package service

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

const developmentSecretEnvelopeKey = "browser.local/platform/development-secret-envelope/v1"

type SecretEnvelope interface {
	Seal(string) (string, error)
	Open(string) (string, error)
}

type aesGCMSecretEnvelope struct {
	key [32]byte
}

func newSecretEnvelope(secret string) *aesGCMSecretEnvelope {
	return &aesGCMSecretEnvelope{key: sha256.Sum256([]byte(secret))}
}

func (envelope *aesGCMSecretEnvelope) Seal(plain string) (string, error) {
	block, err := aes.NewCipher(envelope.key[:])
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err := rand.Read(nonce); err != nil {
		return "", err
	}
	ciphertext := gcm.Seal(nil, nonce, []byte(plain), nil)
	return "enc:v1:" + base64.RawURLEncoding.EncodeToString(nonce) + ":" + base64.RawURLEncoding.EncodeToString(ciphertext), nil
}

func (envelope *aesGCMSecretEnvelope) Open(encrypted string) (string, error) {
	parts := strings.Split(encrypted, ":")
	if len(parts) != 4 || parts[0] != "enc" || parts[1] != "v1" {
		return "", validationError("encrypted key format is invalid")
	}
	nonce, err := base64.RawURLEncoding.DecodeString(parts[2])
	if err != nil {
		return "", err
	}
	ciphertext, err := base64.RawURLEncoding.DecodeString(parts[3])
	if err != nil {
		return "", err
	}
	block, err := aes.NewCipher(envelope.key[:])
	if err != nil {
		return "", err
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", err
	}
	plain, err := gcm.Open(nil, nonce, ciphertext, nil)
	if err != nil {
		return "", err
	}
	return string(plain), nil
}

func (svc *CoreService) ConfigureSecretEnvelopeKey(secret string) error {
	secret = strings.TrimSpace(secret)
	if secret == "" {
		return nil
	}
	if len([]rune(secret)) < 32 {
		return validationError("PLATFORM_SECRET_ENVELOPE_KEY must be at least 32 characters")
	}
	svc.secretEnvelope = newSecretEnvelope(secret)
	return nil
}

func (svc *CoreService) encryptRuntimeKey(plain string) (string, error) {
	return svc.secretEnvelope.Seal(plain)
}

func (svc *CoreService) decryptRuntimeKey(encrypted string) (string, error) {
	return svc.secretEnvelope.Open(encrypted)
}

func encryptRuntimeKey(plain string) (string, error) {
	return newSecretEnvelope(developmentSecretEnvelopeKey).Seal(plain)
}

func decryptRuntimeKey(encrypted string) (string, error) {
	return newSecretEnvelope(developmentSecretEnvelopeKey).Open(encrypted)
}