<?php
/**
 * Rate limiting for the wc-edm REST API.
 *
 * Uses a transient counter per identity (user ID when authenticated,
 * client IP otherwise) inside a rolling window.
 *
 * @package WC_Email_Discount_Manager
 */

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Simple transient-backed request throttle.
 */
class WC_EDM_Rate_Limiter {

	/**
	 * Transient key prefix.
	 */
	const PREFIX = 'wc_edm_rl_';

	/**
	 * Whether rate limiting is active.
	 *
	 * @return bool
	 */
	public static function is_enabled() {
		/**
		 * Filter whether the REST API is rate limited.
		 *
		 * @param bool $enabled Default true.
		 */
		return (bool) apply_filters( 'wc_edm_rate_limit_enabled', true );
	}

	/**
	 * Maximum requests allowed per window.
	 *
	 * @param string $method HTTP method of the current request.
	 * @return int
	 */
	public static function max_requests( $method = 'GET' ) {
		$default = self::is_write_method( $method ) ? 20 : 60;

		/**
		 * Filter the request allowance per window.
		 *
		 * Writes get a tighter default than reads.
		 *
		 * @param int    $default Allowed requests.
		 * @param string $method  HTTP method.
		 */
		return max( 1, (int) apply_filters( 'wc_edm_rate_limit_max_requests', $default, $method ) );
	}

	/**
	 * Length of the rolling window in seconds.
	 *
	 * @param string $method HTTP method of the current request.
	 * @return int
	 */
	public static function window( $method = 'GET' ) {
		/**
		 * Filter the rate limit window in seconds.
		 *
		 * @param int    $seconds Default 60.
		 * @param string $method  HTTP method.
		 */
		return max( 1, (int) apply_filters( 'wc_edm_rate_limit_window', MINUTE_IN_SECONDS, $method ) );
	}

	/**
	 * Whether a method mutates data.
	 *
	 * @param string $method HTTP method.
	 * @return bool
	 */
	public static function is_write_method( $method ) {
		return in_array( strtoupper( (string) $method ), array( 'POST', 'PUT', 'PATCH', 'DELETE' ), true );
	}

	/**
	 * Identity used to bucket requests.
	 *
	 * @return string
	 */
	private static function identity() {
		$user_id = get_current_user_id();

		if ( $user_id ) {
			return 'u' . $user_id;
		}

		$ip = WC_EDM_Audit_Log::get_client_ip();

		return 'i' . md5( $ip ? $ip : 'unknown' );
	}

	/**
	 * Whether this rate limit hit should be written to the audit log.
	 *
	 * A blocked caller that keeps hammering would otherwise write one log row
	 * per rejected request, turning the audit log into an amplifier. Only the
	 * first hit per identity per window is recorded.
	 *
	 * @return bool
	 */
	public static function should_log_limit_hit() {
		$key = self::PREFIX . 'logged_' . self::identity();

		if ( get_transient( $key ) ) {
			return false;
		}

		set_transient( $key, 1, self::window() );

		return true;
	}

	/**
	 * Register a request and report whether the caller is over the limit.
	 *
	 * @param string $method HTTP method.
	 * @return array{limited:bool,count:int,max:int,retry_after:int}
	 */
	public static function check( $method = 'GET' ) {
		$max    = self::max_requests( $method );
		$window = self::window( $method );

		if ( ! self::is_enabled() ) {
			return array(
				'limited'     => false,
				'count'       => 0,
				'max'         => $max,
				'retry_after' => 0,
			);
		}

		// The key carries the window slice, so each window gets its own
		// counter and expires on its own. Re-arming a single transient's TTL
		// on every request would instead extend the block indefinitely.
		$now         = time();
		$slice       = (int) floor( $now / $window );
		$retry_after = ( ( $slice + 1 ) * $window ) - $now;
		$bucket      = self::is_write_method( $method ) ? 'w' : 'r';
		$key         = self::PREFIX . $bucket . '_' . self::identity() . '_' . $slice;

		$count = (int) get_transient( $key ) + 1;

		set_transient( $key, $count, $window );

		return array(
			'limited'     => $count > $max,
			'count'       => $count,
			'max'         => $max,
			'retry_after' => max( 1, $retry_after ),
		);
	}
}