live-studio-audience/cmd/server/main.go

package main

import (
	"context"
	"embed"
	"encoding/base64"
	"encoding/json"
	"flag"
	"fmt"
	"io/fs"
	"log"
	"net/http"
	"os"
	"os/signal"
	"path"
	"regexp"
	"strings"
	"syscall"

	"golang.org/x/time/rate"
)

type Config struct {
	Addr string
	RPS  int
	fsDB string
}

type Handler struct {
	cfg     Config
	limiter *rate.Limiter
	db      DB
}

type DB interface {
	GetQuestions() ([]Question, error)
	GetQuestion(string) (Question, error)
	InsertAnswer(string, string, Answer) error
	GetAnswers(string) ([]Answer, error)
}

type fsDB string

type Question struct {
	ID      string
	Live    bool
	Closed  bool
	Text    string
	Options []string
}

type Answer struct {
	Text string
}

type Session struct {
	User struct {
		ID   string
		Name string
	}
}

func main() {
	ctx, can := signal.NotifyContext(context.Background(), syscall.SIGINT)
	defer can()
	if err := run(ctx); err != nil {
		panic(err)
	}
}

func run(ctx context.Context) error {
	cfg, err := newConfig()
	if err != nil {
		return err
	}
	return runHTTP(ctx, cfg)
}

func newConfig() (Config, error) {
	cfg := Config{}

	fs := flag.NewFlagSet(os.Args[0], flag.ContinueOnError)
	fs.StringVar(&cfg.Addr, "addr", ":8080", "address to listen on")
	fs.IntVar(&cfg.RPS, "rps", 100, "requests per second to serve")
	fs.StringVar(&cfg.fsDB, "fs-db", "/tmp/live-audience.d", "api dir to serve")

	err := fs.Parse(os.Args[1:])
	return cfg, err
}

func (cfg Config) NewHandler() Handler {
	return Handler{
		cfg:     cfg,
		limiter: rate.NewLimiter(rate.Limit(cfg.RPS), 10),
		db:      fsDB(cfg.fsDB),
	}
}

func (s Session) Empty() bool {
	return s == (Session{})
}

func runHTTP(ctx context.Context, cfg Config) error {
	server := &http.Server{
		Addr:    cfg.Addr,
		Handler: cfg.NewHandler(),
	}
	go func() {
		<-ctx.Done()
		server.Close()
	}()
	log.Println("listening on", cfg.Addr)
	if err := server.ListenAndServe(); err != nil && ctx.Err() == nil {
		return err
	}
	return nil
}

func (h Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if err := h.serveHTTP(w, r); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

func (h Handler) serveHTTP(w http.ResponseWriter, r *http.Request) error {
	h.limiter.Wait(r.Context())

	session, err := h.auth(r)
	if err != nil {
		return err
	}
	if session.Empty() {
		w.Header().Set("WWW-Authenticate", "Basic realm=xyz")
		w.WriteHeader(http.StatusUnauthorized)
		w.Write([]byte(`IDENTIFY YOURSELF!`))
		return nil
	}

	return h.handle(session, w, r)
}

func (h Handler) auth(r *http.Request) (Session, error) {
	user, pass, ok := r.BasicAuth()
	if !ok {
		return Session{}, nil
	}
	session := Session{}
	session.User.ID = base64.StdEncoding.EncodeToString([]byte(fmt.Sprintf("%s:%s", user, pass)))
	session.User.Name = user
	return session, nil
}

//go:embed internal/public
var _public embed.FS
var public = func() http.FileSystem {
	d, err := fs.Sub(_public, "internal/public")
	if err != nil {
		panic(err)
	}
	return http.FS(d)
}()

func (h Handler) handle(session Session, w http.ResponseWriter, r *http.Request) error {
	if !strings.HasPrefix(r.URL.Path, "/api/") {
		w.Header().Set("Cache-Control", "private, max-age=60")
		http.FileServer(public).ServeHTTP(w, r)
		return nil
	}

	handlers := map[string]func(Session, http.ResponseWriter, *http.Request) error{
		`^/api/v1/questions$`:               h.handleAPIV1Questions,
		`^/api/v1/questions/[^/]*$`:         h.handleAPIV1Question,
		`^/api/v1/questions/[^/]*/answers$`: h.handleAPIV1QuestionsAnswers,
	}
	for k, v := range handlers {
		if regexp.MustCompile(k).MatchString(r.URL.Path) {
			return v(session, w, r)
		}
	}
	http.NotFound(w, r)
	return nil
}

func (h Handler) handleAPIV1Question(session Session, w http.ResponseWriter, r *http.Request) error {
	qid := path.Base(r.URL.Path)
	q, err := h.db.GetQuestion(qid)
	if err != nil {
		return err
	}
	return json.NewEncoder(w).Encode(q)
}

func (h Handler) handleAPIV1Questions(session Session, w http.ResponseWriter, r *http.Request) error {
	qs, err := h.db.GetQuestions()
	if err != nil {
		return err
	}
	return json.NewEncoder(w).Encode(qs)
}

func (h Handler) handleAPIV1QuestionsAnswers(session Session, w http.ResponseWriter, r *http.Request) error {
	switch r.Method {
	case http.MethodGet:
		return h.handleAPIV1QuestionsAnswersGet(session, w, r)
	case http.MethodPost:
		return h.handleAPIV1QuestionsAnswersPost(session, w, r)
	}
	http.NotFound(w, r)
	return nil
}

func (h Handler) handleAPIV1QuestionsAnswersGet(session Session, w http.ResponseWriter, r *http.Request) error {
	qid := path.Base(path.Dir(r.URL.Path))
	as, err := h.db.GetAnswers(qid)
	if err != nil {
		return err
	}
	return json.NewEncoder(w).Encode(as)
}

func (h Handler) handleAPIV1QuestionsAnswersPost(session Session, w http.ResponseWriter, r *http.Request) error {
	qid := path.Base(path.Dir(r.URL.Path))
	uid := session.User.ID
	var a Answer
	if err := json.NewDecoder(r.Body).Decode(&a); err != nil {
		return fmt.Errorf("failed to read answer: %w", err)
	}
	return h.db.InsertAnswer(qid, uid, a)
}

func (db fsDB) GetQuestion(qid string) (Question, error) {
	p := db.path(qid)
	b, err := os.ReadFile(p)
	if err != nil {
		return Question{}, err
	}

	var q Question
	if err := json.Unmarshal(b, &q); err != nil {
		return Question{}, fmt.Errorf("failed to parse %s as question: %w", b, err)
	}
	q.ID = qid
	return q, nil
}

func (db fsDB) InsertAnswer(qid, uid string, a Answer) error {
	p := path.Join(db.path(qid)+".d", uid)
	os.MkdirAll(path.Dir(p), os.ModePerm)
	b, err := json.Marshal(a)
	if err != nil {
		return err
	}
	if _, err := os.Stat(p); !os.IsNotExist(err) {
		return nil
	}
	return os.WriteFile(p, b, os.ModePerm)
}

func (db fsDB) GetQuestions() ([]Question, error) {
	p := db.path("")
	entries, err := os.ReadDir(p)
	if err != nil {
		return nil, err
	}
	results := []Question{}
	for _, entry := range entries {
		if strings.HasPrefix(path.Base(entry.Name()), ".") || entry.IsDir() {
			continue
		}
		qid := path.Base(entry.Name())
		q, err := db.GetQuestion(qid)
		if err != nil {
			return nil, err
		}
		results = append(results, q)
	}
	return results, nil
}

func (db fsDB) GetAnswers(qid string) ([]Answer, error) {
	p := db.path(qid) + ".d"
	entries, err := os.ReadDir(p)
	if os.IsNotExist(err) {
		return nil, nil
	}
	if err != nil {
		return nil, err
	}
	results := []Answer{}
	for _, entry := range entries {
		if strings.HasPrefix(path.Base(entry.Name()), ".") {
			continue
		}
		b, err := os.ReadFile(path.Join(p, entry.Name()))
		if err != nil {
			return nil, err
		}
		var a Answer
		if err := json.Unmarshal(b, &a); err != nil {
			return nil, fmt.Errorf("failed to parse %s as answer: %w", path.Join(p, entry.Name()), err)
		}
		results = append(results, a)
	}
	return results, nil
}

func (db fsDB) path(q string) string {
	return path.Join(string(db), q)
}