package main

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

	"golang.org/x/crypto/pbkdf2"
)

type Crypto struct {
	serverKey []byte
}

func NewCrypto(serverKeyStr string) (*Crypto, error) {
	// Decode the base64 server key
	serverKey, err := base64.StdEncoding.DecodeString(serverKeyStr)
	if err != nil {
		return nil, err
	}

	if len(serverKey) != 32 {
		return nil, errors.New("invalid server key length")
	}

	logger.Info("Crypto initialized with server key")
	return &Crypto{serverKey: serverKey}, nil
}

func GenerateServerKey() (string, error) {
	key := make([]byte, 32)
	if _, err := rand.Read(key); err != nil {
		return "", err
	}
	return base64.StdEncoding.EncodeToString(key), nil
}

func (c *Crypto) deriveUserKey(userID string) []byte {
	// Derive a 32-byte key from user ID using PBKDF2
	// Using server key as salt for additional security
	return pbkdf2.Key([]byte(userID), c.serverKey, 100000, 32, sha256.New)
}

func (c *Crypto) encrypt(data []byte, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

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

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

	ciphertext := gcm.Seal(nonce, nonce, data, nil)
	return ciphertext, nil
}

func (c *Crypto) decrypt(data []byte, key []byte) ([]byte, error) {
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, err
	}

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

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

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

	return plaintext, nil
}

func (c *Crypto) EncryptWithServerKey(data []byte) ([]byte, error) {
	return c.encrypt(data, c.serverKey)
}

func (c *Crypto) DecryptWithServerKey(data []byte) ([]byte, error) {
	return c.decrypt(data, c.serverKey)
}

func (c *Crypto) EncryptWithUserKey(data []byte, userID string) ([]byte, error) {
	userKey := c.deriveUserKey(userID)
	return c.encrypt(data, userKey)
}

func (c *Crypto) DecryptWithUserKey(data []byte, userID string) ([]byte, error) {
	userKey := c.deriveUserKey(userID)
	return c.decrypt(data, userKey)
}