package app

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

const enterpriseSiteCredentialPrefix = "v1:"

func encryptEnterpriseSiteCredential(secret string, keyMaterial string) (string, error) {
	secret = strings.TrimSpace(secret)
	if secret == "" {
		return "", fmt.Errorf("enterprise site credential is empty")
	}
	key := enterpriseSiteCredentialKey(keyMaterial)
	block, err := aes.NewCipher(key[:])
	if err != nil {
		return "", fmt.Errorf("create enterprise site credential cipher: %w", err)
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("create enterprise site credential gcm: %w", err)
	}
	nonce := make([]byte, aead.NonceSize())
	if _, err := io.ReadFull(rand.Reader, nonce); err != nil {
		return "", fmt.Errorf("generate enterprise site credential nonce: %w", err)
	}
	ciphertext := aead.Seal(nil, nonce, []byte(secret), nil)
	packed := append(nonce, ciphertext...)
	return enterpriseSiteCredentialPrefix + base64.StdEncoding.EncodeToString(packed), nil
}

func decryptEnterpriseSiteCredential(ciphertext string, keyMaterial string) (string, error) {
	ciphertext = strings.TrimSpace(ciphertext)
	if ciphertext == "" {
		return "", fmt.Errorf("enterprise site credential ciphertext is empty")
	}
	if !strings.HasPrefix(ciphertext, enterpriseSiteCredentialPrefix) {
		return "", fmt.Errorf("unsupported enterprise site credential format")
	}
	raw, err := base64.StdEncoding.DecodeString(strings.TrimPrefix(ciphertext, enterpriseSiteCredentialPrefix))
	if err != nil {
		return "", fmt.Errorf("decode enterprise site credential: %w", err)
	}
	key := enterpriseSiteCredentialKey(keyMaterial)
	block, err := aes.NewCipher(key[:])
	if err != nil {
		return "", fmt.Errorf("create enterprise site credential cipher: %w", err)
	}
	aead, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("create enterprise site credential gcm: %w", err)
	}
	if len(raw) <= aead.NonceSize() {
		return "", fmt.Errorf("enterprise site credential payload is invalid")
	}
	nonce := raw[:aead.NonceSize()]
	encrypted := raw[aead.NonceSize():]
	plaintext, err := aead.Open(nil, nonce, encrypted, nil)
	if err != nil {
		return "", fmt.Errorf("decrypt enterprise site credential: %w", err)
	}
	return string(plaintext), nil
}

func enterpriseSiteCredentialKey(keyMaterial string) [32]byte {
	trimmed := strings.TrimSpace(keyMaterial)
	if trimmed == "" {
		trimmed = "geo-rankly-enterprise-site-development-key"
	}
	return sha256.Sum256([]byte("enterprise-site-credential:" + trimmed))
}