<?php

namespace Aws\Crypto\Cipher;

use RuntimeException;

trait CipherBuilderTrait {
	/**
	 * Returns an identifier recognizable by `openssl_*` functions, such as
	 * `aes-256-cbc` or `aes-128-ctr`.
	 *
	 * @param string $cipherName Name of the cipher being used for encrypting
	 *                           or decrypting.
	 * @param int $keySize Size of the encryption key, in bits, that will be
	 *                     used.
	 *
	 * @return string
	 */
	protected function getCipherOpenSslName( $cipherName, $keySize ) {
		return "aes-{$keySize}-{$cipherName}";
	}

	/**
	 * Constructs a CipherMethod for the given name, initialized with the other
	 * data passed for use in encrypting or decrypting.
	 *
	 * @param string $cipherName Name of the cipher to generate for encrypting.
	 * @param string $iv Base Initialization Vector for the cipher.
	 * @param int $keySize Size of the encryption key, in bits, that will be
	 *                     used.
	 *
	 * @return CipherMethod
	 *
	 * @internal
	 */
	protected function buildCipherMethod( $cipherName, $iv, $keySize ) {
		switch ( $cipherName ) {
			case 'cbc':
				return new Cbc(
					$iv,
					$keySize
				);
			default:
				return null;
		}
	}

	/**
	 * Performs a reverse lookup to get the openssl_* cipher name from the
	 * AESName passed in from the MetadataEnvelope.
	 *
	 * @param $aesName
	 *
	 * @return string
	 *
	 * @internal
	 */
	protected function getCipherFromAesName( $aesName ) {
		switch ( $aesName ) {
			case 'AES/GCM/NoPadding':
				return 'gcm';
			case 'AES/CBC/PKCS5Padding':
				return 'cbc';
			default:
				throw new RuntimeException( 'Unrecognized or unsupported'
				                             . ' AESName for reverse lookup.' );
		}
	}
}