// Package matrixbot handles Matrix-native bot behavior.
package matrixbot

import (
	"context"
	"errors"
	"fmt"
	"html"
	"log"
	"strings"
	"time"

	"maunium.net/go/mautrix"
	"maunium.net/go/mautrix/event"
	"maunium.net/go/mautrix/id"

	"musiclink/pkg/config"
)

// TextHandler processes plain text messages and returns a response when applicable.
type TextHandler func(ctx context.Context, text, username string) (string, bool)

// Bot manages Matrix-native sync and message handling.
type Bot struct {
	cfg            config.MatrixConfig
	client         *mautrix.Client
	handler        TextHandler
	allowedRooms   map[id.RoomID]struct{}
	encryptedRooms map[id.RoomID]struct{}
	stateStore     *StateStore
	sendQueue      chan sendRequest
	stats          botStats
}

type sendRequest struct {
	roomID   id.RoomID
	event    *event.Event
	response string
}

// New creates a new Matrix-native bot instance.
func New(cfg config.MatrixConfig, handler TextHandler) (*Bot, error) {
	client, err := mautrix.NewClient(cfg.Server, id.UserID(cfg.UserID), cfg.AccessToken)
	if err != nil {
		return nil, fmt.Errorf("create matrix client: %w", err)
	}

	allowed := make(map[id.RoomID]struct{}, len(cfg.Rooms))
	for _, room := range cfg.Rooms {
		allowed[id.RoomID(room)] = struct{}{}
	}

	store, err := NewStateStore(cfg.StateStorePath)
	if err != nil {
		return nil, fmt.Errorf("init state store: %w", err)
	}
	client.Store = store
	log.Printf("Matrix state store: %s", cfg.StateStorePath)

	bot := &Bot{
		cfg:            cfg,
		client:         client,
		handler:        handler,
		allowedRooms:   allowed,
		encryptedRooms: make(map[id.RoomID]struct{}),
		stateStore:     store,
		sendQueue:      make(chan sendRequest, 100),
	}

	syncer := client.Syncer.(*mautrix.DefaultSyncer)
	syncer.OnEventType(event.EventMessage, bot.onMessage)
	syncer.OnEventType(event.StateMember, bot.onMember)
	syncer.OnEventType(event.StateEncryption, bot.onEncryption)
	syncer.OnSync(bot.onSync)

	return bot, nil
}

// Run starts the sync loop.
func (b *Bot) Run(ctx context.Context) error {
	mode := "active"
	if b.cfg.Shadow {
		mode = "shadow"
	}
	log.Printf("Matrix bot starting (%s mode, rooms: %d)", mode, len(b.allowedRooms))
	log.Printf("Matrix allowlist rooms: %s", strings.Join(roomList(b.allowedRooms), ", "))
	if b.cfg.HealthAddr != "" {
		log.Printf("Matrix health server listening on %s", b.cfg.HealthAddr)
		go b.startHealthServer(ctx)
	}
	if err := b.prefetchEncryptionState(ctx); err != nil {
		log.Printf("Matrix encryption state check failed: %v", err)
	}
	go b.cleanupLoop(ctx)
	go b.sendLoop(ctx)
	return b.client.SyncWithContext(ctx)
}

// Close releases Matrix bot resources.
func (b *Bot) Close() error {
	if b.stateStore != nil {
		return b.stateStore.Close()
	}
	return nil
}

func (b *Bot) onMember(ctx context.Context, evt *event.Event) {
	if evt == nil {
		return
	}
	if evt.GetStateKey() != b.client.UserID.String() {
		return
	}
	member := evt.Content.AsMember()
	if member.Membership != event.MembershipInvite {
		return
	}
	if isEncryptedInvite(evt) {
		log.Printf("Matrix invite ignored (encrypted room): %s", evt.RoomID)
		if _, err := b.client.LeaveRoom(ctx, evt.RoomID); err != nil {
			log.Printf("Matrix invite leave failed for %s: %v", evt.RoomID, err)
		}
		return
	}
	if _, ok := b.allowedRooms[evt.RoomID]; ok {
		if _, err := b.client.JoinRoomByID(ctx, evt.RoomID); err != nil {
			log.Printf("Matrix invite join failed for %s: %v", evt.RoomID, err)
		}
		return
	}
	if _, err := b.client.LeaveRoom(ctx, evt.RoomID); err != nil {
		log.Printf("Matrix invite leave failed for %s: %v", evt.RoomID, err)
	}
}

func (b *Bot) onMessage(ctx context.Context, evt *event.Event) {
	if evt == nil {
		return
	}
	if _, ok := b.allowedRooms[evt.RoomID]; !ok {
		return
	}
	if evt.Sender == b.client.UserID {
		return
	}
	if b.isRoomEncrypted(evt.RoomID) {
		b.stats.markEncryptedSkipped()
		return
	}

	b.stats.markReceived()

	if processed, err := b.stateStore.WasEventProcessed(ctx, evt.ID.String()); err != nil {
		log.Printf("Matrix dedupe check failed (event %s): %v", evt.ID, err)
	} else if processed {
		return
	}

	content := evt.Content.AsMessage()
	if content == nil {
		return
	}
	if !content.MsgType.IsText() {
		return
	}
	if content.RelatesTo != nil && content.RelatesTo.GetReplaceID() != "" {
		return
	}
	if content.Body == "" {
		return
	}

	response, ok := b.handler(ctx, content.Body, evt.Sender.String())
	if !ok {
		return
	}

	if b.cfg.Shadow {
		log.Printf("Matrix shadow reply (room %s, event %s): %s", evt.RoomID, evt.ID, response)
		b.stats.markResponded()
		if _, err := b.stateStore.MarkEventProcessed(ctx, evt.ID.String()); err != nil {
			log.Printf("Matrix dedupe record failed (event %s): %v", evt.ID, err)
		}
		return
	}

	select {
	case b.sendQueue <- sendRequest{roomID: evt.RoomID, event: evt, response: response}:
	default:
		b.stats.markDropped()
		if _, err := b.stateStore.MarkEventProcessed(ctx, evt.ID.String()); err != nil {
			log.Printf("Matrix dedupe record failed after drop (event %s): %v", evt.ID, err)
		}
		log.Printf("Matrix send queue full; dropping response for event %s", evt.ID)
	}
}

func (b *Bot) sendReply(ctx context.Context, evt *event.Event, response string) error {
	body, formatted := formatNoPreview(response)
	content := &event.MessageEventContent{
		MsgType:            event.MsgText,
		Body:               body,
		BeeperLinkPreviews: []*event.BeeperLinkPreview{},
	}
	if formatted != "" {
		content.Format = event.FormatHTML
		content.FormattedBody = formatted
	}

	original := evt.Content.AsMessage()
	if original != nil && original.RelatesTo != nil && original.RelatesTo.GetThreadParent() != "" {
		content.SetThread(evt)
	} else {
		content.SetReply(evt)
	}

	_, err := b.client.SendMessageEvent(ctx, evt.RoomID, event.EventMessage, content)
	return err
}

func (b *Bot) sendLoop(ctx context.Context) {
	for {
		select {
		case <-ctx.Done():
			if pending := len(b.sendQueue); pending > 0 {
				log.Printf("Matrix send queue pending on shutdown: %d", pending)
			}
			return
		case req := <-b.sendQueue:
			b.sendWithRetry(ctx, req)
		}
	}
}

func (b *Bot) cleanupLoop(ctx context.Context) {
	ticker := time.NewTicker(6 * time.Hour)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			if err := b.stateStore.Cleanup(ctx); err != nil {
				log.Printf("Matrix state store cleanup failed: %v", err)
			}
		}
	}
}

func (b *Bot) sendWithRetry(ctx context.Context, req sendRequest) {
	const maxAttempts = 5
	backoff := time.Second

	for attempt := 1; attempt <= maxAttempts; attempt++ {
		if err := b.sendReply(ctx, req.event, req.response); err != nil {
			delay, ok := rateLimitDelay(err)
			if ok {
				b.stats.markRateLimited()
				b.stats.setLastSendError(err.Error())
				if delay <= 0 {
					delay = backoff
				}
				log.Printf("Matrix rate limited (event %s), retrying in %s", req.event.ID, delay)
				if !sleepContext(ctx, delay) {
					return
				}
				backoff = minDuration(backoff*2, 30*time.Second)
				continue
			}
			b.stats.setLastSendError(err.Error())
			log.Printf("Matrix send failed (room %s, event %s): %v", req.roomID, req.event.ID, err)
			return
		}

		b.stats.markResponded()
		if _, err := b.stateStore.MarkEventProcessed(ctx, req.event.ID.String()); err != nil {
			log.Printf("Matrix dedupe record failed (event %s): %v", req.event.ID, err)
		}
		return
	}

	b.stats.setLastSendError("max retries exceeded")
	log.Printf("Matrix send failed after retries (room %s, event %s)", req.roomID, req.event.ID)
}

func rateLimitDelay(err error) (time.Duration, bool) {
	if !errors.Is(err, mautrix.MLimitExceeded) {
		return 0, false
	}

	var httpErr mautrix.HTTPError
	if errors.As(err, &httpErr) && httpErr.RespError != nil {
		if retry, ok := httpErr.RespError.ExtraData["retry_after_ms"]; ok {
			switch value := retry.(type) {
			case float64:
				return time.Duration(value) * time.Millisecond, true
			case int64:
				return time.Duration(value) * time.Millisecond, true
			case int:
				return time.Duration(value) * time.Millisecond, true
			}
		}
	}

	return 0, true
}

func sleepContext(ctx context.Context, delay time.Duration) bool {
	timer := time.NewTimer(delay)
	defer timer.Stop()
	select {
	case <-ctx.Done():
		return false
	case <-timer.C:
		return true
	}
}

func minDuration(a, b time.Duration) time.Duration {
	if a < b {
		return a
	}
	return b
}

func (b *Bot) onEncryption(ctx context.Context, evt *event.Event) {
	if evt == nil {
		return
	}
	if _, ok := b.allowedRooms[evt.RoomID]; !ok {
		return
	}
	if !b.isRoomEncrypted(evt.RoomID) {
		b.encryptedRooms[evt.RoomID] = struct{}{}
		log.Printf("Matrix room marked encrypted; skipping messages: %s", evt.RoomID)
	}
}

func (b *Bot) onSync(ctx context.Context, _ *mautrix.RespSync, _ string) bool {
	b.stats.markSync()
	return true
}

func (b *Bot) isRoomEncrypted(roomID id.RoomID) bool {
	_, ok := b.encryptedRooms[roomID]
	return ok
}

func (b *Bot) prefetchEncryptionState(ctx context.Context) error {
	for roomID := range b.allowedRooms {
		var content event.EncryptionEventContent
		if err := b.client.StateEvent(ctx, roomID, event.StateEncryption, "", &content); err != nil {
			if errors.Is(err, mautrix.MNotFound) {
				continue
			}
			log.Printf("Matrix encryption state fetch failed for %s: %v", roomID, err)
			continue
		}
		if !b.isRoomEncrypted(roomID) {
			b.encryptedRooms[roomID] = struct{}{}
			log.Printf("Matrix room marked encrypted (state fetch); skipping messages: %s", roomID)
		}
	}
	return nil
}

func roomList(rooms map[id.RoomID]struct{}) []string {
	list := make([]string, 0, len(rooms))
	for roomID := range rooms {
		list = append(list, roomID.String())
	}
	return list
}

func formatNoPreview(response string) (string, string) {
	lines := strings.Split(response, "\n")
	bodyLines := make([]string, 0, len(lines))
	formattedLines := make([]string, 0, len(lines))

	for _, line := range lines {
		trimmed := strings.TrimSpace(line)
		if trimmed == "" {
			bodyLines = append(bodyLines, "")
			formattedLines = append(formattedLines, "")
			continue
		}

		label, url, ok := splitLinkLine(trimmed)
		if ok {
			bodyLines = append(bodyLines, fmt.Sprintf("%s: %s", label, obfuscateURL(url)))
			formattedLines = append(formattedLines, fmt.Sprintf("%s: <a href=\"%s\">%s</a>", html.EscapeString(label), html.EscapeString(url), html.EscapeString(url)))
			continue
		}

		bodyLines = append(bodyLines, line)
		formattedLines = append(formattedLines, html.EscapeString(line))
	}

	body := strings.Join(bodyLines, "\n")
	formatted := strings.Join(formattedLines, "<br/>")
	return body, formatted
}

func splitLinkLine(line string) (string, string, bool) {
	parts := strings.SplitN(line, ": ", 2)
	if len(parts) != 2 {
		return "", "", false
	}
	label := parts[0]
	url := strings.TrimSpace(parts[1])
	if !strings.HasPrefix(url, "http://") && !strings.HasPrefix(url, "https://") {
		return "", "", false
	}
	return label, url, true
}

func obfuscateURL(url string) string {
	return url
}

func isEncryptedInvite(evt *event.Event) bool {
	if evt == nil || evt.Unsigned.InviteRoomState == nil {
		return false
	}
	for _, state := range evt.Unsigned.InviteRoomState {
		if state == nil {
			continue
		}
		if state.Type == event.StateEncryption {
			return true
		}
	}
	return false
}