode('',$tokarr);
                    $tokens[$stmtno][] = $ch;
                    $intoken = false;
                }
        }
        $pos += 1;
    }
    if ($intoken) $tokens[$stmtno][] = implode('',$tokarr);

    return $tokens;
}


/**
 * A class defining methods to work directly with database tables.
 *
 * This file is based on the DataDictionary base class from the adodb_lite library
 * which was in turn a fork of the adodb library at approximately 2004.
 *
 * Credits and kudos to the authors of those packages.
 *
 * @package CMS
 * @author Robert Campbell
 * @copyright Copyright (c) 2015, Robert Campbell <calguy1000@cmsmadesimple.org>
 * @since 2.2
 */
abstract class DataDictionary
{

    /**
     * The database connection object.
     *
     * @internal
     */
    protected $connection;

    /**
     * The SQL prefix to use when creating a drop table command.
     *
     * @internal
     */
    protected $dropTable = 'DROP TABLE %s';

    /**
     * The SQL prefix to use when renaming a table.
     *
     * @internal
     */
    protected $renameTable = 'RENAME TABLE %s TO %s';

    /**
     * The SQL prefix to use when dropping an index.
     *
     * @internal
     */
    protected $dropIndex = 'DROP INDEX %s';

    /**
     * The SQL string to use (in the alter table command) when adding a column.
     *
     * @internal
     */
    protected $addCol = ' ADD';

    /**
     * The SQL string to use (in the alter table command) when altering a column.
     *
     * @internal
     */
    protected $alterCol = ' ALTER COLUMN';

    /**
     * The SQL string to use (in the alter table command) when dropping a column.
     *
     * @internal
     */
    protected $dropCol = ' DROP COLUMN';

    /**
     * The SQL command template for renaming a column.
     *
     * @internal
     */
    protected $renameColumn = 'ALTER TABLE %s RENAME COLUMN %s TO %s';	// table, old-column, new-column, column-definitions (not used by default)

    /**
     * @ignore
     */
    protected $nameRegex = '\w';

    /**
     * @ignore
     */
    protected $nameRegexBrackets = 'a-zA-Z0-9_\(\)';

    /**
     * @ignore
     */
    protected $autoIncrement = false;

    /**
     * @ignore
     */
    protected $invalidResizeTypes4 = array('CLOB','BLOB','TEXT','DATE','TIME'); // for changetablesql

    /**
     * Constructor
     *
     * @param \CMSMS\Database\Connection $conn
     */
    protected function __construct(Connection $conn)
    {
        $this->connection = $conn;
    }

    /**
     * A function to return the database type.
     *
     * @internal
     * @return string
     */
    protected function _DBType()
    {
        return $this->connection->DbType();
    }

    /**
     * A function to return the datadictionary meta type for a database column type.
     *
     * @internal
     * @param string $t The database column type
     * @param int $len The length of the field (some database types may ignore this)
     * @param mixed $fieldobj An optional reference to a field object (advanced)
     * @return string
     */
    abstract protected function MetaType($t,$len=-1,$fieldobj=false);

    /**
     * Return the list of tables in the currently connected database.
     *
     * @return string[]
     */
    abstract public function MetaTables();

    /**
     * Return the list of columns in a table within the currently connected database.
     *
     * @param string $table The table name.
     * @return string[]
     */
    abstract public function MetaColumns($table);

    /**
     * Return a database specific column type given a datadictionary meta column type.
     *
     * @internal
     * @param string $meta The datadictionary column type.
     * @return string
     */
    abstract protected function ActualType($meta);

    /**
     * Given a string name, return a quoted name in a form suitable for the database.
     *
     * @internal
     * @param string $name The input name
     * @param bool $allowBrackets wether brackets should be quoted or not.
     * @return string
     */
    protected function NameQuote($name = NULL,$allowBrackets=false)
    {
        if (!is_string($name)) return FALSE;

        $name = trim($name);

        if ( !is_object($this->connection) ) return $name;

        $quote = $this->connection->nameQuote;

        // if name is of the form `name`, quote it
        if ( preg_match('/^`(.+)`$/', $name, $matches) ) return $quote . $matches[1] . $quote;

        // if name contains special characters, quote it
        $regex = ($allowBrackets) ? $this->nameRegexBrackets : $this->nameRegex;

        if ( !preg_match('/^[' . $regex . ']+$/', $name) ) return $quote . $name . $quote;

        return $name;
    }

    /**
     * Given a table name, optionally quote it.
     *
     * @internal
     * @param string $name
     * @return string
     */
    protected function TableName($name)
    {
        return $this->NameQuote($name);
    }

    /**
     * Given an array of SQL commands execute them in sequence.
     *
     * @param string[] $sql An array of sql commands.
     * @param bool $continueOnError wether to continue on errors or not.
     * @return int 2 for no errors, 1 if an error occured.
     */
    public function ExecuteSQLArray($sql, $continueOnError = true)
    {
        $rez = 2;
        $conn = &$this->connection;
        foreach($sql as $line) {
            try {
                $ok = $conn->Execute($line);
                if (!$ok) {
                    if (!$continueOnError) return 0;
                    $rez = 1;
                }
            }
            catch( \Exception $e ) {
                if( !$continueOnError ) throw $e;
                $rez = 1;
                // eat the exception
            }
        }
        return $rez;
    }

    /**
     * Create the SQL commands that will result in a database being created.
     *
     * @param string $dbname
     * @param array  An associative array of database options.
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function CreateDatabase($dbname,$options=false)
    {
        $options = $this->_Options($options);
        $sql = array();

        $s = 'CREATE DATABASE ' . $this->NameQuote($dbname);
        if (isset($options[$this->upperName]))
            $s .= ' '.$options[$this->upperName];

        $sql[] = $s;
        return $sql;
    }

    /**
     * Generate the SQL to create an index.
     *
     * @param string $idxname The index name
     * @param string $tabname The table name
     * @param string|string[] $flds A list of the table fields to create the index with.  Either an array of strings or a comma separated list.
     * @param array An associative array of options
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function CreateIndexSQL($idxname, $tabname, $flds, $idxoptions = false)
    {
        if (!is_array($flds)) {
            $flds = explode(',',$flds);
        }
        foreach($flds as $key => $fld) {
            # some indexes can use partial fields, eg. index first 32 chars of "name" with NAME(32)
            $flds[$key] = $this->NameQuote($fld,$allowBrackets=true);
        }
        return $this->_IndexSQL($this->NameQuote($idxname), $this->TableName($tabname), $flds, $this->_Options($idxoptions));
    }

    /**
     * Generate the SQL to drop an index
     *
     * @param string $idxname The index name
     * @param string $tabname The table name
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function DropIndexSQL ($idxname, $tabname = NULL)
    {
        return array(sprintf($this->dropIndex, $this->NameQuote($idxname), $this->TableName($tabname)));
    }

    /**
     * Generate the SQL to add columns to a table.
     *
     * @param string $tabname The Table name.
     * @param string $flds The column definitions (using DataDictionary meta types)
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     * @see CreateTableSQL
     */
    public function AddColumnSQL($tabname, $flds)
    {
        $tabname = $this->TableName ($tabname);
        $sql = array();
        list($lines,$pkey) = $this->_GenFields($flds);
        $alter = 'ALTER TABLE ' . $tabname . $this->addCol . ' ';
        foreach($lines as $v) {
            $sql[] = $alter . $v;
        }
        return $sql;
    }

    /**
     * Change the definition of one column
     *
     * @param string $tabname table-name
     * @param string $flds column-name and type for the changed column.
     * @param string $tableflds complete defintion of the new table, eg. for postgres, default ''
     * @param array/string $tableoptions options for the new table see CreateTableSQL, default ''
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function AlterColumnSQL($tabname, $flds, $tableflds='',$tableoptions='')
    {
        $tabname = $this->TableName ($tabname);
        $sql = array();
        list($lines,$pkey) = $this->_GenFields($flds);
        $alter = 'ALTER TABLE ' . $tabname . $this->alterCol . ' ';
        foreach($lines as $v) {
            $sql[] = $alter . $v;
        }
        return $sql;
    }

    /**
     * Rename one column in a table.
     *
     * @param string $tabname table-name
     * @param string $oldcolumn column-name to be renamed
     * @param string $newcolumn new column-name
     * @param string $flds complete column-defintion-string like for AddColumnSQL, only used by mysql atm., default=''
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function RenameColumnSQL($tabname,$oldcolumn,$newcolumn,$flds='')
    {
        $tabname = $this->TableName ($tabname);
        if ($flds) {
            list($lines,$pkey) = $this->_GenFields($flds);
            list(,$first) = each($lines);
            list(,$column_def) = split("[\t ]+",$first,2);
        }
        return array(sprintf($this->renameColumn,$tabname,$this->NameQuote($oldcolumn),$this->NameQuote($newcolumn),$column_def));
    }

    /**
     * Drop one column from a table.
     *
     * @param string $tabname table-name
     * @param string $flds column-name and type for the changed column
     * @param string $tableflds complete defintion of the new table, eg. for postgres, default ''
     * @param array/string $tableoptions options for the new table see CreateTableSQL, default ''
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function DropColumnSQL($tabname, $flds, $tableflds='',$tableoptions='')
    {
        $tabname = $this->TableName ($tabname);
        if (!is_array($flds)) $flds = explode(',',$flds);
        $sql = array();
        $alter = 'ALTER TABLE ' . $tabname . $this->dropCol . ' ';
        foreach($flds as $v) {
            $sql[] = $alter . $this->NameQuote($v);
        }
        return $sql;
    }

    /**
     * Drop one table, and all of it's indexes
     *
     * @param string $tabname The table name to drop.
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function DropTableSQL($tabname)
    {
        return array (sprintf($this->dropTable, $this->TableName($tabname)));
    }

    /**
     * Rename a table.
     *
     * @param string $tabname The table name
     * @param string $newname The new table name
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function RenameTableSQL($tabname,$newname)
    {
        return array (sprintf($this->renameTable, $this->TableName($tabname),$this->TableName($newname)));
    }

    /**
     * Generate the SQL to create a new table.
     *
     * The flds string is a comma separated of field definitions, where each definition is of the form
     *    fieldname type columnsize otheroptions
     *
     * The type fields are codes that map to real database types as follows:
     * <dl>
     *  <dt>C</dt>
     *  <dd>Varchar, capped to 255 characters.</dd>
     *  <dt>X</dt>
     *  <dd>Text</dd>
     *  <dt>XL</dt>
     *  <dd>LongText</dd>
     *  <dt>C2</dt>
     *  <dd>Varchar, capped to 255 characters</dd>
     *  <dt>XL</dt>
     *  <dd>LongText</dd>
     *  <dt>B</dt>
     *  <dd>LongBlob</dd>
     *  <dt>D</dt>
     *  <dd>Date</dd>
     *  <dt>DT</dt>
     *  <dd>DateTime</dd>
     *  <dt>T</dt>
     *  <dd>Time</dd>
     *  <dt>TS</dt>
     *  <dd>Timestamp</dd>
     *  <dt>L</dt>
     *  <dd>TinyInt</dd>
     *  <dt>R / I4 / I</dt>
     *  <dd>Integer</dd>
     *  <dt>I1</dt>
     *  <dd>TinyInt</dd>
     *  <dt>I2</dt>
     *  <dd>SmallInt</dd>
     *  <dt>I4</dt>
     *  <dd>BigInt</dd>
     *  <dt>F</dt>
     *  <dd>Double</dd>
     *  <dt>N</dt>
     *  <dd>Numeric</dd>
     *</dl>
     *
     * The otheroptions field includes the following options:
     *<dl>
     *  <dt>AUTO</dt>
     *  <dd>Auto increment. Also sets NOTNULL.</dd>
     *  <dt>AUTOINCREMENT</dt>
     *  <dd>Same as AUTO</dd>
     *  <dt>KEY</dt>
     *  <dd>Primary key field.  Also sets NOTNULL. Compound keys are supported.</dd>
     *  <dt>PRImARY</dt>
     *  <dd>Same as KEY</dd>
     *  <dt>DEFAULT</dt>
     *  <dd>The default value.  Character strings are auto-quoted unless the string begins with a space.  i.e: ' SYSDATE '.</dd>
     *  <dt>DEF</dt>
     *  <dd>Same as DEFAULT</dd>
     *  <dt>CONSTRAINTS</dt>
     *  <dd>Additional constraints defined at the end of the field definition.</dd>
     *</dl>
     *
     * @param string $tabname The table name
     * @param string $flds a comma separated list of field definitions using datadictionary syntax.
     * @param mixed  $tableoptions A string specifying table options (database driver specific) for the table creation command.  Or an associative array of table options, keys being the database type (as available).
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function CreateTableSQL($tabname, $flds, $tableoptions=false)
    {
        if( $tableoptions && is_string($tableoptions)) {
            $dbtype = $this->_DBType();
            $tableoptions = [ $dbtype => $tableoptions ];
        }

        list($lines,$pkey) = $this->_GenFields($flds, true);
        $taboptions = $this->_Options($tableoptions);
        $tabname = $this->TableName ($tabname);
        $sql = $this->_TableSQL($tabname,$lines,$pkey,$taboptions);
        $tsql = $this->_Triggers($tabname,$taboptions);
        foreach($tsql as $s) $sql[] = $s;

        return $sql;
    }

    /**
     * Part of the process of parsing the datadictionary format into database specific commands.
     *
     * @internal
     */
    protected function _GenFields($flds,$widespacing=false)
    {
        if (is_string($flds)) {
            $padding = '	 ';
            $txt = $flds.$padding;
            $flds = array();
            $flds0 = Lens_ParseArgs($txt,',');
            $hasparam = false;
            foreach($flds0 as $f0) {
                if( !count($f0) ) break;
                $f1 = array();
                foreach($f0 as $token) {
                    switch (strtoupper($token)) {
                        case 'CONSTRAINT':
                        case 'DEFAULT':
                            $hasparam = $token;
                            break;
                        default:
                            if ($hasparam) $f1[$hasparam] = $token;
                            else $f1[] = $token;
                            $hasparam = false;
                            break;
                    }
                }
                $flds[] = $f1;
            }
        }
        $this->autoIncrement = false;
        $lines = array();
        $pkey = array();
        foreach($flds as $fld) {
            $fld = _array_change_key_case($fld);
            $fname = false;
            $fdefault = false;
            $fautoinc = false;
            $ftype = false;
            $fsize = false;
            $fprec = false;
            $fprimary = false;
            $fnoquote = false;
            $fdefts = false;
            $fdefdate = false;
            $fconstraint = false;
            $fnotnull = false;
            $funsigned = false;

            //-----------------
            // Parse attributes
            foreach($fld as $attr => $v) {
                if ($attr == 2 && is_numeric($v)) $attr = 'SIZE';
                else if (is_numeric($attr) && $attr > 1 && !is_numeric($v)) $attr = strtoupper($v);
                switch($attr) {
                    case '0':
                    case 'NAME':
                        $fname = $v;
                        break;
                    case '1':
                    case 'TYPE':
                        $ty = $v; $ftype = $this->ActualType(strtoupper($v));
                        break;
                    case 'SIZE':
                        $dotat = strpos($v,'.');
                        if ($dotat === false) $dotat = strpos($v,',');
                        if ($dotat === false) $fsize = $v;
                        else {
                            $fsize = substr($v,0,$dotat);
                            $fprec = substr($v,$dotat+1);
                        }
                        break;
                    case 'UNSIGNED':
                        $funsigned = true;
                        break;
                    case 'AUTOINCREMENT':
                    case 'AUTO':
                        $fautoinc = true;
                        $fnotnull = true;
                        break;
                    case 'KEY':
                    case 'PRIMARY':
                        $fprimary = $v;
                        $fnotnull = true;
                        break;
                    case 'DEF':
                    case 'DEFAULT':
                        $fdefault = $v;
                        break;
                    case 'NOTNULL':
                        $fnotnull = $v;
                        break;
                    case 'NOQUOTE':
                        $fnoquote = $v;
                        break;
                    case 'DEFDATE':
                        $fdefdate = $v;
                        break;
                    case 'DEFTIMESTAMP':
                        $fdefts = $v;
                        break;
                    case 'CONSTRAINT':
                        $fconstraint = $v;
                        break;
                }
            }

            //--------------------
            // VALIDATE FIELD INFO
            if (!strlen($fname)) {
                return false;
            }

            $fid = strtoupper(preg_replace('/^`(.+)`$/', '$1', $fname));
            $fname = $this->NameQuote($fname);

            if (!strlen($ftype)) {
                return false;
            } else {
                $ftype = strtoupper($ftype);
            }

            $ftype = $this->_GetSize($ftype, $ty, $fsize, $fprec);

            if ($ty == 'X' || $ty == 'X2' || $ty == 'B') $fnotnull = false; // some blob types do not accept nulls

            if ($fprimary) $pkey[] = $fname;

            // some databases do not allow blobs to have defaults
            if ($ty == 'X') $fdefault = false;

            //--------------------
            // CONSTRUCT FIELD SQL
            if ($fdefts) {
                if (substr($this->_DbType(),0,5) == 'mysql') {
                    $ftype = 'TIMESTAMP';
                } else {
                    $fdefault = $this->connection->sysTimeStamp;
                }
            } else if ($fdefdate) {
                if (substr($this->_DBType(),0,5) == 'mysql') {
                    $ftype = 'TIMESTAMP';
                } else {
                    $fdefault = $this->connection->sysDate;
                }
            } else if ($fdefault !== false && !$fnoquote)
                if ($ty == 'C' or $ty == 'X' or
                    ( substr($fdefault,0,1) != "'" && !is_numeric($fdefault)))
                    if (strlen($fdefault) != 1 && substr($fdefault,0,1) == ' ' && substr($fdefault,strlen($fdefault)-1) == ' ')
                        $fdefault = trim($fdefault);
            else if (strtolower($fdefault) != 'null')
                        $fdefault = $this->connection->qstr($fdefault);
            $suffix = $this->_CreateSuffix($fname,$ftype,$fnotnull,$fdefault,$fautoinc,$fconstraint,$funsigned);

            if ($widespacing) $fname = str_pad($fname,24);
            $lines[$fid] = $fname.' '.$ftype.$suffix;

            if ($fautoinc) $this->autoIncrement = true;
        } // foreach $flds
        return array($lines,$pkey);
    }

    /**
     * Generate the size part of the datatype.
     *
     * @ignore
     * @internal
     */
    protected function _GetSize($ftype, $ty, $fsize, $fprec)
    {
        if (strlen($fsize) && $ty != 'X' && $ty != 'B' && strpos($ftype,'(') === false) {
            $ftype .= "(".$fsize;
            if (strlen($fprec)) $ftype .= ",".$fprec;
            $ftype .= ')';
        }
        return $ftype;
    }

    /**
     * Create a suffix
     *
     * @internal
     */
    protected function _CreateSuffix($fname,$ftype,$fnotnull,$fdefault,$fautoinc,$fconstraint,$funsigned)
    {
        $suffix = '';
        if (strlen($fdefault)) $suffix .= " DEFAULT $fdefault";
        if ($fnotnull) $suffix .= ' NOT NULL';
        if ($fconstraint) $suffix .= ' '.$fconstraint;
        return $suffix;
    }

    /**
     * build SQL commands for indexes.
     *
     * @internal
     */
    protected function _IndexSQL($idxname, $tabname, $flds, $idxoptions)
    {
        $sql = array();

        if ( isset($idxoptions['REPLACE']) || isset($idxoptions['DROP']) ) {
            $sql[] = sprintf ($this->dropIndex, $idxname);
            if ( isset($idxoptions['DROP']) ) return $sql;
        }

        if ( empty ($flds) ) return $sql;

        $unique = isset($idxoptions['UNIQUE']) ? ' UNIQUE' : '';

        $s = 'CREATE' . $unique . ' INDEX ' . $idxname . ' ON ' . $tabname . ' ';

        if ( isset($idxoptions[$this->upperName]) )
            $s .= $idxoptions[$this->upperName];

        if ( is_array($flds) )	$flds = implode(', ',$flds);
        $s .= '(' . $flds . ')';
        $sql[] = $s;

        return $sql;
    }

    /**
     * A method to drop the auto increment column on a table.
     *
     * @internal
     */
    protected function _DropAutoIncrement($tabname)
    {
        return false;
    }

    /**
     * An internal method to get a list of database type specific options for a command.
     *
     * @internal
     */
    protected function get_dbtype_options($opts,$suffix = null)
    {
        $dbtype = $this->_DBType();
        $list = array($dbtype.$suffix,strtoupper($dbtype).$suffix,strtolower($dbtype).$suffix);

        foreach( $list as $one ) {
            if( isset($opts[$one]) && is_string($opts[$one]) && strlen($opts[$one]) ) return $opts[$one];
        }
    }

    /**
     * Build strings for generating tables.
     *
     * @internal
     */
    protected function _TableSQL($tabname,$lines,$pkey,$tableoptions)
    {
        $sql = array();

        if (isset($tableoptions['REPLACE']) || isset ($tableoptions['DROP'])) {
            $sql[] = sprintf($this->dropTable,$tabname);
            if ($this->autoIncrement) {
                $sInc = $this->_DropAutoIncrement($tabname);
                if ($sInc) $sql[] = $sInc;
            }
            if ( isset ($tableoptions['DROP']) ) {
                return $sql;
            }
        }
        $s = "CREATE TABLE $tabname (\n";
        $s .= implode(",\n", $lines);
        if (sizeof($pkey)>0) {
            $s .= ",\n				 PRIMARY KEY (";
            $s .= implode(", ",$pkey).")";
        }
        if (isset($tableoptions['CONSTRAINTS']))
            $s .= "\n".$tableoptions['CONSTRAINTS'];

        $str = $this->get_dbtype_options($tableoptions,'_CONSTRAINTS');
        if( $str ) $s .= "\n".$str;

        $s .= "\n)";
        $str = $this->get_dbtype_options($tableoptions);
        if( $str ) $s .= $str;
        $sql[] = $s;

        return $sql;
    }

    /**
     * Generate triggers if needed.
	 * This is used when table has auto-incrementing field that is emulated using triggers.
     *
     * @internal
     */
    protected function _Triggers($tabname,$taboptions)
    {
        return array();
    }

    /**
     * Sanitize options,
     *
     * @internal
     */
    protected function _ProcessOptions($opts)
    {
        return $opts;
    }

    /**
     * Convert options into a format usable by the system.
     *
     * @internal
     */
    protected function _Options($opts)
    {
        $opts = $this->_ProcessOptions($opts);
        if (!is_array($opts)) return array();
        $newopts = array();
        foreach($opts as $k => $v) {
            if (is_numeric($k)) $newopts[strtoupper($v)] = $v;
            else $newopts[strtoupper($k)] = $v;
        }
        return $newopts;
    }

    /**
     * Add, drop or change columns within a table.
     *
     * This function changes/adds new fields to your table. You don't
     * have to know if the col is new or not. It will check on its own.
     *
     * @param string $tablename The table name
     * @param string $flds The field definitions
     * @param array  $tableoptions Table options
     * @return string[] An array of strings suitable for use with the ExecuteSQLArray method
     */
    public function ChangeTableSQL($tablename, $flds, $tableoptions = false)
    {
        // check table exists
        $cols = $this->MetaColumns($tablename);

        if ( empty($cols)) {
            return $this->CreateTableSQL($tablename, $flds, $tableoptions);
        }

        if (is_array($flds)) {
            // Cycle through the update fields, comparing
            // existing fields to fields to update.
            // if the Metatype and size is exactly the
            // same, ignore - by Mark Newham
            $holdflds = array();
            foreach($flds as $k=>$v) {
                if ( isset($cols[$k]) && is_object($cols[$k]) ) {
                    $c = $cols[$k];
                    $ml = $c->max_length;
                    $mt = &$this->MetaType($c->type,$ml);
                    if ($ml == -1) $ml = '';
                    if ($mt == 'X') $ml = $v['SIZE'];
                    if (($mt != $v['TYPE']) || $ml != $v['SIZE']) $holdflds[$k] = $v;
                } else {
                    $holdflds[$k] = $v;
                }
            }
            $flds = $holdflds;
        }

        // already exists, alter table instead
        list($lines,$pkey) = $this->_GenFields($flds);
        $alter = 'ALTER TABLE ' . $this->TableName($tablename);
        $sql = array();

        foreach ( $lines as $id => $v ) {
            if ( isset($cols[$id]) && is_object($cols[$id]) ) {
                $flds = Lens_ParseArgs($v,',');
                //  We are trying to change the size of the field, if not allowed, simply ignore the request.
                if ($flds && in_array(strtoupper(substr($flds[0][1],0,4)),$this->invalidResizeTypes4)) continue;

                $sql[] = $alter . $this->alterCol . ' ' . $v;
            } else {
                $sql[] = $alter . $this->addCol . ' ' . $v;
            }
        }
        return $sql;
    }
} // end of class

