package main

import (
	"context"
	"fmt"
	"log/slog"
	"sync"
)

// roomMeta caches per-room classification we need to handle a message: member
// counts (for the 1:1 test, F3), whether any member is outside ALLOWED_SERVERS,
// and encryption state (F15). Lazily fetched from the CS-API on first need
// (appservice transactions carry no room summary) and INVALIDATED whenever a
// third party's membership changes, so a 1:1 that gains a member is reclassified
// out of DM mode (no DM-mode third-party leak) and a newly added foreign member
// is caught.
type roomMeta struct {
	joined, invited     int
	countsKnown         bool
	foreign             bool // a joined/invited member is outside ALLOWED_SERVERS
	encrypted, encKnown bool
}

func (m *roomMeta) isDM() bool { return m.countsKnown && m.joined+m.invited == 2 }

type Bot struct {
	cfg *Config
	log *slog.Logger
	mx  *MatrixClient
	xai *XAIClient
	st  *Store

	// Transactions are delivered one at a time by Synapse, but guard the shared
	// maps/sets anyway so an unexpected concurrent call can't corrupt them.
	mu         sync.Mutex
	seen       *lruSet // event ids already handled (dedup within a session)
	botSent    *lruSet // event ids the bot itself sent (reply-parent detection)
	meta       map[string]*roomMeta
	buf        map[string][]bufferedMsg
	globalNote map[string]string // roomID → UTC date we last sent the global daily-limit notice
}

func NewBot(ctx context.Context, cfg *Config, logger *slog.Logger) (*Bot, error) {
	mx := NewMatrixClient(cfg.HomeserverURL, cfg.ASToken, cfg.BotMXID)
	xai := NewXAIClient(cfg.XAIBaseURL, cfg.XAIAPIKey, logger)

	st, err := OpenStore(cfg.statePath("ai-bot.db"))
	if err != nil {
		return nil, err
	}

	b := &Bot{
		cfg:        cfg,
		log:        logger,
		mx:         mx,
		xai:        xai,
		st:         st,
		seen:       newLRUSet(5000),
		botSent:    newLRUSet(5000),
		meta:       make(map[string]*roomMeta),
		buf:        make(map[string][]bufferedMsg),
		globalNote: make(map[string]string),
	}

	// Confirm the as_token + user_id resolves to BOT_MXID before serving.
	if err := b.verifyIdentity(ctx); err != nil {
		st.Close()
		return nil, err
	}
	// F23: ensure the profile has a display name (best-effort, idempotent).
	if err := mx.SetDisplayName(ctx, cfg.BotDisplayName); err != nil {
		logger.Warn("set display name failed (non-fatal)", "err", err)
	}
	return b, nil
}

func (b *Bot) Close() {
	if b.st != nil {
		_ = b.st.Close()
	}
}

func (b *Bot) verifyIdentity(ctx context.Context) error {
	who, err := b.mx.Whoami(ctx)
	if err != nil {
		return err
	}
	if who != b.cfg.BotMXID {
		return fmt.Errorf("as_token resolves to %q but BOT_MXID is %q", who, b.cfg.BotMXID)
	}
	b.log.Info("authenticated", "mxid", who)
	return nil
}

// Run starts the appservice transaction server and blocks until ctx is cancelled.
func (b *Bot) Run(ctx context.Context) error {
	as := NewAppService(b.cfg, b.log, b.st, b.handleTransaction)
	return as.Serve(ctx)
}

// handleTransaction processes one pushed transaction's events in order.
func (b *Bot) handleTransaction(ctx context.Context, events []Event) {
	b.mu.Lock()
	defer b.mu.Unlock()
	for i := range events {
		b.handleEvent(ctx, &events[i])
	}
}

func (b *Bot) handleEvent(ctx context.Context, ev *Event) {
	if ev.EventID == "" || ev.RoomID == "" {
		return
	}
	if !b.seen.Add(ev.EventID) {
		return // already handled this session (fast in-memory path)
	}
	// Durable dedup across restarts: if a previous run already handled this event
	// but crashed before its transaction was acked, Synapse re-pushes it — don't
	// reprocess (no dup answer / double-bill). On a DB error, fall through; the
	// in-memory set still guards this session.
	if isNew, err := b.st.SeenEvent(ev.EventID); err != nil {
		b.log.Error("durable dedup check failed", "id", ev.EventID, "err", err)
	} else if !isNew {
		return
	}
	b.log.Debug("event", "type", ev.Type, "room", ev.RoomID, "sender", ev.Sender, "id", ev.EventID)
	switch ev.Type {
	case "m.room.member":
		if ev.StateKey != nil && *ev.StateKey == b.cfg.BotMXID {
			b.handleSelfMembership(ctx, ev)
		} else if m := b.meta[ev.RoomID]; m != nil {
			// A third party's membership changed: counts + foreign flag are now
			// stale. Re-probe on the next message so a 1:1 that gains a member drops
			// out of DM mode (no third-party leak) and a new foreign member is caught.
			m.countsKnown = false
		}
	case "m.room.encryption":
		m := b.getMeta(ev.RoomID)
		m.encrypted, m.encKnown = true, true
	case "m.room.message":
		b.handleMessage(ctx, ev)
	}
}

// handleSelfMembership reacts to membership changes for the bot user: auto-join
// invites from allowed servers (F11), reject others, forget rooms we leave.
func (b *Bot) handleSelfMembership(ctx context.Context, ev *Event) {
	switch ev.membershipOf() {
	case "invite":
		if !b.cfg.AllowedServers[serverOf(ev.Sender)] {
			b.log.Warn("rejecting invite (server not allowed)", "room", ev.RoomID, "sender", ev.Sender)
			if err := b.mx.LeaveRoom(ctx, ev.RoomID); err != nil {
				b.log.Error("leave (reject) failed", "room", ev.RoomID, "err", err)
			}
			return
		}
		b.log.Info("accepting invite", "room", ev.RoomID, "sender", ev.Sender)
		if err := b.mx.JoinRoom(ctx, ev.RoomID); err != nil {
			b.log.Error("join failed", "room", ev.RoomID, "err", err)
			return
		}
		// Fully-on-allowed-servers gate: a vojo.chat inviter can still pull the bot
		// into a room that already holds federated third parties — leave at once.
		m := b.getMeta(ev.RoomID)
		b.ensureCounts(ctx, ev.RoomID, m)
		if m.countsKnown && m.foreign {
			b.leaveForeign(ctx, ev.RoomID)
		}
	case "leave", "ban":
		delete(b.meta, ev.RoomID)
		delete(b.buf, ev.RoomID)
	}
}

// leaveForeign leaves a room that contains a member outside ALLOWED_SERVERS, so
// the bot only ever operates in rooms hosted entirely on allowed homeservers.
func (b *Bot) leaveForeign(ctx context.Context, roomID string) {
	b.log.Warn("leaving room — a member is outside ALLOWED_SERVERS", "room", roomID)
	if err := b.mx.LeaveRoom(ctx, roomID); err != nil {
		b.log.Error("leave (foreign) failed", "room", roomID, "err", err)
	}
}

func (b *Bot) handleMessage(ctx context.Context, ev *Event) {
	roomID := ev.RoomID
	m := b.getMeta(roomID)

	// A9/F15: re-check encryption; if (or once) encrypted, warn once and skip —
	// the bot can't read it.
	b.ensureEncryption(ctx, roomID, m)
	if m.encrypted {
		b.log.Debug("skip: encrypted room", "room", roomID)
		b.warnEncryptedOnce(ctx, roomID)
		return
	}

	mc, ok := ev.DecodeMessage()
	if !ok {
		return
	}
	// Edits re-carry m.mentions; never re-trigger or replay them (F16).
	if mc.IsReplace() {
		return
	}
	// Only plain text ever reaches xAI: drop media (m.image/m.file/m.audio/…) and
	// other custom msgtypes outright — the bot doesn't fetch or forward media, and
	// a caption/filename is third-party content we keep out of xAI. m.notice falls
	// through to its existing anti-loop handling below.
	if mc.MsgType != "m.text" && mc.MsgType != "m.emote" && mc.MsgType != "m.notice" {
		b.log.Debug("skip: non-text msgtype", "room", roomID, "sender", ev.Sender, "msgtype", mc.MsgType)
		return
	}

	// Buffer prior context BEFORE classifying so buildContext sees history only.
	history := b.buf[roomID]
	b.appendBuf(roomID, bufferedMsg{sender: ev.Sender, body: mc.Body, isBot: ev.Sender == b.cfg.BotMXID})

	if ev.Sender == b.cfg.BotMXID {
		return // our own message (also tracked via botSent)
	}
	if mc.MsgType == "m.notice" {
		return // anti-loop: ignore notices (ours and other bots')
	}

	b.ensureCounts(ctx, roomID, m)
	// Stay only in rooms hosted entirely on allowed servers — never operate in (or
	// "leak" the bot into) a federated room with non-consenting third parties.
	if m.countsKnown && m.foreign {
		b.leaveForeign(ctx, roomID)
		return
	}
	replyParentIsBot := mc.RelatesTo != nil && mc.RelatesTo.InReplyTo != nil &&
		b.botSent.Has(mc.RelatesTo.InReplyTo.EventID)

	mentioned := mentionsBot(mc, b.cfg.BotMXID, replyParentIsBot)
	if !(m.isDM() || mentioned) {
		b.log.Debug("skip: not addressed (group without mention)", "room", roomID, "sender", ev.Sender,
			"dm", m.isDM(), "joined", m.joined, "invited", m.invited, "countsKnown", m.countsKnown, "mentioned", mentioned)
		return
	}
	b.respond(ctx, roomID, m, ev, mc, history)
}

// unlimitedCap is the effective per-user cap for UNLIMITED_USERS — high enough to
// never trip the per-user gate, while the global DAILY_USD_CEILING still applies.
const unlimitedCap = 1 << 30

func (b *Bot) respond(ctx context.Context, roomID string, m *roomMeta, ev *Event, mc *MessageContent, history []bufferedMsg) {
	perUserCap := b.cfg.PerUserDailyCap
	if b.cfg.UnlimitedUsers[ev.Sender] {
		perUserCap = unlimitedCap
	}
	switch res, err := b.st.Reserve(ev.Sender, perUserCap, b.cfg.DailyUSDCeiling); {
	case err != nil:
		b.log.Error("limiter reserve failed", "sender", ev.Sender, "err", err)
		return
	case res == reserveDeniedUser:
		// Per-user cap (anti-abuse, F24): stop answering, but always tell the user
		// their request hit the limit — no message addressed to the bot is left
		// silent. (m.notice → the anti-loop skip keeps this from re-triggering.)
		b.log.Info("per-user daily cap reached; notifying", "sender", ev.Sender)
		b.sendNotice(ctx, roomID, ev, mc, noticeUserLimit)
		return
	case res == reserveDeniedGlobal:
		// Global USD ceiling — notice once per room per day, then stay quiet.
		b.log.Warn("global daily USD ceiling reached", "room", roomID, "sender", ev.Sender)
		if b.globalNote[roomID] != todayUTC() {
			b.globalNote[roomID] = todayUTC()
			b.sendNotice(ctx, roomID, ev, mc, noticeDailyLimit)
		}
		return
	}

	// Show "Vojo AI печатает…" while we build the answer; the deferred clear fires
	// on every exit (success or failure). Pure UX — typing failures are best-effort.
	b.setTyping(ctx, roomID, true)
	defer b.setTyping(ctx, roomID, false)

	msgs := buildContext(b.cfg.SystemPrompt, history, m.isDM(), mc.Body, b.cfg.MaxCtxEvent, 8000)
	resp, err := b.xai.Complete(ctx, b.cfg.XAIModel, msgs, b.cfg.MaxOutTok, b.cfg.XAITemp)
	if err != nil {
		// at-most-once already retried transient failures inside Complete; refund
		// the reserved request so an xAI outage doesn't burn the user's daily cap,
		// and tell the user we couldn't answer (notice → no anti-loop re-trigger).
		b.log.Error("xai completion failed", "sender", ev.Sender, "err", err)
		if rerr := b.st.RefundRequest(ev.Sender); rerr != nil {
			b.log.Error("refund failed", "sender", ev.Sender, "err", rerr)
		}
		b.sendNotice(ctx, roomID, ev, mc, noticeError)
		return
	}

	// A 2xx from xAI is billed even if the text came back empty — always book the
	// real cost so both caps see it (the old refund-without-reconcile on an empty
	// 200 let such calls bypass the per-user cap and the global ceiling).
	usd := computeUSD(resp.Usage, b.cfg)
	if err := b.st.Reconcile(ev.Sender, usd); err != nil {
		b.log.Error("reconcile spend failed", "sender", ev.Sender, "err", err)
	}

	text := resp.Text()
	if text == "" {
		b.log.Warn("xai returned empty completion (billed, nothing to send)", "sender", ev.Sender, "usd", usd)
		return
	}
	b.log.Info("answered", "room", roomID, "sender", ev.Sender, "dm", m.isDM(),
		"usd", usd, "prompt_tokens", resp.Usage.PromptTokens, "completion_tokens", resp.Usage.CompletionTokens)
	b.sendNotice(ctx, roomID, ev, mc, text)
}

// computeUSD prices the call from the API-returned token usage (authoritative
// counts) and the configured per-1M prices — so the hard ceiling tracks real
// usage even if the model/price changes (only the constants need updating).
func computeUSD(u xaiUsage, cfg *Config) float64 {
	cached := u.PromptTokensDetails.CachedTokens
	nonCached := u.PromptTokens - cached
	if nonCached < 0 {
		nonCached = 0
	}
	return float64(nonCached)/1e6*cfg.PriceInputPerM +
		float64(cached)/1e6*cfg.PriceCachedPerM +
		float64(u.CompletionTokens)/1e6*cfg.PriceOutputPerM
}

func (b *Bot) sendNotice(ctx context.Context, roomID string, trigger *Event, triggerMC *MessageContent, body string) {
	content := buildNoticeContent(trigger.EventID, trigger.Sender, triggerMC.RelatesTo, body)
	id, err := b.mx.SendEvent(ctx, roomID, "m.room.message", content)
	if err != nil {
		b.log.Error("send notice failed", "room", roomID, "err", err)
		return
	}
	// Track our own reply so a future reply-to-it is recognised as addressing us,
	// and add it to the room buffer as an assistant turn for context continuity.
	b.botSent.Add(id)
	b.appendBuf(roomID, bufferedMsg{sender: b.cfg.BotMXID, body: body, isBot: true})
}

// setTyping sets/clears the bot's typing indicator (best-effort UX; failures are
// non-fatal). The 30s timeout comfortably covers a normal completion, and
// respond() defers a clear so the indicator ends the moment the answer is sent
// or fails.
func (b *Bot) setTyping(ctx context.Context, roomID string, typing bool) {
	if err := b.mx.SendTyping(ctx, roomID, typing, 30000); err != nil {
		b.log.Debug("set typing failed", "room", roomID, "typing", typing, "err", err)
	}
}

func (b *Bot) warnEncryptedOnce(ctx context.Context, roomID string) {
	warned, err := b.st.HasWarnedEncrypted(roomID)
	if err != nil {
		b.log.Error("warned-flag read failed", "room", roomID, "err", err)
		return
	}
	if warned {
		return
	}
	content := map[string]any{"msgtype": "m.notice", "body": noticeEncryptedUnsupported}
	if _, err := b.mx.SendEvent(ctx, roomID, "m.room.message", content); err != nil {
		b.log.Error("encrypted-notice failed", "room", roomID, "err", err)
		return
	}
	if err := b.st.SetWarnedEncrypted(roomID); err != nil {
		b.log.Error("persist warned-flag failed", "room", roomID, "err", err)
	}
}

// buildNoticeContent builds the reply. m.notice (not m.text) so the anti-loop
// skip catches our own output. Thread-aware (F27): a trigger from a thread gets a
// thread relation so the answer lands in the thread, not the main timeline.
func buildNoticeContent(replyTo, sender string, triggerRelates *RelatesTo, body string) map[string]any {
	relates := map[string]any{}
	if triggerRelates != nil && triggerRelates.RelType == "m.thread" && triggerRelates.EventID != "" {
		relates["rel_type"] = "m.thread"
		relates["event_id"] = triggerRelates.EventID
		relates["is_falling_back"] = true
		relates["m.in_reply_to"] = map[string]any{"event_id": replyTo}
	} else {
		relates["m.in_reply_to"] = map[string]any{"event_id": replyTo}
	}
	content := map[string]any{
		"msgtype":      "m.notice",
		"body":         body,
		"m.mentions":   map[string]any{"user_ids": []string{sender}},
		"m.relates_to": relates,
	}
	// The model answers in markdown; render it to org.matrix.custom.html so clients
	// show formatting instead of raw `**`, `#`, lists, code fences. Only attach
	// formatted_body when there's actual formatting — a plain answer keeps rendering
	// from `body` exactly as before.
	if html, formatted := markdownToHTML(body); formatted {
		content["format"] = matrixHTMLFormat
		content["formatted_body"] = html
	}
	return content
}

// --- per-room metadata helpers -------------------------------------------------

func (b *Bot) getMeta(roomID string) *roomMeta {
	m := b.meta[roomID]
	if m == nil {
		m = &roomMeta{}
		b.meta[roomID] = m
	}
	return m
}

func (b *Bot) ensureEncryption(ctx context.Context, roomID string, m *roomMeta) {
	if m.encKnown {
		return
	}
	enc, err := b.mx.RoomEncrypted(ctx, roomID)
	if err != nil {
		b.log.Warn("encryption probe failed", "room", roomID, "err", err)
		return // leave unknown; re-probed on the next message
	}
	m.encrypted, m.encKnown = enc, true
}

func (b *Bot) ensureCounts(ctx context.Context, roomID string, m *roomMeta) {
	if m.countsKnown {
		return
	}
	joined, invited, servers, err := b.mx.RoomMembership(ctx, roomID)
	if err != nil {
		b.log.Warn("member probe failed", "room", roomID, "err", err)
		return
	}
	foreign := false
	for s := range servers {
		if !b.cfg.AllowedServers[s] {
			foreign = true
			break
		}
	}
	m.joined, m.invited, m.foreign, m.countsKnown = joined, invited, foreign, true
}

func (b *Bot) appendBuf(roomID string, msg bufferedMsg) {
	limit := b.cfg.MaxCtxEvent * 2
	if limit < 8 {
		limit = 8
	}
	buf := append(b.buf[roomID], msg)
	if len(buf) > limit {
		buf = buf[len(buf)-limit:]
	}
	b.buf[roomID] = buf
}