<?php
/**
 * HMAC signatures for profiling requests.
 *
 * @package Bloatwright
 */

namespace Bloatwright\Services;

/**
 * Sign/verify payloads with the rotating session key.
 */
class Signature {

	/**
	 * Option holding the key.
	 */
	const OPTION = 'bloatwright_signing_key';

	/**
	 * Header name.
	 */
	const HEADER = 'X-BLOATWRIGHT-Profile';

	/**
	 * Cookie name.
	 */
	const COOKIE = 'bloatwright_profile';

	/**
	 * Default lifetime (seconds).
	 */
	const TTL = 600;

	/**
	 * Current key (creates one when missing).
	 */
	public static function key(): string {
		$key = get_option( self::OPTION );
		if ( ! is_string( $key ) || strlen( $key ) < 32 ) {
			$key = self::rotate();
		}
		return $key;
	}

	/**
	 * New random key.
	 */
	public static function rotate(): string {
		$key = wp_generate_password( 48, false, false );
		update_option( self::OPTION, $key, false );
		return $key;
	}

	/**
	 * Delete the key: every outstanding token stops verifying.
	 */
	public static function clear(): void {
		delete_option( self::OPTION );
	}

	/**
	 * Build a token for a payload. Every token carries a random jti so two requests never share one.
	 *
	 * @param array $payload session, url, pass, exclude, mode, exp, jti.
	 */
	public static function sign( array $payload ): string {
		$payload = array_merge(
			array(
				'session' => 0,
				'url'     => '',
				'pass'    => 0,
				'exclude' => '',
				'mode'    => 'auto',
				'exp'     => time() + self::TTL,
				'jti'     => wp_generate_password( 16, false, false ),
			),
			$payload
		);
		$json    = wp_json_encode( $payload );
		$b64     = rtrim( strtr( base64_encode( (string) $json ), '+/', '-_' ), '=' ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode -- URL-safe token transport, not obfuscation.
		return $b64 . '.' . hash_hmac( 'sha256', $b64, self::key() );
	}

	/**
	 * Verify a token; returns the payload or null.
	 *
	 * @param string $token Token.
	 * @param string $key Key override (MU loader passes the stored option).
	 */
	public static function verify( string $token, string $key = '' ): ?array {
		$key = '' !== $key ? $key : (string) get_option( self::OPTION );
		if ( strlen( $key ) < 32 || '' === $token || strlen( $token ) > 4096 || false === strpos( $token, '.' ) ) {
			return null;
		}
		list( $b64, $mac ) = explode( '.', $token, 2 );
		if ( ! hash_equals( hash_hmac( 'sha256', $b64, $key ), $mac ) ) {
			return null;
		}
		$json    = base64_decode( strtr( $b64, '-_', '+/' ), true ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_decode -- URL-safe token transport, not obfuscation.
		$payload = is_string( $json ) ? json_decode( $json, true ) : null;
		if ( ! is_array( $payload ) || empty( $payload['exp'] ) || (int) $payload['exp'] < time() || empty( $payload['jti'] ) || ! is_string( $payload['jti'] ) ) {
			return null;
		}
		return $payload;
	}
}