<?php
/**
 * Plugin upgrades.
 *
 * @package Yangra\Conditional
 */

namespace Yangra\Conditional;

defined( 'ABSPATH' ) || exit;

/**
 * Runs the upgrade steps when the plugin's code is newer than the version
 * recorded in the database.
 *
 * Updates don't fire the activation hook, so the check runs on every load. It
 * compares VERSION_OPTION with YANGRA_CONDITIONAL_VERSION, runs every step for
 * a version above the saved one in order (settings, options, cron events),
 * then saves the new version. Rules are not rewritten here: they're migrated
 * in memory when read, and saved in the new format on their next save.
 */
class Upgrader {

	/**
	 * Option holding the plugin version the database was last upgraded to.
	 */
	const VERSION_OPTION = 'yangra_conditional_version';

	/**
	 * Upgrade steps, as version => callable, or null for the built-in steps().
	 *
	 * @var array<string, callable>|null
	 */
	private $steps;

	/**
	 * The plugin version the code is at.
	 *
	 * @var string
	 */
	private $current;

	/**
	 * Constructor.
	 *
	 * @param array<string, callable>|null $steps   Upgrade steps; null for the built-in ones.
	 * @param string|null                  $current The code's version; null for YANGRA_CONDITIONAL_VERSION.
	 */
	public function __construct( ?array $steps = null, ?string $current = null ) {
		$this->steps   = $steps;
		$this->current = null !== $current ? $current : YANGRA_CONDITIONAL_VERSION;
	}

	/**
	 * Registers hooks. Runs early on `init`, before other code reads settings.
	 *
	 * @return void
	 */
	public function register(): void {
		add_action( 'init', array( $this, 'maybe_upgrade' ), 1 );
	}

	/**
	 * Runs the steps for every version above the saved one, then saves the
	 * current version. Does nothing when the saved version is current or newer
	 * (e.g. after a downgrade).
	 *
	 * A missing option means the version was never recorded, so every step
	 * runs. Steps must be safe to run more than once.
	 *
	 * @return void
	 */
	public function maybe_upgrade(): void {
		$saved = (string) get_option( self::VERSION_OPTION, '' );
		if ( '' !== $saved && version_compare( $saved, $this->current, '>=' ) ) {
			return;
		}

		$steps = $this->steps();
		uksort( $steps, 'version_compare' );
		foreach ( $steps as $version => $step ) {
			if ( version_compare( (string) $version, $this->current, '>' ) ) {
				break;
			}
			if ( '' === $saved || version_compare( $saved, (string) $version, '<' ) ) {
				call_user_func( $step );
			}
		}

		update_option( self::VERSION_OPTION, $this->current, false );
	}

	/**
	 * Upgrade steps, as the version that needs them => callable. Add a step
	 * whenever a release changes stored settings, options or cron events.
	 *
	 * @return array<string, callable>
	 */
	public function steps(): array {
		if ( null !== $this->steps ) {
			return $this->steps;
		}

		return array();
	}
}