package handler

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"encoding/base64"
	"os"
	"strings"
)

// getSecretKey returns the AES key derived from SECRET_KEY env var.
// Mirrors Python's crypto._get_key(): first 32 bytes of utf-8 encoded key, zero-padded.
func getSecretKey() []byte {
	keyStr := os.Getenv("SECRET_KEY")
	if keyStr == "" {
		keyStr = "dev-secret-key-change-in-production"
	}
	raw := []byte(keyStr)
	if len(raw) >= 32 {
		return raw[:32]
	}
	padded := make([]byte, 32)
	copy(padded, raw)
	return padded
}

// decryptPassword decrypts a base64-encoded AES-256-GCM ciphertext.
// Mirrors Python's crypto.decrypt_password().
// Handles "enc:" prefix automatically. If not valid encrypted data, returns as-is.
func decryptPassword(encrypted string) (string, error) {
	// Strip "enc:" prefix if present
	if strings.HasPrefix(encrypted, "enc:") {
		encrypted = strings.TrimPrefix(encrypted, "enc:")
	}
	raw, err := base64.StdEncoding.DecodeString(encrypted)
	if err != nil {
		return encrypted, nil // not valid base64 — plaintext
	}

	nonceSize := 12
	if len(raw) <= nonceSize {
		return encrypted, nil
	}

	nonce := raw[:nonceSize]
	ct := raw[nonceSize:]
	key := getSecretKey()

	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}

	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	plaintext, err := aesgcm.Open(nil, nonce, ct, nil)
	if err != nil {
		return encrypted, nil // decryption failed — return as-is
	}

	return string(plaintext), nil
}

// encryptPassword encrypts a plaintext password using AES-256-GCM.
// Returns base64(nonce + ciphertext), same format as Python's encrypt_password.
func encryptPassword(plaintext string) (string, error) {
	key := getSecretKey()
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", err
	}
	aesgcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}

	nonce := make([]byte, 12)
	if _, err := rand.Read(nonce); err != nil {
		return "", err
	}

	ct := aesgcm.Seal(nil, nonce, []byte(plaintext), nil)
	return base64.StdEncoding.EncodeToString(append(nonce, ct...)), nil
}