package oauth

import (
	"context"
	"crypto/rand"
	"fmt"
	"log"
	"net/http"
	"sync"

	"golang.org/x/oauth2"
)

func GenerateToken(
	ctx *context.Context,
	oauth2Config *oauth2.Config,
) (*oauth2.Token, error) {
	verifier := oauth2.GenerateVerifier()

	state := rand.Text()

	var token *oauth2.Token
	wg := sync.WaitGroup{}

	var server http.Server
	server.Addr = "127.0.0.1"
	server.Handler = http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			code := r.URL.Query().Get("code")
			scope := r.URL.Query().Get("scope")
			resState := r.URL.Query().Get("state")

			if len(code) == 0 || len(scope) == 0 || resState != state {
				http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
				return
			}

			t, err := oauth2Config.Exchange(*ctx, code, oauth2.VerifierOption(verifier))
			if err != nil {
				log.Fatalf("Could not exchange OAuth2 code: %v", err)
				http.Error( w,
					fmt.Sprintf("Could not exchange OAuth2 code: %v", err),
					http.StatusBadRequest,
				)
				return
			}

			token = t
			http.Error(
				w,
				"Authentication successful! You may now close this tab.",
				http.StatusOK,
			)
			if f, ok := w.(http.Flusher); ok {
				f.Flush()
			}

			wg.Done()
			server.Close()
		},
	)

	url := oauth2Config.AuthCodeURL(
		state,
		oauth2.AccessTypeOffline,
		oauth2.S256ChallengeOption(verifier),
	)
	log.Printf("Log in with Twitch: %s\n\n", url)

	wg.Add(1)
	if err := server.ListenAndServe(); err != http.ErrServerClosed {
		return nil, fmt.Errorf("http: %v", err)
	}
	wg.Wait()

	return token, nil
}