package crypto

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

// Encrypt seals a secret with AES-GCM. The master key can be any string;
// it is hashed to a fixed-size AES key.
func Encrypt(plaintext, masterKey string) (string, error) {
	key := sha256.Sum256([]byte(masterKey))
	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 base64.StdEncoding.EncodeToString(sealed), nil
}

// Decrypt opens a ciphertext produced by Encrypt.
func Decrypt(ciphertext, masterKey string) (string, error) {
	key := sha256.Sum256([]byte(masterKey))
	data, err := base64.StdEncoding.DecodeString(ciphertext)
	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
	}
	if len(data) < gcm.NonceSize() {
		return "", errors.New("ciphertext too short")
	}
	nonce, sealed := data[:gcm.NonceSize()], data[gcm.NonceSize():]
	plain, err := gcm.Open(nil, nonce, sealed, nil)
	if err != nil {
		return "", fmt.Errorf("decrypt failed (bad master key?): %w", err)
	}
	return string(plain), nil
}

// HashSHA256 returns the hex SHA-256 of a string (used for API key lookup).
func HashSHA256(s string) string {
	sum := sha256.Sum256([]byte(s))
	return fmt.Sprintf("%x", sum)
}