<?php

namespace App\Support;

use RuntimeException;

class ChannelEntryEncryption
{
    public const ALGORITHM = 'RSA-OAEP-2048';

    /**
     * @return array{public_key: string, private_key: string}
     */
    public static function generateKeyPair(): array
    {
        $key = openssl_pkey_new([
            'private_key_bits' => 2048,
            'private_key_type' => OPENSSL_KEYTYPE_RSA,
        ]);

        if ($key === false || ! openssl_pkey_export($key, $privateKey)) {
            throw new RuntimeException('Unable to generate channel encryption private key.');
        }

        $details = openssl_pkey_get_details($key);
        $publicKey = is_array($details) ? ($details['key'] ?? null) : null;
        if (! is_string($publicKey) || trim($publicKey) === '') {
            throw new RuntimeException('Unable to generate channel encryption public key.');
        }

        return [
            'public_key' => trim($publicKey),
            'private_key' => trim($privateKey),
        ];
    }

    public static function encrypt(string $plaintext, string $publicKey): string
    {
        if (! openssl_public_encrypt($plaintext, $ciphertext, $publicKey, OPENSSL_PKCS1_OAEP_PADDING)) {
            throw new RuntimeException('Unable to encrypt channel entry parameter.');
        }

        return self::base64UrlEncode($ciphertext);
    }

    public static function decrypt(string $ciphertext, string $privateKey): string
    {
        $decoded = self::base64UrlDecode($ciphertext);
        if ($decoded === null
            || ! openssl_private_decrypt($decoded, $plaintext, $privateKey, OPENSSL_PKCS1_OAEP_PADDING)) {
            throw new RuntimeException('Unable to decrypt channel entry parameter.');
        }

        return trim($plaintext);
    }

    private static function base64UrlEncode(string $value): string
    {
        return rtrim(strtr(base64_encode($value), '+/', '-_'), '=');
    }

    private static function base64UrlDecode(string $value): ?string
    {
        if ($value === '' || ! preg_match('/^[A-Za-z0-9_-]+$/', $value)) {
            return null;
        }

        $padding = strlen($value) % 4;
        if ($padding !== 0) {
            $value .= str_repeat('=', 4 - $padding);
        }

        $decoded = base64_decode(strtr($value, '-_', '+/'), true);

        return $decoded === false ? null : $decoded;
    }
}