package localdb

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"
	"sync"
)

const encryptionKeyFileName = "local_secret.key"

var (
	encryptionStateMu sync.RWMutex
	encryptionKeyDir  string
)

func configureEncryption(dir string) {
	encryptionStateMu.Lock()
	defer encryptionStateMu.Unlock()
	encryptionKeyDir = dir
}

func getEncryptionKey() ([]byte, error) {
	if key := strings.TrimSpace(os.Getenv("PRICEFORGE_ENCRYPTION_KEY")); key != "" {
		hash := sha256.Sum256([]byte(key))
		return hash[:], nil
	}
	if key := strings.TrimSpace(os.Getenv("QUOTEFORGE_ENCRYPTION_KEY")); key != "" {
		hash := sha256.Sum256([]byte(key))
		return hash[:], nil
	}
	return loadOrCreateKeyFile()
}

func loadOrCreateKeyFile() ([]byte, error) {
	keyPath, err := encryptionKeyPath()
	if err != nil {
		return nil, err
	}
	if err := os.MkdirAll(filepath.Dir(keyPath), 0700); err != nil {
		return nil, fmt.Errorf("create encryption key dir: %w", err)
	}
	if data, err := os.ReadFile(keyPath); err == nil {
		trimmed := strings.TrimSpace(string(data))
		if trimmed == "" {
			return nil, fmt.Errorf("encryption key file %s is empty", keyPath)
		}
		hash := sha256.Sum256([]byte(trimmed))
		return hash[:], nil
	}

	raw := make([]byte, 32)
	if _, err := io.ReadFull(rand.Reader, raw); err != nil {
		return nil, fmt.Errorf("generate encryption key: %w", err)
	}
	encoded := base64.StdEncoding.EncodeToString(raw)
	if err := os.WriteFile(keyPath, []byte(encoded), 0600); err != nil {
		return nil, fmt.Errorf("write encryption key file: %w", err)
	}
	hash := sha256.Sum256([]byte(encoded))
	return hash[:], nil
}

func encryptionKeyPath() (string, error) {
	encryptionStateMu.RLock()
	dir := encryptionKeyDir
	encryptionStateMu.RUnlock()
	if strings.TrimSpace(dir) == "" {
		return "", errors.New("encryption key directory is not configured")
	}
	return filepath.Join(dir, encryptionKeyFileName), nil
}

func legacyEncryptionKey() []byte {
	hostname, _ := os.Hostname()
	hash := sha256.Sum256([]byte(hostname + "priceforge-salt-2024"))
	return hash[:]
}

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

	key, err := getEncryptionKey()
	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
	}

	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
	}

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

	key, err := getEncryptionKey()
	if err == nil {
		plaintext, decryptErr := decryptWithKey(data, key)
		if decryptErr == nil {
			return plaintext, nil
		}
	}

	return decryptWithKey(data, legacyEncryptionKey())
}

func decryptWithKey(data []byte, key []byte) (string, error) {
	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
}