<?php
/**
 * Atomic worker lock for one migration at a time.
 *
 * @package Shiftora\Migration
 */

declare(strict_types=1);

namespace Shiftora\Migration;

// Prevent direct file access.
if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Single-statement UPDATE guard on the migration row.
 *
 * Each method is one UPDATE whose affected-row count is the verdict, so two
 * workers cannot both win. An owner token scopes release so a stale worker
 * never touches a newer lock.
 */
final class MigrationWorkerLock {

	public const DEFAULT_TTL = 90;

	/** Token of the lock this instance holds; null when not held. */
	private ?string $token = null;

	/** @var callable(): string */
	private $clock;

	public function __construct(
		private readonly \wpdb $wpdb,
		?callable $clock = null
	) {
		$this->clock = $clock ?? static fn(): string => current_time( 'mysql', true );
	}

	public function set_clock( callable $clock ): void {
		$this->clock = $clock;
	}

		/**
		 * The token this instance holds, or null when it does not hold the lock.
		 * Callers embed it in guarded row updates so they apply only while the claim is theirs.
		 */
	public function token(): ?string {
		return $this->token;
	}

	private function now(): string {
		return ( $this->clock )();
	}

	private function fresh_token(): string {
		return bin2hex( random_bytes( 16 ) );
	}

	/**
	 * Claim the lock for a migration. Returns true only when this call won.
	 */
	public function claim( int $migration_id ): bool {
		$wpdb = $this->wpdb;

		$now     = $this->now();
		$expires = gmdate( 'Y-m-d H:i:s', strtotime( $now ) + self::DEFAULT_TTL );
		$token   = $this->fresh_token();

		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- custom table, fresh read required
		$affected = (int) $wpdb->query(
			$wpdb->prepare(
				'UPDATE %i
					SET worker_lock_owner = %s, worker_lock_expires = %s, updated_at = %s
				 WHERE id = %d
				   AND (worker_lock_owner IS NULL OR worker_lock_expires IS NULL OR worker_lock_expires < %s)',
				$wpdb->prefix . 'shiftora_migrations',
				$token,
				$expires,
				$now,
				$migration_id,
				$now
			)
		);

		if ( $affected > 0 ) {
			$this->token = $token;
		}

		return $affected > 0;
	}

	/**
	 * Release the lock this instance holds. Scoped to the token so a stale
	 * worker cannot release a newer claim.
	 */
	public function release( int $migration_id ): void {
		$wpdb = $this->wpdb;

		if ( null === $this->token ) {
			return;
		}

		// phpcs:ignore WordPress.DB.DirectDatabaseQuery -- custom table, fresh read required
		$wpdb->query(
			$wpdb->prepare(
				'UPDATE %i
					SET worker_lock_owner = NULL, worker_lock_expires = NULL, updated_at = %s
				 WHERE id = %d AND worker_lock_owner = %s',
				$wpdb->prefix . 'shiftora_migrations',
				$this->now(),
				$migration_id,
				$this->token
			)
		);

		$this->token = null;
	}
}