// Package encryption provides functions to encode/decode AES encrypted secrets.
//
// Encryption is used to store sensitive information in the database, such as 2FA TOTP secrets
// for users who have 2FA authentication enabled.
//
// For new key generation, see pkg/config/variable.go#NewAESKey.
package encryption

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"errors"
	"fmt"
	"io"

	"code.nonshy.com/nonshy/website/pkg/config"
)

// Encrypt a byte stream using the site's AES passphrase.
func Encrypt(input []byte) ([]byte, error) {
	if len(config.Current.Encryption.AESKey) == 0 {
		return nil, errors.New("AES key not configured")
	}

	// Generate a new AES cipher.
	c, err := aes.NewCipher(config.Current.Encryption.AESKey)
	if err != nil {
		return nil, err
	}

	// gcm or Galois/Counter Mode
	gcm, err := cipher.NewGCM(c)
	if err != nil {
		return nil, err
	}

	// Create a new byte array the size of the GCM nonce
	// which must be passed to Seal.
	nonce := make([]byte, gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return nil, fmt.Errorf("populating the nonce: %s", err)
	}

	// Encrypt the text using the Seal function.
	// Seal encrypts and authenticates plaintext, authenticates the
	// additional data and appends the result to dst, returning the
	// updated slice. The nonce must be NonceSize() bytes long and
	// unique for all time, for a given key.
	result := gcm.Seal(nonce, nonce, input, nil)
	return result, nil
}

// EncryptString encrypts a string value and returns the cipher text.
func EncryptString(input string) ([]byte, error) {
	return Encrypt([]byte(input))
}

// Decrypt a byte stream using the site's AES passphrase.
func Decrypt(data []byte) ([]byte, error) {
	if len(config.Current.Encryption.AESKey) == 0 {
		return nil, errors.New("AES key not configured")
	}

	c, err := aes.NewCipher(config.Current.Encryption.AESKey)
	if err != nil {
		return nil, err
	}

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

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

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

// DecryptString decrypts a string value from ciphertext.
func DecryptString(data []byte) (string, error) {
	decoded, err := Decrypt(data)
	if err != nil {
		return "", err
	}
	return string(decoded), nil
}

// Hash a byte array as SHA256 and returns the hex string.
func Hash(input []byte) string {
	h := sha256.New()
	h.Write(input)
	return fmt.Sprintf("%x", h.Sum(nil))
}

// VerifyHash hashes a byte array and checks the result.
func VerifyHash(input []byte, expect string) bool {
	return Hash(input) == expect
}