package cm509

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"fmt"
	"io"
)

func EncryptAES256(b64data string, key string) (string, error) {
	var res string
	var err error

	const aes256KeyLen = 32

	bKey := []byte(key)
	keyLen := len(bKey)
	switch {
	case keyLen > aes256KeyLen:
		bKey = bKey[:aes256KeyLen]
	case keyLen < aes256KeyLen:
		padding := make([]byte, aes256KeyLen-keyLen)
		bKey = append(bKey, padding...)
	case keyLen == 0:
		return res, fmt.Errorf("Zero lenght key")
	}

	data, err := base64.StdEncoding.DecodeString(b64data)
	if err != nil {
		return res, err
	}

	block, err := aes.NewCipher(bKey)
	if err != nil {
		return res, err
	}

	nonce := make([]byte, 12)
	_, err = io.ReadFull(rand.Reader, nonce)
	if err != nil {
		return res, err
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return res, err
	}

	ciphertext := aesgcm.Seal(nil, nonce, data, nil)
	ciphertext = append(nonce, ciphertext...)

	res = base64.StdEncoding.EncodeToString(ciphertext)

	return res, err

}

func DecryptAES256(b64ciphertext string, key string) (string, error) {
	var res string
	var err error

	const aes256KeyLen = 32

	bKey := []byte(key)
	keyLen := len(bKey)
	switch {
	case keyLen > aes256KeyLen:
		bKey = bKey[:aes256KeyLen]
	case keyLen < aes256KeyLen:
		padding := make([]byte, aes256KeyLen-keyLen)
		bKey = append(bKey, padding...)
	case keyLen == 0:
		return res, fmt.Errorf("Zero lenght key")
	}

	ciphertext, err := base64.StdEncoding.DecodeString(b64ciphertext)
	if err != nil {
		return res, err
	}

	block, err := aes.NewCipher(bKey)
	if err != nil {
		return res, err
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return res, err
	}

	nonceSize := aesgcm.NonceSize()
	nonce, ciphertext := ciphertext[:nonceSize], ciphertext[nonceSize:]

	plaintext, err := aesgcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return res, err
	}

	res = base64.StdEncoding.EncodeToString(plaintext)
	return res, err
}