<?php

namespace App\LegacyEncrypter;

use Illuminate\Contracts\Encryption\DecryptException;

abstract class BaseEncrypter
{
    /**
     * The encryption key.
     *
     * @var string
     */
    protected $key;

    /**
     * Create a MAC for the given value.
     *
     * @param  string  $iv
     * @param  string  $value
     * @return string
     */
    protected function hash($iv, $value)
    {
        return hash_hmac('sha256', $iv.$value, $this->key);
    }

    /**
     * Get the JSON array from the given payload.
     *
     * @param  string  $payload
     * @return array
     *
     * @throws \Illuminate\Contracts\Encryption\DecryptException
     */
    protected function getJsonPayload($payload)
    {
        $payload = json_decode(base64_decode($payload), true);

        // If the payload is not valid JSON or does not have the proper keys set we will
        // assume it is invalid and bail out of the routine since we will not be able
        // to decrypt the given value. We'll also check the MAC for this encryption.
        if (! $payload || $this->invalidPayload($payload)) {
            throw new DecryptException('The payload is invalid.');
        }

        if (! $this->validMac($payload)) {
            throw new DecryptException('The MAC is invalid.');
        }

        return $payload;
    }

    /**
     * Verify that the encryption payload is valid.
     *
     * @param  array|mixed  $data
     * @return bool
     */
    protected function invalidPayload($data)
    {
        return ! is_array($data) || ! isset($data['iv']) || ! isset($data['value']) || ! isset($data['mac']);
    }

    /**
     * Determine if the MAC for the given payload is valid.
     *
     * @param  array  $payload
     * @return bool
     *
     * @throws \RuntimeException
     */
    protected function validMac(array $payload)
    {
        $bytes = random_bytes(16);

        $calcMac = hash_hmac('sha256', $this->hash($payload['iv'], $payload['value']), $bytes, true);

        return hash_equals(hash_hmac('sha256', $payload['mac'], $bytes, true), $calcMac);
    }
}