package main

import (
	"encoding/base64"
	"encoding/json"
	"errors"
	"hash/crc32"
	"net/http"
	"os"
	"time"

	"github.com/google/uuid"
)

var cookieSecret = os.Getenv("COOKIE_SECRET")

type User struct {
	User   string
	Groups []string
}

type Cookie struct {
	Hash  string
	Salt  string
	Value string
}

func (server *Server) authenticate(w http.ResponseWriter, r *http.Request) (*Server, bool, error) {
	if done, err := server.parseLogin(w, r); err != nil {
		return nil, false, err
	} else if done {
		return nil, true, nil
	}

	if ok, err := needsLogin(r); err != nil {
		return nil, false, err
	} else if ok {
		promptLogin(w)
		return nil, true, nil
	}

	user, _ := loginCookie(r)
	namespace, _ := namespaceCookie(r)
	return server.WithLoggedIn(user.User, namespace, user.Groups), false, nil
}

func promptLogin(w http.ResponseWriter) {
	w.Header().Set("WWW-Authenticate", "Basic")
	w.WriteHeader(http.StatusUnauthorized)
}

func (server *Server) parseLogin(w http.ResponseWriter, r *http.Request) (bool, error) {
	username, password, ok := r.BasicAuth()
	if !ok {
		return false, nil
	}
	ok, err := server.auth.Login(username, password)
	if err != nil {
		return false, err
	}
	if !ok {
		promptLogin(w)
		return true, nil
	}
	groups, err := server.auth.Groups(username)
	if err != nil {
		return false, err
	}
	if len(groups) == 0 {
		return false, errors.New("user has no groups")
	}
	setLoginCookie(w, r, User{
		User:   username,
		Groups: groups,
	})
	setNamespaceCookie(w, r, groups[0])
	return false, nil
}

func needsLogin(r *http.Request) (bool, error) {
	user, ok := loginCookie(r)
	if !ok {
		return true, nil
	}
	group, ok := namespaceCookie(r)
	if !ok {
		return true, nil
	}
	for i := range user.Groups {
		if group == user.Groups[i] {
			return false, nil
		}
	}
	return true, nil
}

func setLoginCookie(w http.ResponseWriter, r *http.Request, user User) {
	cookie := &http.Cookie{
		Name:    "login",
		Value:   encodeUserCookie(user),
		Expires: time.Now().Add(time.Hour * 24),
	}
	w.Header().Add("Set-Cookie", cookie.String())
	r.AddCookie(cookie)
}

func loginCookie(r *http.Request) (User, bool) {
	c, ok := getCookie("login", r)
	if !ok {
		return User{}, false
	}
	return decodeUserCookie(c)
}

func setNamespaceCookie(w http.ResponseWriter, r *http.Request, s string) {
	cookie := &http.Cookie{
		Name:    "namespace",
		Value:   s,
		Expires: time.Now().Add(time.Hour * 24),
	}
	w.Header().Add("Set-Cookie", cookie.String())
	r.AddCookie(cookie)
}

func namespaceCookie(r *http.Request) (string, bool) {
	return getCookie("namespace", r)
}

func getCookie(key string, r *http.Request) (string, bool) {
	cookies := r.Cookies()
	for i := range cookies {
		if cookies[i].Name == key && (cookies[i].Expires.IsZero() || time.Now().Before(cookies[i].Expires)) {
			return cookies[i].Value, true
		}
	}
	return "", false
}

func decodeUserCookie(raw string) (User, bool) {
	decoded, ok := decodeCookie(raw)
	if !ok {
		return User{}, ok
	}
	var user User
	err := json.Unmarshal([]byte(decoded), &user)
	return user, err == nil
}

func encodeUserCookie(user User) string {
	b, err := json.Marshal(user)
	if err != nil {
		panic(err)
	}
	return encodeCookie(string(b))
}

func encodeCookie(s string) string {
	cookie := Cookie{
		Salt:  uuid.New().String(),
		Value: s,
	}
	hash := crc32.NewIEEE()
	hash.Write([]byte(cookieSecret))
	hash.Write([]byte(cookie.Salt))
	hash.Write([]byte(cookie.Value))
	cookie.Hash = base64.StdEncoding.EncodeToString(hash.Sum(nil))
	b, err := json.Marshal(cookie)
	if err != nil {
		panic(err)
	}
	return base64.StdEncoding.EncodeToString(b)
}

func decodeCookie(s string) (string, bool) {
	b, err := base64.StdEncoding.DecodeString(s)
	if err != nil {
		return "", false
	}
	var cookie Cookie
	if err := json.Unmarshal(b, &cookie); err != nil {
		return "", false
	}
	hash := crc32.NewIEEE()
	hash.Write([]byte(cookieSecret))
	hash.Write([]byte(cookie.Salt))
	hash.Write([]byte(cookie.Value))
	if got := base64.StdEncoding.EncodeToString(hash.Sum(nil)); cookie.Hash != got {
		return "", false
	}
	return cookie.Value, true
}