<?php
namespace ActiriseAdmin\Includes;

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly
}

/**
 * Mutual exclusion for a migrations run.
 *
 * Migrations used to have a single entry point, `admin_init`. The cron fallback
 * adds a second one, and the two fire together right after an update: without
 * a lock both would read the same "not yet applied" list and play the same
 * migration twice.
 *
 * The lock is a row of the core options table, taken with `INSERT IGNORE` on
 * its unique `option_name`, so the database settles the race rather than a read
 * followed by a write. `add_option()` cannot do this: its
 * `ON DUPLICATE KEY UPDATE` succeeds for both callers. A lock left behind by a
 * run that died is taken over once it is older than {@see self::TTL}.
 *
 * A caller that finds the lock held skips its run instead of waiting: the
 * holder is already playing the same migrations, and the next admin load or
 * cron tick retries anything left.
 *
 * @link       https://actirise.com
 * @since      4.3.2
 * @package    actirise
 * @subpackage actirise/admin/includes
 * @author     actirise <wordpress@actirise.com>
 */
final class MigrationsLock {
	/**
	 * Name of the options row holding the lock.
	 *
	 * @since 4.3.2
	 * @var   string
	 */
	const OPTION = 'actirise_migrations_lock';

	/**
	 * Age after which a held lock is considered abandoned, in seconds.
	 *
	 * @since 4.3.2
	 * @var   int
	 */
	const TTL = 600;

	/**
	 * Take the lock.
	 *
	 * @since 4.3.2
	 * @return bool Whether this caller now holds it.
	 */
	public static function acquire() {
		/** @var \wpdb $wpdb */
		global $wpdb;

		$now = (string) time();

		$insert = $wpdb->prepare(
			// @phpstan-ignore-next-line argument.type
			"INSERT IGNORE INTO {$wpdb->options} (option_name, option_value, autoload) VALUES (%s, %s, 'no')", // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
			self::OPTION,
			$now
		);

		if ( is_string( $insert ) && 1 === $wpdb->query( $insert ) ) { // phpcs:ignore WordPress.DB.DirectDatabaseQuery, WordPress.DB.PreparedSQL.NotPrepared -- Prepared just above.
			return true;
		}

		$held_since = $wpdb->get_var( // phpcs:ignore WordPress.DB.DirectDatabaseQuery
			$wpdb->prepare(
				// @phpstan-ignore-next-line argument.type
				"SELECT option_value FROM {$wpdb->options} WHERE option_name = %s", // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
				self::OPTION
			)
		);

		if ( is_numeric( $held_since ) && (int) $now - (int) $held_since < self::TTL ) {
			return false;
		}

		// Conditional on the value just read, so of two callers finding the same
		// stale lock only one takes it over.
		$takeover = $wpdb->prepare(
			// @phpstan-ignore-next-line argument.type
			"UPDATE {$wpdb->options} SET option_value = %s WHERE option_name = %s AND option_value = %s", // phpcs:ignore WordPress.DB.PreparedSQL.InterpolatedNotPrepared
			$now,
			self::OPTION,
			is_scalar( $held_since ) ? (string) $held_since : ''
		);

		return is_string( $takeover ) && 1 === $wpdb->query( $takeover ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery, WordPress.DB.PreparedSQL.NotPrepared -- Prepared just above.
	}

	/**
	 * Release the lock.
	 *
	 * @since 4.3.2
	 * @return void
	 */
	public static function release() {
		/** @var \wpdb $wpdb */
		global $wpdb;

		$wpdb->delete( $wpdb->options, array( 'option_name' => self::OPTION ) ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery
	}
}