package weixin_ilink

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net/http"
	"strings"
	"time"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/channel/adapter"
)

const (
	// msgTypeUser marks an inbound user message (bot messages are type 2).
	msgTypeUser = 1
	// item type codes from the iLink reference (design 03 §1).
	itemText  = 1
	itemImage = 2
	itemVoice = 3
	itemFile  = 4
	itemVideo = 5

	// retryFastCount is how many consecutive failures use the fast retry.
	retryFastCount = 3
	// retryFastDelay is the delay before the first failures.
	retryFastDelay = 2 * time.Second
	// retrySlowDelay is the backoff after retryFastCount consecutive failures.
	retrySlowDelay = 30 * time.Second
)

// getupdatesResp is the getupdates (long-poll) response envelope.
type getupdatesResp struct {
	// Ret is the top-level business result; non-zero is a transient error.
	Ret int `json:"ret"`
	// Errcode is the platform error code; -14 means the session expired.
	Errcode int `json:"errcode"`
	// Msgs holds the raw inbound messages delivered in this poll.
	Msgs []json.RawMessage `json:"msgs"`
	// GetUpdatesBuf is the next Cursor to echo back.
	GetUpdatesBuf string `json:"get_updates_buf"`
	// LongPollTimeoutMs is the server's suggested hold time.
	LongPollTimeoutMs int `json:"longpolling_timeout_ms"`
}

// rawMsg is the parsed common fields of an inbound WeixinMessage. iLink media
// field names are only partially public, so item_list entries are decoded
// defensively in parseItem.
type rawMsg struct {
	ClientID     string            `json:"client_id"`
	FromUserID   string            `json:"from_user_id"`
	ToUserID     string            `json:"to_user_id"`
	MessageType  int               `json:"message_type"`
	MessageState int               `json:"message_state"`
	ContextToken string            `json:"context_token"`
	GroupID      string            `json:"group_id"`
	RoomID       string            `json:"room_id"`
	ItemList     []json.RawMessage `json:"item_list"`
}

// ReadMessages runs the long-poll read loop until ctx is canceled. Each
// converted inbound message is delivered to the handler installed via
// SetMessageHandler when one is present, otherwise to emit. The loop is
// cooperative with ctx: a canceled context returns immediately and no timers
// outlive it.
func (a *Adapter) ReadMessages(ctx context.Context, emit func(adapter.UnifiedMessage)) {
	a.mu.RLock()
	connected := a.connected
	a.mu.RUnlock()
	if !connected {
		a.log.Warn("read loop started while disconnected")
		return
	}

	failures := 0
	for {
		resp, err := a.fetchUpdates(ctx)
		if err != nil {
			if ctx.Err() != nil {
				return
			}
			// A long-poll timeout is the normal "no messages yet" path.
			if errors.Is(err, context.DeadlineExceeded) {
				continue
			}
			failures++
			a.log.Warn("getupdates failed", "err", err, "failures", failures)
			if !a.wait(ctx, a.retryDelay(failures)) {
				return
			}
			continue
		}

		failures = 0
		if resp.Errcode == errSessionExpired {
			a.log.Warn("session expired (errcode=-14); stop polling, re-scan required")
			a.mu.Lock()
			a.connected = false
			a.mu.Unlock()
			return
		}
		if resp.Ret != 0 {
			failures++
			a.log.Warn("getupdates business error", "ret", resp.Ret)
			if !a.wait(ctx, a.retryDelay(failures)) {
				return
			}
			continue
		}
		a.setCursor(resp.GetUpdatesBuf)

		for _, raw := range resp.Msgs {
			token, m := a.convertMessage(raw)
			if m == nil {
				continue
			}
			a.recordInbound(token, *m)
			a.deliver(ctx, *m, emit)
		}
		if !a.wait(ctx, a.cfg.PollInterval) {
			return
		}
	}
}

// deliver routes a normalized message to the handler when installed, else to
// the emit callback (design/08 §1: push-style vs pull-style delivery).
func (a *Adapter) deliver(ctx context.Context, m adapter.UnifiedMessage, emit func(adapter.UnifiedMessage)) {
	if h := a.handlerLocked(); h != nil {
		h(ctx, m)
		return
	}
	if emit != nil {
		emit(m)
	}
}

// fetchUpdates performs one long poll. The request context is bounded by
// LongPollTimeout if the caller has not already set a tighter deadline.
func (a *Adapter) fetchUpdates(ctx context.Context) (*getupdatesResp, error) {
	reqCtx, cancel := context.WithTimeout(ctx, a.cfg.LongPollTimeout)
	defer cancel()

	body, err := json.Marshal(map[string]any{
		"get_updates_buf": a.cursor(),
		"base_info":       map[string]string{"channel_version": channelVersion},
	})
	if err != nil {
		return nil, fmt.Errorf("weixin_ilink: encode getupdates: %w", err)
	}
	var out getupdatesResp
	if err := a.doJSON(reqCtx, http.MethodPost, a.apiURL("/ilink/bot/getupdates"),
		bytes.NewReader(body), &out); err != nil {
		return nil, fmt.Errorf("weixin_ilink: getupdates: %w", err)
	}
	return &out, nil
}

// wait sleeps for d or returns false when ctx is canceled. A non-positive
// delay returns immediately.
func (a *Adapter) wait(ctx context.Context, d time.Duration) bool {
	if d <= 0 {
		return true
	}
	t := time.NewTimer(d)
	defer t.Stop()
	select {
	case <-ctx.Done():
		return false
	case <-t.C:
		return true
	}
}

// retryDelay grows from the fast retry to the slow backoff after enough
// consecutive failures (design/08 §5.4).
func (a *Adapter) retryDelay(failures int) time.Duration {
	if failures <= retryFastCount {
		return retryFastDelay
	}
	return retrySlowDelay
}

// convertMessage maps a raw iLink message to a UnifiedMessage and returns the
// raw context_token so the caller can track it per peer. It returns nil when
// the message is not an inbound user message or cannot be parsed.
func (a *Adapter) convertMessage(raw json.RawMessage) (string, *adapter.UnifiedMessage) {
	var rm rawMsg
	if err := json.Unmarshal(raw, &rm); err != nil {
		a.log.Warn("decode inbound message", "err", err)
		return "", nil
	}
	if rm.MessageType != msgTypeUser {
		return "", nil
	}

	group := resolveGroup(&rm)
	m := &adapter.UnifiedMessage{
		Platform:   platformName,
		SenderID:   rm.FromUserID,
		SenderName: rm.FromUserID,
		MessageID:  rm.ClientID,
		Timestamp:  a.clock(),
		RawData:    raw,
	}
	if group != "" {
		m.ChannelType = adapter.ChannelGroup
		m.GroupID = group
		m.ChannelID = group
	} else {
		m.ChannelType = adapter.ChannelDirect
		m.ChannelID = rm.FromUserID
	}
	m.Sender = adapter.Actor{
		Role:        adapter.RoleUnknown,
		UserID:      rm.FromUserID,
		DisplayName: rm.FromUserID,
		IsGroup:     group != "",
		GroupID:     group,
	}
	m.Content, m.ContentType, m.Media = a.convertItems(rm.ItemList)
	return rm.ContextToken, m
}

// convertItems drains the item list into text, a primary content type and a
// media slice. Text from text items is concatenated; voice items contribute
// their ASR transcript; image/file/video items are attached lazily as CDN
// references (never downloaded during the poll).
func (a *Adapter) convertItems(rawItems []json.RawMessage) (string, adapter.ContentType, []adapter.Media) {
	var text strings.Builder
	var media []adapter.Media
	firstMedia := adapter.ContentType("")

	for _, raw := range rawItems {
		item := parseItem(raw)
		switch item.kind {
		case itemText:
			text.WriteString(item.text)
		case itemVoice:
			text.WriteString(item.text)
			media = append(media, item.media)
			firstMedia = adapter.ContentVoice
		case itemImage:
			media = append(media, item.media)
			firstMedia = adapter.ContentImage
		case itemFile, itemVideo:
			media = append(media, item.media)
			firstMedia = adapter.ContentFile
		}
	}

	content := strings.TrimRight(text.String(), "\n")
	if firstMedia != "" {
		return content, firstMedia, media
	}
	return content, adapter.ContentText, nil
}

// resolveGroup returns the group identifier when the message carries one,
// otherwise "" (direct chat). WeChat group signalling is ⚠️ per design/08 §4,
// so several candidate fields are checked defensively.
func resolveGroup(rm *rawMsg) string {
	if rm.GroupID != "" {
		return rm.GroupID
	}
	return rm.RoomID
}

// parsedItem is a normalized view of a single native item_list entry.
type parsedItem struct {
	kind  int
	text  string
	media adapter.Media
}

// parseItem decodes one item_list entry defensively. iLink media field names
// are not fully public, so a generic map is scanned for the CDN reference and
// metadata with several fallback keys.
func parseItem(raw json.RawMessage) parsedItem {
	var m map[string]any
	if err := json.Unmarshal(raw, &m); err != nil {
		return parsedItem{}
	}
	kind := intOf(m["type"])
	switch kind {
	case itemText:
		return parsedItem{kind: itemText, text: textOf(m, "text_item")}
	case itemVoice:
		return parsedItem{kind: itemVoice, text: textOf(m, "voice_item"), media: mediaOf(m, adapter.MediaVoice)}
	case itemImage:
		return parsedItem{kind: itemImage, media: mediaOf(m, adapter.MediaImage)}
	case itemFile:
		return parsedItem{kind: itemFile, media: mediaOf(m, adapter.MediaFile)}
	case itemVideo:
		return parsedItem{kind: itemVideo, media: mediaOf(m, adapter.MediaVideo)}
	default:
		return parsedItem{kind: kind}
	}
}

// textOf reads the text payload from the named nested sub-object, falling back
// to a flat "text" key.
func textOf(m map[string]any, sub string) string {
	if inner, ok := m[sub].(map[string]any); ok {
		if s, ok := inner["text"].(string); ok {
			return s
		}
	}
	if s, ok := m["text"].(string); ok {
		return s
	}
	return ""
}

// mediaOf builds an adapter.Media from a media item, resolving the CDN URL and
// metadata from the flat item or a nested sub-object.
func mediaOf(m map[string]any, kind adapter.MediaKind) adapter.Media {
	res := adapter.Media{Kind: kind}
	res.URL = firstString(m, "url", "cdn_url", "download_url", "file_url", "cdn_ref")
	res.Name = firstString(m, "file_name", "name")
	res.Size = firstInt64(m, "size", "file_size")
	res.MIMEType = firstString(m, "mime", "mime_type", "content_type")
	if res.URL != "" {
		return res
	}
	// Bounded scan of the common nested sub-objects for the CDN reference.
	for _, sub := range []string{"image_item", "file_item", "video_item", "media_item", "cdn_item"} {
		inner, ok := m[sub].(map[string]any)
		if !ok {
			continue
		}
		res.URL = firstString(inner, "url", "cdn_url", "download_url", "file_url", "cdn_ref")
		if res.Name == "" {
			res.Name = firstString(inner, "file_name", "name")
		}
		if res.Size == 0 {
			res.Size = firstInt64(inner, "size", "file_size")
		}
		if res.MIMEType == "" {
			res.MIMEType = firstString(inner, "mime", "mime_type", "content_type")
		}
		if res.URL != "" {
			return res
		}
	}
	return res
}

// intOf coerces a JSON number to int, returning 0 for missing or non-numeric.
func intOf(v any) int {
	f, ok := v.(float64)
	if !ok {
		return 0
	}
	return int(f)
}

// firstString returns the first non-empty string among keys.
func firstString(m map[string]any, keys ...string) string {
	for _, k := range keys {
		if s, ok := m[k].(string); ok && s != "" {
			return s
		}
	}
	return ""
}

// firstInt64 returns the first non-zero integer among keys.
func firstInt64(m map[string]any, keys ...string) int64 {
	for _, k := range keys {
		if f, ok := m[k].(float64); ok && f != 0 {
			return int64(f)
		}
	}
	return 0
}