package main

import (
	"context"
	"crypto/tls"
	"crypto/x509"
	"encoding/base64"
	"fmt"
	"github.com/Masterminds/sprig"
	"github.com/gorilla/sessions"
	"github.com/jmoiron/sqlx"
	_ "github.com/mattn/go-sqlite3"
	"gopkg.in/yaml.v2"
	"html/template"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"strconv"
	"strings"
)

var logger *log.Logger
var config *Config
var store *sessions.CookieStore

const sessionCookieName = "votesession"

func getTemplateFilenames(templates []string) (result []string) {
	result = make([]string, len(templates))
	for i := range templates {
		result[i] = fmt.Sprintf("templates/%s", templates[i])
	}
	return result
}

func renderTemplate(w http.ResponseWriter, templates []string, context interface{}) {
	t := template.Must(template.New(templates[0]).Funcs(sprig.FuncMap()).ParseFiles(getTemplateFilenames(templates)...))
	if err := t.Execute(w, context); err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
	}
}

type contextKey int

const (
	ctxNeedsAuth contextKey = iota
	ctxVoter     contextKey = iota
	ctxDecision  contextKey = iota
)

func authenticateRequest(w http.ResponseWriter, r *http.Request, handler func(http.ResponseWriter, *http.Request)) {
	for _, cert := range r.TLS.PeerCertificates {
		for _, extKeyUsage := range cert.ExtKeyUsage {
			if extKeyUsage == x509.ExtKeyUsageClientAuth {
				for _, emailAddress := range cert.EmailAddresses {
					voter, err := FindVoterByAddress(emailAddress)
					if err != nil {
						http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
						return
					}
					if voter != nil {
						handler(w, r.WithContext(context.WithValue(r.Context(), ctxVoter, voter)))
						return
					}
				}
			}
		}
	}
	needsAuth, ok := r.Context().Value(ctxNeedsAuth).(bool)
	if ok && needsAuth {
		w.WriteHeader(http.StatusForbidden)
		renderTemplate(w, []string{"denied.html"}, nil)
		return
	}
	handler(w, r)
}

type motionParameters struct {
	ShowVotes bool
}

type motionListParameters struct {
	Page int64
	Flags struct {
		Confirmed, Withdraw, Unvoted bool
	}
}

func parseMotionParameters(r *http.Request) motionParameters {
	var m = motionParameters{}
	m.ShowVotes, _ = strconv.ParseBool(r.URL.Query().Get("showvotes"))
	return m
}

func parseMotionListParameters(r *http.Request) motionListParameters {
	var m = motionListParameters{}
	if page, err := strconv.ParseInt(r.URL.Query().Get("page"), 10, 0); err != nil {
		m.Page = 1
	} else {
		m.Page = page
	}
	m.Flags.Withdraw, _ = strconv.ParseBool(r.URL.Query().Get("withdraw"))
	m.Flags.Unvoted, _ = strconv.ParseBool(r.URL.Query().Get("unvoted"))

	if r.Method == http.MethodPost {
		m.Flags.Confirmed, _ = strconv.ParseBool(r.PostFormValue("confirm"))
	}
	return m
}

func motionListHandler(w http.ResponseWriter, r *http.Request) {
	params := parseMotionListParameters(r)
	session, err := store.Get(r, sessionCookieName)
	if err != nil {
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}

	var templateContext struct {
		Decisions          []*DecisionForDisplay
		Voter              *Voter
		Params             *motionListParameters
		PrevPage, NextPage int64
		PageTitle          string
		Flashes            interface{}
	}
	if voter, ok := r.Context().Value(ctxVoter).(*Voter); ok {
		templateContext.Voter = voter
	}
	if flashes := session.Flashes(); len(flashes) > 0 {
		templateContext.Flashes = flashes
	}
	session.Save(r, w)
	templateContext.Params = &params

	if params.Flags.Unvoted && templateContext.Voter != nil {
		if templateContext.Decisions, err = FindVotersUnvotedDecisionsForDisplayOnPage(
			params.Page, templateContext.Voter); err != nil {
			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
			return
		}
	} else {
		if templateContext.Decisions, err = FindDecisionsForDisplayOnPage(params.Page); err != nil {
			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
			return
		}
	}

	if len(templateContext.Decisions) > 0 {
		olderExists, err := templateContext.Decisions[len(templateContext.Decisions)-1].OlderExists()
		if err != nil {
			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
			return
		}
		if olderExists {
			templateContext.NextPage = params.Page + 1
		}
	}

	if params.Page > 1 {
		templateContext.PrevPage = params.Page - 1
	}

	renderTemplate(w, []string{"motions.html", "motion_fragments.html", "header.html", "footer.html"}, templateContext)
}

func motionHandler(w http.ResponseWriter, r *http.Request) {
	params := parseMotionParameters(r)

	decision, ok := getDecisionFromRequest(r)
	if !ok {
		http.Error(w, http.StatusText(http.StatusPreconditionFailed), http.StatusPreconditionFailed)
		return
	}

	var templateContext struct {
		Decision           *DecisionForDisplay
		Voter              *Voter
		Params             *motionParameters
		PrevPage, NextPage int64
		PageTitle          string
		Flashes            interface{}
	}
	voter, ok := getVoterFromRequest(r)
	if ok {
		templateContext.Voter = voter
	}
	templateContext.Params = &params
	if params.ShowVotes {
		if err := decision.LoadVotes(); err != nil {
			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
			return
		}
	}
	templateContext.Decision = decision
	templateContext.PageTitle = fmt.Sprintf("Motion %s: %s", decision.Tag, decision.Title)
	renderTemplate(w, []string{"motion.html", "motion_fragments.html", "header.html", "footer.html"}, templateContext)
}

func singleDecisionHandler(w http.ResponseWriter, r *http.Request, tag string, handler func(http.ResponseWriter, *http.Request)) {
	decision, err := FindDecisionForDisplayByTag(tag)
	if err != nil {
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}
	if decision == nil {
		http.NotFound(w, r)
		return
	}
	handler(w, r.WithContext(context.WithValue(r.Context(), ctxDecision, decision)))
}

type motionActionHandler interface {
	Handle(w http.ResponseWriter, r *http.Request)
	NeedsAuth() bool
}

type authenticationRequiredHandler struct{}

func (authenticationRequiredHandler) NeedsAuth() bool {
	return true
}

type withDrawMotionAction struct {
	authenticationRequiredHandler
}

func getVoterFromRequest(r *http.Request) (voter *Voter, ok bool) {
	voter, ok = r.Context().Value(ctxVoter).(*Voter)
	return
}

func getDecisionFromRequest(r *http.Request) (decision *DecisionForDisplay, ok bool) {
	decision, ok = r.Context().Value(ctxDecision).(*DecisionForDisplay)
	return
}

func (withDrawMotionAction) Handle(w http.ResponseWriter, r *http.Request) {
	voter, voter_ok := getVoterFromRequest(r)
	decision, decision_ok := getDecisionFromRequest(r)

	if !voter_ok || !decision_ok || decision.Status != voteStatusPending {
		http.Error(w, http.StatusText(http.StatusPreconditionFailed), http.StatusPreconditionFailed)
		return
	}

	switch r.Method {
	case http.MethodPost:
		if confirm, err := strconv.ParseBool(r.PostFormValue("confirm")); err != nil {
			log.Println("could not parse confirm parameter:", err)
			http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
		} else if confirm {
			WithdrawMotion(&decision.Decision, voter)
		} else {
			http.Error(w, http.StatusText(http.StatusBadRequest), http.StatusBadRequest)
		}
		http.Redirect(w, r, "/motions/", http.StatusTemporaryRedirect)
		return
	default:
		fmt.Fprintln(w, "Withdraw motion", decision.Tag)
	}
}

type editMotionAction struct {
	authenticationRequiredHandler
}

func (editMotionAction) Handle(w http.ResponseWriter, r *http.Request) {
	decision, ok := getDecisionFromRequest(r)
	if !ok || decision.Status != voteStatusPending {
		http.Error(w, http.StatusText(http.StatusPreconditionFailed), http.StatusPreconditionFailed)
		return
	}
	fmt.Fprintln(w, "Edit motion", decision.Tag)
	// TODO: implement
}

type motionsHandler struct{}

func (h motionsHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if err := db.Ping(); err != nil {
		logger.Fatal(err)
	}

	subURL := r.URL.Path

	var motionActionMap = map[string]motionActionHandler{
		"withdraw": withDrawMotionAction{},
		"edit":     editMotionAction{},
	}

	switch {
	case subURL == "":
		authenticateRequest(w, r.WithContext(context.WithValue(r.Context(), ctxNeedsAuth, false)), motionListHandler)
		return
	case strings.Count(subURL, "/") == 1:
		parts := strings.Split(subURL, "/")
		logger.Printf("handle %v\n", parts)
		motionTag := parts[0]
		action, ok := motionActionMap[parts[1]]
		if !ok {
			http.NotFound(w, r)
			return
		}
		authenticateRequest(
			w, r.WithContext(context.WithValue(r.Context(), ctxNeedsAuth, action.NeedsAuth())),
			func(w http.ResponseWriter, r *http.Request) {
				singleDecisionHandler(w, r, motionTag, action.Handle)
			})
		logger.Printf("motion: %s, action: %s\n", motionTag, action)
		return
	case strings.Count(subURL, "/") == 0:
		authenticateRequest(w, r.WithContext(context.WithValue(r.Context(), ctxNeedsAuth, false)),
			func(w http.ResponseWriter, r *http.Request) {
				singleDecisionHandler(w, r, subURL, motionHandler)
			})
		return
	default:
		http.NotFound(w, r)
		return
	}
}

func newMotionHandler(w http.ResponseWriter, r *http.Request) {
	voter, ok := getVoterFromRequest(r)
	if !ok {
		http.Error(w, http.StatusText(http.StatusPreconditionFailed), http.StatusPreconditionFailed)
	}

	templates := []string{"newmotion_form.html", "header.html", "footer.html"}
	var templateContext struct {
		Form      NewDecisionForm
		PageTitle string
		Voter     *Voter
		Flashes   interface{}
	}
	switch r.Method {
	case http.MethodPost:
		form := NewDecisionForm{
			Title:    r.FormValue("Title"),
			Content:  r.FormValue("Content"),
			VoteType: r.FormValue("VoteType"),
			Due:      r.FormValue("Due"),
		}

		if valid, data := form.Validate(); !valid {
			templateContext.Voter = voter
			templateContext.Form = form
			renderTemplate(w, templates, templateContext)
		} else {
			if err := CreateMotion(data, voter); err != nil {
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
				return
			}
			session, err := store.Get(r, sessionCookieName)
			if err != nil {
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
				return
			}
			session.AddFlash("The motion has been proposed!")
			session.Save(r, w)

			http.Redirect(w, r, "/motions/", http.StatusTemporaryRedirect)
		}

		return
	default:
		templateContext.Voter = voter
		templateContext.Form = NewDecisionForm{
			VoteType: strconv.FormatInt(voteTypeMotion, 10),
		}
		renderTemplate(w, templates, templateContext)
	}
}

type Config struct {
	BoardMailAddress     string `yaml:"board_mail_address"`
	NoticeSenderAddress  string `yaml:"notice_sender_address"`
	DatabaseFile         string `yaml:"database_file"`
	ClientCACertificates string `yaml:"client_ca_certificates"`
	ServerCert           string `yaml:"server_certificate"`
	ServerKey            string `yaml:"server_key"`
	CookieSecret         string `yaml:"cookie_secret"`
}

func init() {
	logger = log.New(os.Stderr, "boardvoting: ", log.LstdFlags|log.LUTC|log.Lshortfile)

	source, err := ioutil.ReadFile("config.yaml")
	if err != nil {
		logger.Fatal(err)
	}
	if err := yaml.Unmarshal(source, &config); err != nil {
		logger.Fatal(err)
	}

	cookieSecret, err := base64.StdEncoding.DecodeString(config.CookieSecret)
	if err != nil {
		logger.Fatal(err)
	}
	if len(cookieSecret) < 32 {
		logger.Fatalln("Cookie secret is less than 32 bytes long")
	}
	store = sessions.NewCookieStore(cookieSecret)
	logger.Println("read configuration")
}

func main() {
	var err error
	db, err = sqlx.Open("sqlite3", config.DatabaseFile)
	if err != nil {
		logger.Fatal(err)
	}
	defer db.Close()

	http.Handle("/motions/", http.StripPrefix("/motions/", motionsHandler{}))
	http.HandleFunc("/newmotion/", func(w http.ResponseWriter, r *http.Request) {
		authenticateRequest(w, r.WithContext(context.WithValue(r.Context(), ctxNeedsAuth, true)), newMotionHandler)
	})
	http.Handle("/static/", http.FileServer(http.Dir(".")))
	http.Handle("/", http.RedirectHandler("/motions/", http.StatusMovedPermanently))

	// load CA certificates for client authentication
	caCert, err := ioutil.ReadFile(config.ClientCACertificates)
	if err != nil {
		logger.Fatal(err)
	}
	caCertPool := x509.NewCertPool()
	if !caCertPool.AppendCertsFromPEM(caCert) {
		logger.Fatal("could not initialize client CA certificate pool")
	}

	// setup HTTPS server
	tlsConfig := &tls.Config{
		ClientCAs:  caCertPool,
		ClientAuth: tls.VerifyClientCertIfGiven,
	}
	tlsConfig.BuildNameToCertificate()

	server := &http.Server{
		Addr:      ":8443",
		TLSConfig: tlsConfig,
	}

	logger.Printf("Launching application on https://localhost%s/\n", server.Addr)

	if err = server.ListenAndServeTLS(config.ServerCert, config.ServerKey); err != nil {
		logger.Fatal("ListenAndServerTLS: ", err)
	}
}