package service

import (
	"encoding/base64"
	"fmt"
	"net/http"
	"opencatd-open/internal/store"
	"opencatd-open/pkg/config"
	"strconv"
	"strings"
	"time"

	"github.com/go-webauthn/webauthn/protocol"
	"github.com/go-webauthn/webauthn/webauthn"
	"gorm.io/gorm"
)

type WebAuthnUser struct {
	User        *store.User
	Credentials []webauthn.Credential
}

func (u *WebAuthnUser) WebAuthnID() []byte {
	return []byte(strconv.FormatUint(u.User.ID, 10))
}

func (u *WebAuthnUser) WebAuthnName() string {
	return u.User.Username
}

func (u *WebAuthnUser) WebAuthnDisplayName() string {
	return u.User.Username
}

func (u *WebAuthnUser) WebAuthnCredentials() []webauthn.Credential {
	return u.Credentials
}

func (u *WebAuthnUser) WebAuthnCredentialDescriptors() (descriptors []protocol.CredentialDescriptor) {
	credentials := u.WebAuthnCredentials()
	descriptors = make([]protocol.CredentialDescriptor, len(credentials))
	for i, credential := range credentials {
		descriptors[i] = credential.Descriptor()
	}
	return descriptors
}

type WebAuthnService struct {
	cfg      *config.Config
	DB       *gorm.DB
	WebAuthn *webauthn.WebAuthn
}

func NewWebAuthnService(cfg *config.Config, db *gorm.DB) (*WebAuthnService, error) {
	wconfig := &webauthn.Config{
		RPDisplayName: cfg.AppName,
		RPID:          cfg.RPID,
		RPOrigins:     cfg.RPOrigins,
		AuthenticatorSelection: protocol.AuthenticatorSelection{
			RequireResidentKey: protocol.ResidentKeyRequired(),
			ResidentKey:        protocol.ResidentKeyRequirementRequired,
			UserVerification:   protocol.VerificationPreferred,
		},
	}

	wa, err := webauthn.New(wconfig)
	if err != nil {
		return nil, err
	}

	return &WebAuthnService{
		cfg:      cfg,
		DB:       db,
		WebAuthn: wa,
	}, nil
}

func (s *WebAuthnService) GetUserWithCredentials(userID uint64) (*WebAuthnUser, error) {
	var user store.User
	if err := s.DB.First(&user, userID).Error; err != nil {
		return nil, err
	}

	var passkeys []store.Passkey
	if err := s.DB.Where("user_id = ?", userID).Find(&passkeys).Error; err != nil {
		return nil, err
	}

	credentials := make([]webauthn.Credential, len(passkeys))
	for i, pk := range passkeys {
		credentialIDBytes, err := base64.StdEncoding.DecodeString(pk.CredentialID)
		if err != nil {
			return nil, fmt.Errorf("failed to decode CredentialID: %w", err)
		}
		publicKeyBytes, err := base64.StdEncoding.DecodeString(pk.PublicKey)
		if err != nil {
			return nil, fmt.Errorf("failed to decode PublicKey: %w", err)
		}
		aaguidBytes, err := base64.StdEncoding.DecodeString(pk.AAGUID)
		if err != nil {
			return nil, fmt.Errorf("failed to decode AAGUID: %w", err)
		}

		var transport []protocol.AuthenticatorTransport
		if pk.Transport != "" {
			transport = []protocol.AuthenticatorTransport{protocol.AuthenticatorTransport(pk.Transport)}
		}

		credentials[i] = webauthn.Credential{
			ID:              credentialIDBytes,
			PublicKey:       publicKeyBytes,
			AttestationType: pk.AttestationType,
			Transport:       transport,
			Flags: webauthn.CredentialFlags{
				UserPresent:    true,
				UserVerified:   true,
				BackupEligible: pk.BackupEligible,
				BackupState:    pk.BackupState,
			},
			Authenticator: webauthn.Authenticator{
				AAGUID:    aaguidBytes,
				SignCount: uint32(pk.SignCount),
			},
		}
	}

	return &WebAuthnUser{
		User:        &user,
		Credentials: credentials,
	}, nil
}

func (s *WebAuthnService) BeginRegistration(userID uint64) (*protocol.CredentialCreation, error) {
	user, err := s.GetUserWithCredentials(userID)
	if err != nil {
		return nil, err
	}

	options, _, err := s.WebAuthn.BeginRegistration(user)
	if err != nil {
		return nil, err
	}

	return options, nil
}

func (s *WebAuthnService) FinishRegistration(userID uint64, response *http.Request, deviceName string) (*store.Passkey, error) {
	user, err := s.GetUserWithCredentials(userID)
	if err != nil {
		return nil, err
	}

	credential, err := s.WebAuthn.FinishRegistration(user, webauthn.SessionData{}, response)
	if err != nil {
		return nil, err
	}

	var transport string
	if len(credential.Transport) > 0 {
		transport = string(credential.Transport[0])
	}

	passkey := &store.Passkey{
		UserID:          userID,
		CredentialID:    base64.StdEncoding.EncodeToString(credential.ID),
		PublicKey:       base64.StdEncoding.EncodeToString(credential.PublicKey),
		AttestationType: string(credential.AttestationType),
		AAGUID:          base64.StdEncoding.EncodeToString(credential.Authenticator.AAGUID),
		SignCount:       uint64(credential.Authenticator.SignCount),
		Name:            deviceName,
		DeviceType:      strings.TrimSpace(fmt.Sprintf("%s", deviceName)),
		LastUsedAt:      time.Now().Unix(),
		BackupEligible:  credential.Flags.BackupEligible,
		BackupState:     credential.Flags.BackupState,
		Transport:       transport,
	}

	if err := s.DB.Create(passkey).Error; err != nil {
		return nil, err
	}

	return passkey, nil
}

func (s *WebAuthnService) BeginLogin() (*protocol.CredentialAssertion, error) {
	options, _, err := s.WebAuthn.BeginDiscoverableLogin()
	if err != nil {
		return nil, err
	}
	return options, nil
}

func (s *WebAuthnService) ListPasskeys(userID uint64) ([]store.Passkey, error) {
	var passkeys []store.Passkey
	if err := s.DB.Where("user_id = ?", userID).Find(&passkeys).Error; err != nil {
		return nil, err
	}
	return passkeys, nil
}

func (s *WebAuthnService) DeletePasskey(userID uint64, passkeyID uint64) error {
	return s.DB.Where("id = ? AND user_id = ?", passkeyID, userID).Delete(&store.Passkey{}).Error
}