<?php
class Utf8Conversion extends Migration
{
    public function description()
    {
        return 'Convert database to utf8mb4';
    }

    public function up()
    {
        // create a separate connection to the db to create the needed function in MySQL
        // since StudipPDO prevents this kind of query
        $pdo = new PDO('mysql:host=' . $GLOBALS['DB_STUDIP_HOST'] .
            ';dbname=' . $GLOBALS['DB_STUDIP_DATABASE'] .
            ';charset=utf8',
            $GLOBALS['DB_STUDIP_USER'],
            $GLOBALS['DB_STUDIP_PASSWORD']
        );
        $pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

        // check if the necessary MySQL-settings are present
        // MariaDB deprecated these settings and removed them in v10.3
        if (!$this->checkMariaDB($pdo, '10.3')) {
            $result = $pdo->query("SHOW VARIABLES LIKE 'innodb_file_format'");
            $var = $result->fetch(PDO::FETCH_KEY_PAIR);
            if ($var && $var['innodb_file_format'] !== '' && mb_strtolower($var['innodb_file_format']) !== 'barracuda') {
                throw new Exception('Could not convert Database: You need to set \'innodb_file_format\' = \'Barracuda\'');
            }

            $result = $pdo->query("SHOW VARIABLES LIKE 'innodb_large_prefix'");
            $var = $result->fetch(PDO::FETCH_KEY_PAIR);
            if ($var && $var['innodb_large_prefix'] !== '' && mb_strtolower($var['innodb_large_prefix']) !== 'on') {
                throw new Exception('Could not convert Database: You need to set \'innodb_large_prefix\' = 1');
            }
        }

        // create a helper-function in MySQL
        $pdo->exec("DROP FUNCTION IF EXISTS entity_decode");
        $pdo->exec("
        CREATE FUNCTION entity_decode(txt MEDIUMTEXT CHARSET utf8mb4) RETURNS MEDIUMTEXT
            CHARSET utf8mb4
                NO SQL
                DETERMINISTIC
            BEGIN

                DECLARE tmp     MEDIUMTEXT CHARSET utf8mb4 DEFAULT txt;
                DECLARE entity  TEXT CHARSET utf8mb4;
                DECLARE pos1    INT DEFAULT 1;
                DECLARE pos2    INT;
                DECLARE codepoint   INT;

                IF txt IS NULL THEN
                    RETURN NULL;
                END IF;
                LOOP
                    SET pos1 = LOCATE('&#', tmp, pos1);
                    IF pos1 = 0 THEN
                        RETURN tmp;
                    END IF;
                    SET pos2 = LOCATE(';', tmp, pos1 + 2);
                    IF pos2 > pos1 THEN
                        SET entity = SUBSTRING(tmp, pos1, pos2 - pos1 + 1);
                        IF entity REGEXP '^&#[[:digit:]]+;$' THEN
                            SET codepoint = CAST(SUBSTRING(entity, 3, pos2 - pos1 -
            2) AS UNSIGNED);
                            IF codepoint > 31 THEN
                                SET tmp = CONCAT(LEFT(tmp, pos1 - 1), CONVERT(CONVERT(UNHEX(HEX(codepoint)) USING utf32) USING utf8mb4), SUBSTRING(tmp, pos2 + 1));
                            END IF;
                        END IF;
                    END IF;
                    SET pos1 = pos1 + 1;
                END LOOP;
            END
        ");

        // close connection again
        $pdo = null;

        $db = DBManager::get();

        // convert selected columns from serialized data to JSON data
        $this->convert_to_json('extern_config', 'config');
        $this->convert_to_json('aux_lock_rules', 'attributes');
        $this->convert_to_json('aux_lock_rules', 'sorting');
        $this->convert_to_json('user_config', 'value', "field = 'MY_COURSES_ADMIN_VIEW_FILTER_ARGS'");
        $this->convert_to_json('mail_queue_entries', 'mail');

        // convert database to utf-8
        $db->exec("ALTER DATABASE `{$GLOBALS['DB_STUDIP_DATABASE']}`
            CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci");

        // convert tables and columns to utf-8
        foreach($db->query("SHOW TABLES")->fetchAll() as $data) {
            try {
                // TODO: check EVERY column for the current collation and keep the correct type (bin, etc.)
                // $this->write('Converting table: ' . $data[0]);

                $query = 'ALTER TABLE `'. $data[0] .'` ';
                $change_query = [];
                $update_query = [];
                $table_data = $db->query("SHOW FULL COLUMNS FROM `{$data[0]}`")->fetchAll();

                foreach ($table_data as $column) {
                    $collation = false;

                    // convert index columns to latin1_bin to save space and speed things up
                    if (mb_strpos($column['Type'], 'char') !== false) {
                        $matches = [];
                        preg_match('/char\((.*)\)/', $column['Type'], $matches);

                        if ((int)$matches[1] <= 32) {
                            $charset = 'latin1';
                            $collation = 'latin1_bin';
                        }
                    }

                    if (mb_strpos($column['Type'], 'enum') !== false) {
                        $charset = 'latin1';
                        $collation = 'latin1_bin';
                    } elseif ($data[0] === 'plugins_activated' && $column['Field'] === 'poiid') {
                        $charset = 'latin1';
                        $collation = 'latin1_bin';
                    }

                    if (!$collation) {
                        if (mb_strpos($column['Collation'], '_bin') !== false) {    // if we hav a bin column, preserve it
                            $charset = 'utf8mb4';
                            $collation = 'utf8mb4_bin';
                        } else if ($column['Collation']) {                          // only convert if there is a collation at all (int f.e. has no collation!)
                            $charset = 'utf8mb4';
                            $collation = 'utf8mb4_unicode_ci';
                        }
                    }

                    if ($collation) {
                        $null    = $column['Null'] === 'YES' ? ' NULL' : ' NOT NULL';
                        $default = isset($column['Default']) ? ' DEFAULT ' . $db->quote($column['Default']) : '';
                        $extra   = $column['Extra'] != '' ? ' ' . $column['Extra'] : '';
                        $comment = $column['Comment'] != '' ? ' COMMENT ' . $db->quote($column['Comment']) : '';
                        $change_query[] = ' CHANGE `'. $column[0] .'` `'. $column[0] .'` '
                           . $column[1] . ' CHARACTER SET '. $charset .' COLLATE ' . $collation . $null . $default . $extra . $comment;
                    }

                    if ($collation && $collation !== 'latin1_bin') {
                        $update_query[] = '`' . $column['Field'] . '` = entity_decode(`' . $column['Field'] . '`)';
                    }
                }

                // do all changes at once, or multi-column-indexes will prevent conversion
                $db->exec($query . implode(',', $change_query));

                if ($update_query) {
                    $db->exec("UPDATE `{$data[0]}` SET " . implode(',', $update_query));
                }

                // change default encoding of table itself
                $db->exec($query = "ALTER TABLE `{$data[0]}` CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci");

            } catch (PDOException $e) {
                $this->write($query);
                $this->write($e->getMessage());
            }
        }

        $db->exec("ALTER TABLE `session_data` CHANGE COLUMN `val` `val` mediumblob NOT NULL");

        // drop helper-function
        $db->exec("DROP FUNCTION IF EXISTS entity_decode");
    }

    private function legacy_studip_utf8encode($data)
    {
        if (is_array($data)) {
            $new_data = [];
            foreach ($data as $key => $value) {
                $key = $this->legacy_studip_utf8encode($key);
                $new_data[$key] = $this->legacy_studip_utf8encode($value);
            }
            return $new_data;
        }

        if (!preg_match('/[\200-\377]/', $data) && !preg_match("'&#[0-9]+;'", $data)) {
            return $data;
        } else {
            return mb_decode_numericentity(
                mb_convert_encoding($data,'UTF-8', 'WINDOWS-1252'),
                [0x100, 0xffff, 0, 0xffff],
                'UTF-8'
            );
        }
    }

    private function convert_to_json($table, $column, $where = null)
    {
        $db = DBManager::get();

        // get primary keys
        $result = $db->query("SHOW KEYS FROM $table WHERE Key_name = 'PRIMARY'");
        $keys = [];

        while ($data = $result->fetch(PDO::FETCH_ASSOC)) {
            $keys[] = $data['Column_name'];
        }

        // retrieve and convert data
        $result = $db->query("SELECT `". implode('`,`', $keys) ."`, `$column` FROM `$table` WHERE ". ($where ?: '1'));

        while ($data = $result->fetch(PDO::FETCH_ASSOC)) {
            $content = unserialize(legacy_studip_utf8decode($data[$column]));

            if ($content !== false) {
                // encode all data
                $json = json_encode($this->legacy_studip_utf8encode($content), true);

                $query = "UPDATE `$table` SET `$column` = ". $db->quote($json) ."\n WHERE ";

                $where_query = [];
                foreach ($keys as $key) {
                    $where_query[] = "`$key` = ". $db->quote($data[$key]);
                }

                $db->exec($query . implode(' AND ', $where_query));
            }
        }
    }

    public function down()
    {
    }

    private function checkMariaDB(PDO $connection, $check_version = null, $check_operator = '>=')
    {
        $version = $connection->query("SELECT VERSION()")->fetchColumn();
        if (!preg_match('/MariaDB$/', $version)) {
            return false;
        }
        if ($version === null) {
            return true;
        }
        return version_compare($version, $check_version, $check_operator);
    }
}