package oidc

import (
	"context"
	"database/sql"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"strings"
	"time"

	"github.com/golang-jwt/jwt/v5"
	"trankilou.fr/lassistanoque/backend/internal/domain"
	"trankilou.fr/lassistanoque/backend/internal/service/auth"
)

var (
	ErrRegistrationUnsupported = errors.New("registration via OIDC is not supported: users are provisioned at login")
	ErrNoEmail                = errors.New("id token does not contain an email claim")
	ErrUserDisabled           = errors.New("user is disabled")
)

// tokenResponse est la réponse de l'endpoint token du fournisseur.
type tokenResponse struct {
	AccessToken string `json:"access_token"`
	IDToken     string `json:"id_token"`
	TokenType   string `json:"token_type"`
	ExpiresIn   int    `json:"expires_in"`
}

// idTokenClaims sont les claims du token ID émis par le fournisseur.
type idTokenClaims struct {
	Email             string `json:"email"`
	GivenName         string `json:"given_name"`
	FamilyName        string `json:"family_name"`
	Name              string `json:"name"`
	PreferredUsername string `json:"preferred_username"`
	Picture           string `json:"picture"`
	jwt.RegisteredClaims
}

type OIDCAuthenticator struct {
	tokenManager   auth.TokenManager
	oidcRepository domain.OIDCProviderRepository
	userRepository domain.UserRepository
	discovery      *discovery
	jwks           *jwksStore
	httpClient     *http.Client
}

func NewOIDCAuthenticator(
	tokenManager auth.TokenManager,
	oidcRepository domain.OIDCProviderRepository,
	userRepository domain.UserRepository,
) *OIDCAuthenticator {
	return &OIDCAuthenticator{
		tokenManager:   tokenManager,
		oidcRepository: oidcRepository,
		userRepository: userRepository,
		discovery:      newDiscovery(),
		jwks:           newJwksStore(),
		httpClient:     &http.Client{Timeout: 10 * time.Second},
	}
}

// AuthorizeURL construit l'URL d'autorisation vers laquelle rediriger l'utilisateur.
func (s *OIDCAuthenticator) AuthorizeURL(ctx context.Context, provider *domain.OIDCProvider, redirectURI string, state string) (string, error) {
	metadata, err := s.discovery.Metadata(provider)
	if err != nil {
		return "", err
	}

	params := url.Values{}
	params.Set("client_id", provider.ClientID)
	params.Set("redirect_uri", redirectURI)
	params.Set("response_type", "code")
	params.Set("scope", "openid profile email")
	params.Set("state", state)

	return metadata.AuthorizationEndpoint + "?" + params.Encode(), nil
}

// ExchangeCode échange le code d'autorisation contre un token ID, le valide,
// puis délivre une session applicative.
func (s *OIDCAuthenticator) ExchangeCode(ctx context.Context, provider *domain.OIDCProvider, code string, redirectURI string) (*auth.Session, error) {
	metadata, err := s.discovery.Metadata(provider)
	if err != nil {
		return nil, err
	}

	tokens, err := s.requestTokens(metadata.TokenEndpoint, provider, code, redirectURI)
	if err != nil {
		return nil, err
	}
	if tokens.IDToken == "" {
		return nil, fmt.Errorf("provider %s did not return an id token", provider.ID)
	}

	claims, err := s.validateIDToken(provider, metadata, tokens.IDToken)
	if err != nil {
		return nil, err
	}
	if claims.Email == "" {
		return nil, ErrNoEmail
	}

	user, err := s.provisionUser(claims)
	if err != nil {
		return nil, err
	}

	accessToken, expiresAt, err := s.tokenManager.GenerateAccessToken(user)
	if err != nil {
		return nil, fmt.Errorf("unable to generate access token: %s", err)
	}
	refreshToken, _, err := s.tokenManager.GenerateRefreshToken(user.ID)
	if err != nil {
		return nil, fmt.Errorf("unable to generate refresh token: %s", err)
	}

	return &auth.Session{
		User:         user,
		AccessToken:  accessToken,
		RefreshToken: refreshToken,
		ExpiresAt:    expiresAt,
	}, nil
}

// Authenticate implémente auth.Authenticator: le flux OIDC passe par le state
// signé qui transporte l'id du fournisseur, puis l'échange du code.
func (s *OIDCAuthenticator) Authenticate(ctx context.Context, creds auth.Credentials) (*auth.Session, error) {
	providerID, err := s.tokenManager.ParseStateToken(creds.OIDCState)
	if err != nil {
		return nil, fmt.Errorf("invalid oidc state: %s", err)
	}
	provider, err := s.oidcRepository.FindOIDCProvider(providerID)
	if err != nil {
		return nil, fmt.Errorf("unknown oidc provider: %s", providerID)
	}
	return s.ExchangeCode(ctx, provider, creds.OIDCCode, creds.RedirectURI)
}

func (s *OIDCAuthenticator) Register(ctx context.Context, registration auth.Registration) (*auth.Session, error) {
	return nil, ErrRegistrationUnsupported
}

func (s *OIDCAuthenticator) requestTokens(tokenEndpoint string, provider *domain.OIDCProvider, code string, redirectURI string) (*tokenResponse, error) {
	form := url.Values{}
	form.Set("grant_type", "authorization_code")
	form.Set("code", code)
	form.Set("redirect_uri", redirectURI)
	form.Set("client_id", provider.ClientID)
	form.Set("client_secret", provider.ClientSecret)

	res, err := s.httpClient.Post(tokenEndpoint, "application/x-www-form-urlencoded", strings.NewReader(form.Encode()))
	if err != nil {
		return nil, fmt.Errorf("error calling token endpoint: %s", err)
	}
	defer res.Body.Close()
	body, err := io.ReadAll(res.Body)
	if err != nil {
		return nil, err
	}
	if res.StatusCode != http.StatusOK {
		return nil, fmt.Errorf("token endpoint returned status %d: %s", res.StatusCode, string(body))
	}

	tokens := &tokenResponse{}
	if err := json.Unmarshal(body, tokens); err != nil {
		return nil, err
	}
	return tokens, nil
}

func (s *OIDCAuthenticator) validateIDToken(provider *domain.OIDCProvider, metadata *providerMetadata, idToken string) (*idTokenClaims, error) {
	claims := &idTokenClaims{}
	_, err := jwt.ParseWithClaims(idToken, claims, s.jwks.KeyFunc(provider.ID, metadata.JwksURI),
		jwt.WithValidMethods([]string{"RS256", "RS384", "RS512", "ES256", "ES384", "ES521"}),
		jwt.WithIssuer(metadata.Issuer),
		jwt.WithAudience(provider.ClientID),
	)
	if err != nil {
		return nil, fmt.Errorf("invalid id token: %s", err)
	}
	return claims, nil
}

func (s *OIDCAuthenticator) provisionUser(claims *idTokenClaims) (*domain.User, error) {
	user, err := s.userRepository.FindUserByEmail(claims.Email)
	if err == nil {
		if !user.Enabled {
			return nil, ErrUserDisabled
		}
		return user, nil
	}
	if !errors.Is(err, sql.ErrNoRows) {
		return nil, err
	}

	firstname := claims.GivenName
	if firstname == "" {
		firstname = claims.PreferredUsername
	}
	user, err = s.userRepository.CreateUser(&domain.User{
		Email:     claims.Email,
		Firstname: firstname,
		Lastname:  claims.FamilyName,
		Enabled:   true,
	})
	if err != nil {
		return nil, fmt.Errorf("error creating oidc user %s: %s", claims.Email, err)
	}

	_, err = s.userRepository.CreateTeam(user.ID, &domain.Team{
		Label:       "Espace personnel",
		DateCreated: time.Now(),
	})
	if err != nil {
		return nil, fmt.Errorf("error creating personal team for oidc user %s: %s", claims.Email, err)
	}

	return user, nil
}