// GoToSocial
// Copyright (C) GoToSocial Authors admin@gotosocial.org
// SPDX-License-Identifier: AGPL-3.0-or-later
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU Affero General Public License for more details.
//
// You should have received a copy of the GNU Affero General Public License
// along with this program.  If not, see <http://www.gnu.org/licenses/>.

package router

import (
	"context"
	"crypto/tls"
	"fmt"
	"net"
	"net/http"
	"time"

	"codeberg.org/gruf/go-bytesize"
	"codeberg.org/gruf/go-debug"
	"github.com/gin-gonic/gin"
	"github.com/superseriousbusiness/gotosocial/internal/config"
	"github.com/superseriousbusiness/gotosocial/internal/log"
	"golang.org/x/crypto/acme/autocert"
)

const (
	readTimeout        = 60 * time.Second
	writeTimeout       = 30 * time.Second
	idleTimeout        = 30 * time.Second
	readHeaderTimeout  = 30 * time.Second
	shutdownTimeout    = 30 * time.Second
	maxMultipartMemory = int64(8 * bytesize.MiB)
)

// Router provides the REST interface for gotosocial, using gin.
type Router interface {
	// Attach global gin middlewares to this router.
	AttachGlobalMiddleware(handlers ...gin.HandlerFunc) gin.IRoutes
	// AttachGroup attaches the given handlers into a group with the given relativePath as
	// base path for that group. It then returns the *gin.RouterGroup so that the caller
	// can add any extra middlewares etc specific to that group, as desired.
	AttachGroup(relativePath string, handlers ...gin.HandlerFunc) *gin.RouterGroup
	// Attach a single gin handler to the router with the given method and path.
	// To make middleware management easier, AttachGroup should be preferred where possible.
	// However, this function can be used for attaching single handlers that only require
	// global middlewares.
	AttachHandler(method string, path string, handler gin.HandlerFunc)

	// Attach 404 NoRoute handler
	AttachNoRouteHandler(handler gin.HandlerFunc)
	// Start the router
	Start()
	// Stop the router
	Stop(ctx context.Context) error
}

// router fulfils the Router interface using gin and logrus
type router struct {
	engine      *gin.Engine
	srv         *http.Server
	certManager *autocert.Manager
}

// Start starts the router nicely. It will serve two handlers if letsencrypt is enabled, and only the web/API handler if letsencrypt is not enabled.
func (r *router) Start() {
	// listen is the server start function, by
	// default pointing to regular HTTP listener,
	// but updated to TLS if LetsEncrypt is enabled.
	listen := r.srv.ListenAndServe

	// During config validation we already checked that both Chain and Key are set
	// so we can forego checking for both here
	if chain := config.GetTLSCertificateChain(); chain != "" {
		pkey := config.GetTLSCertificateKey()
		cer, err := tls.LoadX509KeyPair(chain, pkey)
		if err != nil {
			log.Fatalf(
				nil,
				"tls: failed to load keypair from %s and %s, ensure they are PEM-encoded and can be read by this process: %s",
				chain, pkey, err,
			)
		}
		r.srv.TLSConfig = &tls.Config{
			MinVersion:   tls.VersionTLS12,
			Certificates: []tls.Certificate{cer},
		}
		// TLS is enabled, update the listen function
		listen = func() error { return r.srv.ListenAndServeTLS("", "") }
	}

	if config.GetLetsEncryptEnabled() {
		// LetsEncrypt support is enabled

		// Prepare an HTTPS-redirect handler for LetsEncrypt fallback
		redirect := http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
			target := "https://" + r.Host + r.URL.Path
			if len(r.URL.RawQuery) > 0 {
				target += "?" + r.URL.RawQuery
			}
			http.Redirect(rw, r, target, http.StatusTemporaryRedirect)
		})

		go func() {
			// Take our own copy of HTTP server
			// with updated autocert manager endpoint
			srv := (*r.srv) //nolint
			srv.Handler = r.certManager.HTTPHandler(redirect)
			srv.Addr = fmt.Sprintf("%s:%d",
				config.GetBindAddress(),
				config.GetLetsEncryptPort(),
			)

			// Start the LetsEncrypt autocert manager HTTP server.
			log.Infof(nil, "letsencrypt listening on %s", srv.Addr)
			if err := srv.ListenAndServe(); err != nil &&
				err != http.ErrServerClosed {
				log.Fatalf(nil, "letsencrypt: listen: %s", err)
			}
		}()

		// TLS is enabled, update the listen function
		listen = func() error { return r.srv.ListenAndServeTLS("", "") }
	}

	// Pass the server handler through a debug pprof middleware handler.
	// For standard production builds this will be a no-op, but when the
	// "debug" or "debugenv" build-tag is set pprof stats will be served
	// at the standard "/debug/pprof" URL.
	r.srv.Handler = debug.WithPprof(r.srv.Handler)
	if debug.DEBUG {
		// Profiling requires timeouts longer than 30s, so reset these.
		log.Warn(nil, "resetting http.Server{} timeout to support profiling")
		r.srv.ReadTimeout = 0
		r.srv.WriteTimeout = 0
	}

	// Start the main listener.
	go func() {
		log.Infof(nil, "listening on %s", r.srv.Addr)
		if err := listen(); err != nil && err != http.ErrServerClosed {
			log.Fatalf(nil, "listen: %s", err)
		}
	}()
}

// Stop shuts down the router nicely
func (r *router) Stop(ctx context.Context) error {
	log.Infof(nil, "shutting down http router with %s grace period", shutdownTimeout)
	timeout, cancel := context.WithTimeout(ctx, shutdownTimeout)
	defer cancel()

	if err := r.srv.Shutdown(timeout); err != nil {
		return fmt.Errorf("error shutting down http router: %s", err)
	}

	log.Info(nil, "http router closed connections and shut down gracefully")
	return nil
}

// New returns a new Router.
//
// The router's Attach functions should be used *before* the router is Started.
//
// When the router's work is finished, Stop should be called on it to close connections gracefully.
//
// The provided context will be used as the base context for all requests passing
// through the underlying http.Server, so this should be a long-running context.
func New(ctx context.Context) (Router, error) {
	gin.SetMode(gin.TestMode)

	// create the actual engine here -- this is the core request routing handler for gts
	engine := gin.New()
	engine.MaxMultipartMemory = maxMultipartMemory
	engine.HandleMethodNotAllowed = true

	// set up IP forwarding via x-forward-* headers.
	trustedProxies := config.GetTrustedProxies()
	if err := engine.SetTrustedProxies(trustedProxies); err != nil {
		return nil, err
	}

	// set template functions
	LoadTemplateFunctions(engine)

	// load templates onto the engine
	if err := LoadTemplates(engine); err != nil {
		return nil, err
	}

	// use the passed-in command context as the base context for the server,
	// since we'll never want the server to live past the command anyway
	baseCtx := func(_ net.Listener) context.Context {
		return ctx
	}

	bindAddress := config.GetBindAddress()
	port := config.GetPort()
	addr := fmt.Sprintf("%s:%d", bindAddress, port)

	s := &http.Server{
		Addr:              addr,
		Handler:           engine, // use gin engine as handler
		ReadTimeout:       readTimeout,
		ReadHeaderTimeout: readHeaderTimeout,
		WriteTimeout:      writeTimeout,
		IdleTimeout:       idleTimeout,
		BaseContext:       baseCtx,
	}

	// We need to spawn the underlying server slightly differently depending on whether lets encrypt is enabled or not.
	// In either case, the gin engine will still be used for routing requests.
	leEnabled := config.GetLetsEncryptEnabled()

	var m *autocert.Manager
	if leEnabled {
		// le IS enabled, so roll up an autocert manager for handling letsencrypt requests
		host := config.GetHost()
		leCertDir := config.GetLetsEncryptCertDir()
		leEmailAddress := config.GetLetsEncryptEmailAddress()
		m = &autocert.Manager{
			Prompt:     autocert.AcceptTOS,
			HostPolicy: autocert.HostWhitelist(host),
			Cache:      autocert.DirCache(leCertDir),
			Email:      leEmailAddress,
		}
		s.TLSConfig = m.TLSConfig()
	}

	return &router{
		engine:      engine,
		srv:         s,
		certManager: m,
	}, nil
}