/*
Copyright CAcert Inc.
SPDX-License-Identifier: Apache-2.0

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    https://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package main

import (
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/base64"
	"errors"
	"fmt"
	"log/slog"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"sync/atomic"
	"time"

	"github.com/gorilla/csrf"
	"github.com/knadh/koanf"
	"github.com/knadh/koanf/parsers/toml"
	"github.com/knadh/koanf/providers/confmap"
	hydra "github.com/ory/hydra-client-go/v2"

	"code.cacert.org/cacert/oidc-idp/internal/handlers"
	"code.cacert.org/cacert/oidc-idp/internal/services"
	"code.cacert.org/cacert/oidc-idp/ui"
)

const (
	IdleTimeout     = 30 * time.Second
	ShutdownTimeout = 30 * time.Second
	ReadTimeOut     = 20 * time.Second
	WriteTimeOut    = 20 * time.Second

	DefaultCSRFMaxAge = 600

	httpsDefaultPort = 443

	sessionKeyLength     = 32
	sessionAuthKeyLength = 64

	minCSRFKeyLength = 32
)

var (
	version = "local"
	commit  = "unknown"
	date    = "unknown"
)

func main() {
	var (
		logLevel   = new(slog.LevelVar)
		logHandler slog.Handler
		logger     *slog.Logger
	)

	logHandler = slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: logLevel})
	logger = slog.New(logHandler)
	slog.SetDefault(logger)

	config, err := services.ConfigureApplication(logger, "IDP", services.DefaultConfig)
	if err != nil {
		logger.Error("error loading configuration", "err", err)
		os.Exit(1)
	}

	if level := config.Bytes("log.level"); level != nil {
		err := logLevel.UnmarshalText(level)
		if err != nil {
			logger.Error("could not parse log level", "error", err)
			os.Exit(1)
		}

		slog.SetLogLoggerLevel(logLevel.Level())
	}

	if config.Bool("log.json") {
		logHandler = slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{Level: logLevel})
		logger = slog.New(logHandler)
		slog.SetDefault(logger)
	}

	logger.Info("Starting CAcert OpenID Connect Identity Provider",
		"version", version, "commit", commit, "date", date,
	)
	logger.Info("Server is starting")
	i18nService := services.InitI18n(logger, config.Strings("i18n.languages"))

	if err = i18nService.AddMessages(); err != nil {
		logger.Error("could not add messages for i18n", "error", err)
		os.Exit(1)
	}

	sessionAuthKey, sessionEncKey, csrfKey, err := configureSessionParameters(config)
	if err != nil {
		logger.Error("could not configure session parameters", "error", err)
		os.Exit(1)
	}

	services.InitSessionStore(sessionAuthKey, sessionEncKey)

	clientTransport, err := configureAdminClient(config)
	if err != nil {
		logger.Error("could not configure Hydra admin client", "error", err)
		os.Exit(1)
	}

	tc := handlers.PopulateTemplateCache()

	needsAuth := handlers.NewAuthMiddleware(logger, tc, i18nService).NeedsAuth

	indexHandler := handlers.NewIndex(logger, tc, i18nService)
	manageConsentHandler := handlers.NewManageConsent(logger, tc, i18nService, clientTransport.OAuth2API)
	revokeConsentHandler := handlers.NewRevokeConsent(logger, tc, i18nService, clientTransport.OAuth2API)

	loginHandler := handlers.NewLoginHandler(logger, tc, i18nService, clientTransport.OAuth2API)
	consentHandler := handlers.NewConsentHandler(logger, tc, i18nService, clientTransport.OAuth2API)
	logoutHandler := handlers.NewLogout(logger, clientTransport.OAuth2API)

	logoutSuccessHandler := handlers.NewLogoutSuccess(logger, tc, i18nService)
	errorHandler := handlers.NewErrorHandler(logger, i18nService)
	staticFiles := http.FileServer(http.FS(ui.Static))

	router := http.NewServeMux()
	router.HandleFunc("/", needsAuth(indexHandler))
	router.Handle("/manage-consent", needsAuth(manageConsentHandler))
	router.Handle("/revoke-consent/", needsAuth(revokeConsentHandler))
	router.Handle("/login", loginHandler)
	router.Handle("/consent", consentHandler)
	router.Handle("/logout", logoutHandler)
	router.Handle("/error", errorHandler)
	router.Handle("/logout-successful", logoutSuccessHandler)
	router.Handle("/health", handlers.NewHealthHandler())
	router.Handle("/images/", staticFiles)
	router.Handle("/css/", staticFiles)
	router.Handle("/js/", staticFiles)

	nextRequestID := func() string {
		return fmt.Sprintf("%d", time.Now().UnixNano())
	}

	tracing := handlers.Tracing(nextRequestID)
	logging := handlers.Logging(logger)
	hsts := handlers.EnableHSTS()
	csrfProtect := csrf.Protect(
		csrfKey,
		csrf.Secure(true),
		csrf.SameSite(csrf.SameSiteStrictMode),
		csrf.MaxAge(DefaultCSRFMaxAge))

	errorMiddleware, err := handlers.ErrorHandling(logger, tc, i18nService)
	if err != nil {
		logger.Error("could not initialize request error handling", "error", err)
		os.Exit(1)
	}

	handlerChain := tracing(logging(hsts(errorMiddleware(csrfProtect(router)))))

	err = startServer(logger, config, handlerChain)
	if err != nil {
		logger.Error("server start failed", "error", err)
		os.Exit(1)
	}
}

func configureAdminClient(config *koanf.Koanf) (*hydra.APIClient, error) {
	adminURL, err := url.Parse(config.MustString("admin.url"))
	if err != nil {
		return nil, fmt.Errorf("error parsing admin URL: %w", err)
	}

	configuration := hydra.NewConfiguration()
	configuration.Servers = []hydra.ServerConfiguration{
		{
			URL: adminURL.String(),
		},
	}

	tlsClientConfig := &tls.Config{MinVersion: tls.VersionTLS12, ServerName: adminURL.Hostname()}

	if config.Exists("api-client.rootCAs") {
		rootCAFile := config.MustString("api-client.rootCAs")
		caCertPool := x509.NewCertPool()

		pemBytes, err := os.ReadFile(rootCAFile)
		if err != nil {
			return nil, fmt.Errorf("could not read CA certificate file: %w", err)
		}

		caCertPool.AppendCertsFromPEM(pemBytes)
		tlsClientConfig.RootCAs = caCertPool
	}

	tlsClientTransport := &http.Transport{TLSClientConfig: tlsClientConfig}

	c := hydra.NewAPIClient(configuration)

	configuration.HTTPClient.Transport = tlsClientTransport

	return c, nil
}

func startServer(logger *slog.Logger, config *koanf.Koanf, handlerChain http.Handler) error {
	clientCertificateCAFile := config.MustString("security.client.ca-file")
	serverBindAddress := config.String("server.bind_address")
	serverName := config.String("server.name")
	serverPort := config.Int("server.port")

	clientCertPool := x509.NewCertPool()

	pemBytes, err := os.ReadFile(clientCertificateCAFile)
	if err != nil {
		return fmt.Errorf("could not load client CA certificates: %w", err)
	}

	clientCertPool.AppendCertsFromPEM(pemBytes)

	tlsConfig := &tls.Config{
		ServerName: serverName,
		MinVersion: tls.VersionTLS12,
		ClientAuth: tls.VerifyClientCertIfGiven,
		ClientCAs:  clientCertPool,
	}
	server := &http.Server{
		Addr:         fmt.Sprintf("%s:%d", serverBindAddress, serverPort),
		Handler:      handlerChain,
		ReadTimeout:  ReadTimeOut,
		WriteTimeout: WriteTimeOut,
		IdleTimeout:  IdleTimeout,
		TLSConfig:    tlsConfig,
	}

	done := make(chan bool)
	quit := make(chan os.Signal, 1)
	signal.Notify(quit, os.Interrupt)

	go func() {
		<-quit
		logger.Info("Server is shutting down...")
		atomic.StoreInt32(&handlers.Healthy, 0)

		ctx, cancel := context.WithTimeout(context.Background(), ShutdownTimeout)
		defer cancel()

		server.SetKeepAlivesEnabled(false)

		if err := server.Shutdown(ctx); err != nil {
			logger.Error("could not shutdown server gracefully", "error", err)
		}

		close(done)
	}()

	logger.Info(
		"Server is ready to handle requests",
		"address", server.Addr, "url", publicAddress(serverName, serverPort),
	)
	atomic.StoreInt32(&handlers.Healthy, 1)

	if err := server.ListenAndServeTLS(
		config.String("server.certificate"), config.String("server.key"),
	); err != nil && !errors.Is(err, http.ErrServerClosed) {
		logger.Error("could not listen on configured server address", "server_addr", server.Addr)

		return fmt.Errorf("could not create listener: %w", err)
	}

	<-done
	logger.Info("Server stopped")

	return nil
}

func publicAddress(serverName string, serverPort int) string {
	if serverPort != httpsDefaultPort {
		return fmt.Sprintf("https://%s:%d/", serverName, serverPort)
	}

	return fmt.Sprintf("https://%s/", serverName)
}

func configureSessionParameters(config *koanf.Koanf) ([]byte, []byte, []byte, error) { //nolint:cyclop
	sessionAuthKey, err := base64.StdEncoding.DecodeString(config.String("session.auth-key"))
	if err != nil {
		return nil, nil, nil, fmt.Errorf("could not decode session auth key: %w", err)
	}

	sessionEncKey, err := base64.StdEncoding.DecodeString(config.String("session.enc-key"))
	if err != nil {
		return nil, nil, nil, fmt.Errorf("could not decode session encryption key: %w", err)
	}

	csrfKey, err := base64.StdEncoding.DecodeString(config.String("security.csrf.key"))
	if err != nil {
		return nil, nil, nil, fmt.Errorf("could not decode CSRF key bytes: %w", err)
	}

	generated := false

	if len(sessionAuthKey) != sessionAuthKeyLength {
		sessionAuthKey, err = services.GenerateKey(sessionAuthKeyLength)
		if err != nil {
			return nil, nil, nil, fmt.Errorf("could not generate session authentication key: %w", err)
		}

		generated = true
	}

	if len(sessionEncKey) != sessionKeyLength {
		sessionEncKey, err = services.GenerateKey(sessionKeyLength)
		if err != nil {
			return nil, nil, nil, fmt.Errorf("could not generate session encryption key: %w", err)
		}

		generated = true
	}

	if len(csrfKey) < minCSRFKeyLength {
		csrfKey, err = services.GenerateKey(minCSRFKeyLength)
		if err != nil {
			return nil, nil, nil, fmt.Errorf("could not generate CSRF key: %w", err)
		}

		generated = true
	}

	if generated {
		_ = config.Load(confmap.Provider(map[string]interface{}{
			"session.auth-key":  base64.StdEncoding.EncodeToString(sessionAuthKey),
			"session.enc-key":   base64.StdEncoding.EncodeToString(sessionEncKey),
			"security.csrf.key": base64.StdEncoding.EncodeToString(csrfKey),
		}, "."), nil)

		tomlData, err := config.Marshal(toml.Parser())
		if err != nil {
			return nil, nil, nil, fmt.Errorf("could not encode session config: %w", err)
		}

		slog.Info("generated configuration values, put the following into your idp.toml")
		fmt.Printf("------\n%s------\n", string(tomlData)) //nolint:forbidigo
	}

	return sessionAuthKey, sessionEncKey, csrfKey, nil
}