package main

import (
	"context"
	"log"
	"sync"
)

// roomMeta caches per-room classification we need to handle a message: member
// counts (for the 1:1 test, F3) and encryption state (F15). Rebuilt per process;
// unknown fields are lazily fetched from the CS-API on first need — appservice
// transactions carry no room summary.
type roomMeta struct {
	joined, invited     int
	countsKnown         bool
	encrypted, encKnown bool
}

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

type Bot struct {
	cfg *Config
	log *log.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 daily-limit notice
}

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

	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.Printf("set display name failed (non-fatal): %v", 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 {
		b.log.Fatalf("as_token resolves to %q but BOT_MXID is %q", who, b.cfg.BotMXID)
	}
	b.log.Printf("authenticated as %s", 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
	}
	switch ev.Type {
	case "m.room.member":
		if ev.StateKey != nil && *ev.StateKey == b.cfg.BotMXID {
			b.handleSelfMembership(ctx, ev)
		}
	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.Printf("accepting invite to %s from %s", ev.RoomID, ev.Sender)
			if err := b.mx.JoinRoom(ctx, ev.RoomID); err != nil {
				b.log.Printf("join %s failed: %v", ev.RoomID, err)
			}
		} else {
			b.log.Printf("rejecting invite to %s from %q (server not allowed)", ev.RoomID, ev.Sender)
			if err := b.mx.LeaveRoom(ctx, ev.RoomID); err != nil {
				b.log.Printf("leave (reject) %s failed: %v", ev.RoomID, err)
			}
		}
	case "leave", "ban":
		delete(b.meta, ev.RoomID)
		delete(b.buf, ev.RoomID)
	}
}

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.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
	}

	// 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)
	replyParentIsBot := mc.RelatesTo != nil && mc.RelatesTo.InReplyTo != nil &&
		b.botSent.Has(mc.RelatesTo.InReplyTo.EventID)

	if !(m.isDM() || mentionsBot(mc, b.cfg.BotMXID, replyParentIsBot)) {
		return
	}
	b.respond(ctx, roomID, m, ev, mc, history)
}

func (b *Bot) respond(ctx context.Context, roomID string, m *roomMeta, ev *Event, mc *MessageContent, history []bufferedMsg) {
	switch res, err := b.st.Reserve(ev.Sender, b.cfg.PerUserDailyCap, b.cfg.DailyUSDCeiling); {
	case err != nil:
		b.log.Printf("limiter reserve failed: %v", err)
		return
	case res == reserveDeniedUser:
		// Silent drop — per-user cap is anti-abuse (F24).
		return
	case res == reserveDeniedGlobal:
		// Global USD ceiling — notice once per room per day, then stay quiet.
		if b.globalNote[roomID] != todayUTC() {
			b.globalNote[roomID] = todayUTC()
			b.sendNotice(ctx, roomID, ev, mc, noticeDailyLimit)
		}
		return
	}

	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.
		b.log.Printf("xai completion failed for %s: %v", ev.Sender, err)
		if rerr := b.st.RefundRequest(ev.Sender); rerr != nil {
			b.log.Printf("refund failed: %v", rerr)
		}
		return
	}

	usd := computeUSD(resp.Usage, b.cfg)
	if err := b.st.Reconcile(ev.Sender, usd); err != nil {
		b.log.Printf("reconcile spend failed: %v", err)
	}

	b.sendNotice(ctx, roomID, ev, mc, resp.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.Printf("send notice to %s failed: %v", roomID, 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})
}

func (b *Bot) warnEncryptedOnce(ctx context.Context, roomID string) {
	warned, err := b.st.HasWarnedEncrypted(roomID)
	if err != nil {
		b.log.Printf("warned-flag read failed: %v", 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.Printf("encrypted-notice to %s failed: %v", roomID, err)
		return
	}
	if err := b.st.SetWarnedEncrypted(roomID); err != nil {
		b.log.Printf("persist warned-flag failed: %v", 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}
	}
	return map[string]any{
		"msgtype":      "m.notice",
		"body":         body,
		"m.mentions":   map[string]any{"user_ids": []string{sender}},
		"m.relates_to": relates,
	}
}

// --- 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.Printf("encryption probe %s failed: %v", roomID, 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, err := b.mx.MemberCounts(ctx, roomID)
	if err != nil {
		b.log.Printf("member-count probe %s failed: %v", roomID, err)
		return
	}
	m.joined, m.invited, m.countsKnown = joined, invited, 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
}