package encryptedstring

import (
	"crypto/rand"
	"os"
	"path"
)

const (
	// EncryptionKeyFileName is the name of the file for storage of the en-/decryption key
	EncryptionKeyFileName = ".esk"
)

type defaultDataCryptor struct {
	encryptionKey []byte
}

func (ddc *defaultDataCryptor) keyByte(index int) byte {
	index = index % len(ddc.encryptionKey)
	return ddc.encryptionKey[index]
}

func (ddc *defaultDataCryptor) xorCrypt(in []byte) (out []byte) {
	out = make([]byte, 0)
	for i := 0; i < len(in); i++ {
		out = append(out, in[i]^ddc.keyByte(i))
	}
	return out
}

// Encrypt tries to encrypt the given binary with the appropriate cipher.
func (ddc *defaultDataCryptor) Encrypt(binary []byte) (encrypted []byte, err error) {
	return ddc.xorCrypt(binary), nil
}

// Decrypt tries to decrypt the given binary with the appropriate cipher.
func (ddc *defaultDataCryptor) Decrypt(binary []byte) (decrypted []byte, err error) {
	return ddc.xorCrypt(binary), nil
}

func (ddc *defaultDataCryptor) init() (err error) {
	// Get the startup directory path
	dir := getLocalPath()
	if _, err := os.Stat(dir); err != nil {
		os.MkdirAll(dir, os.ModePerm)
	}

	// Check for the key-file
	keyFilePath := path.Join(dir, EncryptionKeyFileName)
	_, err = os.Stat(keyFilePath)
	if err == nil {
		// Read the file
		if ddc.encryptionKey, err = os.ReadFile(keyFilePath); err == nil {
			// We got the key!
			return
		}
	}

	// Create a new key-file
	ddc.encryptionKey = make([]byte, 1024)
	_, err = rand.Read(ddc.encryptionKey)
	if err != nil {
		return
	}

	var keyFile *os.File
	if keyFile, err = os.Create(keyFilePath); err == nil {
		_, err = keyFile.Write(ddc.encryptionKey)
		if err == nil {
			err = keyFile.Sync()
		}
		keyFile.Close()
	}
	if err == nil {
		err = setHidden(keyFilePath)
	}
	return
}

// NewDefaultDataCryptor creates a new XOR-based
// IDataCryptor-interface the key of which is situated
// in a file called '.esk' in the startup directory of
// the application.
func NewDefaultDataCryptor() IDataCryptor {
	ddc := &defaultDataCryptor{}
	if err := ddc.init(); err != nil {
		panic(err)
	}
	return ddc
}