package security

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

type CredentialCipher struct {
	aead cipher.AEAD
}

func NewCredentialCipher(encodedKey string) (*CredentialCipher, error) {
	key, err := base64.StdEncoding.DecodeString(encodedKey)
	if err != nil {
		return nil, fmt.Errorf("decode credential key: %w", err)
	}
	if len(key) != 32 {
		return nil, errors.New("credential key must be a base64-encoded 32-byte key")
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, fmt.Errorf("create credential cipher: %w", err)
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("create credential AEAD: %w", err)
	}
	return &CredentialCipher{aead: aead}, nil
}

func (c *CredentialCipher) Encrypt(plaintext string) ([]byte, error) {
	if plaintext == "" {
		return nil, errors.New("credential cannot be empty")
	}
	nonce := make([]byte, c.aead.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, fmt.Errorf("generate credential nonce: %w", err)
	}
	return c.aead.Seal(nonce, nonce, []byte(plaintext), nil), nil
}

func (c *CredentialCipher) Decrypt(ciphertext []byte) (string, error) {
	if len(ciphertext) < c.aead.NonceSize() {
		return "", errors.New("credential ciphertext is truncated")
	}
	nonce := ciphertext[:c.aead.NonceSize()]
	plaintext, err := c.aead.Open(nil, nonce, ciphertext[c.aead.NonceSize():], nil)
	if err != nil {
		return "", errors.New("decrypt credential: authentication failed")
	}
	return string(plaintext), nil
}