core/handlers/handlers.go

package api

import (
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"path/filepath"
	"runtime/debug"

	"gogs.carducci-dante.gov.it/karmen/core/orm"
	"gogs.carducci-dante.gov.it/karmen/core/renderer"

	jwtmiddleware "github.com/auth0/go-jwt-middleware"
	jwt "github.com/dgrijalva/jwt-go"
	"github.com/gorilla/mux"
	"github.com/gorilla/sessions"
)

var (
	signingKey    = []byte("secret")
	store         = sessions.NewCookieStore([]byte("something-very-secret"))
	jwtMiddleware = jwtmiddleware.New(jwtmiddleware.Options{
		ValidationKeyGetter: func(token *jwt.Token) (interface{}, error) {
			return signingKey, nil
		},
		SigningMethod: jwt.SigningMethodHS256,
		Extractor:     fromCookie,
		ErrorHandler:  onError,
	})

	crud []string = []string{"add", "show", "update", "delete"}
)

type User struct {
	Name  string
	Admin bool
}

// Generate CRUD handlers
func generateHandler(r *mux.Router, base string) {
	r.Handle(fmt.Sprintf("/%s", base), jwtMiddleware.Handler(recoverHandler(generalHandler(base, fmt.Sprintf("/%s", base))))).Methods("GET")
	r.Handle(fmt.Sprintf("/%s/{id}", base), jwtMiddleware.Handler(recoverHandler(generalHandler(base, fmt.Sprintf("/%s/{id}", base))))).Methods("GET")
	r.Handle(fmt.Sprintf("/%s/add/", base), jwtMiddleware.Handler(recoverHandler(generalHandler(base, fmt.Sprintf("/%s/add/", base))))).Methods("GET", "POST")
	r.Handle(fmt.Sprintf("/%s/{id}/update", base), jwtMiddleware.Handler(recoverHandler(generalHandler(base, fmt.Sprintf("/%s/{id}/update", base))))).Methods("GET", "POST")
	r.Handle(fmt.Sprintf("/%s/{id}/delete", base), jwtMiddleware.Handler(recoverHandler(generalHandler(base, fmt.Sprintf("/%s/{id}/delete", base))))).Methods("POST")
}

func Handlers() *mux.Router {
	r := mux.NewRouter()

	// Authentication

	r.Handle("/login", loginHandler())
	r.Handle("/logout", logoutHandler())

	// Dashboard

	r.Handle("/", jwtMiddleware.Handler(recoverHandler(dashboardHandler())))

	// Generate handlers

	for _, model := range []string{"teachers", "activities"} {
		generateHandler(r, model)
	}

	// Static file server

	r.PathPrefix("/").Handler(http.FileServer(http.Dir("./dist/")))

	return r
}

func onError(w http.ResponseWriter, r *http.Request, err string) {
	http.Redirect(w, r, "/login", http.StatusTemporaryRedirect)
}

func respondWithStaticFile(w http.ResponseWriter, filename string) error {
	f, err := ioutil.ReadFile(filepath.Join("public/html", filename))
	if err != nil {
		return err
	}
	w.Write(f)
	return nil
}

func fromCookie(r *http.Request) (string, error) {
	session, err := store.Get(r, "login-session")
	if err != nil {
		return "", nil
	}

	if session.Values["token"] == nil {
		return "", nil
	}

	token := session.Values["token"].([]uint8)

	return string(token), nil
}

func recoverHandler(next http.Handler) http.Handler {
	fn := func(w http.ResponseWriter, r *http.Request) {
		defer func() {
			if err := recover(); err != nil {
				panicMsg := fmt.Sprintf("PANIC: %v\n\n== STACKTRACE ==\n%s", err, debug.Stack())
				log.Print(panicMsg)
				http.Error(w, panicMsg, http.StatusInternalServerError)
			}
		}()
		next.ServeHTTP(w, r)
	}
	return http.HandlerFunc(fn)
}

func generalHandler(base, path string) http.Handler {
	fn := func(w http.ResponseWriter, r *http.Request) {
		var (
			ok     bool
			getFn  orm.GetFn
			postFn orm.PostFn
		)
		if r.Method == "GET" {
			getFn, ok = orm.Get[path]
		} else {
			postFn, ok = orm.Post[path]
		}
		if !ok {
			renderer.Render[r.URL.Query()["format"][0]](w, r, fmt.Errorf("Can't find ORM function for path %s!", path))
		} else {
			if r.Method == "GET" {
				data, err := getFn(mux.Vars(r))
				if err != nil {
					renderer.Render[r.URL.Query()["format"][0]](w, r, err)
				} else {
					renderer.Render[r.URL.Query()["format"][0]](w, r, data, r.URL.Query())
				}
			} else {
				data, err := postFn(mux.Vars(r), r)
				if err != nil {
					renderer.Render["html"](w, r, err)
				} else {
					if mux.Vars(r)["id"] != "" {
						http.Redirect(w, r,
							fmt.Sprintf(
								"/%s/%s?format=html&tpl_layout=base&tpl_content=%s_show",
								base,
								mux.Vars(r)["id"],
								base,
							),
							http.StatusSeeOther,
						)
					} else {
						http.Redirect(w, r,
							fmt.Sprintf(
								"/%s/%d?format=html&tpl_layout=base&tpl_content=%s_show",
								base,
								data.GetID(),
								base,
							),
							http.StatusSeeOther,
						)
					}

				}
			}
		}
	}

	return http.HandlerFunc(fn)
}