package engine

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"sync"
	"time"

	"github.com/jackc/pgx/v5/pgtype"

	"github.com/multica-ai/multica/server/internal/integrations/channel"
	"github.com/multica-ai/multica/server/internal/service"
)

// Router is the channel-agnostic inbound pipeline — the generalization of the
// Feishu-only lark.Dispatcher (+ the Hub's handleEvent outbound seam). It is
// the single shared channel.InboundHandler the Supervisor injects into every
// Channel: a Channel translates its platform payload into a
// channel.InboundMessage and calls Handle, which routes by ChannelType to that
// platform's registered resolver set and runs the same ordered pipeline for
// every platform — installation route → two-phase dedup → group @bot filter →
// identity + membership → ensure session → append+mark → /issue → debounced
// run trigger — then drives the detached outbound replier + typing indicator.
//
// The core contains no platform specifics: everything platform-shaped lives
// behind the resolver interfaces (a feishu ResolverSet is the first
// implementation). Adding a platform is "register a ResolverSet", not "edit
// the Router".
type Router struct {
	mu   sync.RWMutex
	sets map[channel.Type]ResolverSet

	issues IssueCreator
	tasks  TaskEnqueuer
	reader SessionReader

	batcher *pendingBatcher

	replyTimeout time.Duration
	replyWg      sync.WaitGroup

	logger *slog.Logger

	pendingFreshMu sync.Mutex
	pendingFresh   map[string]bool
}

// Config tunes the Router. Zero values default.
type RouterConfig struct {
	// ReplyTimeout caps a single detached OutboundReplier.Reply / typing
	// call. It runs off the connector ACK path, so it must stay strictly
	// under the platform ACK deadline (Lark: 3s). Defaults to 2.5s.
	ReplyTimeout time.Duration
	Logger       *slog.Logger
}

// NewRouter builds a Router around the shared (platform-agnostic) services:
// the IssueCreator + TaskEnqueuer that /issue and chat runs go through, and a
// SessionReader for the debounced flush. Register a platform's ResolverSet
// with Register before Handle is called.
func NewRouter(issues IssueCreator, tasks TaskEnqueuer, reader SessionReader, cfg RouterConfig) *Router {
	if cfg.ReplyTimeout == 0 {
		cfg.ReplyTimeout = 2500 * time.Millisecond
	}
	if cfg.Logger == nil {
		cfg.Logger = slog.Default()
	}
	return &Router{
		sets:         make(map[channel.Type]ResolverSet),
		issues:       issues,
		tasks:        tasks,
		reader:       reader,
		replyTimeout: cfg.ReplyTimeout,
		logger:       cfg.Logger,
		pendingFresh: make(map[string]bool),
	}
}

// Register binds a platform's ResolverSet under t. Call at boot, before Run.
// Registering an empty Type or a set missing a required resolver is ignored.
func (r *Router) Register(t channel.Type, set ResolverSet) {
	if t == "" || set.Installation == nil || set.Identity == nil || set.Dedup == nil || set.Session == nil || set.Audit == nil {
		r.logger.Warn("channel router: ignoring incomplete resolver set", "channel_type", string(t))
		return
	}
	r.mu.Lock()
	defer r.mu.Unlock()
	r.sets[t] = set
}

// EnableRunBatching installs the debouncer in front of the per-session run
// trigger. Call once at boot. A non-positive window uses
// DefaultChatRunBatchWindow. Without it, runs fire inline (used by tests).
func (r *Router) EnableRunBatching(window time.Duration) {
	r.batcher = newPendingBatcher(window)
}

// Drain flushes debounced run triggers and joins in-flight reply goroutines.
// Call on shutdown AFTER the Supervisor has stopped delivering events.
func (r *Router) Drain() {
	if r.batcher != nil {
		r.batcher.FlushAll()
	}
	r.replyWg.Wait()
}

// ErrNoResolverSet is returned by Handle when a message arrives for a channel
// type that has no registered ResolverSet — a boot/registration bug. It is an
// infrastructure error so the adapter surfaces it rather than silently
// dropping.
var ErrNoResolverSet = errors.New("channel router: no resolver set for channel type")

// Handle is the shared channel.InboundHandler. It runs the pipeline and then
// drives the detached outbound side; it returns a non-nil error only for
// infrastructure failures (the adapter reconnects). Product outcomes (dropped,
// needs-binding, …) are not errors.
func (r *Router) Handle(ctx context.Context, msg channel.InboundMessage) error {
	r.mu.RLock()
	set, ok := r.sets[msg.Source.ChannelType]
	r.mu.RUnlock()
	if !ok {
		r.logger.Error("channel router: no resolver set", "channel_type", string(msg.Source.ChannelType))
		return ErrNoResolverSet
	}

	res, inst, err := r.dispatch(ctx, set, msg)
	if err != nil {
		r.logger.Error("channel router: dispatch error",
			"channel_type", string(msg.Source.ChannelType),
			"event_id", msg.EventID,
			"error", err,
		)
		return err
	}
	r.logger.Debug("channel router: dispatch outcome",
		"channel_type", string(msg.Source.ChannelType),
		"event_id", msg.EventID,
		"outcome", string(res.Outcome),
		"drop_reason", string(res.DropReason),
	)

	// Typing indicator on ingest, detached so the reaction HTTP call never
	// blocks the connector ACK path.
	if res.Outcome == OutcomeIngested && set.Typing != nil {
		go func() {
			tctx, cancel := context.WithTimeout(context.Background(), r.replyTimeout)
			defer cancel()
			set.Typing.OnIngested(tctx, inst, msg, res.ChatSessionID)
		}()
	}
	r.scheduleReply(set, inst, msg, res)
	return nil
}

// dispatch runs the pipeline and returns the typed result plus the resolved
// installation (needed by the outbound side). Mirrors lark.Dispatcher.Handle.
func (r *Router) dispatch(ctx context.Context, set ResolverSet, msg channel.InboundMessage) (Result, ResolvedInstallation, error) {
	// 1. Route to installation. The adapter maps the platform routing key
	//    (carried on the message) to its installation row. These drop
	//    branches run BEFORE the dedup claim because they have no valid
	//    installation to attach a claim to.
	inst, err := set.Installation.ResolveInstallation(ctx, msg)
	if err != nil {
		if errors.Is(err, ErrInstallationNotFound) {
			_ = set.Audit.RecordDrop(ctx, pgtype.UUID{}, msg, DropReasonInvalidEvent)
			return Result{Outcome: OutcomeDropped, DropReason: DropReasonInvalidEvent}, ResolvedInstallation{}, nil
		}
		return Result{}, ResolvedInstallation{}, fmt.Errorf("resolve installation: %w", err)
	}
	if !inst.Active {
		return r.drop(ctx, set, msg, inst.ID, DropReasonRevokedInstallation), inst, nil
	}

	// 2. Two-phase dedup claim with owner fencing — before group filter and
	//    identity so a reconnect replay cannot re-trigger a binding prompt,
	//    re-write a drop audit, or re-touch the session. Empty MessageID
	//    means there is no key to dedup by; skip the claim.
	var claimToken pgtype.UUID
	claimed := false
	if msg.MessageID != "" {
		token, err := set.Dedup.Claim(ctx, inst.ID, msg.MessageID)
		if err != nil {
			if errors.Is(err, ErrDuplicate) {
				return r.drop(ctx, set, msg, inst.ID, DropReasonDuplicate), inst, nil
			}
			return Result{}, inst, fmt.Errorf("dedup claim: %w", err)
		}
		claimToken = token
		claimed = true
	}

	res, finalize, err := r.processClaimed(ctx, set, msg, inst, claimToken)

	if claimed {
		r.applyFinalize(ctx, set, inst.ID, msg.MessageID, claimToken, finalize)
	}

	// ErrClaimLost: another worker holds the claim. Surface as duplicate.
	if errors.Is(err, ErrClaimLost) {
		return r.drop(ctx, set, msg, inst.ID, DropReasonDuplicate), inst, nil
	}
	return res, inst, err
}

// dedupFinalize tells dispatch how to land the claim row after processClaimed.
type dedupFinalize int

const (
	finalizeNone dedupFinalize = iota
	finalizeMark
	finalizeRelease
)

// processClaimed runs the post-dedup pipeline. Mirrors
// lark.Dispatcher.processClaimed; see its boundary contract per step.
func (r *Router) processClaimed(ctx context.Context, set ResolverSet, msg channel.InboundMessage, inst ResolvedInstallation, claimToken pgtype.UUID) (Result, dedupFinalize, error) {
	// 3. Group-mention filter (group chats only), before identity so an
	//    unbound user's idle group chatter never spams a binding card.
	if msg.Source.ChatType == channel.ChatTypeGroup && !msg.AddressedToBot {
		return r.drop(ctx, set, msg, inst.ID, DropReasonNotAddressedInGroup), finalizeMark, nil
	}

	// 4. Identity check: map the platform sender to a Multica user and
	//    re-verify workspace membership (no binding->member FK; MUL-3515 §4).
	identity, err := set.Identity.ResolveSender(ctx, inst, msg)
	if err != nil {
		switch {
		case errors.Is(err, ErrSenderUnbound):
			_ = set.Audit.RecordDrop(ctx, inst.ID, msg, DropReasonUnboundUser)
			return Result{
				Outcome:        OutcomeNeedsBinding,
				DropReason:     DropReasonUnboundUser,
				InstallationID: inst.ID,
				Sender:         msg.Source.SenderID,
			}, finalizeMark, nil
		case errors.Is(err, ErrSenderNotMember):
			return r.drop(ctx, set, msg, inst.ID, DropReasonNonWorkspaceMember), finalizeMark, nil
		default:
			return Result{}, finalizeRelease, fmt.Errorf("resolve sender: %w", err)
		}
	}

	// 5. Resolve the chat_session. Group sessions are created by the INSTALLER
	//    (stable workspace identity that won't churn with group membership);
	//    p2p sessions by the sole human sender.
	sessionCreator := identity.UserID
	if msg.Source.ChatType == channel.ChatTypeGroup {
		sessionCreator = inst.InstallerUserID
	}
	sessionID, err := set.Session.EnsureSession(ctx, EnsureSessionParams{
		Installation: inst,
		Sender:       sessionCreator,
		Message:      msg,
	})
	if err != nil {
		// Single tx; an error rolled it back, nothing landed. Release.
		return Result{}, finalizeRelease, fmt.Errorf("ensure chat session: %w", err)
	}

	// 6. Append message + in-tx dedup Mark — the durable transition point.
	appendRes, err := set.Session.AppendMessage(ctx, AppendParams{
		SessionID:      sessionID,
		Sender:         identity.UserID,
		InstallationID: inst.ID,
		Message:        msg,
		ClaimToken:     claimToken,
	})
	if err != nil {
		if errors.Is(err, ErrClaimLost) {
			return Result{}, finalizeNone, err
		}
		return Result{}, finalizeRelease, fmt.Errorf("append user message: %w", err)
	}

	// Post-append paths must NOT Release (chat_message + Mark already
	// committed). Mark-again is a no-op, so finalizeNone — unless the binder
	// did not Mark in-tx (defensive), then fall back to a post-pipeline Mark.
	postAppendFinalize := finalizeNone
	if !appendRes.DedupMarked {
		postAppendFinalize = finalizeMark
	}

	res := Result{
		Outcome:        OutcomeIngested,
		InstallationID: inst.ID,
		ChatSessionID:  sessionID,
		Sender:         msg.Source.SenderID,
	}

	// 7. /issue command, if present. chat_message is already durable; all
	//    error returns from here signal finalizeNone (or the defensive Mark).
	if appendRes.IssueCommand != nil {
		issueRes, err := r.createIssue(ctx, inst, set.OriginType, identity.UserID, sessionID, *appendRes.IssueCommand)
		if err != nil {
			return Result{}, postAppendFinalize, fmt.Errorf("create issue from command: %w", err)
		}
		res.IssueID = issueRes.Issue.ID
		res.IssueNumber = issueRes.Issue.Number
		res.IssueTitle = issueRes.Issue.Title
		if ws, werr := r.reader.GetWorkspace(ctx, inst.WorkspaceID); werr == nil && ws.IssuePrefix != "" {
			res.IssueIdentifier = fmt.Sprintf("%s-%d", ws.IssuePrefix, issueRes.Issue.Number)
		} else {
			res.IssueIdentifier = fmt.Sprintf("#%d", issueRes.Issue.Number)
		}
	}

	// 8. Debounce the run trigger. The synchronous outcome is OutcomeIngested
	//    with no TaskID — the task row is created at flush. identity.UserID is
	//    THIS message's sender (the task initiator), deliberately not the
	//    session creator (group sessions are creator=installer). Latest sender
	//    in a window wins (MUL-2645).
	r.scheduleRun(set, inst, msg, sessionID, identity.UserID)
	return res, postAppendFinalize, nil
}

// scheduleRun hands the per-session run trigger to the debouncer (or fires it
// inline when batching is disabled).
func (r *Router) scheduleRun(set ResolverSet, inst ResolvedInstallation, msg channel.InboundMessage, sessionID, initiatorUserID pgtype.UUID) {
	key := keyForSession(sessionID)
	fresh := msg.ForceFresh
	if r.batcher == nil {
		r.flushChatRun(set, inst, msg, sessionID, initiatorUserID, fresh)
		return
	}
	if fresh {
		r.markPendingFresh(key)
	}
	flush := func() {
		r.flushChatRun(set, inst, msg, sessionID, initiatorUserID, r.takePendingFresh(key, fresh))
	}
	r.batcher.Schedule(key, flush)
}

// chatRunFlushTimeout bounds the detached flush (session reload + enqueue +
// notice), which runs on its own fresh context.
const chatRunFlushTimeout = 10 * time.Second

// flushChatRun is the debounced run-trigger: reload session, enqueue exactly
// one chat task for the window, and emit the offline/archived notice (only
// known here now) via the replier. Errors are logged, not returned.
func (r *Router) flushChatRun(set ResolverSet, inst ResolvedInstallation, msg channel.InboundMessage, sessionID, initiatorUserID pgtype.UUID, forceFresh bool) {
	ctx, cancel := context.WithTimeout(context.Background(), chatRunFlushTimeout)
	defer cancel()

	session, err := r.reader.GetChatSession(ctx, sessionID)
	if err != nil {
		r.logger.Error("channel router: flush reload chat session failed",
			"chat_session_id", uuidString(sessionID), "err", err.Error())
		r.clearTyping(ctx, set, sessionID)
		return
	}
	if _, err := r.tasks.EnqueueChatTask(ctx, session, initiatorUserID, forceFresh); err != nil {
		// No task was enqueued, so no task lifecycle event will ever publish and
		// the platform's bus-driven typing clear can never fire. Clear the
		// indicator here (before any notice) so the "processing" reaction does
		// not stick on the user's message.
		r.clearTyping(ctx, set, sessionID)
		switch {
		case errors.Is(err, service.ErrChatTaskAgentNoRuntime):
			r.emitFlushReply(ctx, set, inst, msg, sessionID, OutcomeAgentOffline)
		case errors.Is(err, service.ErrChatTaskAgentArchived):
			r.emitFlushReply(ctx, set, inst, msg, sessionID, OutcomeAgentArchived)
		default:
			r.logger.Error("channel router: flush enqueue chat task failed",
				"chat_session_id", uuidString(sessionID), "err", err.Error())
		}
	}
}

// clearTyping asks the platform to drop the "processing" indicator for a session
// whose flush produced no task run. A nil TypingNotifier (platform without the
// feature) is a no-op.
func (r *Router) clearTyping(ctx context.Context, set ResolverSet, sessionID pgtype.UUID) {
	if set.Typing != nil {
		set.Typing.OnSettled(ctx, sessionID)
	}
}

func (r *Router) markPendingFresh(key string) {
	r.pendingFreshMu.Lock()
	defer r.pendingFreshMu.Unlock()
	r.pendingFresh[key] = true
}

func (r *Router) takePendingFresh(key string, fallback bool) bool {
	r.pendingFreshMu.Lock()
	defer r.pendingFreshMu.Unlock()
	fresh := fallback || r.pendingFresh[key]
	delete(r.pendingFresh, key)
	return fresh
}

// emitFlushReply delivers an offline/archived notice for a flushed run.
func (r *Router) emitFlushReply(ctx context.Context, set ResolverSet, inst ResolvedInstallation, msg channel.InboundMessage, sessionID pgtype.UUID, outcome Outcome) {
	if set.Replier == nil {
		return
	}
	set.Replier.Reply(ctx, inst, msg, Result{
		Outcome:        outcome,
		InstallationID: inst.ID,
		ChatSessionID:  sessionID,
		Sender:         msg.Source.SenderID,
	})
}

// scheduleReply detaches the OutboundReplier from the ACK critical path. The
// reply goroutine uses a fresh context with a ReplyTimeout deadline so it is
// independent of the inbound emit ctx (which the adapter cancels when its
// receive loop exits). A nil replier short-circuits — no goroutine.
func (r *Router) scheduleReply(set ResolverSet, inst ResolvedInstallation, msg channel.InboundMessage, res Result) {
	if set.Replier == nil {
		return
	}
	r.replyWg.Add(1)
	go func() {
		defer r.replyWg.Done()
		ctx, cancel := context.WithTimeout(context.Background(), r.replyTimeout)
		defer cancel()
		set.Replier.Reply(ctx, inst, msg, res)
		if ctx.Err() == context.DeadlineExceeded {
			r.logger.Warn("channel router: outbound reply timed out",
				"event_id", msg.EventID, "outcome", string(res.Outcome),
				"timeout", r.replyTimeout.String())
		}
	}()
}

// keyForSession is the batcher key. chat_session_id is globally unique.
func keyForSession(sessionID pgtype.UUID) string {
	return string(sessionID.Bytes[:])
}

// applyFinalize flips the in-flight claim row to its terminal state,
// token-fenced. Best-effort: a transport failure cannot abort the outcome.
func (r *Router) applyFinalize(ctx context.Context, set ResolverSet, instID pgtype.UUID, messageID string, claimToken pgtype.UUID, action dedupFinalize) {
	switch action {
	case finalizeMark:
		_ = set.Dedup.Mark(ctx, instID, messageID, claimToken)
	case finalizeRelease:
		_ = set.Dedup.Release(ctx, instID, messageID, claimToken)
	case finalizeNone:
	}
}

func (r *Router) drop(ctx context.Context, set ResolverSet, msg channel.InboundMessage, instID pgtype.UUID, reason DropReason) Result {
	_ = set.Audit.RecordDrop(ctx, instID, msg, reason)
	return Result{Outcome: OutcomeDropped, DropReason: reason, InstallationID: instID}
}

func (r *Router) createIssue(ctx context.Context, inst ResolvedInstallation, originType string, creatorUserID, sessionID pgtype.UUID, cmd IssueCommand) (service.IssueCreateResult, error) {
	if cmd.Title == "" {
		return service.IssueCreateResult{}, ErrEmptyIssueTitle
	}
	params := service.IssueCreateParams{
		WorkspaceID:  inst.WorkspaceID,
		Title:        cmd.Title,
		Description:  pgtype.Text{String: cmd.Description, Valid: cmd.Description != ""},
		Status:       "todo",
		Priority:     "none",
		AssigneeType: pgtype.Text{String: "agent", Valid: true},
		AssigneeID:   inst.AgentID,
		CreatorType:  "member",
		CreatorID:    creatorUserID,
		OriginType:   pgtype.Text{String: originType, Valid: originType != ""},
		OriginID:     sessionID,
	}
	return r.issues.Create(ctx, params, service.IssueCreateOpts{})
}

// ErrEmptyIssueTitle is returned by createIssue when /issue has no title and
// the binder's previous-message fallback found nothing usable.
var ErrEmptyIssueTitle = errors.New("issue title is empty")

var _ channel.InboundHandler = (*Router)(nil).Handle