package main

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/sha256"
	"crypto/x509"
	"encoding/asn1"
	"encoding/base64"
	"encoding/json"
	"encoding/pem"
	"fmt"
)

const KeyBitSize = 4096

// Приватный ключ - отдаётся серверу
// Публичный ключ - сохраняется на клиенте

func signRequest(req Request, key *rsa.PublicKey) (string, error) {
	body, _ := json.Marshal(req)
	based := base64.StdEncoding.EncodeToString(body)
	h := sha256.Sum256([]byte(based))
	requestHash := fmt.Sprintf("%x", h)

	ciphertext, err := rsa.EncryptPKCS1v15(rand.Reader, key, []byte(requestHash))
	if err != nil {
		return "", nil
	}

	signature := base64.StdEncoding.EncodeToString(ciphertext)
	return fmt.Sprintf("%s.%s", based, signature), nil
}

func parseKey(keyBytes []byte) (*rsa.PublicKey, error) {
	block, _ := pem.Decode(keyBytes)
	return x509.ParsePKCS1PublicKey(block.Bytes)
}

func generateKeys() (private []byte, public []byte, err error) {
	key, err := rsa.GenerateKey(rand.Reader, KeyBitSize)
	if err != nil {
		return nil, nil, err
	}

	var privateKey = &pem.Block{
		Type:  "PRIVATE KEY",
		Bytes: x509.MarshalPKCS1PrivateKey(key),
	}

	asn1Bytes, _ := asn1.Marshal(key.PublicKey)
	var publicKey = &pem.Block{
		Type:  "PUBLIC KEY",
		Bytes: asn1Bytes,
	}

	bytePrivate := pem.EncodeToMemory(privateKey)
	bytePublic := pem.EncodeToMemory(publicKey)
	return bytePrivate, bytePublic, nil
}