elon-eats-my-tweets/httpserver/httpserver.go

package httpserver

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"path/filepath"
	"text/template"

	"git.netflux.io/rob/elon-eats-my-tweets/config"
	"github.com/go-chi/chi"
	"github.com/go-chi/chi/middleware"
	"golang.org/x/oauth2"
)

type handler struct {
	templates    *template.Template
	oauth2Config *oauth2.Config
}

func newHandler(cfg config.Config, templates *template.Template) *handler {
	return &handler{
		templates: templates,
		oauth2Config: &oauth2.Config{
			ClientID:     cfg.Twitter.ClientID,
			ClientSecret: cfg.Twitter.ClientSecret,
			RedirectURL:  cfg.Twitter.CallbackURL,
			Scopes:       []string{"tweet.read", "tweet.write", "users.read", "offline.access"},
			Endpoint: oauth2.Endpoint{
				AuthURL:  "https://twitter.com/i/oauth2/authorize",
				TokenURL: "https://api.twitter.com/2/oauth2/token",
			},
		},
	}
}

func (h *handler) getIndex(w http.ResponseWriter, r *http.Request) {
	if err := h.templates.ExecuteTemplate(w, "index", nil); err != nil {
		log.Printf("error rendering template: %v", err)
		http.Error(w, "error rendering template", http.StatusInternalServerError)
		return
	}
}

func (h *handler) getLogin(w http.ResponseWriter, r *http.Request) {
	url := h.oauth2Config.AuthCodeURL(
		// TODO: implement state and code_challenge tokens
		"state",
		oauth2.SetAuthURLParam("code_challenge", "challenge"),
		oauth2.SetAuthURLParam("code_challenge_method", "plain"),
	)
	http.Redirect(w, r, url, http.StatusTemporaryRedirect)
}

func (h *handler) getCallback(w http.ResponseWriter, r *http.Request) {
	code := r.URL.Query().Get("code")
	if code == "" {
		http.Error(w, "empty code", http.StatusBadRequest)
		return
	}

	_, err := h.oauth2Config.Exchange(context.Background(), code, oauth2.SetAuthURLParam("code_verifier", "challenge"))
	if err != nil {
		log.Printf("error exchanging code: %v", err)
		http.Error(w, "error exchanging code", http.StatusInternalServerError)
		return
	}

	w.WriteHeader(http.StatusOK)
	w.Header().Set("content-type", "text/html")
	if _, err = w.Write([]byte("ok")); err != nil {
		log.Printf("error writing response: %v", err)
	}
}

func Start(cfg config.Config) error {
	r := chi.NewRouter()
	r.Use(middleware.RequestID)
	r.Use(middleware.RealIP)
	r.Use(middleware.Logger)
	r.Use(middleware.Recoverer)

	templates, err := template.ParseGlob(filepath.Join(cfg.PublicPath, "views", "*.html"))
	if err != nil {
		return fmt.Errorf("error loading templates: %v", err)
	}

	h := newHandler(cfg, templates)
	r.Get("/", h.getIndex)
	r.Get("/login", h.getLogin)
	r.Get("/callback", h.getCallback)

	return http.ListenAndServe(":8000", r)
}