<?php
namespace Aws\Crypto;

use GuzzleHttp\Psr7;
use GuzzleHttp\Psr7\AppendStream;
use GuzzleHttp\Psr7\Stream;

trait EncryptionTrait
{
    private static $allowedOptions = [
        'Cipher' => true,
        'KeySize' => true,
        'Aad' => true,
    ];

    /**
     * Dependency to generate a CipherMethod from a set of inputs for loading
     * in to an AesEncryptingStream.
     *
     * @param string $cipherName Name of the cipher to generate for encrypting.
     * @param string $iv Base Initialization Vector for the cipher.
     * @param int $keySize Size of the encryption key, in bits, that will be
     *                     used.
     *
     * @return Cipher\CipherMethod
     *
     * @internal
     */
    abstract protected function buildCipherMethod($cipherName, $iv, $keySize);

    /**
     * Builds an AesStreamInterface and populates encryption metadata into the
     * supplied envelope.
     *
     * @param Stream $plaintext Plain-text data to be encrypted using the
     *                          materials, algorithm, and data provided.
     * @param array $cipherOptions Options for use in determining the cipher to
     *                             be used for encrypting data.
     * @param MaterialsProvider $provider A provider to supply and encrypt
     *                                    materials used in encryption.
     * @param MetadataEnvelope $envelope A storage envelope for encryption
     *                                   metadata to be added to.
     *
     * @return AesStreamInterface
     *
     * @throws \InvalidArgumentException Thrown when a value in $cipherOptions
     *                                   is not valid.
     *
     * @internal
     */
    public function encrypt(
        Stream $plaintext,
        array $cipherOptions,
        MaterialsProvider $provider,
        MetadataEnvelope $envelope
    ) {
        $materialsDescription = $provider->getMaterialsDescription();

        $cipherOptions = array_intersect_key(
            $cipherOptions,
            self::$allowedOptions
        );

        if (empty($cipherOptions['Cipher'])) {
            throw new \InvalidArgumentException('An encryption cipher must be'
                . ' specified in the "cipher_options".');
        }

        if (!self::isSupportedCipher($cipherOptions['Cipher'])) {
            throw new \InvalidArgumentException('The cipher requested is not'
                . ' supported by the SDK.');
        }

        if (empty($cipherOptions['KeySize'])) {
            $cipherOptions['KeySize'] = 256;
        }
        if (!is_int($cipherOptions['KeySize'])) {
            throw new \InvalidArgumentException('The cipher "KeySize" must be'
                . ' an integer.');
        }

        if (!MaterialsProvider::isSupportedKeySize(
            $cipherOptions['KeySize']
        )) {
            throw new \InvalidArgumentException('The cipher "KeySize" requested'
                . ' is not supported by AES (128, 192, or 256).');
        }

        $cipherOptions['Iv'] = $provider->generateIv(
            $this->getCipherOpenSslName(
                $cipherOptions['Cipher'],
                $cipherOptions['KeySize']
            )
        );

        $cek = $provider->generateCek($cipherOptions['KeySize']);

        list($encryptingStream, $aesName) = $this->getEncryptingStream(
            $plaintext,
            $cek,
            $cipherOptions
        );

        // Populate envelope data
        $envelope[MetadataEnvelope::CONTENT_KEY_V2_HEADER] =
            $provider->encryptCek(
                $cek,
                $materialsDescription
            );
        unset($cek);

        $envelope[MetadataEnvelope::IV_HEADER] =
            base64_encode($cipherOptions['Iv']);
        $envelope[MetadataEnvelope::KEY_WRAP_ALGORITHM_HEADER] =
            $provider->getWrapAlgorithmName();
        $envelope[MetadataEnvelope::CONTENT_CRYPTO_SCHEME_HEADER] = $aesName;
        $envelope[MetadataEnvelope::UNENCRYPTED_CONTENT_LENGTH_HEADER] =
            strlen($plaintext);
        $envelope[MetadataEnvelope::MATERIALS_DESCRIPTION_HEADER] =
            json_encode($materialsDescription);
        if (!empty($cipherOptions['Tag'])) {
            $envelope[MetadataEnvelope::CRYPTO_TAG_LENGTH_HEADER] =
                strlen($cipherOptions['Tag']) * 8;
        }

        return $encryptingStream;
    }

    /**
     * Generates a stream that wraps the plaintext with the proper cipher and
     * uses the content encryption key (CEK) to encrypt the data when read.
     *
     * @param Stream $plaintext Plain-text data to be encrypted using the
     *                          materials, algorithm, and data provided.
     * @param string $cek A content encryption key for use by the stream for
     *                    encrypting the plaintext data.
     * @param array $cipherOptions Options for use in determining the cipher to
     *                             be used for encrypting data.
     *
     * @return [AesStreamInterface, string]
     *
     * @internal
     */
    protected function getEncryptingStream(
        Stream $plaintext,
        $cek,
        &$cipherOptions
    ) {
        switch ($cipherOptions['Cipher']) {
            case 'gcm':
                $cipherOptions['TagLength'] = 16;

                $cipherTextStream = new AesGcmEncryptingStream(
                    $plaintext,
                    $cek,
                    $cipherOptions['Iv'],
                    $cipherOptions['Aad'] = isset($cipherOptions['Aad'])
                        ? $cipherOptions['Aad']
                        : null,
                    $cipherOptions['TagLength'],
                    $cipherOptions['KeySize']
                );

                if (!empty($cipherOptions['Aad'])) {
                    trigger_error("'Aad' has been supplied for content encryption"
                        . " with " . $cipherTextStream->getAesName() . ". The"
                        . " PHP SDK encryption client can decrypt an object"
                        . " encrypted in this way, but other AWS SDKs may not be"
                        . " able to.", E_USER_WARNING);
                }

                $appendStream = new AppendStream([
                    $cipherTextStream->createStream()
                ]);
                $cipherOptions['Tag'] = $cipherTextStream->getTag();
                $appendStream->addStream(Psr7\Utils::streamFor($cipherOptions['Tag']));
                return [$appendStream, $cipherTextStream->getAesName()];
            default:
                $cipherMethod = $this->buildCipherMethod(
                    $cipherOptions['Cipher'],
                    $cipherOptions['Iv'],
                    $cipherOptions['KeySize']
                );
                $cipherTextStream = new AesEncryptingStream(
                    $plaintext,
                    $cek,
                    $cipherMethod
                );
                return [$cipherTextStream, $cipherTextStream->getAesName()];
        }
    }
}