<?php
/**
 * Encryption-at-rest and token hashing helpers derived from WordPress salts.
 *
 * @package HandyMCP
 */

namespace HandyMCP\Support;

defined( 'ABSPATH' ) || exit;

/**
 * Never hard-codes keys: all keys are derived from the site's salts.
 */
final class Crypto {

	/**
	 * Derive a purpose-bound 32-byte key.
	 *
	 * @param string $purpose Purpose label.
	 */
	private static function key( string $purpose ): string {
		$material = wp_salt( 'auth' ) . '|' . wp_salt( 'secure_auth' ) . '|handymcp|' . $purpose;
		return hash_hmac( 'sha256', $purpose, $material, true );
	}

	/**
	 * Keyed hash for storing tokens (never stored in plain text).
	 *
	 * @param string $token Raw token.
	 */
	public static function hash_token( string $token ): string {
		return hash_hmac( 'sha256', $token, self::key( 'token-hash' ) );
	}

	/**
	 * Cryptographically secure random token with a readable prefix.
	 *
	 * @param string $kind  Short kind label (at, rt, pat, code).
	 * @param int    $bytes Entropy bytes.
	 */
	public static function random_token( string $kind, int $bytes = 32 ): string {
		$raw = rtrim( strtr( base64_encode( random_bytes( $bytes ) ), '+/', '-_' ), '=' ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode
		return 'handymcp_' . $kind . '_' . $raw;
	}

	/**
	 * Encrypt a string for storage.
	 *
	 * @param string $plain Plain text.
	 */
	public static function encrypt( string $plain ): string {
		if ( function_exists( 'sodium_crypto_secretbox' ) ) {
			$nonce = random_bytes( SODIUM_CRYPTO_SECRETBOX_NONCEBYTES );
			$box   = sodium_crypto_secretbox( $plain, $nonce, self::key( 'at-rest' ) );
			return 's1:' . base64_encode( $nonce . $box ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode
		}
		$iv     = random_bytes( 16 );
		$cipher = openssl_encrypt( $plain, 'aes-256-cbc', self::key( 'at-rest' ), OPENSSL_RAW_DATA, $iv );
		$mac    = hash_hmac( 'sha256', $iv . $cipher, self::key( 'at-rest-mac' ), true );
		return 'o1:' . base64_encode( $iv . $mac . $cipher ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode
	}

	/**
	 * Decrypt a stored string. Returns null on tamper or failure.
	 *
	 * @param string $stored Stored value.
	 */
	public static function decrypt( string $stored ): ?string {
		$prefix = substr( $stored, 0, 3 );
		$data   = base64_decode( substr( $stored, 3 ), true ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_decode
		if ( false === $data ) {
			return null;
		}
		if ( 's1:' === $prefix && function_exists( 'sodium_crypto_secretbox_open' ) ) {
			$nonce = substr( $data, 0, SODIUM_CRYPTO_SECRETBOX_NONCEBYTES );
			$box   = substr( $data, SODIUM_CRYPTO_SECRETBOX_NONCEBYTES );
			$plain = sodium_crypto_secretbox_open( $box, $nonce, self::key( 'at-rest' ) );
			return false === $plain ? null : $plain;
		}
		if ( 'o1:' === $prefix ) {
			$iv     = substr( $data, 0, 16 );
			$mac    = substr( $data, 16, 32 );
			$cipher = substr( $data, 48 );
			if ( ! hash_equals( hash_hmac( 'sha256', $iv . $cipher, self::key( 'at-rest-mac' ), true ), $mac ) ) {
				return null;
			}
			$plain = openssl_decrypt( $cipher, 'aes-256-cbc', self::key( 'at-rest' ), OPENSSL_RAW_DATA, $iv );
			return false === $plain ? null : $plain;
		}
		return null;
	}

	/**
	 * Recursively sort keys for canonical hashing.
	 *
	 * @param mixed $value Value.
	 * @return mixed
	 */
	private static function canonical( $value ) {
		if ( is_object( $value ) ) {
			$value = get_object_vars( $value );
		}
		if ( is_array( $value ) ) {
			$is_list = array_keys( $value ) === range( 0, count( $value ) - 1 );
			if ( ! $is_list ) {
				ksort( $value );
			}
			foreach ( $value as $k => $v ) {
				$value[ $k ] = self::canonical( $v );
			}
		}
		return $value;
	}
}