// Package transportunibus implements transport.Transport over the unibus message
// bus (github.com/enmanuel/unibus). A bot built on the neutral
// transport.Transport speaks unibus instead of Matrix: it discovers the rooms it
// has been invited to, joins them, and replies in the room a message arrived on.
//
// Room-based model ("everything is a room"):
//
//   - There is no inbox/outbox subject convention. A conversation is a unibus
//     room; a 1:1 DM is just a room with two members. A human peer creates an
//     encrypted room (room.ModeMatrix), invites the bot by its endpoint id, and
//     publishes a message. The bot finds the room by polling ListMyRooms,
//     Joins (fetching the sealed room key), Subscribes, and answers in place.
//   - The control plane is pull-based: there is no server push of invitations,
//     so the bot polls ListMyRooms on a ticker and reacts to rooms it has not
//     seen before.
//
// This adapter carries no Matrix (mautrix) types, so the agent core driving it
// stays transport-neutral.
package transportunibus

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"strings"
	"sync"
	"time"

	"github.com/enmanuel/agents/internal/config"
	"github.com/enmanuel/agents/pkg/message"
	"github.com/enmanuel/agents/pkg/transport"
	"github.com/enmanuel/unibus/pkg/client"
	"github.com/enmanuel/unibus/pkg/frame"
)

// defaultCommandPrefix marks a command message (e.g. "!ping") when the bot's
// config does not override it.
const defaultCommandPrefix = "!"

// discoveryInterval is how often the bot polls the control plane for rooms it
// has been invited to. The control plane has no push, so this is the latency a
// human waits between inviting the bot and the bot joining.
const discoveryInterval = 2 * time.Second

// Transport is a unibus-backed transport.Transport for one bot. It discovers
// rooms, subscribes to them, and replies in the room each message came from.
type Transport struct {
	handle        string
	commandPrefix string
	client        *client.Client
	endpoint      string // this bot's own endpoint id, to skip its own messages
	ctrlURL       string
	http          *http.Client
	logger        *slog.Logger

	mu          sync.Mutex
	subscribed  map[string]*client.Sub // roomID -> active subscription
	memberCount map[string]int         // roomID -> cached member count (for IsDirectMsg)
}

// compile-time assertion that Transport satisfies the neutral interface.
var _ transport.Transport = (*Transport)(nil)

// New connects to a unibus deployment using the bot's BusCfg. It loads (or
// creates) the bot's long-term identity, connects to the NATS data plane and
// the membershipd control plane, and records the handle used for mention
// detection. It does not create or join any room: rooms are discovered at Run
// time as the bot is invited to them.
func New(busCfg config.BusCfg, logger *slog.Logger) (*Transport, error) {
	id, err := client.LoadOrCreateIdentity(busCfg.IdentityPath)
	if err != nil {
		return nil, fmt.Errorf("transportunibus: identity: %w", err)
	}
	c, err := client.New(busCfg.NatsURL, busCfg.CtrlURL, id)
	if err != nil {
		return nil, fmt.Errorf("transportunibus: connect: %w", err)
	}
	if logger == nil {
		logger = slog.Default()
	}
	prefix := busCfg.CommandPrefix
	if prefix == "" {
		prefix = defaultCommandPrefix
	}
	return &Transport{
		handle:        busCfg.Handle,
		commandPrefix: prefix,
		client:        c,
		endpoint:      c.Endpoint().ID,
		ctrlURL:       busCfg.CtrlURL,
		http:          &http.Client{Timeout: 10 * time.Second},
		logger:        logger,
		subscribed:    map[string]*client.Sub{},
		memberCount:   map[string]int{},
	}, nil
}

// Endpoint returns this bot's public endpoint id. A human peer needs it to
// invite the bot to a room (the bot logs it at startup; a directory is a later
// step).
func (t *Transport) Endpoint() string { return t.endpoint }

// BusEndpoint returns this bot's full public endpoint (id + signing/key-exchange
// public keys). A peer inviting the bot to an encrypted room needs the public
// keys to seal the room key for it.
func (t *Transport) BusEndpoint() client.Endpoint { return t.client.Endpoint() }

// Run polls the control plane for rooms the bot has been invited to, joins and
// subscribes to each new one, and delivers every decrypted frame to handler as
// a neutral InboundMessage. It blocks until ctx is cancelled.
func (t *Transport) Run(ctx context.Context, handler transport.Handler) error {
	t.logger.Info("unibus transport running", "handle", t.handle, "endpoint", t.endpoint)

	ticker := time.NewTicker(discoveryInterval)
	defer ticker.Stop()
	defer t.unsubscribeAll()

	// Discover immediately so we don't wait a full interval on startup.
	t.discover(ctx, handler)

	for {
		select {
		case <-ctx.Done():
			return ctx.Err()
		case <-ticker.C:
			t.discover(ctx, handler)
		}
	}
}

// discover lists the bot's rooms and joins+subscribes to any it has not seen.
func (t *Transport) discover(ctx context.Context, handler transport.Handler) {
	rooms, err := t.client.ListMyRooms()
	if err != nil {
		t.logger.Warn("unibus discover: list rooms failed", "err", err)
		return
	}
	for _, r := range rooms {
		t.mu.Lock()
		_, already := t.subscribed[r.RoomID]
		t.mu.Unlock()
		if already {
			continue
		}

		if err := t.client.Join(r.RoomID); err != nil {
			t.logger.Warn("unibus discover: join failed", "room", r.RoomID, "err", err)
			continue
		}

		roomID := r.RoomID
		sub, err := t.client.Subscribe(roomID, func(f frame.Frame, plaintext []byte) {
			t.onFrame(ctx, handler, roomID, f, plaintext)
		})
		if err != nil {
			t.logger.Warn("unibus discover: subscribe failed", "room", roomID, "err", err)
			continue
		}

		t.mu.Lock()
		t.subscribed[roomID] = sub
		t.mu.Unlock()
		t.logger.Info("joined and subscribed to room", "room", roomID, "subject", r.Subject)
	}
}

// onFrame maps a decrypted frame to a neutral InboundMessage and delivers it.
// It skips the bot's own messages (to avoid replying to itself), parses any
// command, and computes IsDirectMsg (2-member room) and IsMention (handle in
// body) so the agent core's command/LLM flow behaves exactly as it did on
// Matrix.
func (t *Transport) onFrame(ctx context.Context, handler transport.Handler, roomID string, f frame.Frame, plaintext []byte) {
	if f.Sender == t.endpoint {
		return // never react to our own messages
	}

	body := string(plaintext)
	isDM := t.roomMemberCount(roomID) == 2
	isMention := t.handle != "" && strings.Contains(strings.ToLower(body), strings.ToLower(t.handle))

	// Reuse the pure command parser so "!cmd args" is split the same way the
	// Matrix listener split it.
	parsed := message.Parse(body, f.Sender, roomID, 0, isDM, message.ParseOptions{
		CommandPrefix: t.commandPrefix,
	})

	handler(ctx, transport.InboundMessage{
		RoomID:      roomID,
		Subject:     f.Subject,
		SenderID:    f.Sender,
		MsgID:       f.MsgID,
		ThreadID:    f.ThreadID,
		ReplyTo:     f.ReplyTo,
		Body:        body,
		Command:     parsed.Command,
		Args:        parsed.Args,
		IsDirectMsg: isDM,
		IsMention:   isMention,
	})
}

// Reply publishes a reply into the room the message came from. When the reply
// carries a ReplyTo / ThreadID anchor it is published as a threaded reply so
// receivers can render the conversation tree.
func (t *Transport) Reply(_ context.Context, out transport.OutboundReply) error {
	if out.ReplyTo != "" || out.ThreadID != "" {
		return t.client.PublishReply(out.RoomID, []byte(out.Markdown), out.ReplyTo, out.ThreadID)
	}
	return t.client.Publish(out.RoomID, []byte(out.Markdown))
}

// Send posts a standalone message into a room.
func (t *Transport) Send(_ context.Context, roomID, markdown string) error {
	return t.client.Publish(roomID, []byte(markdown))
}

// Close unsubscribes from every room and releases the unibus client connection.
func (t *Transport) Close() error {
	t.unsubscribeAll()
	return t.client.Close()
}

// Sender returns an adapter that satisfies the effects/cron/tools Sender
// interface, letting the agent's effects runner, scheduler, and bus_send tool
// publish into rooms over this transport.
func (t *Transport) Sender() *busSender { return &busSender{t: t} }

// unsubscribeAll cancels every active room subscription.
func (t *Transport) unsubscribeAll() {
	t.mu.Lock()
	subs := t.subscribed
	t.subscribed = map[string]*client.Sub{}
	t.mu.Unlock()
	for roomID, sub := range subs {
		if err := sub.Unsubscribe(); err != nil {
			t.logger.Warn("unibus: unsubscribe failed", "room", roomID, "err", err)
		}
	}
}

// roomMemberCount returns the number of members in a room, used to decide
// IsDirectMsg. The control plane exposes GET /rooms/{id}/members; the result is
// cached per room since membership rarely changes during a conversation.
func (t *Transport) roomMemberCount(roomID string) int {
	t.mu.Lock()
	if n, ok := t.memberCount[roomID]; ok {
		t.mu.Unlock()
		return n
	}
	t.mu.Unlock()

	n, err := t.fetchMemberCount(roomID)
	if err != nil {
		t.logger.Warn("unibus: member count fetch failed", "room", roomID, "err", err)
		return 0 // unknown → treat as not-a-DM (mention still drives the LLM)
	}
	t.mu.Lock()
	t.memberCount[roomID] = n
	t.mu.Unlock()
	return n
}

// memberJSON mirrors the membership server's GET /rooms/{id}/members element.
// Only the count matters here, so the body fields are ignored.
type memberJSON struct {
	Endpoint string `json:"endpoint"`
}

// fetchMemberCount calls the membershipd control plane directly to count the
// members of a room. unibus's client does not expose this, and the task forbids
// modifying unibus, so the minimal HTTP GET lives here.
func (t *Transport) fetchMemberCount(roomID string) (int, error) {
	url := strings.TrimRight(t.ctrlURL, "/") + "/rooms/" + roomID + "/members"
	resp, err := t.http.Get(url)
	if err != nil {
		return 0, fmt.Errorf("get members: %w", err)
	}
	defer resp.Body.Close()
	if resp.StatusCode >= 300 {
		return 0, fmt.Errorf("get members: status %d", resp.StatusCode)
	}
	var members []memberJSON
	if err := json.NewDecoder(resp.Body).Decode(&members); err != nil {
		return 0, fmt.Errorf("decode members: %w", err)
	}
	return len(members), nil
}

// busSender adapts a *Transport to the effects.Sender / cron.Sender / tools
// Sender interface (SendText/SendMarkdown/SendReplyMarkdown/SendThreadMarkdown/
// SendTyping). All sends publish into the given room; SendTyping is a no-op
// because unibus has no typing-indicator concept.
type busSender struct{ t *Transport }

func (s *busSender) SendText(_ context.Context, roomID, text string) error {
	return s.t.client.Publish(roomID, []byte(text))
}

func (s *busSender) SendMarkdown(_ context.Context, roomID, markdown string) error {
	return s.t.client.Publish(roomID, []byte(markdown))
}

func (s *busSender) SendReplyMarkdown(_ context.Context, roomID, inReplyTo, markdown string) error {
	return s.t.client.PublishReply(roomID, []byte(markdown), inReplyTo, "")
}

func (s *busSender) SendThreadMarkdown(_ context.Context, roomID, threadRootID, inReplyTo, markdown string) error {
	return s.t.client.PublishReply(roomID, []byte(markdown), inReplyTo, threadRootID)
}

// SendTyping is a no-op: unibus has no typing indicator.
func (s *busSender) SendTyping(_ context.Context, _ string, _ bool) error { return nil }