package security

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
)

type SecretBox struct {
	aead cipher.AEAD
}

func NewSecretBox(secret string) (*SecretBox, error) {
	key := sha256.Sum256([]byte(secret))
	block, err := aes.NewCipher(key[:])
	if err != nil {
		return nil, err
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return nil, err
	}
	return &SecretBox{aead: aead}, nil
}

func (b *SecretBox) Encrypt(plaintext string) (string, error) {
	nonce := make([]byte, b.aead.NonceSize())
	if _, err := rand.Read(nonce); err != nil {
		return "", err
	}
	sealed := b.aead.Seal(nonce, nonce, []byte(plaintext), nil)
	return base64.RawURLEncoding.EncodeToString(sealed), nil
}

func (b *SecretBox) Decrypt(ciphertext string) (string, error) {
	raw, err := base64.RawURLEncoding.DecodeString(ciphertext)
	if err != nil {
		return "", err
	}
	if len(raw) < b.aead.NonceSize() {
		return "", fmt.Errorf("ciphertext is too short")
	}
	nonce := raw[:b.aead.NonceSize()]
	payload := raw[b.aead.NonceSize():]
	plaintext, err := b.aead.Open(nil, nonce, payload, nil)
	if err != nil {
		return "", err
	}
	return string(plaintext), nil
}