// Package overlays contains a server to host overlays and interact
// with the bot using sockets and a pre-defined Javascript client
package overlays

import (
	"embed"
	"encoding/json"
	"fmt"
	"net/http"
	"os"
	"sort"
	"strconv"
	"strings"
	"sync"
	"time"

	"github.com/gofrs/uuid"
	"github.com/gorilla/mux"
	"github.com/gorilla/websocket"
	"github.com/pkg/errors"
	log "github.com/sirupsen/logrus"
	"gorm.io/gorm"

	"github.com/Luzifer/go_helpers/v2/fieldcollection"
	"github.com/Luzifer/go_helpers/v2/str"
	"github.com/Luzifer/twitch-bot/v3/pkg/database"
	"github.com/Luzifer/twitch-bot/v3/plugins"
)

const (
	authTimeout     = 10 * time.Second
	bufferSizeByte  = 1024
	socketKeepAlive = 5 * time.Second

	msgTypeRequestAuth = "_auth"
)

type (
	// sendReason contains an enum of reasons why the message is
	// transmitted to the listening overlay sockets
	sendReason string

	// socketMessage represents the message overlay sockets will receive
	socketMessage struct {
		EventID uint64                           `json:"event_id"`
		IsLive  bool                             `json:"is_live"`
		Reason  sendReason                       `json:"reason"`
		Time    time.Time                        `json:"time"`
		Type    string                           `json:"type"`
		Fields  *fieldcollection.FieldCollection `json:"fields"`
	}
)

// Collection of SendReason entries
const (
	sendReasonLive         sendReason = "live-event"
	sendReasonBulkReplay   sendReason = "bulk-replay"
	sendReasonSingleReplay sendReason = "single-replay"
)

var (
	//go:embed default/**
	embeddedOverlays embed.FS

	db database.Connector

	fsStack httpFSStack

	ptrStringEmpty = func(v string) *string { return &v }("")

	storeExemption = []string{
		"join", "part", // Those make no sense for replay
	}

	subscribers     = map[string]func(socketMessage){}
	subscribersLock sync.RWMutex

	upgrader = websocket.Upgrader{
		ReadBufferSize:  bufferSizeByte,
		WriteBufferSize: bufferSizeByte,
	}

	validateToken plugins.ValidateTokenFunc
)

// Register provides the plugins.RegisterFunc
//
//nolint:funlen
func Register(args plugins.RegistrationArguments) (err error) {
	db = args.GetDatabaseConnector()
	if err = db.DB().AutoMigrate(&overlaysEvent{}); err != nil {
		return errors.Wrap(err, "applying schema migration")
	}

	args.RegisterCopyDatabaseFunc("overlay_events", func(src, target *gorm.DB) error {
		return database.CopyObjects(src, target, &overlaysEvent{})
	})

	validateToken = args.ValidateToken

	if err = args.RegisterAPIRoute(plugins.HTTPRouteRegistrationArgs{
		Description:  "Trigger a re-distribution of an event to all subscribed overlays",
		HandlerFunc:  handleSingleEventReplay,
		Method:       http.MethodPut,
		Module:       "overlays",
		Name:         "Replay Single Event",
		Path:         "/event/{event_id}/replay",
		ResponseType: plugins.HTTPRouteResponseTypeNo200,
		RouteParams: []plugins.HTTPRouteParamDocumentation{
			{
				Description: "Event ID to replay (unique ID in database)",
				Name:        "event_id",
			},
		},
	}); err != nil {
		return fmt.Errorf("registering API route: %w", err)
	}

	if err = args.RegisterAPIRoute(plugins.HTTPRouteRegistrationArgs{
		Description:  "Websocket subscriber for bot events",
		HandlerFunc:  handleSocketSubscription,
		Method:       http.MethodGet,
		Module:       "overlays",
		Name:         "Websocket",
		Path:         "/events.sock",
		ResponseType: plugins.HTTPRouteResponseTypeMultiple,
	}); err != nil {
		return fmt.Errorf("registering API route: %w", err)
	}

	if err = args.RegisterAPIRoute(plugins.HTTPRouteRegistrationArgs{
		Description: "Fetch past events for the given channel",
		HandlerFunc: handleEventsReplay,
		Method:      http.MethodGet,
		Module:      "overlays",
		Name:        "Replay",
		Path:        "/events/{channel}",
		QueryParams: []plugins.HTTPRouteParamDocumentation{
			{
				Description: "ISO / RFC3339 timestamp to fetch the events after",
				Name:        "since",
				Required:    false,
				Type:        "string",
			},
		},
		RequiresWriteAuth: true,
		ResponseType:      plugins.HTTPRouteResponseTypeJSON,
		RouteParams: []plugins.HTTPRouteParamDocumentation{
			{
				Description: "Channel to fetch the events from",
				Name:        "channel",
			},
		},
	}); err != nil {
		return fmt.Errorf("registering API route: %w", err)
	}

	if err = args.RegisterAPIRoute(plugins.HTTPRouteRegistrationArgs{
		Description:       "Shares the overlays folder as WebDAV filesystem",
		HandlerFunc:       getDAVHandler(),
		IsPrefix:          true,
		Module:            "overlays",
		Name:              "WebDAV Overlays",
		Path:              "/dav/",
		RequiresWriteAuth: true,
		ResponseType:      plugins.HTTPRouteResponseTypeMultiple,
		SkipDocumentation: true,
	}); err != nil {
		return fmt.Errorf("registering API route: %w", err)
	}

	if err = args.RegisterAPIRoute(plugins.HTTPRouteRegistrationArgs{
		HandlerFunc:       handleServeOverlayAsset,
		IsPrefix:          true,
		Method:            http.MethodGet,
		Module:            "overlays",
		Path:              "/",
		ResponseType:      plugins.HTTPRouteResponseTypeMultiple,
		SkipDocumentation: true,
	}); err != nil {
		return fmt.Errorf("registering API route: %w", err)
	}

	if err = args.RegisterEventHandler(func(event string, eventData *fieldcollection.FieldCollection) (err error) {
		subscribersLock.RLock()
		defer subscribersLock.RUnlock()

		msg := socketMessage{
			IsLive: true,
			Reason: sendReasonLive,
			Time:   time.Now(),
			Type:   event,
			Fields: eventData,
		}

		if !str.StringInSlice(event, storeExemption) {
			if msg.EventID, err = addChannelEvent(db, plugins.DeriveChannel(nil, eventData), socketMessage{
				IsLive: false,
				Time:   time.Now(),
				Type:   event,
				Fields: eventData,
			}); err != nil {
				return errors.Wrap(err, "storing event")
			}
		}

		for _, fn := range subscribers {
			fn(msg)
		}

		return nil
	}); err != nil {
		return fmt.Errorf("registering event handler: %w", err)
	}

	fsStack = httpFSStack{
		newPrefixedFS("default", http.FS(embeddedOverlays)),
	}

	overlaysDir := os.Getenv("OVERLAYS_DIR")
	if ds, err := os.Stat(overlaysDir); err != nil || overlaysDir == "" || !ds.IsDir() {
		log.WithField("dir", overlaysDir).Warn("Overlays dir not specified, no dir or non existent")
	} else {
		fsStack = append(httpFSStack{http.Dir(overlaysDir)}, fsStack...)
	}

	return nil
}

func handleEventsReplay(w http.ResponseWriter, r *http.Request) {
	var (
		channel = mux.Vars(r)["channel"]
		msgs    []socketMessage
		since   = time.Time{}
	)

	if s, err := time.Parse(time.RFC3339, r.URL.Query().Get("since")); err == nil {
		since = s
	}

	events, err := getChannelEvents(db, "#"+strings.TrimLeft(channel, "#"))
	if err != nil {
		http.Error(w, errors.Wrap(err, "getting channel events").Error(), http.StatusInternalServerError)
		return
	}

	for _, msg := range events {
		if msg.Time.Before(since) {
			continue
		}

		msg.Reason = sendReasonBulkReplay
		msgs = append(msgs, msg)
	}

	sort.Slice(msgs, func(i, j int) bool { return msgs[i].Time.Before(msgs[j].Time) })

	if err := json.NewEncoder(w).Encode(msgs); err != nil {
		http.Error(w, errors.Wrap(err, "encoding response").Error(), http.StatusInternalServerError)
		return
	}
}

func handleServeOverlayAsset(w http.ResponseWriter, r *http.Request) {
	http.StripPrefix("/overlays", http.FileServer(fsStack)).ServeHTTP(w, r)
}

func handleSingleEventReplay(w http.ResponseWriter, r *http.Request) {
	eventID, err := strconv.ParseUint(mux.Vars(r)["event_id"], 10, 64)
	if err != nil {
		http.Error(w, errors.Wrap(err, "parsing event_id").Error(), http.StatusBadRequest)
		return
	}

	evt, err := getEventByID(db, eventID)
	if err != nil {
		http.Error(w, errors.Wrap(err, "fetching event").Error(), http.StatusInternalServerError)
		return
	}

	evt.Reason = sendReasonSingleReplay

	subscribersLock.RLock()
	defer subscribersLock.RUnlock()

	for _, fn := range subscribers {
		fn(evt)
	}
}

//nolint:funlen,gocognit,gocyclo // Not split in order to keep the socket logic in one place
func handleSocketSubscription(w http.ResponseWriter, r *http.Request) {
	var (
		connID = uuid.Must(uuid.NewV4()).String()
		logger = log.WithField("conn_id", connID)
	)

	// Upgrade connection to socket
	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		logger.WithError(err).Error("Unable to upgrade socket")
		return
	}
	defer conn.Close() //nolint:errcheck // We don't really care about this

	var (
		authTimeout  = time.NewTimer(authTimeout)
		connLock     = new(sync.Mutex)
		errC         = make(chan error, 1)
		isAuthorized bool
		sendMsgC     = make(chan socketMessage, 1)
	)

	// Register listener
	unsub := subscribeSocket(func(msg socketMessage) { sendMsgC <- msg })
	defer unsub()

	keepAlive := time.NewTicker(socketKeepAlive)
	defer keepAlive.Stop()
	go func() {
		for range keepAlive.C {
			connLock.Lock()

			if err := conn.WriteMessage(websocket.PingMessage, nil); err != nil {
				logger.WithError(err).Error("Unable to send ping message")
				connLock.Unlock()
				conn.Close() //nolint:errcheck,gosec
				return
			}

			connLock.Unlock()
		}
	}()

	go func() {
		// Handle socket
		for {
			messageType, p, err := conn.ReadMessage()
			if err != nil {
				errC <- errors.Wrap(err, "reading from socket")
				return
			}

			switch messageType {
			case websocket.TextMessage:
				// This is fine and expected

			case websocket.BinaryMessage:
				// Wat?
				errC <- errors.New("binary message received")
				return

			case websocket.CloseMessage:
				// They want to go? Fine, have it that way!
				errC <- nil
				return

			default:
				logger.Debugf("Got unhandled message from socket: %d", messageType)
				continue
			}

			var recvMsg socketMessage
			if err = json.Unmarshal(p, &recvMsg); err != nil {
				errC <- errors.Wrap(err, "decoding message")
				return
			}

			if !isAuthorized && recvMsg.Type != msgTypeRequestAuth {
				// Socket is requesting stuff but is not authorized, we don't want them to be here!
				errC <- nil
				return
			}

			switch recvMsg.Type {
			case msgTypeRequestAuth:
				if err := validateToken(recvMsg.Fields.MustString("token", ptrStringEmpty), "overlays"); err != nil {
					errC <- errors.Wrap(err, "validating auth token")
					return
				}

				authTimeout.Stop()
				isAuthorized = true
				sendMsgC <- socketMessage{
					IsLive: true,
					Time:   time.Now(),
					Type:   msgTypeRequestAuth,
				}

			default:
				logger.WithField("type", recvMsg.Type).Warn("Got unexpected message type from frontend")
			}
		}
	}()

	for {
		select {
		case <-authTimeout.C:
			// Timeout was not stopped, no auth was done
			logger.Warn("socket failed to auth")
			return

		case err := <-errC:
			var cErr *websocket.CloseError
			switch {
			case err == nil:
				// We use nil-error to close the connection

			case errors.As(err, &cErr):
				switch cErr.Code {
				case websocket.CloseAbnormalClosure:
					logger.WithError(err).Warn("overlay websocket was closed abnormally")

				case websocket.CloseNormalClosure, websocket.CloseGoingAway:
					// We don't need to log when the remote closes the websocket gracefully

				default:
					logger.WithError(err).Error("message processing caused error")
				}

			default:
				logger.WithError(err).Error("message processing caused error")
			}
			return // All errors need to quit this function

		case msg := <-sendMsgC:
			if !isAuthorized {
				// Not authorized, we're silently dropping messages
				continue
			}

			connLock.Lock()
			if err := conn.WriteJSON(msg); err != nil {
				logger.WithError(err).Error("Unable to send socket message")
				connLock.Unlock()
				conn.Close() //nolint:errcheck,gosec
			}
			connLock.Unlock()
		}
	}
}

func subscribeSocket(fn func(socketMessage)) func() {
	id := uuid.Must(uuid.NewV4()).String()

	subscribersLock.Lock()
	defer subscribersLock.Unlock()

	subscribers[id] = fn

	return func() { unsubscribeSocket(id) }
}

func unsubscribeSocket(id string) {
	subscribersLock.Lock()
	defer subscribersLock.Unlock()

	delete(subscribers, id)
}