package localdb

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"errors"
	"io"
	"os"
)

// getEncryptionKey derives a 32-byte key from environment variable or machine ID
func getEncryptionKey() []byte {
	key := os.Getenv("QUOTEFORGE_ENCRYPTION_KEY")
	if key == "" {
		// Fallback to a machine-based key (hostname + fixed salt)
		hostname, _ := os.Hostname()
		key = hostname + "quoteforge-salt-2024"
	}
	// Hash to get exactly 32 bytes for AES-256
	hash := sha256.Sum256([]byte(key))
	return hash[:]
}

// Encrypt encrypts plaintext using AES-256-GCM
func Encrypt(plaintext string) (string, error) {
	if plaintext == "" {
		return "", nil
	}

	key := getEncryptionKey()
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

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

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

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

// Decrypt decrypts ciphertext that was encrypted with Encrypt
func Decrypt(ciphertext string) (string, error) {
	if ciphertext == "" {
		return "", nil
	}

	key := getEncryptionKey()
	data, err := base64.StdEncoding.DecodeString(ciphertext)
	if err != nil {
		return "", err
	}

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

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

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

	nonce, ciphertextBytes := data[:nonceSize], data[nonceSize:]
	plaintext, err := gcm.Open(nil, nonce, ciphertextBytes, nil)
	if err != nil {
		return "", err
	}

	return string(plaintext), nil
}