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

package httpserver

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

	"git.netflux.io/rob/elon-eats-my-tweets/config"
	"github.com/labstack/echo/v4"
	"golang.org/x/oauth2"
)

type handler struct {
	oauth2Config *oauth2.Config
}

func newHandler(cfg config.Config) *handler {
	return &handler{
		&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(c echo.Context) error {
	return c.Render(http.StatusOK, "index", nil)
}

func (h *handler) getLogin(c echo.Context) error {
	url := h.oauth2Config.AuthCodeURL(
		// TODO: implement state and code_challenge tokens
		"state",
		oauth2.SetAuthURLParam("code_challenge", "challenge"),
		oauth2.SetAuthURLParam("code_challenge_method", "plain"),
	)
	return c.Redirect(http.StatusTemporaryRedirect, url)
}

func (h *handler) getCallback(c echo.Context) error {
	code := c.QueryParam("code")
	if code == "" {
		return echo.NewHTTPError(http.StatusBadRequest, "empty code")
	}

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

	return c.String(http.StatusOK, "ok")
}

func Start(cfg config.Config) error {
	e := echo.New()

	e.Renderer = &Template{
		templates: template.Must(template.ParseGlob(filepath.Join(cfg.PublicPath, "views/", "*.html"))),
	}

	h := newHandler(cfg)
	e.GET("/", h.getIndex)
	e.GET("/login", h.getLogin)
	e.GET("/callback", h.getCallback)

	return e.Start(":8000")
}