<?php
/**
 * Atomic, owned locks in the current blog's options table.
 *
 * @package TurtleReport
 */

namespace TurtleReport\Support;

defined( 'ABSPATH' ) || exit;

/** An expired worker can neither renew nor release a replacement's lock. */
final class OptionLock {

	/**
	 * Option name.
	 *
	 * @var string
	 */
	private $name;

	/**
	 * Current ownership value.
	 *
	 * @var string
	 */
	private $value;

	/**
	 * Owning options table.
	 *
	 * @var string
	 */
	private $table;

	/**
	 * Owning blog.
	 *
	 * @var int
	 */
	private $blog;

	/**
	 * Remembers the exact acquired owner.
	 *
	 * @param string $name  Option name.
	 * @param string $value Ownership value.
	 * @param string $table Owning table.
	 * @param int    $blog  Owning blog.
	 */
	private function __construct( $name, $value, $table, $blog ) {
		$this->name  = $name;
		$this->value = $value;
		$this->table = $table;
		$this->blog  = $blog;
	}

	/**
	 * Takes a lock, including conditional takeover of an expired value.
	 *
	 * @param string   $name Option name.
	 * @param int      $ttl  Lifetime in seconds.
	 * @param int|null $now  Current time override for deterministic tests.
	 * @return self|null Null when busy or storage fails.
	 */
	public static function acquire( $name, $ttl, $now = null ) {
		global $wpdb;
		$now   = null === $now ? time() : (int) $now;
		$value = ( $now + max( 1, (int) $ttl ) ) . '|' . wp_generate_uuid4();
		$table = $wpdb->options;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Atomic INSERT; caching cannot establish ownership.
		$won = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO %i (option_name, option_value, autoload) VALUES (%s, %s, 'no')", $table, $name, $value ) );
		if ( 0 === $won ) {
			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Read the exact stored value for compare-and-swap, bypassing stale cache entries.
			$held = $wpdb->get_var( $wpdb->prepare( 'SELECT option_value FROM %i WHERE option_name = %s', $table, $name ) );
			if ( ! is_string( $held ) || ! preg_match( '/^(\d+)\|[a-f0-9-]+$/D', $held, $parts ) || (int) $parts[1] > $now ) {
				return null;
			}
			// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Exactly one contender can replace the observed expired owner.
			$won = $wpdb->query( $wpdb->prepare( "UPDATE %i SET option_value = %s, autoload = 'no' WHERE option_name = %s AND BINARY option_value = %s", $table, $value, $name, $held ) );
		}
		if ( 1 !== $won ) {
			return null;
		}
		$lock = new self( $name, $value, $table, get_current_blog_id() );
		$lock->invalidate();
		return $lock;
	}

	/**
	 * Extends the lifetime only if this worker still owns the lock.
	 *
	 * @param int      $ttl Lifetime in seconds.
	 * @param int|null $now Time override.
	 * @return bool
	 */
	public function renew( $ttl, $now = null ) {
		global $wpdb;
		$now   = null === $now ? time() : (int) $now;
		$value = ( $now + max( 1, (int) $ttl ) ) . '|' . wp_generate_uuid4();
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Ownership-aware renewal, including when expiry times are equal.
		$won = $wpdb->query( $wpdb->prepare( 'UPDATE %i SET option_value = %s WHERE option_name = %s AND BINARY option_value = %s', $this->table, $value, $this->name, $this->value ) );
		if ( 1 !== $won ) {
			return false;
		}
		$this->value = $value;
		$this->invalidate();
		return true;
	}

	/** Releases only the value owned by this instance. @return void */
	public function release() {
		global $wpdb;
		// phpcs:ignore WordPress.DB.DirectDatabaseQuery.DirectQuery, WordPress.DB.DirectDatabaseQuery.NoCaching -- Conditional deletion cannot release a replacement owner.
		$wpdb->query( $wpdb->prepare( 'DELETE FROM %i WHERE option_name = %s AND BINARY option_value = %s', $this->table, $this->name, $this->value ) );
		$this->invalidate();
	}

	/** Clears Core's option caches in the owning blog. @return void */
	private function invalidate() {
		$switched = get_current_blog_id() !== $this->blog;
		if ( $switched ) {
			switch_to_blog( $this->blog );
		}
		try {
			wp_cache_delete( $this->name, 'options' );
			wp_cache_delete( 'notoptions', 'options' );
		} finally {
			if ( $switched ) {
				restore_current_blog();
			}
		}
	}
}