<?php
/**
 * Fixed-window rate limiting, shared across workers (one atomic upsert per
 * hit). Spec 4.3: over the limit, answer 429 with Retry-After. Guides: limit
 * by client_id, by user and by session, not by turning agents away.
 *
 * @package AgentAdapt
 */

defined( 'ABSPATH' ) || exit;

/**
 * Rate limiter.
 */
final class AgentAdapt_Rate_Limit {

	/**
	 * Count one hit against a bucket.
	 *
	 * @param string $bucket Identifier (hashed before storage).
	 * @param int    $limit  Hits allowed per window.
	 * @param int    $window Window length in seconds.
	 * @return array{allowed: bool, retry_after: int}
	 */
	public static function hit( string $bucket, int $limit, int $window ): array {
		global $wpdb;
		/**
		 * Adjust a limit. Return 0 to disable that bucket entirely.
		 *
		 * @param int    $limit  Hits per window.
		 * @param string $bucket Bucket name (prefix before the first ':' names the kind).
		 */
		$limit = (int) apply_filters( 'agentadapt_rate_limit', $limit, $bucket );
		if ( $limit <= 0 ) {
			return array( 'allowed' => true, 'retry_after' => 0 );
		}
		$now   = time();
		$start = $now - ( $now % $window );
		$key   = hash( 'sha256', $bucket );
		$t     = AgentAdapt_Schema::table( 'rate' );
		// phpcs:disable WordPress.DB.DirectDatabaseQuery
		$wpdb->query( $wpdb->prepare( "INSERT INTO %i (bucket, window_start, hits) VALUES (%s, %d, 1) ON DUPLICATE KEY UPDATE hits = hits + 1", $t, $key, $start ) );
		$hits = (int) $wpdb->get_var( $wpdb->prepare( "SELECT hits FROM %i WHERE bucket = %s AND window_start = %d", $t, $key, $start ) );
		// phpcs:enable
		return array(
			'allowed'     => $hits <= $limit,
			'retry_after' => $hits <= $limit ? 0 : max( 1, $start + $window - $now ),
		);
	}

	/**
	 * Delete windows older than a day.
	 */
	public static function purge(): void {
		global $wpdb;
		$t = AgentAdapt_Schema::table( 'rate' );
		$wpdb->query( $wpdb->prepare( "DELETE FROM %i WHERE window_start < %d", $t, time() - DAY_IN_SECONDS ) ); // phpcs:ignore WordPress.DB.DirectDatabaseQuery
	}
}