<?php
/**
 * At-rest encryption for secret options (connection keys, credentials, tokens).
 *
 * Secrets are encrypted with a key derived from the site's salts in wp-config.php,
 * so a copied database alone does not reveal them. If the salts change, decryption
 * fails and the admin is asked to regenerate or reconnect.
 *
 * @package AccessNow\Replica
 */

namespace AccessNow\Replica;

defined( 'ABSPATH' ) || exit;

/**
 * Encrypts and decrypts small secrets and secret options.
 */
final class Secrets {

	/**
	 * Option names that hold secrets. They are never exported by the source API
	 * and are always preserved on the destination during restores.
	 */
	const OPTIONS = array(
		'accessnow_replica_source_keys',
		'accessnow_replica_connections',
		'accessnow_replica_destinations',
		'accessnow_replica_drive_token',
	);

	/**
	 * 32-byte key derived from the wp-config salts.
	 */
	private static function key() {
		$material = '';
		foreach ( array( 'AUTH_KEY', 'SECURE_AUTH_KEY', 'AUTH_SALT', 'SECURE_AUTH_SALT' ) as $constant ) {
			$material .= defined( $constant ) ? (string) constant( $constant ) : '';
		}
		if ( '' === $material && function_exists( 'wp_salt' ) ) {
			$material = wp_salt( 'auth' ) . wp_salt( 'secure_auth' );
		}
		return hash_hmac( 'sha256', 'accessnow-replica-secrets-v1', $material, true );
	}

	/**
	 * Encrypts a string.
	 *
	 * @param string $plain Plaintext.
	 */
	public static function encrypt( $plain ) {
		$key = self::key();
		if ( self::has_gcm() ) {
			$iv  = random_bytes( 12 );
			$tag = '';
			$ct  = openssl_encrypt( $plain, 'aes-256-gcm', $key, OPENSSL_RAW_DATA, $iv, $tag );
			return 'g1:' . base64_encode( $iv . $tag . $ct ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode -- Binary to text.
		}
		$nonce = random_bytes( SODIUM_CRYPTO_SECRETBOX_NONCEBYTES );
		return 's1:' . base64_encode( $nonce . sodium_crypto_secretbox( $plain, $nonce, $key ) ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode
	}

	/**
	 * Decrypts a string from encrypt(). Returns null if it cannot be decrypted.
	 *
	 * @param string $blob Encrypted text.
	 */
	public static function decrypt( $blob ) {
		if ( ! is_string( $blob ) || strlen( $blob ) < 4 ) {
			return null;
		}
		$raw = base64_decode( substr( $blob, 3 ), true ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_decode
		if ( false === $raw ) {
			return null;
		}
		$key = self::key();
		if ( 0 === strpos( $blob, 'g1:' ) && self::has_gcm() && strlen( $raw ) >= 28 ) {
			$plain = openssl_decrypt( substr( $raw, 28 ), 'aes-256-gcm', $key, OPENSSL_RAW_DATA, substr( $raw, 0, 12 ), substr( $raw, 12, 16 ) );
			return false === $plain ? null : $plain;
		}
		if ( 0 === strpos( $blob, 's1:' ) && strlen( $raw ) > SODIUM_CRYPTO_SECRETBOX_NONCEBYTES ) {
			try {
				$plain = sodium_crypto_secretbox_open( substr( $raw, SODIUM_CRYPTO_SECRETBOX_NONCEBYTES ), substr( $raw, 0, SODIUM_CRYPTO_SECRETBOX_NONCEBYTES ), $key );
			} catch ( \Throwable $e ) {
				return null;
			}
			return false === $plain ? null : $plain;
		}
		return null;
	}

	/**
	 * Whether openssl AES-256-GCM is available.
	 */
	public static function has_gcm() {
		return function_exists( 'openssl_encrypt' ) && in_array( 'aes-256-gcm', openssl_get_cipher_methods(), true );
	}

	/**
	 * Reads an encrypted array option. Returns the default when missing or undecryptable.
	 *
	 * @param string $name    Option name.
	 * @param array  $default Default.
	 * @return array
	 */
	public static function get_option( $name, $default = array() ) {
		$blob = get_option( $name, '' );
		if ( '' === $blob || ! is_string( $blob ) ) {
			return $default;
		}
		$plain = self::decrypt( $blob );
		if ( null === $plain ) {
			return $default;
		}
		$data = json_decode( $plain, true );
		return is_array( $data ) ? $data : $default;
	}

	/**
	 * Whether an encrypted option exists but cannot be decrypted (salts changed).
	 *
	 * @param string $name Option name.
	 */
	public static function is_unreadable( $name ) {
		$blob = get_option( $name, '' );
		return is_string( $blob ) && '' !== $blob && null === self::decrypt( $blob );
	}

	/**
	 * Saves an array option encrypted, never autoloaded.
	 *
	 * @param string $name  Option name.
	 * @param array  $value Value.
	 */
	public static function update_option( $name, array $value ) {
		update_option( $name, self::encrypt( (string) wp_json_encode( $value ) ), false );
	}

	/**
	 * URL-safe base64 helpers.
	 *
	 * @param string $bytes Bytes.
	 */
	public static function b64url_encode( $bytes ) {
		return rtrim( strtr( base64_encode( $bytes ), '+/', '-_' ), '=' ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_encode
	}

	/**
	 * Decodes URL-safe base64. Returns false when invalid.
	 *
	 * @param string $text Text.
	 * @return string|false
	 */
	public static function b64url_decode( $text ) {
		$text = strtr( (string) $text, '-_', '+/' );
		$pad  = strlen( $text ) % 4;
		if ( $pad ) {
			$text .= str_repeat( '=', 4 - $pad );
		}
		return base64_decode( $text, true ); // phpcs:ignore WordPress.PHP.DiscouragedPHPFunctions.obfuscation_base64_decode
	}
}