package channels

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

// EncryptSecret encrypts plaintext using AES-256-GCM with a random nonce.
// Returns base64(nonce || ciphertext).
func EncryptSecret(key [32]byte, plaintext string) (string, error) {
	block, err := aes.NewCipher(key[:])
	if err != nil {
		return "", fmt.Errorf("aes cipher: %w", err)
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("gcm: %w", err)
	}

	nonce := make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", fmt.Errorf("nonce: %w", err)
	}

	ciphertext := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return base64.StdEncoding.EncodeToString(ciphertext), nil
}

// DecryptSecret decrypts a value produced by EncryptSecret.
func DecryptSecret(key [32]byte, encoded string) (string, error) {
	data, err := base64.StdEncoding.DecodeString(encoded)
	if err != nil {
		return "", fmt.Errorf("base64 decode: %w", err)
	}

	block, err := aes.NewCipher(key[:])
	if err != nil {
		return "", fmt.Errorf("aes cipher: %w", err)
	}

	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("gcm: %w", err)
	}

	nonceSize := gcm.NonceSize()
	if len(data) < nonceSize {
		return "", fmt.Errorf("ciphertext too short")
	}

	nonce, ciphertext := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", fmt.Errorf("decrypt: %w", err)
	}

	return string(plaintext), nil
}