<?php
/**
 * Migration runner.
 *
 * @package HostKhata
 */

namespace HostKhata\Database;

defined( 'ABSPATH' ) || exit;

use HostKhata\Database\Migrations\Migration;
use HostKhata\Database\Migrations\Migration0001CreateTables;
use HostKhata\Database\Migrations\Migration0002AddCustomerNames;
use HostKhata\Database\Migrations\Migration0003AddProductAddons;
use Throwable;
use wpdb;

/**
 * Runs pending migrations in order and records the schema version.
 *
 * @since 0.1.0
 */
final class Migrator {

	/**
	 * Option holding the installed schema version.
	 */
	const VERSION_OPTION = 'hostkhata_db_version';

	/**
	 * Option holding the last migration error message.
	 */
	const ERROR_OPTION = 'hostkhata_migration_error';

	/**
	 * Option used as a lock while migrating.
	 */
	const LOCK_OPTION = 'hostkhata_migration_lock';

	/**
	 * A lock older than this many seconds is considered stale.
	 */
	const LOCK_TTL = 300;

	/**
	 * Database object.
	 *
	 * @var wpdb
	 */
	private $wpdb;

	/**
	 * Constructor.
	 *
	 * @param wpdb $wpdb WordPress database object.
	 */
	public function __construct( wpdb $wpdb ) {
		$this->wpdb = $wpdb;
	}

	/**
	 * All known migrations, ordered by version.
	 *
	 * @since 0.1.0
	 *
	 * @return Migration[]
	 */
	public function migrations(): array {
		$migrations = array(
			new Migration0001CreateTables(),
			new Migration0002AddCustomerNames(),
			new Migration0003AddProductAddons(),
		);

		usort(
			$migrations,
			static function ( Migration $a, Migration $b ) {
				return $a->version() <=> $b->version();
			}
		);

		return $migrations;
	}

	/**
	 * Installed schema version, 0 when nothing was installed yet.
	 *
	 * @since 0.1.0
	 *
	 * @return int
	 */
	public function current_version(): int {
		return (int) get_option( self::VERSION_OPTION, 0 );
	}

	/**
	 * Highest schema version known to the code.
	 *
	 * @since 0.1.0
	 *
	 * @return int
	 */
	public function latest_version(): int {
		$latest = 0;

		foreach ( $this->migrations() as $migration ) {
			$latest = max( $latest, $migration->version() );
		}

		return $latest;
	}

	/**
	 * Tells whether the database is behind the code.
	 *
	 * @since 0.1.0
	 *
	 * @return bool
	 */
	public function needs_upgrade(): bool {
		return $this->current_version() < $this->latest_version();
	}

	/**
	 * Runs every pending migration.
	 *
	 * @since 0.1.0
	 *
	 * @return bool True when the database is up to date afterwards.
	 */
	public function migrate(): bool {
		if ( ! $this->needs_upgrade() ) {
			return true;
		}

		if ( ! $this->acquire_lock() ) {
			return false;
		}

		$ok = true;

		try {
			foreach ( $this->migrations() as $migration ) {
				if ( $migration->version() <= $this->current_version() ) {
					continue;
				}

				$migration->up( $this->wpdb );
				update_option( self::VERSION_OPTION, $migration->version(), true );
			}

			delete_option( self::ERROR_OPTION );
		} catch ( Throwable $error ) {
			$ok = false;
			update_option( self::ERROR_OPTION, $error->getMessage(), false );
		}

		delete_option( self::LOCK_OPTION );

		return $ok;
	}

	/**
	 * Last migration error, or an empty string.
	 *
	 * @since 0.1.0
	 *
	 * @return string
	 */
	public function last_error(): string {
		return (string) get_option( self::ERROR_OPTION, '' );
	}

	/**
	 * Takes the migration lock. add_option() is atomic, so only one request wins.
	 *
	 * @return bool
	 */
	private function acquire_lock(): bool {
		if ( add_option( self::LOCK_OPTION, time(), '', false ) ) {
			return true;
		}

		$started = (int) get_option( self::LOCK_OPTION, 0 );

		if ( time() - $started > self::LOCK_TTL ) {
			update_option( self::LOCK_OPTION, time(), false );
			return true;
		}

		return false;
	}
}