package models

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"errors"
	"io"
	"os"
	"strings"

	"rocketgit.ru/rsmon/worker/config/secrets"
)

const credentialKeyEnv = "RSMON_CRED_KEY"

// encryptSecret encrypts plaintext with AES-GCM. If no key is configured
// (dev/test), stores the value with a "plain:" prefix. Production deployments
// must set RSMON_CRED_KEY or config/secrets.yml crypto.pepper.
func encryptSecret(plaintext string) (string, error) {
	key := credentialKey()
	if key == "" {
		return "plain:" + plaintext, nil
	}
	block, err := aes.NewCipher(deriveKey(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 "enc:" + base64.StdEncoding.EncodeToString(sealed), nil
}

// decryptSecret decrypts a value produced by encryptSecret. Values without a
// known prefix are returned as-is for backward compatibility with legacy
// plaintext records.
func decryptSecret(stored string) (string, error) {
	if stored == "" {
		return "", nil
	}
	switch {
	case strings.HasPrefix(stored, "plain:"):
		return strings.TrimPrefix(stored, "plain:"), nil
	case strings.HasPrefix(stored, "enc:"):
		key := credentialKey()
		if key == "" {
			return "", errors.New("credential key not configured but secret is encrypted")
		}
		raw, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(stored, "enc:"))
		if err != nil {
			return "", err
		}
		block, err := aes.NewCipher(deriveKey(key))
		if err != nil {
			return "", err
		}
		gcm, err := cipher.NewGCM(block)
		if err != nil {
			return "", err
		}
		if len(raw) < gcm.NonceSize() {
			return "", errors.New("ciphertext too short")
		}
		nonce, ciphertext := raw[:gcm.NonceSize()], raw[gcm.NonceSize():]
		plaintext, err := gcm.Open(nil, nonce, ciphertext, nil)
		if err != nil {
			return "", err
		}
		return string(plaintext), nil
	default:
		return stored, nil
	}
}

func deriveKey(s string) []byte {
	h := sha256.Sum256([]byte(s))
	return h[:32]
}

func credentialKey() string {
	if k := os.Getenv(credentialKeyEnv); k != "" {
		return k
	}
	if secrets.Crypto != nil && secrets.Crypto.Pepper != "" {
		return secrets.Crypto.Pepper
	}
	return ""
}