package handlers

import (
	"database/sql"
	"encoding/json"
	"net/http"
	"strconv"
	"strings"
	"time"

	"github.com/go-chi/chi"
)

// authUser extracts the user from the Authorization header (Bearer token).
func (s *Handlers) authUser(r *http.Request) (int64, string, error) {
	auth := r.Header.Get("Authorization")
	if !strings.HasPrefix(auth, "Bearer ") {
		return 0, "", sql.ErrNoRows
	}
	token := strings.TrimPrefix(auth, "Bearer ")
	return s.params.Database.GetUserByToken(r.Context(), token)
}

func (s *Handlers) requireAuth(w http.ResponseWriter, r *http.Request) (int64, string, bool) {
	uid, nick, err := s.authUser(r)
	if err != nil {
		s.respondJSON(w, r, map[string]string{"error": "unauthorized"}, http.StatusUnauthorized)
		return 0, "", false
	}
	return uid, nick, true
}

// fanOut stores a message and enqueues it to all specified user IDs, then notifies them.
func (s *Handlers) fanOut(ctx *http.Request, command, from, to string, body json.RawMessage, userIDs []int64) error {
	dbID, _, err := s.params.Database.InsertMessage(ctx.Context(), command, from, to, body, nil)
	if err != nil {
		return err
	}
	for _, uid := range userIDs {
		if err := s.params.Database.EnqueueMessage(ctx.Context(), uid, dbID); err != nil {
			s.log.Error("enqueue failed", "error", err, "user_id", uid)
		}
		s.broker.Notify(uid)
	}
	return nil
}

// fanOutRaw stores and fans out, returning the message DB ID.
func (s *Handlers) fanOutDirect(ctx *http.Request, command, from, to string, body json.RawMessage, userIDs []int64) (int64, string, error) {
	dbID, msgUUID, err := s.params.Database.InsertMessage(ctx.Context(), command, from, to, body, nil)
	if err != nil {
		return 0, "", err
	}
	for _, uid := range userIDs {
		if err := s.params.Database.EnqueueMessage(ctx.Context(), uid, dbID); err != nil {
			s.log.Error("enqueue failed", "error", err, "user_id", uid)
		}
		s.broker.Notify(uid)
	}
	return dbID, msgUUID, nil
}

// getChannelMembers gets all member IDs for a channel by name.
func (s *Handlers) getChannelMemberIDs(r *http.Request, channelName string) (int64, []int64, error) {
	var chID int64
	err := s.params.Database.GetDB().QueryRowContext(r.Context(),
		"SELECT id FROM channels WHERE name = ?", channelName).Scan(&chID)
	if err != nil {
		return 0, nil, err
	}
	ids, err := s.params.Database.GetChannelMemberIDs(r.Context(), chID)
	return chID, ids, err
}

// HandleCreateSession creates a new user session and returns the auth token.
func (s *Handlers) HandleCreateSession() http.HandlerFunc {
	type request struct {
		Nick string `json:"nick"`
	}
	type response struct {
		ID    int64  `json:"id"`
		Nick  string `json:"nick"`
		Token string `json:"token"`
	}
	return func(w http.ResponseWriter, r *http.Request) {
		var req request
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			s.respondJSON(w, r, map[string]string{"error": "invalid request"}, http.StatusBadRequest)
			return
		}
		req.Nick = strings.TrimSpace(req.Nick)
		if req.Nick == "" || len(req.Nick) > 32 {
			s.respondJSON(w, r, map[string]string{"error": "nick must be 1-32 characters"}, http.StatusBadRequest)
			return
		}
		id, token, err := s.params.Database.CreateUser(r.Context(), req.Nick)
		if err != nil {
			if strings.Contains(err.Error(), "UNIQUE") {
				s.respondJSON(w, r, map[string]string{"error": "nick already taken"}, http.StatusConflict)
				return
			}
			s.log.Error("create user failed", "error", err)
			s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
			return
		}
		s.respondJSON(w, r, &response{ID: id, Nick: req.Nick, Token: token}, http.StatusCreated)
	}
}

// HandleState returns the current user's info and joined channels.
func (s *Handlers) HandleState() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		uid, nick, ok := s.requireAuth(w, r)
		if !ok {
			return
		}
		channels, err := s.params.Database.ListChannels(r.Context(), uid)
		if err != nil {
			s.log.Error("list channels failed", "error", err)
			s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
			return
		}
		s.respondJSON(w, r, map[string]any{
			"id":       uid,
			"nick":     nick,
			"channels": channels,
		}, http.StatusOK)
	}
}

// HandleListAllChannels returns all channels on the server.
func (s *Handlers) HandleListAllChannels() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		_, _, ok := s.requireAuth(w, r)
		if !ok {
			return
		}
		channels, err := s.params.Database.ListAllChannels(r.Context())
		if err != nil {
			s.log.Error("list all channels failed", "error", err)
			s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
			return
		}
		s.respondJSON(w, r, channels, http.StatusOK)
	}
}

// HandleChannelMembers returns members of a channel.
func (s *Handlers) HandleChannelMembers() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		_, _, ok := s.requireAuth(w, r)
		if !ok {
			return
		}
		name := "#" + chi.URLParam(r, "channel")
		var chID int64
		err := s.params.Database.GetDB().QueryRowContext(r.Context(),
			"SELECT id FROM channels WHERE name = ?", name).Scan(&chID)
		if err != nil {
			s.respondJSON(w, r, map[string]string{"error": "channel not found"}, http.StatusNotFound)
			return
		}
		members, err := s.params.Database.ChannelMembers(r.Context(), chID)
		if err != nil {
			s.log.Error("channel members failed", "error", err)
			s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
			return
		}
		s.respondJSON(w, r, members, http.StatusOK)
	}
}

// HandleGetMessages returns messages via long-polling from the client's queue.
func (s *Handlers) HandleGetMessages() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		uid, _, ok := s.requireAuth(w, r)
		if !ok {
			return
		}
		afterID, _ := strconv.ParseInt(r.URL.Query().Get("after"), 10, 64)
		timeout, _ := strconv.Atoi(r.URL.Query().Get("timeout"))
		if timeout <= 0 {
			timeout = 0
		}
		if timeout > 30 {
			timeout = 30
		}

		// First check for existing messages.
		msgs, lastQID, err := s.params.Database.PollMessages(r.Context(), uid, afterID, 100)
		if err != nil {
			s.log.Error("poll messages failed", "error", err)
			s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
			return
		}

		if len(msgs) > 0 || timeout == 0 {
			s.respondJSON(w, r, map[string]any{
				"messages": msgs,
				"last_id":  lastQID,
			}, http.StatusOK)
			return
		}

		// Long-poll: wait for notification or timeout.
		waitCh := s.broker.Wait(uid)
		timer := time.NewTimer(time.Duration(timeout) * time.Second)
		defer timer.Stop()

		select {
		case <-waitCh:
		case <-timer.C:
		case <-r.Context().Done():
			s.broker.Remove(uid, waitCh)
			return
		}
		s.broker.Remove(uid, waitCh)

		// Check again after notification.
		msgs, lastQID, err = s.params.Database.PollMessages(r.Context(), uid, afterID, 100)
		if err != nil {
			s.log.Error("poll messages failed", "error", err)
			s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
			return
		}
		s.respondJSON(w, r, map[string]any{
			"messages": msgs,
			"last_id":  lastQID,
		}, http.StatusOK)
	}
}

// HandleSendCommand handles all C2S commands via POST /messages.
func (s *Handlers) HandleSendCommand() http.HandlerFunc {
	type request struct {
		Command string          `json:"command"`
		To      string          `json:"to"`
		Body    json.RawMessage `json:"body,omitempty"`
		Meta    json.RawMessage `json:"meta,omitempty"`
	}
	return func(w http.ResponseWriter, r *http.Request) {
		uid, nick, ok := s.requireAuth(w, r)
		if !ok {
			return
		}
		var req request
		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
			s.respondJSON(w, r, map[string]string{"error": "invalid request"}, http.StatusBadRequest)
			return
		}
		req.Command = strings.ToUpper(strings.TrimSpace(req.Command))
		req.To = strings.TrimSpace(req.To)

		bodyLines := func() []string {
			if req.Body == nil {
				return nil
			}
			var lines []string
			if err := json.Unmarshal(req.Body, &lines); err != nil {
				return nil
			}
			return lines
		}

		switch req.Command {
		case "PRIVMSG", "NOTICE":
			if req.To == "" {
				s.respondJSON(w, r, map[string]string{"error": "to field required"}, http.StatusBadRequest)
				return
			}
			lines := bodyLines()
			if len(lines) == 0 {
				s.respondJSON(w, r, map[string]string{"error": "body required"}, http.StatusBadRequest)
				return
			}

			if strings.HasPrefix(req.To, "#") {
				// Channel message — fan out to all channel members.
				_, memberIDs, err := s.getChannelMemberIDs(r, req.To)
				if err != nil {
					s.respondJSON(w, r, map[string]string{"error": "channel not found"}, http.StatusNotFound)
					return
				}
				_, msgUUID, err := s.fanOutDirect(r, req.Command, nick, req.To, req.Body, memberIDs)
				if err != nil {
					s.log.Error("send message failed", "error", err)
					s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
					return
				}
				s.respondJSON(w, r, map[string]string{"id": msgUUID, "status": "sent"}, http.StatusCreated)
			} else {
				// DM — fan out to recipient + sender.
				targetUID, err := s.params.Database.GetUserByNick(r.Context(), req.To)
				if err != nil {
					s.respondJSON(w, r, map[string]string{"error": "user not found"}, http.StatusNotFound)
					return
				}
				recipients := []int64{targetUID}
				if targetUID != uid {
					recipients = append(recipients, uid) // echo to sender
				}
				_, msgUUID, err := s.fanOutDirect(r, req.Command, nick, req.To, req.Body, recipients)
				if err != nil {
					s.log.Error("send dm failed", "error", err)
					s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
					return
				}
				s.respondJSON(w, r, map[string]string{"id": msgUUID, "status": "sent"}, http.StatusCreated)
			}

		case "JOIN":
			if req.To == "" {
				s.respondJSON(w, r, map[string]string{"error": "to field required"}, http.StatusBadRequest)
				return
			}
			channel := req.To
			if !strings.HasPrefix(channel, "#") {
				channel = "#" + channel
			}
			chID, err := s.params.Database.GetOrCreateChannel(r.Context(), channel)
			if err != nil {
				s.log.Error("get/create channel failed", "error", err)
				s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
				return
			}
			if err := s.params.Database.JoinChannel(r.Context(), chID, uid); err != nil {
				s.log.Error("join channel failed", "error", err)
				s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
				return
			}
			// Broadcast JOIN to all channel members (including the joiner).
			memberIDs, _ := s.params.Database.GetChannelMemberIDs(r.Context(), chID)
			_ = s.fanOut(r, "JOIN", nick, channel, nil, memberIDs)
			s.respondJSON(w, r, map[string]string{"status": "joined", "channel": channel}, http.StatusOK)

		case "PART":
			if req.To == "" {
				s.respondJSON(w, r, map[string]string{"error": "to field required"}, http.StatusBadRequest)
				return
			}
			channel := req.To
			if !strings.HasPrefix(channel, "#") {
				channel = "#" + channel
			}
			var chID int64
			err := s.params.Database.GetDB().QueryRowContext(r.Context(),
				"SELECT id FROM channels WHERE name = ?", channel).Scan(&chID)
			if err != nil {
				s.respondJSON(w, r, map[string]string{"error": "channel not found"}, http.StatusNotFound)
				return
			}
			// Broadcast PART before removing the member.
			memberIDs, _ := s.params.Database.GetChannelMemberIDs(r.Context(), chID)
			_ = s.fanOut(r, "PART", nick, channel, req.Body, memberIDs)

			if err := s.params.Database.PartChannel(r.Context(), chID, uid); err != nil {
				s.log.Error("part channel failed", "error", err)
				s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
				return
			}
			// Delete channel if empty (ephemeral).
			_ = s.params.Database.DeleteChannelIfEmpty(r.Context(), chID)
			s.respondJSON(w, r, map[string]string{"status": "parted", "channel": channel}, http.StatusOK)

		case "NICK":
			lines := bodyLines()
			if len(lines) == 0 {
				s.respondJSON(w, r, map[string]string{"error": "body required (new nick)"}, http.StatusBadRequest)
				return
			}
			newNick := strings.TrimSpace(lines[0])
			if newNick == "" || len(newNick) > 32 {
				s.respondJSON(w, r, map[string]string{"error": "nick must be 1-32 characters"}, http.StatusBadRequest)
				return
			}
			if err := s.params.Database.ChangeNick(r.Context(), uid, newNick); err != nil {
				if strings.Contains(err.Error(), "UNIQUE") {
					s.respondJSON(w, r, map[string]string{"error": "nick already in use"}, http.StatusConflict)
					return
				}
				s.log.Error("change nick failed", "error", err)
				s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
				return
			}
			// Broadcast NICK to all channels the user is in.
			channels, _ := s.params.Database.GetAllChannelMembershipsForUser(r.Context(), uid)
			notified := map[int64]bool{uid: true}
			body, _ := json.Marshal([]string{newNick})
			// Notify self.
			dbID, _, _ := s.params.Database.InsertMessage(r.Context(), "NICK", nick, "", json.RawMessage(body), nil)
			_ = s.params.Database.EnqueueMessage(r.Context(), uid, dbID)
			s.broker.Notify(uid)

			for _, ch := range channels {
				memberIDs, _ := s.params.Database.GetChannelMemberIDs(r.Context(), ch.ID)
				for _, mid := range memberIDs {
					if !notified[mid] {
						notified[mid] = true
						_ = s.params.Database.EnqueueMessage(r.Context(), mid, dbID)
						s.broker.Notify(mid)
					}
				}
			}
			s.respondJSON(w, r, map[string]string{"status": "ok", "nick": newNick}, http.StatusOK)

		case "TOPIC":
			if req.To == "" {
				s.respondJSON(w, r, map[string]string{"error": "to field required"}, http.StatusBadRequest)
				return
			}
			lines := bodyLines()
			if len(lines) == 0 {
				s.respondJSON(w, r, map[string]string{"error": "body required (topic text)"}, http.StatusBadRequest)
				return
			}
			topic := strings.Join(lines, " ")
			channel := req.To
			if !strings.HasPrefix(channel, "#") {
				channel = "#" + channel
			}
			if err := s.params.Database.SetTopic(r.Context(), channel, topic); err != nil {
				s.log.Error("set topic failed", "error", err)
				s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
				return
			}
			// Broadcast TOPIC to channel members.
			_, memberIDs, _ := s.getChannelMemberIDs(r, channel)
			_ = s.fanOut(r, "TOPIC", nick, channel, req.Body, memberIDs)
			s.respondJSON(w, r, map[string]string{"status": "ok", "topic": topic}, http.StatusOK)

		case "QUIT":
			// Broadcast QUIT to all channels, then remove user.
			channels, _ := s.params.Database.GetAllChannelMembershipsForUser(r.Context(), uid)
			notified := map[int64]bool{}
			var dbID int64
			if len(channels) > 0 {
				dbID, _, _ = s.params.Database.InsertMessage(r.Context(), "QUIT", nick, "", req.Body, nil)
			}
			for _, ch := range channels {
				memberIDs, _ := s.params.Database.GetChannelMemberIDs(r.Context(), ch.ID)
				for _, mid := range memberIDs {
					if mid != uid && !notified[mid] {
						notified[mid] = true
						_ = s.params.Database.EnqueueMessage(r.Context(), mid, dbID)
						s.broker.Notify(mid)
					}
				}
				_ = s.params.Database.PartChannel(r.Context(), ch.ID, uid)
				_ = s.params.Database.DeleteChannelIfEmpty(r.Context(), ch.ID)
			}
			_ = s.params.Database.DeleteUser(r.Context(), uid)
			s.respondJSON(w, r, map[string]string{"status": "quit"}, http.StatusOK)

		case "PING":
			s.respondJSON(w, r, map[string]string{"command": "PONG", "from": s.params.Config.ServerName}, http.StatusOK)

		default:
			s.respondJSON(w, r, map[string]string{"error": "unknown command: " + req.Command}, http.StatusBadRequest)
		}
	}
}

// HandleGetHistory returns message history for a specific target.
func (s *Handlers) HandleGetHistory() http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		_, _, ok := s.requireAuth(w, r)
		if !ok {
			return
		}
		target := r.URL.Query().Get("target")
		if target == "" {
			s.respondJSON(w, r, map[string]string{"error": "target required"}, http.StatusBadRequest)
			return
		}
		beforeID, _ := strconv.ParseInt(r.URL.Query().Get("before"), 10, 64)
		limit, _ := strconv.Atoi(r.URL.Query().Get("limit"))
		if limit <= 0 {
			limit = 50
		}
		msgs, err := s.params.Database.GetHistory(r.Context(), target, beforeID, limit)
		if err != nil {
			s.log.Error("get history failed", "error", err)
			s.respondJSON(w, r, map[string]string{"error": "internal error"}, http.StatusInternalServerError)
			return
		}
		s.respondJSON(w, r, msgs, http.StatusOK)
	}
}

// HandleServerInfo returns server metadata.
func (s *Handlers) HandleServerInfo() http.HandlerFunc {
	type response struct {
		Name string `json:"name"`
		MOTD string `json:"motd"`
	}
	return func(w http.ResponseWriter, r *http.Request) {
		s.respondJSON(w, r, &response{
			Name: s.params.Config.ServerName,
			MOTD: s.params.Config.MOTD,
		}, http.StatusOK)
	}
}