<?php

namespace Aws\S3\Crypto;

use Aws\Crypto\MetadataEnvelope;
use Aws\Crypto\MetadataStrategyInterface;
use Aws\S3\S3Client;

/**
 * Stores and reads encryption MetadataEnvelope information in a file on Amazon
 * S3.
 *
 * A file with the contents of a MetadataEnvelope will be created or read from
 * alongside the base file on Amazon S3. The provided client will be used for
 * reading or writing this object. A specified suffix (default of '.instruction'
 * will be applied to each of the operations involved with the instruction file.
 *
 * If there is a failure after an instruction file has been uploaded, it will
 * not be automatically deleted.
 */
class InstructionFileMetadataStrategy implements MetadataStrategyInterface {
	const DEFAULT_FILE_SUFFIX = '.instruction';

	private $client;
	private $suffix;

	/**
	 * @param S3Client $client Client for use in uploading the instruction file.
	 * @param string|null $suffix Optional override suffix for instruction file
	 *                            object keys.
	 */
	public function __construct( S3Client $client, $suffix = null ) {
		$this->suffix = empty( $suffix )
			? self::DEFAULT_FILE_SUFFIX
			: $suffix;
		$this->client = $client;
	}

	/**
	 * Places the information in the MetadataEnvelope to a location on S3.
	 *
	 * @param MetadataEnvelope $envelope Encryption data to save according to
	 *                                   the strategy.
	 * @param array $args Starting arguments for PutObject, used for saving
	 *                    extra the instruction file.
	 *
	 * @return array Updated arguments for PutObject.
	 */
	public function save( MetadataEnvelope $envelope, array $args ) {
		$this->client->putObject( [
			'Bucket' => $args['Bucket'],
			'Key'    => $args['Key'] . $this->suffix,
			'Body'   => json_encode( $envelope )
		] );

		return $args;
	}

	/**
	 * Uses the strategy's client to retrieve the instruction file from S3 and generates
	 * a MetadataEnvelope from its contents.
	 *
	 * @param array $args Arguments from Command and Result that contains
	 *                    S3 Object information, relevant headers, and command
	 *                    configuration.
	 *
	 * @return MetadataEnvelope
	 */
	public function load( array $args ) {
		$result = $this->client->getObject( [
			'Bucket' => $args['Bucket'],
			'Key'    => $args['Key'] . $this->suffix
		] );

		$metadataHeaders = json_decode( $result['Body'], true );
		$envelope        = new MetadataEnvelope();
		$constantValues  = MetadataEnvelope::getConstantValues();

		foreach ( $constantValues as $constant ) {
			if ( ! empty( $metadataHeaders[ $constant ] ) ) {
				$envelope[ $constant ] = $metadataHeaders[ $constant ];
			}
		}

		return $envelope;
	}
}
