package main

import (
	"context"
	"encoding/json"
	"errors"
	"io/ioutil"
	"net/http"

	"github.com/go-chi/chi"
	"github.com/gorilla/websocket"
	"github.com/knadh/niltalk/internal/hub"
	"golang.org/x/crypto/bcrypt"
)

const (
	hasAuth = 1 << iota
	hasRoom
)

type sess struct {
	ID     string
	Handle string
}

// reqCtx is the context injected into every request.
type reqCtx struct {
	app  *App
	room *hub.Room
	sess sess
}

// jsonResp is the envelope for all JSON API responses.
type jsonResp struct {
	Error *string     `json:"error"`
	Data  interface{} `json:"data"`
}

// tplWrap is the envelope for all HTML template executions.
type tpl struct {
	Config *hub.Config
	Data   tplData
}

type tplData struct {
	Title       string
	Description string
	Room        interface{}
	Auth        bool
}

type reqRoom struct {
	Name     string `json:"name"`
	Handle   string `json:"handle"`
	Password string `json:"password"`
}

var upgrader = websocket.Upgrader{CheckOrigin: func(r *http.Request) bool {
	return true
}}

// handleIndex renders the homepage.
func handleIndex(w http.ResponseWriter, r *http.Request) {
	var (
		ctx = r.Context().Value("ctx").(*reqCtx)
		app = ctx.app
	)
	respondHTML("index", tplData{
		Title: app.cfg.Name,
	}, http.StatusOK, w, app)
}

// handleRoomPage renders the chat room page.
func handleRoomPage(w http.ResponseWriter, r *http.Request) {
	var (
		ctx  = r.Context().Value("ctx").(*reqCtx)
		app  = ctx.app
		room = ctx.room
	)

	if room == nil {
		respondHTML("room-not-found", tplData{}, http.StatusNotFound, w, app)
		return
	}

	out := tplData{
		Title: room.Name,
		Room:  room,
	}
	if ctx.sess.ID != "" {
		out.Auth = true
	}

	// Disable browser caching.
	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
	w.Header().Set("Pragma", "no-cache")
	w.Header().Set("Expires", "0")
	respondHTML("room", out, http.StatusOK, w, app)
}

// handleLogin authenticates a peer into a room.
func handleLogin(w http.ResponseWriter, r *http.Request) {
	var (
		ctx  = r.Context().Value("ctx").(*reqCtx)
		app  = ctx.app
		room = ctx.room
	)

	if room == nil {
		respondJSON(w, nil, errors.New("room is invalid or has expired"), http.StatusBadRequest)
		return
	}

	var req reqRoom
	if err := readJSONReq(r, &req); err != nil {
		respondJSON(w, nil, errors.New("error parsing JSON request"), http.StatusBadRequest)
		return
	}

	if req.Handle == "" {
		h, err := hub.GenerateGUID(8)
		if err != nil {
			app.logger.Printf("error generating uniq handle: %v", err)
			respondJSON(w, nil, errors.New("error generating uniq handle"), http.StatusInternalServerError)
			return
		}
		req.Handle = h
	}

	// Validate password.
	if err := bcrypt.CompareHashAndPassword(room.Password, []byte(req.Password)); err != nil {
		respondJSON(w, nil, errors.New("incorrect password"), http.StatusForbidden)
		return
	}

	// Register a new session for the peer in the DB.
	sessID, err := hub.GenerateGUID(32)
	if err != nil {
		app.logger.Printf("error generating session ID: %v", err)
		respondJSON(w, nil, errors.New("error generating session ID"), http.StatusInternalServerError)
		return
	}

	if err := app.hub.Store.AddSession(sessID, req.Handle, room.ID, app.cfg.RoomAge); err != nil {
		app.logger.Printf("error creating session: %v", err)
		respondJSON(w, nil, errors.New("error creating session"), http.StatusInternalServerError)
		return
	}

	// Set the session cookie.
	ck := &http.Cookie{Name: app.cfg.SessionCookie, Value: sessID, Path: "/"}
	http.SetCookie(w, ck)
	respondJSON(w, true, nil, http.StatusOK)
}

// handleLogout logs out a peer.
func handleLogout(w http.ResponseWriter, r *http.Request) {
	var (
		ctx  = r.Context().Value("ctx").(*reqCtx)
		app  = ctx.app
		room = ctx.room
	)

	if room == nil {
		respondJSON(w, nil, errors.New("room is invalid or has expired"), http.StatusBadRequest)
		return
	}

	if err := app.hub.Store.RemoveSession(ctx.sess.ID, room.ID); err != nil {
		app.logger.Printf("error removing session: %v", err)
		respondJSON(w, nil, errors.New("error removing session"), http.StatusInternalServerError)
		return
	}

	// Delete the session cookie.
	ck := &http.Cookie{Name: app.cfg.SessionCookie, Value: "", MaxAge: -1, Path: "/"}
	http.SetCookie(w, ck)
	respondJSON(w, true, nil, http.StatusOK)
}

// handleWS handles incoming connections.
func handleWS(w http.ResponseWriter, r *http.Request) {
	var (
		ctx  = r.Context().Value("ctx").(*reqCtx)
		app  = ctx.app
		room = ctx.room
	)

	if ctx.sess.ID == "" {
		respondJSON(w, nil, errors.New("invalid session"), http.StatusForbidden)
		return
	}

	// Create the WS connection.
	ws, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		app.logger.Printf("Websocket upgrade failed: %s: %v", r.RemoteAddr, err)
		return
	}

	// Create a new peer instance and add to the room.
	room.AddPeer(ctx.sess.ID, ctx.sess.Handle, ws)
}

// respondJSON responds to an HTTP request with a generic payload or an error.
func respondJSON(w http.ResponseWriter, data interface{}, err error, statusCode int) {
	if statusCode == 0 {
		statusCode = http.StatusOK
	}

	w.WriteHeader(statusCode)
	w.Header().Set("Content-Type", "application/json; charset=utf-8")

	out := jsonResp{Data: data}
	if err != nil {
		e := err.Error()
		out.Error = &e
	}
	b, err := json.Marshal(out)
	if err != nil {
		logger.Printf("error marshalling JSON response: %v", err)
		http.Error(w, "Internal server error", http.StatusInternalServerError)
		return
	}
	w.Write(b)
}

// respondHTML responds to an HTTP request with the HTML output of a given template.
func respondHTML(tplName string, data tplData, statusCode int, w http.ResponseWriter, app *App) {
	if statusCode > 0 {
		w.WriteHeader(statusCode)
	}

	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	err := app.tpl.ExecuteTemplate(w, tplName, tpl{
		Config: app.cfg,
		Data:   data,
	})
	if err != nil {
		app.logger.Printf("error rendering template %s: %s", tplName, err)
		w.Write([]byte("error rendering template"))
	}
}

// handleCreateRoom handles the creation of a new room.
func handleCreateRoom(w http.ResponseWriter, r *http.Request) {
	var (
		ctx = r.Context().Value("ctx").(*reqCtx)
		app = ctx.app
	)

	var req reqRoom
	if err := readJSONReq(r, &req); err != nil {
		respondJSON(w, nil, errors.New("error parsing JSON request"), http.StatusBadRequest)
		return
	}

	if req.Name != "" && (len(req.Name) < 3 || len(req.Name) > 100) {
		respondJSON(w, nil, errors.New("invalid room name (6 - 100 chars)"), http.StatusBadRequest)
		return
	}

	if len(req.Password) < 6 || len(req.Password) > 100 {
		respondJSON(w, nil, errors.New("invalid password (6 - 100 chars)"), http.StatusBadRequest)
		return
	}

	// Hash the password.
	pwdHash, err := bcrypt.GenerateFromPassword([]byte(req.Password), 8)
	if err != nil {
		app.logger.Printf("error hashing password: %v", err)
		respondJSON(w, "Error hashing password", nil, http.StatusInternalServerError)
		return
	}

	// Create and activate the new room.
	room, err := app.hub.AddRoom(req.Name, pwdHash)
	if err != nil {
		respondJSON(w, nil, err, http.StatusInternalServerError)
		return
	}

	respondJSON(w, struct {
		ID string `json:"id"`
	}{room.ID}, nil, http.StatusOK)
}

// wrap is a middleware that handles auth and room check for various HTTP handlers.
// It attaches the app and room contexts to handlers.
func wrap(next http.HandlerFunc, app *App, opts uint8) http.HandlerFunc {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		var (
			req    = &reqCtx{app: app}
			roomID = chi.URLParam(r, "roomID")
		)

		// Check if the request is authenticated.
		if opts&hasAuth != 0 {
			ck, _ := r.Cookie(app.cfg.SessionCookie)
			if ck != nil && ck.Value != "" {
				s, err := app.hub.Store.GetSession(ck.Value, roomID)
				if err != nil {
					app.logger.Printf("error checking session: %v", err)
					respondJSON(w, nil, errors.New("error checking session"), http.StatusForbidden)
					return
				}
				req.sess = sess{
					ID:     s.ID,
					Handle: s.Handle,
				}
			}
		}

		// Check if the room is valid and active.
		if opts&hasRoom != 0 {
			// If the room's not found, req.room will be null in the target
			// handler. It's the handler's responsibility to throw an error,
			// API or HTML response.
			room, err := app.hub.ActivateRoom(roomID)
			if err == nil {
				req.room = room
			}
		}

		// Attach the request context.
		ctx := context.WithValue(r.Context(), "ctx", req)
		next.ServeHTTP(w, r.WithContext(ctx))
	})
}

// readJSONReq reads the JSON body from a request and unmarshals it to the given target.
func readJSONReq(r *http.Request, o interface{}) error {
	defer r.Body.Close()
	b, err := ioutil.ReadAll(r.Body)
	if err != nil {
		return err
	}
	return json.Unmarshal(b, o)
}