package main

import (
	"context"
	"encoding/json"
	"log"
	"log/slog"
	"net/http"
	"sync/atomic"

	"github.com/bluesky-social/indigo/api/bsky"
	"github.com/bluesky-social/indigo/atproto/syntax"
	"github.com/bluesky-social/indigo/xrpc"
	"github.com/bluesky-social/jetstream/pkg/client"
	"github.com/bluesky-social/jetstream/pkg/models"
	"github.com/cornelk/hashmap"
	"github.com/google/uuid"
	"github.com/gorilla/mux"
	"github.com/gorilla/websocket"
)

type Set[T comparable] map[T]struct{}

const ListenTypeNone = "none"
const ListenTypeFollows = "follows"

type SubscriberData struct {
	SubscribedTo syntax.DID
	Conn         *websocket.Conn
	ListenType   string
	ListenTo     Set[syntax.DID]
}

type UserData struct {
	targets       *hashmap.Map[string, *SubscriberData]
	likes         map[syntax.RecordKey]bsky.FeedLike
	follows       *hashmap.Map[syntax.RecordKey, bsky.GraphFollow]
	followsCursor atomic.Pointer[string]
}

type NotificationMessage struct {
	Liked     bool         `json:"liked"`
	ByDid     syntax.DID   `json:"did"`
	RepostURI syntax.ATURI `json:"repost_uri"`
}

type SubscriberMessage struct {
	Type    string          `json:"type"`
	Content json.RawMessage `json:"content"`
}

type SubscriberUpdateListenTo struct {
	ListenTo []syntax.DID `json:"listen_to"`
}

var (
	// storing the subscriber data in both Should Be Fine
	// we dont modify subscriber data at the same time in two places
	subscribers = hashmap.New[string, *SubscriberData]()
	userData    = hashmap.New[syntax.DID, *UserData]()

	likeStream   *client.Client
	followStream *client.Client

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

	logger *slog.Logger
)

func getSubscriberDids() []string {
	_dids := make(Set[string], subscribers.Len())
	subscribers.Range(func(s string, sd *SubscriberData) bool {
		_dids[string(sd.SubscribedTo)] = struct{}{}
		return true
	})
	dids := make([]string, 0, len(_dids))
	for k := range _dids {
		dids = append(dids, k)
	}
	return dids
}

func getUserData(did syntax.DID) *UserData {
	ud, _ := userData.GetOrInsert(did, &UserData{
		targets: hashmap.New[string, *SubscriberData](),
		likes:   make(map[syntax.RecordKey]bsky.FeedLike),
		follows: hashmap.New[syntax.RecordKey, bsky.GraphFollow](),
	})
	return ud
}

func startListeningTo(sid string, sd *SubscriberData, did syntax.DID) {
	ud := getUserData(did)
	ud.targets.Insert(sid, sd)
}

func stopListeningTo(sid string, did syntax.DID) {
	if ud, exists := userData.Get(did); exists {
		ud.targets.Del(sid)
	}
}

func main() {
	logger = slog.Default()

	go startJetstreamLoop(logger, &likeStream, "like_tracker", HandleLikeEvent, getLikeStreamOpts)
	go startJetstreamLoop(logger, &followStream, "subscriber", HandleFollowEvent, getFollowStreamOpts)

	r := mux.NewRouter()
	r.HandleFunc("/subscribe/{did}", handleSubscribe).Methods("GET")

	log.Println("server starting on :8080")
	if err := http.ListenAndServe(":8080", r); err != nil {
		log.Fatalf("error while serving: %s", err)
	}
}

func handleSubscribe(w http.ResponseWriter, r *http.Request) {
	vars := mux.Vars(r)
	did, err := syntax.ParseDID(vars["did"])
	if err != nil {
		http.Error(w, "not a valid did", http.StatusBadRequest)
		return
	}
	sid := uuid.New().String()

	query := r.URL.Query()
	listenType := query.Get("listenTo")
	if len(listenType) == 0 {
		listenType = ListenTypeFollows
	}

	logger := logger.With("did", did, "subscriberId", sid)

	conn, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		logger.Error("WebSocket upgrade failed", "error", err)
		return
	}
	defer conn.Close()

	logger.Info("new subscriber")

	pdsURI, err := findUserPDS(r.Context(), did)
	if err != nil {
		logger.Error("cant resolve user pds", "error", err)
		return
	}
	logger = logger.With("pds", pdsURI)

	xrpcClient := &xrpc.Client{
		Host: pdsURI,
	}

	ud := getUserData(did)
	sd := &SubscriberData{
		SubscribedTo: did,
		Conn:         conn,
		ListenType:   listenType,
	}

	switch listenType {
	case ListenTypeFollows:
		follows, err := fetchFollows(r.Context(), xrpcClient, ud.followsCursor.Load(), did)
		if err != nil {
			logger.Error("error fetching follows", "error", err)
			return
		}
		sd.ListenTo = make(Set[syntax.DID])
		if len(follows) > 0 {
			// store cursor for later requests so we dont have to fetch the whole thing again
			ud.followsCursor.Store((*string)(&follows[len(follows)-1].rkey))
			for _, f := range follows {
				ud.follows.Insert(f.rkey, f.follow)
				sd.ListenTo[syntax.DID(f.follow.Subject)] = struct{}{}
			}
		}
		logger.Info("fetched follows")
	case ListenTypeNone:
		sd.ListenTo = make(Set[syntax.DID])
	default:
		http.Error(w, "invalid listen type", http.StatusBadRequest)
		return
	}

	subscribers.Set(sid, sd)
	for listenDid := range sd.ListenTo {
		startListeningTo(sid, sd, listenDid)
	}
	updateFollowStreamOpts()
	// delete subscriber after we are done
	defer func() {
		for listenDid := range sd.ListenTo {
			stopListeningTo(sid, listenDid)
		}
		subscribers.Del(sid)
		updateFollowStreamOpts()
	}()

	logger.Info("serving subscriber")

	for {
		var msg SubscriberMessage
		err := conn.ReadJSON(&msg)
		if err != nil {
			logger.Info("WebSocket connection closed", "error", err)
			break
		}
		switch msg.Type {
		case "update_listen_to":
			// only allow this if we arent managing listen to
			if sd.ListenType != ListenTypeNone {
				continue
			}

			var innerMsg SubscriberUpdateListenTo
			if err := json.Unmarshal(msg.Content, &innerMsg); err != nil {
				logger.Info("invalid message", "error", err)
				break
			}
			// remove all current listens and add the ones the user requested
			for listenDid := range sd.ListenTo {
				stopListeningTo(sid, listenDid)
				delete(sd.ListenTo, listenDid)
			}
			for _, listenDid := range innerMsg.ListenTo {
				sd.ListenTo[listenDid] = struct{}{}
				startListeningTo(sid, sd, listenDid)
			}
		}
	}
}

func getLikeStreamOpts() models.SubscriberOptionsUpdatePayload {
	return models.SubscriberOptionsUpdatePayload{
		WantedCollections: []string{"app.bsky.feed.like"},
	}
}

func getFollowStreamOpts() models.SubscriberOptionsUpdatePayload {
	return models.SubscriberOptionsUpdatePayload{
		WantedCollections: []string{"app.bsky.graph.follow"},
		WantedDIDs:        getSubscriberDids(),
	}
}

func updateFollowStreamOpts() {
	opts := getFollowStreamOpts()
	err := followStream.SendOptionsUpdate(opts)
	if err != nil {
		logger.Error("couldnt update follow stream opts", "error", err)
		return
	}
	logger.Info("updated follow stream opts", "userCount", len(opts.WantedDIDs))
}

func HandleLikeEvent(ctx context.Context, event *models.Event) error {
	if event == nil || event.Commit == nil {
		return nil
	}

	byDid := syntax.DID(event.Did)
	// skip handling event if its not from a source we are listening to
	ud, exists := userData.Get(byDid)
	if !exists || ud.targets.Len() == 0 {
		return nil
	}

	deleted := event.Commit.Operation == models.CommitOperationDelete
	rkey := syntax.RecordKey(event.Commit.RKey)

	var like bsky.FeedLike
	if deleted {
		if l, exists := ud.likes[rkey]; exists {
			like = l
			defer delete(ud.likes, rkey)
		} else {
			logger.Error("like record not found", "rkey", rkey)
			return nil
		}
	} else {
		if err := json.Unmarshal(event.Commit.Record, &like); err != nil {
			logger.Error("failed to unmarshal like", "error", err)
			return nil
		}
	}

	// if there is no via it means its not a repost anyway
	if like.Via == nil {
		return nil
	}

	// store for later when it gets deleted so we can fetch the record
	if !deleted {
		ud.likes[rkey] = like
	}

	repostURI := syntax.ATURI(like.Via.Uri)
	// if not a repost we dont care
	if repostURI.Collection() != "app.bsky.feed.repost" {
		return nil
	}
	reposterDID, err := repostURI.Authority().AsDID()
	if err != nil {
		return err
	}
	ud.targets.Range(func(sid string, sd *SubscriberData) bool {
		if sd.SubscribedTo != reposterDID {
			return true
		}

		notification := NotificationMessage{
			Liked:     !deleted,
			ByDid:     byDid,
			RepostURI: repostURI,
		}

		if err := sd.Conn.WriteJSON(notification); err != nil {
			logger.Error("failed to send notification", "subscriber", sd.SubscribedTo, "error", err)
		}
		return true
	})

	return nil
}

func HandleFollowEvent(ctx context.Context, event *models.Event) error {
	if event == nil || event.Commit == nil {
		return nil
	}

	byDid := syntax.DID(event.Did)
	ud, exists := userData.Get(byDid)
	if !exists || ud.targets.Len() == 0 {
		return nil
	}

	deleted := event.Commit.Operation == models.CommitOperationDelete
	rkey := syntax.RecordKey(event.Commit.RKey)

	switch event.Commit.Collection {
	case "app.bsky.graph.follow":
		var r bsky.GraphFollow
		if deleted {
			if f, exists := ud.follows.Get(rkey); exists {
				r = f
			} else {
				logger.Error("follow record not found", "rkey", rkey)
				return nil
			}
			ud.follows.Del(rkey)
		} else {
			if err := unmarshalEvent(event, &r); err != nil {
				logger.Error("could not unmarshal follow event", "error", err)
				return nil
			}
			ud.follows.Insert(rkey, r)
		}
		ud.targets.Range(func(sid string, sd *SubscriberData) bool {
			// if we arent managing then we dont need to update anything
			if sd.ListenType != ListenTypeFollows {
				return true
			}
			subjectDid := syntax.DID(r.Subject)
			if deleted {
				stopListeningTo(sid, subjectDid)
				delete(sd.ListenTo, subjectDid)
			} else {
				sd.ListenTo[subjectDid] = struct{}{}
				startListeningTo(sid, sd, subjectDid)
			}
			return true
		})
	}

	return nil
}

func unmarshalEvent[v any](event *models.Event, val *v) error {
	if err := json.Unmarshal(event.Commit.Record, val); err != nil {
		logger.Error("failed to unmarshal", "error", err, "raw", event.Commit.Record)
		return nil
	}
	return nil
}