<?php
/**
 * @copyright Copyright (c) 2017 Joas Schilling <coding@schilljs.com>
 * @copyright Copyright (c) 2017, ownCloud GmbH
 *
 * @author Joas Schilling <coding@schilljs.com>
 *
 * @license AGPL-3.0
 *
 * This code is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * 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 Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License, version 3,
 * along with this program.  If not, see <http://www.gnu.org/licenses/>
 *
 */

namespace OC\DB;

use Doctrine\DBAL\Schema\SchemaException;
use OC\IntegrityCheck\Helpers\AppLocator;
use OC\Migration\SimpleOutput;
use OCP\AppFramework\App;
use OCP\AppFramework\QueryException;
use OCP\IDBConnection;
use OCP\Migration\IMigrationStep;
use OCP\Migration\IOutput;
use Doctrine\DBAL\Schema\Column;
use Doctrine\DBAL\Schema\Table;
use Doctrine\DBAL\Types\Type;

class MigrationService {

	/** @var boolean */
	private $migrationTableCreated;
	/** @var array */
	private $migrations;
	/** @var IOutput */
	private $output;
	/** @var Connection */
	private $connection;
	/** @var string */
	private $appName;

	/**
	 * MigrationService constructor.
	 *
	 * @param $appName
	 * @param IDBConnection $connection
	 * @param AppLocator $appLocator
	 * @param IOutput|null $output
	 * @throws \Exception
	 */
	public function __construct($appName, IDBConnection $connection, IOutput $output = null, AppLocator $appLocator = null) {
		$this->appName = $appName;
		$this->connection = $connection;
		$this->output = $output;
		if (null === $this->output) {
			$this->output = new SimpleOutput(\OC::$server->getLogger(), $appName);
		}

		if ($appName === 'core') {
			$this->migrationsPath = \OC::$SERVERROOT . '/core/Migrations';
			$this->migrationsNamespace = 'OC\\Core\\Migrations';
		} else {
			if (null === $appLocator) {
				$appLocator = new AppLocator();
			}
			$appPath = $appLocator->getAppPath($appName);
			$namespace = App::buildAppNamespace($appName);
			$this->migrationsPath = "$appPath/lib/Migration";
			$this->migrationsNamespace = $namespace . '\\Migration';
		}
	}

	/**
	 * Returns the name of the app for which this migration is executed
	 *
	 * @return string
	 */
	public function getApp() {
		return $this->appName;
	}

	/**
	 * @return bool
	 * @codeCoverageIgnore - this will implicitly tested on installation
	 */
	private function createMigrationTable() {
		if ($this->migrationTableCreated) {
			return false;
		}

		$schema = new SchemaWrapper($this->connection);

		/**
		 * We drop the table when it has different columns or the definition does not
		 * match. E.g. ownCloud uses a length of 177 for app and 14 for version.
		 */
		try {
			$table = $schema->getTable('migrations');
			$columns = $table->getColumns();

			if (count($columns) === 2) {
				try {
					$column = $table->getColumn('app');
					$schemaMismatch = $column->getLength() !== 255;

					if (!$schemaMismatch) {
						$column = $table->getColumn('version');
						$schemaMismatch = $column->getLength() !== 255;
					}
				} catch (SchemaException $e) {
					// One of the columns is missing
					$schemaMismatch = true;
				}

				if (!$schemaMismatch) {
					// Table exists and schema matches: return back!
					$this->migrationTableCreated = true;
					return false;
				}
			}

			// Drop the table, when it didn't match our expectations.
			$this->connection->dropTable('migrations');

			// Recreate the schema after the table was dropped.
			$schema = new SchemaWrapper($this->connection);

		} catch (SchemaException $e) {
			// Table not found, no need to panic, we will create it.
		}

		$table = $schema->createTable('migrations');
		$table->addColumn('app', Type::STRING, ['length' => 255]);
		$table->addColumn('version', Type::STRING, ['length' => 255]);
		$table->setPrimaryKey(['app', 'version']);

		$this->connection->migrateToSchema($schema->getWrappedSchema());

		$this->migrationTableCreated = true;

		return true;
	}

	/**
	 * Returns all versions which have already been applied
	 *
	 * @return string[]
	 * @codeCoverageIgnore - no need to test this
	 */
	public function getMigratedVersions() {
		$this->createMigrationTable();
		$qb = $this->connection->getQueryBuilder();

		$qb->select('version')
			->from('migrations')
			->where($qb->expr()->eq('app', $qb->createNamedParameter($this->getApp())))
			->orderBy('version');

		$result = $qb->execute();
		$rows = $result->fetchAll(\PDO::FETCH_COLUMN);
		$result->closeCursor();

		return $rows;
	}

	/**
	 * Returns all versions which are available in the migration folder
	 *
	 * @return array
	 */
	public function getAvailableVersions() {
		$this->ensureMigrationsAreLoaded();
		return array_map('strval', array_keys($this->migrations));
	}

	protected function findMigrations() {
		$directory = realpath($this->migrationsPath);
		if (!file_exists($directory) || !is_dir($directory)) {
			return [];
		}

		$iterator = new \RegexIterator(
			new \RecursiveIteratorIterator(
				new \RecursiveDirectoryIterator($directory, \FilesystemIterator::SKIP_DOTS),
				\RecursiveIteratorIterator::LEAVES_ONLY
			),
			'#^.+\\/Version[^\\/]{1,255}\\.php$#i',
			\RegexIterator::GET_MATCH);

		$files = array_keys(iterator_to_array($iterator));
		uasort($files, function ($a, $b) {
			preg_match('/^Version(\d+)Date(\d+)\\.php$/', basename($a), $matchA);
			preg_match('/^Version(\d+)Date(\d+)\\.php$/', basename($b), $matchB);
			if (!empty($matchA) && !empty($matchB)) {
				if ($matchA[1] !== $matchB[1]) {
					return ($matchA[1] < $matchB[1]) ? -1 : 1;
				}
				return ($matchA[2] < $matchB[2]) ? -1 : 1;
			}
			return (basename($a) < basename($b)) ? -1 : 1;
		});

		$migrations = [];

		foreach ($files as $file) {
			$className = basename($file, '.php');
			$version = (string) substr($className, 7);
			if ($version === '0') {
				throw new \InvalidArgumentException(
					"Cannot load a migrations with the name '$version' because it is a reserved number"
				);
			}
			$migrations[$version] = sprintf('%s\\%s', $this->migrationsNamespace, $className);
		}

		return $migrations;
	}

	/**
	 * @param string $to
	 * @return string[]
	 */
	private function getMigrationsToExecute($to) {
		$knownMigrations = $this->getMigratedVersions();
		$availableMigrations = $this->getAvailableVersions();

		$toBeExecuted = [];
		foreach ($availableMigrations as $v) {
			if ($to !== 'latest' && $v > $to) {
				continue;
			}
			if ($this->shallBeExecuted($v, $knownMigrations)) {
				$toBeExecuted[] = $v;
			}
		}

		return $toBeExecuted;
	}

	/**
	 * @param string $m
	 * @param string[] $knownMigrations
	 * @return bool
	 */
	private function shallBeExecuted($m, $knownMigrations) {
		if (in_array($m, $knownMigrations)) {
			return false;
		}

		return true;
	}

	/**
	 * @param string $version
	 */
	private function markAsExecuted($version) {
		$this->connection->insertIfNotExist('*PREFIX*migrations', [
			'app' => $this->appName,
			'version' => $version
		]);
	}

	/**
	 * Returns the name of the table which holds the already applied versions
	 *
	 * @return string
	 */
	public function getMigrationsTableName() {
		return $this->connection->getPrefix() . 'migrations';
	}

	/**
	 * Returns the namespace of the version classes
	 *
	 * @return string
	 */
	public function getMigrationsNamespace() {
		return $this->migrationsNamespace;
	}

	/**
	 * Returns the directory which holds the versions
	 *
	 * @return string
	 */
	public function getMigrationsDirectory() {
		return $this->migrationsPath;
	}

	/**
	 * Return the explicit version for the aliases; current, next, prev, latest
	 *
	 * @param string $alias
	 * @return mixed|null|string
	 */
	public function getMigration($alias) {
		switch($alias) {
			case 'current':
				return $this->getCurrentVersion();
			case 'next':
				return $this->getRelativeVersion($this->getCurrentVersion(), 1);
			case 'prev':
				return $this->getRelativeVersion($this->getCurrentVersion(), -1);
			case 'latest':
				$this->ensureMigrationsAreLoaded();

				$migrations = $this->getAvailableVersions();
				return @end($migrations);
		}
		return '0';
	}

	/**
	 * @param string $version
	 * @param int $delta
	 * @return null|string
	 */
	private function getRelativeVersion($version, $delta) {
		$this->ensureMigrationsAreLoaded();

		$versions = $this->getAvailableVersions();
		array_unshift($versions, 0);
		$offset = array_search($version, $versions, true);
		if ($offset === false || !isset($versions[$offset + $delta])) {
			// Unknown version or delta out of bounds.
			return null;
		}

		return (string) $versions[$offset + $delta];
	}

	/**
	 * @return string
	 */
	private function getCurrentVersion() {
		$m = $this->getMigratedVersions();
		if (count($m) === 0) {
			return '0';
		}
		$migrations = array_values($m);
		return @end($migrations);
	}

	/**
	 * @param string $version
	 * @return string
	 * @throws \InvalidArgumentException
	 */
	private function getClass($version) {
		$this->ensureMigrationsAreLoaded();

		if (isset($this->migrations[$version])) {
			return $this->migrations[$version];
		}

		throw new \InvalidArgumentException("Version $version is unknown.");
	}

	/**
	 * Allows to set an IOutput implementation which is used for logging progress and messages
	 *
	 * @param IOutput $output
	 */
	public function setOutput(IOutput $output) {
		$this->output = $output;
	}

	/**
	 * Applies all not yet applied versions up to $to
	 *
	 * @param string $to
	 * @throws \InvalidArgumentException
	 */
	public function migrate($to = 'latest') {
		// read known migrations
		$toBeExecuted = $this->getMigrationsToExecute($to);
		foreach ($toBeExecuted as $version) {
			$this->executeStep($version);
		}
	}

	/**
	 * @param string $version
	 * @return mixed
	 * @throws \InvalidArgumentException
	 */
	protected function createInstance($version) {
		$class = $this->getClass($version);
		try {
			$s = \OC::$server->query($class);
		} catch (QueryException $e) {
			if (class_exists($class)) {
				$s = new $class();
			} else {
				throw new \InvalidArgumentException("Migration step '$class' is unknown");
			}
		}

		return $s;
	}

	/**
	 * Executes one explicit version
	 *
	 * @param string $version
	 * @throws \InvalidArgumentException
	 */
	public function executeStep($version) {
		$instance = $this->createInstance($version);
		if (!$instance instanceof IMigrationStep) {
			throw new \InvalidArgumentException('Not a valid migration');
		}

		$instance->preSchemaChange($this->output, function() {
			return new SchemaWrapper($this->connection);
		}, ['tablePrefix' => $this->connection->getPrefix()]);

		$toSchema = $instance->changeSchema($this->output, function() {
			return new SchemaWrapper($this->connection);
		}, ['tablePrefix' => $this->connection->getPrefix()]);

		if ($toSchema instanceof SchemaWrapper) {
			$this->connection->migrateToSchema($toSchema->getWrappedSchema());
			$toSchema->performDropTableCalls();
		}

		$instance->postSchemaChange($this->output, function() {
			return new SchemaWrapper($this->connection);
		}, ['tablePrefix' => $this->connection->getPrefix()]);

		$this->markAsExecuted($version);
	}

	private function ensureMigrationsAreLoaded() {
		if (empty($this->migrations)) {
			$this->migrations = $this->findMigrations();
		}
	}
}