<?php
/**
*
* @package db
* @copyright (c) 2011 phpBB Group
* @license http://opensource.org/licenses/gpl-license.php GNU Public License v2
*
*/

namespace phpbb\db\migration;

/**
* Abstract base class for database migrations
*
* Each migration consists of a set of schema and data changes to be implemented
* in a subclass. This class provides various utility methods to simplify editing
* a phpBB.
*
* @package db
*/
abstract class migration
{
	/** @var \phpbb\config\config */
	protected $config;

	/** @var \phpbb\db\driver\driver */
	protected $db;

	/** @var \phpbb\db\tools */
	protected $db_tools;

	/** @var string */
	protected $table_prefix;

	/** @var string */
	protected $phpbb_root_path;

	/** @var string */
	protected $php_ext;

	/** @var array Errors, if any occurred */
	protected $errors;

	/** @var array List of queries executed through $this->sql_query() */
	protected $queries = array();

	/**
	* Constructor
	*
	* @param \phpbb\config\config $config
	* @param \phpbb\db\driver\driver $db
	* @param \phpbb\db\tools $db_tools
	* @param string $phpbb_root_path
	* @param string $php_ext
	* @param string $table_prefix
	*/
	public function __construct(\phpbb\config\config $config, \phpbb\db\driver\driver $db, \phpbb\db\tools $db_tools, $phpbb_root_path, $php_ext, $table_prefix)
	{
		$this->config = $config;
		$this->db = $db;
		$this->db_tools = $db_tools;
		$this->table_prefix = $table_prefix;

		$this->phpbb_root_path = $phpbb_root_path;
		$this->php_ext = $php_ext;

		$this->errors = array();
	}

	/**
	* Defines other migrations to be applied first
	*
	* @return array An array of migration class names
	*/
	static public function depends_on()
	{
		return array();
	}

	/**
	* Allows you to check if the migration is effectively installed (entirely optional)
	*
	* This is checked when a migration is installed. If true is returned, the migration will be set as
	* installed without performing the database changes.
	* This function is intended to help moving to migrations from a previous database updater, where some
	* migrations may have been installed already even though they are not yet listed in the migrations table.
	*
	* @return bool True if this migration is installed, False if this migration is not installed (checked on install)
	*/
	public function effectively_installed()
	{
		return false;
	}

	/**
	* Updates the database schema by providing a set of change instructions
	*
	* @return array Array of schema changes (compatible with db_tools->perform_schema_changes())
	*/
	public function update_schema()
	{
		return array();
	}

	/**
	* Reverts the database schema by providing a set of change instructions
	*
	* @return array Array of schema changes (compatible with db_tools->perform_schema_changes())
	*/
	public function revert_schema()
	{
		return array();
	}

	/**
	* Updates data by returning a list of instructions to be executed
	*
	* @return array Array of data update instructions
	*/
	public function update_data()
	{
		return array();
	}

	/**
	* Reverts data by returning a list of instructions to be executed
	*
	* @return array Array of data instructions that will be performed on revert
	* 	NOTE: calls to tools (such as config.add) are automatically reverted when
	* 		possible, so you should not attempt to revert those, this is mostly for
	* 		otherwise unrevertable calls (custom functions for example)
	*/
	public function revert_data()
	{
		return array();
	}

	/**
	* Wrapper for running queries to generate user feedback on updates
	*
	* @param string $sql SQL query to run on the database
	* @return mixed Query result from db->sql_query()
	*/
	protected function sql_query($sql)
	{
		$this->queries[] = $sql;

		$this->db->sql_return_on_error(true);

		if ($sql === 'begin')
		{
			$result = $this->db->sql_transaction('begin');
		}
		else if ($sql === 'commit')
		{
			$result = $this->db->sql_transaction('commit');
		}
		else
		{
			$result = $this->db->sql_query($sql);
			if ($this->db->sql_error_triggered)
			{
				$this->errors[] = array(
					'sql'	=> $this->db->sql_error_sql,
					'code'	=> $this->db->sql_error_returned,
				);
			}
		}

		$this->db->sql_return_on_error(false);

		return $result;
	}

	/**
	* Get the list of queries run
	*
	* @return array
	*/
	public function get_queries()
	{
		return $this->queries;
	}
}