<?php
/**
 * @file src/Database/DBStructure.php
 */
namespace Friendica\Database;

use Exception;
use Friendica\Core\Addon;
use Friendica\Core\Config;
use Friendica\Core\L10n;
use Friendica\Util\DateTimeFormat;

require_once 'boot.php';
require_once 'include/dba.php';
require_once 'include/enotify.php';
require_once 'include/text.php';

/**
 * @brief This class contain functions for the database management
 *
 * This class contains functions that doesn't need to know if pdo, mysqli or whatever is used.
 */
class DBStructure
{
	/*
	 * Converts all tables from MyISAM to InnoDB
	 */
	public static function convertToInnoDB() {
		$r = q("SELECT `TABLE_NAME` FROM `information_schema`.`tables` WHERE `engine` = 'MyISAM' AND `table_schema` = '%s'",
			DBA::escape(DBA::databaseName()));

		if (!DBA::isResult($r)) {
			echo L10n::t('There are no tables on MyISAM.')."\n";
			return;
		}

		foreach ($r AS $table) {
			$sql = sprintf("ALTER TABLE `%s` engine=InnoDB;", DBA::escape($table['TABLE_NAME']));
			echo $sql."\n";

			$result = DBA::e($sql);
			if (!DBA::isResult($result)) {
				self::printUpdateError($sql);
			}
		}
	}

	/*
	 * send the email and do what is needed to do on update fails
	 *
	 * @param update_id		(int) number of failed update
	 * @param error_message	(str) error message
	 */
	public static function updateFail($update_id, $error_message) {
		$a = get_app();

		//send the administrators an e-mail
		$admin_mail_list = "'".implode("','", array_map(['Friendica\Database\DBA', 'escape'], explode(",", str_replace(" ", "", Config::get('config', 'admin_email')))))."'";
		$adminlist = q("SELECT uid, language, email FROM user WHERE email IN (%s)",
			$admin_mail_list
		);

		// No valid result?
		if (!DBA::isResult($adminlist)) {
			logger(sprintf('Cannot notify administrators about update_id=%d, error_message=%s', $update_id, $error_message), LOGGER_INFO);

			// Don't continue
			return;
		}

		// every admin could had different language
		foreach ($adminlist as $admin) {
			$lang = (($admin['language'])?$admin['language']:'en');
			L10n::pushLang($lang);

			$preamble = deindent(L10n::t("
				The friendica developers released update %s recently,
				but when I tried to install it, something went terribly wrong.
				This needs to be fixed soon and I can't do it alone. Please contact a
				friendica developer if you can not help me on your own. My database might be invalid."));
			$body = L10n::t("The error message is\n[pre]%s[/pre]");
			$preamble = sprintf($preamble, $update_id);
			$body = sprintf($body, $error_message);

			notification([
				'uid'      => $admin['uid'],
				'type'     => SYSTEM_EMAIL,
				'to_email' => $admin['email'],
				'preamble' => $preamble,
				'body'     => $body,
				'language' => $lang]
			);
			L10n::popLang();
		}

		//try the logger
		logger("CRITICAL: Database structure update failed: ".$error_message);
	}


	private static function tableStructure($table) {
		$structures = q("DESCRIBE `%s`", $table);

		$full_columns = q("SHOW FULL COLUMNS FROM `%s`", $table);

		$indexes = q("SHOW INDEX FROM `%s`", $table);

		$table_status = q("SHOW TABLE STATUS WHERE `name` = '%s'", $table);

		if (DBA::isResult($table_status)) {
			$table_status = $table_status[0];
		} else {
			$table_status = [];
		}

		$fielddata = [];
		$indexdata = [];

		if (DBA::isResult($indexes)) {
			foreach ($indexes AS $index) {
				if ($index['Key_name'] != 'PRIMARY' && $index['Non_unique'] == '0' && !isset($indexdata[$index["Key_name"]])) {
					$indexdata[$index["Key_name"]] = ['UNIQUE'];
				}

				$column = $index["Column_name"];

				if ($index["Sub_part"] != "") {
					$column .= "(".$index["Sub_part"].")";
				}

				$indexdata[$index["Key_name"]][] = $column;
			}
		}
		if (DBA::isResult($structures)) {
			foreach ($structures AS $field) {
				// Replace the default size values so that we don't have to define them
				$search = ['tinyint(1)', 'tinyint(3) unsigned', 'tinyint(4)', 'smallint(5) unsigned', 'smallint(6)', 'mediumint(8) unsigned', 'mediumint(9)', 'bigint(20)', 'int(10) unsigned', 'int(11)'];
				$replace = ['boolean', 'tinyint unsigned', 'tinyint', 'smallint unsigned', 'smallint', 'mediumint unsigned', 'mediumint', 'bigint', 'int unsigned', 'int'];
				$field["Type"] = str_replace($search, $replace, $field["Type"]);

				$fielddata[$field["Field"]]["type"] = $field["Type"];
				if ($field["Null"] == "NO") {
					$fielddata[$field["Field"]]["not null"] = true;
				}

				if (isset($field["Default"])) {
					$fielddata[$field["Field"]]["default"] = $field["Default"];
				}

				if ($field["Extra"] != "") {
					$fielddata[$field["Field"]]["extra"] = $field["Extra"];
				}

				if ($field["Key"] == "PRI") {
					$fielddata[$field["Field"]]["primary"] = true;
				}
			}
		}
		if (DBA::isResult($full_columns)) {
			foreach ($full_columns AS $column) {
				$fielddata[$column["Field"]]["Collation"] = $column["Collation"];
				$fielddata[$column["Field"]]["comment"] = $column["Comment"];
			}
		}

		return ["fields" => $fielddata, "indexes" => $indexdata, "table_status" => $table_status];
	}

	public static function printStructure() {
		$database = self::definition();

		echo "-- ------------------------------------------\n";
		echo "-- ".FRIENDICA_PLATFORM." ".FRIENDICA_VERSION." (".FRIENDICA_CODENAME,")\n";
		echo "-- DB_UPDATE_VERSION ".DB_UPDATE_VERSION."\n";
		echo "-- ------------------------------------------\n\n\n";
		foreach ($database AS $name => $structure) {
			echo "--\n";
			echo "-- TABLE $name\n";
			echo "--\n";
			self::createTable($name, $structure, true, false);

			echo "\n";
		}
	}

	/**
	 * @brief Print out database error messages
	 *
	 * @param string $message Message to be added to the error message
	 *
	 * @return string Error message
	 */
	private static function printUpdateError($message) {
		echo L10n::t("\nError %d occurred during database update:\n%s\n",
			DBA::errorNo(), DBA::errorMessage());

		return L10n::t('Errors encountered performing database changes: ').$message.EOL;
	}

	/**
	 * Updates DB structure and returns eventual errors messages
	 *
	 * @param bool  $verbose
	 * @param bool  $action     Whether to actually apply the update
	 * @param bool  $install    Is this the initial update during the installation?
	 * @param array $tables     An array of the database tables
	 * @param array $definition An array of the definition tables
	 * @return string Empty string if the update is successful, error messages otherwise
	 */
	public static function update($verbose, $action, $install = false, array $tables = null, array $definition = null) {
		if ($action && !$install) {
			Config::set('system', 'maintenance', 1);
			Config::set('system', 'maintenance_reason', L10n::t('%s: Database update', DateTimeFormat::utcNow().' '.date('e')));
		}

		$errors = '';

		logger('updating structure', LOGGER_DEBUG);

		// Get the current structure
		$database = [];

		if (is_null($tables)) {
			$tables = q("SHOW TABLES");
		}

		if (DBA::isResult($tables)) {
			foreach ($tables AS $table) {
				$table = current($table);

				logger(sprintf('updating structure for table %s ...', $table), LOGGER_DEBUG);
				$database[$table] = self::tableStructure($table);
			}
		}

		// Get the definition
		if (is_null($definition)) {
			$definition = self::definition();
		}

		// MySQL >= 5.7.4 doesn't support the IGNORE keyword in ALTER TABLE statements
		if ((version_compare(DBA::serverInfo(), '5.7.4') >= 0) &&
			!(strpos(DBA::serverInfo(), 'MariaDB') !== false)) {
			$ignore = '';
		} else {
			$ignore = ' IGNORE';
		}

		// Compare it
		foreach ($definition AS $name => $structure) {
			$is_new_table = false;
			$group_by = "";
			$sql3 = "";
			$is_unique = false;
			$temp_name = $name;
			if (!isset($database[$name])) {
				$r = self::createTable($name, $structure, $verbose, $action);
				if (!DBA::isResult($r)) {
					$errors .= self::printUpdateError($name);
				}
				$is_new_table = true;
			} else {
				foreach ($structure["indexes"] AS $indexname => $fieldnames) {
					if (isset($database[$name]["indexes"][$indexname])) {
						$current_index_definition = implode(",",$database[$name]["indexes"][$indexname]);
					} else {
						$current_index_definition = "__NOT_SET__";
					}
					$new_index_definition = implode(",",$fieldnames);
					if ($current_index_definition != $new_index_definition) {
						if ($fieldnames[0] == "UNIQUE") {
							$is_unique = true;
							if ($ignore == "") {
								$temp_name = "temp-".$name;
							}
						}
					}
				}

				/*
				 * Drop the index if it isn't present in the definition
				 * or the definition differ from current status
				 * and index name doesn't start with "local_"
				 */
				foreach ($database[$name]["indexes"] as $indexname => $fieldnames) {
					$current_index_definition = implode(",",$fieldnames);
					if (isset($structure["indexes"][$indexname])) {
						$new_index_definition = implode(",",$structure["indexes"][$indexname]);
					} else {
						$new_index_definition = "__NOT_SET__";
					}
					if ($current_index_definition != $new_index_definition && substr($indexname, 0, 6) != 'local_') {
						$sql2=self::dropIndex($indexname);
						if ($sql3 == "") {
							$sql3 = "ALTER".$ignore." TABLE `".$temp_name."` ".$sql2;
						} else {
							$sql3 .= ", ".$sql2;
						}
					}
				}
				// Compare the field structure field by field
				foreach ($structure["fields"] AS $fieldname => $parameters) {
					if (!isset($database[$name]["fields"][$fieldname])) {
						$sql2=self::addTableField($fieldname, $parameters);
						if ($sql3 == "") {
							$sql3 = "ALTER" . $ignore . " TABLE `".$temp_name."` ".$sql2;
						} else {
							$sql3 .= ", ".$sql2;
						}
					} else {
						// Compare the field definition
						$field_definition = $database[$name]["fields"][$fieldname];

						// Remove the relation data that is used for the referential integrity
						unset($parameters['relation']);

						// We change the collation after the indexes had been changed.
						// This is done to avoid index length problems.
						// So here we always ensure that there is no need to change it.
						unset($parameters['Collation']);
						unset($field_definition['Collation']);

						// Only update the comment when it is defined
						if (!isset($parameters['comment'])) {
							$parameters['comment'] = "";
						}

						$current_field_definition = DBA::cleanQuery(implode(",", $field_definition));
						$new_field_definition = DBA::cleanQuery(implode(",", $parameters));
						if ($current_field_definition != $new_field_definition) {
							$sql2 = self::modifyTableField($fieldname, $parameters);
							if ($sql3 == "") {
								$sql3 = "ALTER" . $ignore . " TABLE `".$temp_name."` ".$sql2;
							} else {
								$sql3 .= ", ".$sql2;
							}
						}
					}
				}
			}

			/*
			 * Create the index if the index don't exists in database
			 * or the definition differ from the current status.
			 * Don't create keys if table is new
			 */
			if (!$is_new_table) {
				foreach ($structure["indexes"] AS $indexname => $fieldnames) {
					if (isset($database[$name]["indexes"][$indexname])) {
						$current_index_definition = implode(",",$database[$name]["indexes"][$indexname]);
					} else {
						$current_index_definition = "__NOT_SET__";
					}
					$new_index_definition = implode(",",$fieldnames);
					if ($current_index_definition != $new_index_definition) {
						$sql2 = self::createIndex($indexname, $fieldnames);

						// Fetch the "group by" fields for unique indexes
						if ($fieldnames[0] == "UNIQUE") {
							$group_by = self::groupBy($indexname, $fieldnames);
						}
						if ($sql2 != "") {
							if ($sql3 == "") {
								$sql3 = "ALTER" . $ignore . " TABLE `".$temp_name."` ".$sql2;
							} else {
								$sql3 .= ", ".$sql2;
							}
						}
					}
				}

				if (isset($database[$name]["table_status"]["Comment"])) {
					if ($database[$name]["table_status"]["Comment"] != $structure['comment']) {
						$sql2 = "COMMENT = '".DBA::escape($structure['comment'])."'";

						if ($sql3 == "") {
							$sql3 = "ALTER" . $ignore . " TABLE `".$temp_name."` ".$sql2;
						} else {
							$sql3 .= ", ".$sql2;
						}
					}
				}

				if (isset($database[$name]["table_status"]["Engine"]) && isset($structure['engine'])) {
					if ($database[$name]["table_status"]["Engine"] != $structure['engine']) {
						$sql2 = "ENGINE = '".DBA::escape($structure['engine'])."'";

						if ($sql3 == "") {
							$sql3 = "ALTER" . $ignore . " TABLE `".$temp_name."` ".$sql2;
						} else {
							$sql3 .= ", ".$sql2;
						}
					}
				}

				if (isset($database[$name]["table_status"]["Collation"])) {
					if ($database[$name]["table_status"]["Collation"] != 'utf8mb4_general_ci') {
						$sql2 = "DEFAULT COLLATE utf8mb4_general_ci";

						if ($sql3 == "") {
							$sql3 = "ALTER" . $ignore . " TABLE `".$temp_name."` ".$sql2;
						} else {
							$sql3 .= ", ".$sql2;
						}
					}
				}

				if ($sql3 != "") {
					$sql3 .= "; ";
				}

				// Now have a look at the field collations
				// Compare the field structure field by field
				foreach ($structure["fields"] AS $fieldname => $parameters) {
					// Compare the field definition
					$field_definition = defaults($database[$name]["fields"], $fieldname, ['Collation' => '']);

					// Define the default collation if not given
					if (!isset($parameters['Collation']) && !empty($field_definition['Collation'])) {
						$parameters['Collation'] = 'utf8mb4_general_ci';
					} else {
						$parameters['Collation'] = null;
					}

					if ($field_definition['Collation'] != $parameters['Collation']) {
						$sql2 = self::modifyTableField($fieldname, $parameters);
						if (($sql3 == "") || (substr($sql3, -2, 2) == "; ")) {
							$sql3 .= "ALTER" . $ignore . " TABLE `".$temp_name."` ".$sql2;
						} else {
							$sql3 .= ", ".$sql2;
						}
					}
				}
			}

			if ($sql3 != "") {
				if (substr($sql3, -2, 2) != "; ") {
					$sql3 .= ";";
				}

				$field_list = '';
				if ($is_unique && $ignore == '') {
					foreach ($database[$name]["fields"] AS $fieldname => $parameters) {
						$field_list .= 'ANY_VALUE(`' . $fieldname . '`),';
					}
					$field_list = rtrim($field_list, ',');
				}

				if ($verbose) {
					// Ensure index conversion to unique removes duplicates
					if ($is_unique && ($temp_name != $name)) {
						if ($ignore != "") {
							echo "SET session old_alter_table=1;\n";
						} else {
							echo "DROP TABLE IF EXISTS `".$temp_name."`;\n";
							echo "CREATE TABLE `".$temp_name."` LIKE `".$name."`;\n";
						}
					}

					echo $sql3."\n";

					if ($is_unique && ($temp_name != $name)) {
						if ($ignore != "") {
							echo "SET session old_alter_table=0;\n";
						} else {
							echo "INSERT INTO `".$temp_name."` SELECT ".DBA::anyValueFallback($field_list)." FROM `".$name."`".$group_by.";\n";
							echo "DROP TABLE `".$name."`;\n";
							echo "RENAME TABLE `".$temp_name."` TO `".$name."`;\n";
						}
					}
				}

				if ($action) {
					if (!$install) {
						Config::set('system', 'maintenance_reason', L10n::t('%s: updating %s table.', DateTimeFormat::utcNow().' '.date('e'), $name));
					}

					// Ensure index conversion to unique removes duplicates
					if ($is_unique && ($temp_name != $name)) {
						if ($ignore != "") {
							DBA::e("SET session old_alter_table=1;");
						} else {
							$r = DBA::e("DROP TABLE IF EXISTS `".$temp_name."`;");
							if (!DBA::isResult($r)) {
								$errors .= self::printUpdateError($sql3);
								return $errors;
							}

							$r = DBA::e("CREATE TABLE `".$temp_name."` LIKE `".$name."`;");
							if (!DBA::isResult($r)) {
								$errors .= self::printUpdateError($sql3);
								return $errors;
							}
						}
					}

					$r = DBA::e($sql3);
					if (!DBA::isResult($r)) {
						$errors .= self::printUpdateError($sql3);
					}
					if ($is_unique && ($temp_name != $name)) {
						if ($ignore != "") {
							DBA::e("SET session old_alter_table=0;");
						} else {
							$r = DBA::e("INSERT INTO `".$temp_name."` SELECT ".$field_list." FROM `".$name."`".$group_by.";");
							if (!DBA::isResult($r)) {
								$errors .= self::printUpdateError($sql3);
								return $errors;
							}
							$r = DBA::e("DROP TABLE `".$name."`;");
							if (!DBA::isResult($r)) {
								$errors .= self::printUpdateError($sql3);
								return $errors;
							}
							$r = DBA::e("RENAME TABLE `".$temp_name."` TO `".$name."`;");
							if (!DBA::isResult($r)) {
								$errors .= self::printUpdateError($sql3);
								return $errors;
							}
						}
					}
				}
			}
		}

		if ($action && !$install) {
			Config::set('system', 'maintenance', 0);
			Config::set('system', 'maintenance_reason', '');

			if ($errors) {
				Config::set('system', 'dbupdate', DB_UPDATE_FAILED);
			} else {
				Config::set('system', 'dbupdate', DB_UPDATE_SUCCESSFUL);
			}
		}

		return $errors;
	}

	private static function FieldCommand($parameters, $create = true) {
		$fieldstruct = $parameters["type"];

		if (isset($parameters["Collation"])) {
			$fieldstruct .= " COLLATE ".$parameters["Collation"];
		}

		if (isset($parameters["not null"])) {
			$fieldstruct .= " NOT NULL";
		}

		if (isset($parameters["default"])) {
			if (strpos(strtolower($parameters["type"]),"int")!==false) {
				$fieldstruct .= " DEFAULT ".$parameters["default"];
			} else {
				$fieldstruct .= " DEFAULT '".$parameters["default"]."'";
			}
		}
		if (isset($parameters["extra"])) {
			$fieldstruct .= " ".$parameters["extra"];
		}

		if (isset($parameters["comment"])) {
			$fieldstruct .= " COMMENT '".DBA::escape($parameters["comment"])."'";
		}

		/*if (($parameters["primary"] != "") && $create)
			$fieldstruct .= " PRIMARY KEY";*/

		return($fieldstruct);
	}

	private static function createTable($name, $structure, $verbose, $action) {
		$r = true;

		$engine = "";
		$comment = "";
		$sql_rows = [];
		$primary_keys = [];
		foreach ($structure["fields"] AS $fieldname => $field) {
			$sql_rows[] = "`".DBA::escape($fieldname)."` ".self::FieldCommand($field);
			if (x($field,'primary') && $field['primary']!='') {
				$primary_keys[] = $fieldname;
			}
		}

		if (!empty($structure["indexes"])) {
			foreach ($structure["indexes"] AS $indexname => $fieldnames) {
				$sql_index = self::createIndex($indexname, $fieldnames, "");
				if (!is_null($sql_index)) {
					$sql_rows[] = $sql_index;
				}
			}
		}

		if (isset($structure["engine"])) {
			$engine = " ENGINE=" . $structure["engine"];
		}

		if (isset($structure["comment"])) {
			$comment = " COMMENT='" . DBA::escape($structure["comment"]) . "'";
		}

		$sql = implode(",\n\t", $sql_rows);

		$sql = sprintf("CREATE TABLE IF NOT EXISTS `%s` (\n\t", DBA::escape($name)).$sql.
				"\n)" . $engine . " DEFAULT COLLATE utf8mb4_general_ci" . $comment;
		if ($verbose) {
			echo $sql.";\n";
		}

		if ($action) {
			$r = DBA::e($sql);
		}

		return $r;
	}

	private static function addTableField($fieldname, $parameters) {
		$sql = sprintf("ADD `%s` %s", DBA::escape($fieldname), self::FieldCommand($parameters));
		return($sql);
	}

	private static function modifyTableField($fieldname, $parameters) {
		$sql = sprintf("MODIFY `%s` %s", DBA::escape($fieldname), self::FieldCommand($parameters, false));
		return($sql);
	}

	private static function dropIndex($indexname) {
		$sql = sprintf("DROP INDEX `%s`", DBA::escape($indexname));
		return($sql);
	}

	private static function createIndex($indexname, $fieldnames, $method = "ADD") {
		$method = strtoupper(trim($method));
		if ($method!="" && $method!="ADD") {
			throw new Exception("Invalid parameter 'method' in self::createIndex(): '$method'");
		}

		if ($fieldnames[0] == "UNIQUE") {
			array_shift($fieldnames);
			$method .= ' UNIQUE';
		}

		$names = "";
		foreach ($fieldnames AS $fieldname) {
			if ($names != "") {
				$names .= ",";
			}

			if (preg_match('|(.+)\((\d+)\)|', $fieldname, $matches)) {
				$names .= "`".DBA::escape($matches[1])."`(".intval($matches[2]).")";
			} else {
				$names .= "`".DBA::escape($fieldname)."`";
			}
		}

		if ($indexname == "PRIMARY") {
			return sprintf("%s PRIMARY KEY(%s)", $method, $names);
		}


		$sql = sprintf("%s INDEX `%s` (%s)", $method, DBA::escape($indexname), $names);
		return($sql);
	}

	private static function groupBy($indexname, $fieldnames) {
		if ($fieldnames[0] != "UNIQUE") {
			return "";
		}

		array_shift($fieldnames);

		$names = "";
		foreach ($fieldnames AS $fieldname) {
			if ($names != "") {
				$names .= ",";
			}

			if (preg_match('|(.+)\((\d+)\)|', $fieldname, $matches)) {
				$names .= "`".DBA::escape($matches[1])."`";
			} else {
				$names .= "`".DBA::escape($fieldname)."`";
			}
		}

		$sql = sprintf(" GROUP BY %s", $names);
		return $sql;
	}

	/**
	 * 	Check if a table exists
	 *
	 * @param string $table Table name
	 *
	 * @return boolean Does the table exist?
	 */
	public static function existsTable($table)
	{
		if (empty($table)) {
			return false;
		}

		$table = DBA::escape($table);

		$sql = "SHOW TABLES LIKE '" . $table . "';";

		$stmt = DBA::p($sql);

		if (is_bool($stmt)) {
			$retval = $stmt;
		} else {
			$retval = (DBA::numRows($stmt) > 0);
		}

		DBA::close($stmt);

		return $retval;
	}

	/**
	 * 	Check if the columns of the table exists
	 *
	 * @param string $table   Table name
	 * @param array  $columns Columns to check ( Syntax: [ $col1, $col2, .. ] )
	 *
	 * @return boolean Does the table exist?
	 */
	public static function existsColumn($table, $columns = []) {
		if (empty($table)) {
			return false;
		}

		if (is_null($columns) || empty($columns)) {
			return self::existsTable($table);
		}

		$table = DBA::escape($table);

		foreach ($columns AS $column) {
			$sql = "SHOW COLUMNS FROM `" . $table . "` LIKE '" . $column . "';";

			$stmt = DBA::p($sql);

			if (is_bool($stmt)) {
				$retval = $stmt;
			} else {
				$retval = (DBA::numRows($stmt) > 0);
			}

			DBA::close($stmt);

			if (!$retval) {
				return false;
			}
		}

		return true;
	}

	const RENAME_COLUMN = 0;
	const RENAME_PRIMARY_KEY = 1;

	/**
	 * Renames columns or the primary key of a table
	 * @todo You cannot rename a primary key if "auto increment" is set
	 *
	 * @param string $table    Table name
	 * @param array  $columns  Columns Syntax for Rename: [ $old1 => [ $new1, $type1 ], $old2 => [ $new2, $type2 ], ... ] )
	 *                                 Syntax for Primary Key: [ $col1, $col2, ...] )
	 * @param int    $type     The type of renaming (Default is Column)
	 *
	 * @return boolean Was the renaming successful?
	 *
	 */
	public static function rename($table, $columns, $type = self::RENAME_COLUMN) {
		if (empty($table) || empty($columns)) {
			return false;
		}

		if (!is_array($columns)) {
			return false;
		}

		$table = DBA::escape($table);

		$sql = "ALTER TABLE `" . $table . "`";
		switch ($type) {
			case self::RENAME_COLUMN:
				if (!self::existsColumn($table, array_keys($columns))) {
					return false;
				}
				$sql .= implode(',', array_map(
					function ($to, $from) {
						return " CHANGE `" . $from . "` `" . $to[0] . "` " . $to[1];
					},
					$columns,
					array_keys($columns)
				));
				break;
			case self::RENAME_PRIMARY_KEY:
				if (!self::existsColumn($table, $columns)) {
					return false;
				}
				$sql .= " DROP PRIMARY KEY, ADD PRIMARY KEY(`" . implode('`, `', $columns) . "`)";
				break;
			default:
				return false;
		}

		$sql .= ";";

		$stmt = DBA::p($sql);

		if (is_bool($stmt)) {
			$retval = $stmt;
		} else {
			$retval = true;
		}

		DBA::close($stmt);

		return $retval;
	}

	/**
	 * Loads the database structure definition from the /config/dbstructure.json file
	 *
	 * Expected format:
	 * "table_name": {
	 *   "comment": "meaningful table comment",
	 *   "fields": {
	 *     "field_name1": {"type": "int unsigned", "not null": "1", "extra": "auto_increment", "primary": "1", "comment": "meaningful field comment"},
	 *     "field_name2": {"type": "varchar(50)", "not null": "1", "default": "", "comment": "meaningful field comment"},
	 *   },
	 *   "indexes": {
	 *     "PRIMARY": ["field_name1"],
	 *     "name": ["UNIQUE", "field_name2"]
	 *   }
	 * }
	 *
	 * @return array
	 * @throws Exception
	 */
	public static function definition() {
		$a = \Friendica\BaseObject::getApp();

		$filename = $a->getBasePath() . '/config/dbstructure.json';

		if (!is_readable($filename)) {
			throw new Exception('Missing database structure config file config/dbstructure.json');
		}

		$json = file_get_contents($filename);

		$database = json_decode($json, true);

		if (!$database) {
			throw new Exception('Corrupted database structure config file config/dbstructure.json');
		}

		Addon::callHooks('dbstructure_definition', $database);

		return $database;
	}
}