<?php
/**
 * Atomic option-row locks.
 *
 * @package AdminPowerups
 */

namespace SmartWP\AdminPowerups\Support;

defined( 'ABSPATH' ) || exit;

/**
 * A lock held as one option row (autoload off) whose value is `expiry:random`.
 *
 * Taken with INSERT IGNORE, so only one request can get it; a lock left by a request that died
 * is taken over once its expiry passed. Raw queries on purpose: add_option() upserts, so two
 * requests could both "get" the lock. The options cache is cleared after every write.
 *
 * @since 1.0.0
 */
final class Lock {

	/**
	 * Take a lock. Returns the token to release it with, or '' when another request holds it.
	 *
	 * @since 1.0.0
	 * @param string $name Option name of the lock row (use an `apwc_` name).
	 * @param int    $ttl  Seconds after which the lock counts as abandoned and may be taken over.
	 * @return string
	 */
	public static function acquire( string $name, int $ttl = 120 ): string {
		global $wpdb;
		if ( '' === $name ) {
			return '';
		}
		$now   = time();
		$token = ( $now + max( 1, $ttl ) ) . ':' . wp_generate_password( 12, false );
		// phpcs:disable WordPress.DB.DirectDatabaseQuery -- atomic lock row; must not be cached.
		$taken = (int) $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO %i (option_name, option_value, autoload) VALUES (%s, %s, 'off')", $wpdb->options, $name, $token ) );
		if ( ! $taken ) {
			// A request that died leaves its lock: take it over once it expired.
			$taken = (int) $wpdb->query( $wpdb->prepare( "UPDATE %i SET option_value = %s WHERE option_name = %s AND CAST( SUBSTRING_INDEX( option_value, ':', 1 ) AS UNSIGNED ) < %d", $wpdb->options, $token, $name, $now ) );
		}
		// phpcs:enable
		self::forget_cache( $name );
		return $taken ? $token : '';
	}

	/**
	 * Release a lock, only when it is still ours (its value equals the token).
	 *
	 * @since 1.0.0
	 * @param string $name  Option name of the lock row.
	 * @param string $token Token returned by acquire().
	 * @return void
	 */
	public static function release( string $name, string $token ): void {
		global $wpdb;
		if ( '' === $name || '' === $token ) {
			return;
		}
		$wpdb->query( $wpdb->prepare( 'DELETE FROM %i WHERE option_name = %s AND option_value = %s', $wpdb->options, $name, $token ) ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery -- atomic lock row; must not be cached.
		self::forget_cache( $name );
	}

	/**
	 * Remove a lock whoever holds it (deactivate, Data section).
	 *
	 * @since 1.0.0
	 * @param string $name Option name of the lock row.
	 * @return void
	 */
	public static function clear( string $name ): void {
		global $wpdb;
		if ( '' === $name ) {
			return;
		}
		$wpdb->query( $wpdb->prepare( 'DELETE FROM %i WHERE option_name = %s', $wpdb->options, $name ) ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery -- atomic lock row; must not be cached.
		self::forget_cache( $name );
	}

	/**
	 * Drop cached copies of the lock option (it's written with raw queries).
	 *
	 * @since 1.0.0
	 * @param string $name Option name.
	 * @return void
	 */
	private static function forget_cache( string $name ): void {
		wp_cache_delete( $name, 'options' );
		$missing = wp_cache_get( 'notoptions', 'options' );
		if ( is_array( $missing ) && isset( $missing[ $name ] ) ) {
			unset( $missing[ $name ] );
			wp_cache_set( 'notoptions', $missing, 'options' );
		}
	}
}