package services

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

func encryptionKey() ([]byte, error) {
	raw := os.Getenv("KEY_ENCRYPTION_KEY")
	if raw == "" {
		return nil, fmt.Errorf("KEY_ENCRYPTION_KEY is not set")
	}
	key, err := hex.DecodeString(raw)
	if err != nil || len(key) != 32 {
		return nil, fmt.Errorf("KEY_ENCRYPTION_KEY must be a 64-character hex string (32 bytes)")
	}
	return key, nil
}

func encryptPrivateKey(plaintext string) (string, error) {
	key, err := encryptionKey()
	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
	}
	sealed := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return hex.EncodeToString(sealed), nil
}

func decryptPrivateKey(ciphertextHex string) (string, error) {
	key, err := encryptionKey()
	if err != nil {
		return "", err
	}
	data, err := hex.DecodeString(ciphertextHex)
	if err != nil {
		return "", fmt.Errorf("invalid ciphertext encoding")
	}
	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 "", fmt.Errorf("ciphertext too short")
	}
	plaintext, err := gcm.Open(nil, data[:nonceSize], data[nonceSize:], nil)
	if err != nil {
		return "", fmt.Errorf("decryption failed")
	}
	return string(plaintext), nil
}