package store

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"encoding/hex"
	"fmt"
	"io"
	"strings"
)

const encryptedPrefix = "enc:"

type Encryptor struct {
	gcm cipher.AEAD
}

func NewEncryptor(hexKey string) (*Encryptor, error) {
	key, err := hex.DecodeString(hexKey)
	if err != nil {
		return nil, fmt.Errorf("invalid encryption key: must be hex-encoded: %w", err)
	}
	if len(key) != 32 {
		return nil, fmt.Errorf("invalid encryption key: must be 32 bytes (64 hex chars), got %d bytes", len(key))
	}
	block, err := aes.NewCipher(key)
	if err != nil {
		return nil, fmt.Errorf("create cipher: %w", err)
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return nil, fmt.Errorf("create GCM: %w", err)
	}
	return &Encryptor{gcm: gcm}, nil
}

func (e *Encryptor) Encrypt(plaintext string) (string, error) {
	nonce := make([]byte, e.gcm.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", fmt.Errorf("generate nonce: %w", err)
	}
	ciphertext := e.gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return encryptedPrefix + base64.StdEncoding.EncodeToString(ciphertext), nil
}

func (e *Encryptor) Decrypt(data string) (string, error) {
	if !strings.HasPrefix(data, encryptedPrefix) {
		return data, nil
	}
	raw, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(data, encryptedPrefix))
	if err != nil {
		return "", fmt.Errorf("decode base64: %w", err)
	}
	nonceSize := e.gcm.NonceSize()
	if len(raw) < nonceSize {
		return "", fmt.Errorf("ciphertext too short")
	}
	nonce, ciphertext := raw[:nonceSize], raw[nonceSize:]
	plaintext, err := e.gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", fmt.Errorf("decrypt: %w", err)
	}
	return string(plaintext), nil
}

func IsEncrypted(data string) bool {
	return strings.HasPrefix(data, encryptedPrefix)
}