<?php

declare(strict_types=1);

namespace App\Lib\Axepta;

use Carbon\Carbon;
use Carbon\CarbonInterface;
use Psr\Log\LoggerInterface;

class AxeptaSignatureVerifier
{
    private const int PERMITTED_TIMESTAMP_SKEW_IN_MINUTES = 5;

    private const string USING_API_VERSION = 'v1';

    public function __construct(
        private readonly AxeptaConfig $config,
        private readonly LoggerInterface $logger
    ) {
    }

    public function verify(string $version, string $signature, string $timestamp, string $rawPayload): bool
    {
        $time = Carbon::createFromTimestampUTC($timestamp);

        return $this->isValidSignatureVersion($version) && $this->requestTimestampIsAcceptable($time) && $this->isValidSignature($signature, $time, $rawPayload);
    }

    private function isValidSignatureVersion(string $version): bool
    {
        if ($version !== self::USING_API_VERSION) {
            $this->logger->error('Version is not accepted', [
                'request_version'  => $version,
                'accepted_version' => self::USING_API_VERSION,
            ]);

            return false;
        }

        return true;
    }

    private function requestTimestampIsAcceptable(CarbonInterface $timestamp): bool
    {
        $calculatedDiff = Carbon::now('UTC')->diffInMinutes($timestamp, true);
        if ($calculatedDiff > self::PERMITTED_TIMESTAMP_SKEW_IN_MINUTES) {
            $this->logger->error('request timestamp skew is not matched', [
                'request_timestamp'   => $timestamp,
                'diff'                => $calculatedDiff,
                'max_skew_in_minutes' => self::PERMITTED_TIMESTAMP_SKEW_IN_MINUTES,
            ]);

            return false;
        }

        return true;
    }

    private function isValidSignature(
        #[\SensitiveParameter] string $signature,
        CarbonInterface $timestamp,
        #[\SensitiveParameter] string $rawPayload
    ): bool {
        $providedSignature = $this->extractSignatureFromCurrentVersion($signature);

        if (! $providedSignature) {
            $this->logger->error("Could not extract signature from '{$signature}'");

            return false;
        }

        $expectedSignature = hash_hmac('sha256', "{$timestamp->timestamp}.{$rawPayload}", $this->config->hmac);
        $signatureIsValid  = hash_equals(
            $expectedSignature,
            $providedSignature
        );

        if (! $signatureIsValid) {
            $this->logger->debug('Could not validate expected signature', [
                'request_signature' => $signature,
                'expected'          => $expectedSignature,
            ]);
        }

        return $signatureIsValid;
    }

    private function extractSignatureFromCurrentVersion(#[\SensitiveParameter] string $signature): ?string
    {
        $signatures = explode(',', $signature);

        foreach ($signatures as $sig) {
            $parts = explode('=', trim($sig));

            if (count($parts) === 2 && trim($parts[0]) === self::USING_API_VERSION) {
                $hex = trim($parts[1]);

                if (strlen($hex) === 64) {
                    return strtolower($hex);
                }
            }
        }

        return null;
    }
}