// Package telegram implements the Telegram Bot API as a channel adapter for
// Cyrene v2. It conforms to internal/channel/adapter.PlatformAdapter, translating
// Telegram updates (getUpdates long polling, or a registered webhook) into the
// normalized UnifiedMessage model and delivering outbound replies through the
// Bot API send* methods.
//
// Media is carried by Telegram file_id values: inbound attachments populate
// UnifiedMessage.Media with URL set to the file_id (plus size/name/mime when the
// update provides them), and outbound image/voice/documents are sent back by
// file_id via sendPhoto/sendVoice/sendDocument. The design authority is
// DevDocs/design/08-渠道接入.md section 4; the contract is defined in sections
// 0-2. Proactive push is enabled (design: Telegram is a strong push channel).
//
// The adapter is self-contained: it depends only on the standard library plus
// the project's internal adapter, config-independent logger, and channel/actor
// model. Tokens are never logged.
package telegram

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"net/http"
	"sort"
	"sync"

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

// Compile-time assertion that Adapter satisfies the shared contract.
var _ adapter.PlatformAdapter = (*Adapter)(nil)

// Adapter is a Telegram Bot API channel adapter. It is safe for concurrent use.
// The zero use is via New; do not copy it after first use.
type Adapter struct {
	mu      sync.RWMutex
	cfg     Config
	client  *http.Client
	baseURL string
	log     *slog.Logger

	connected  bool
	closed     bool
	webhook    bool
	handler    adapter.MessageHandler
	pollCancel context.CancelFunc
	runID      uint64

	offset int64
	chats  map[string]adapter.ChannelInfo
}

// Name returns the platform identifier.
func (a *Adapter) Name() string { return "telegram" }

// Config returns a snapshot of the adapter's configuration. The BotToken is the
// sensitive field; callers that persist this map must treat it as a secret.
func (a *Adapter) Config() map[string]any {
	a.mu.RLock()
	defer a.mu.RUnlock()
	return map[string]any{
		"bot_token":   a.cfg.BotToken,
		"webhook_url": a.cfg.WebhookURL,
	}
}

// Connect establishes the session. It is idempotent. When WebhookURL is
// configured the webhook is registered with the Bot API and long polling is
// disabled; otherwise the adapter prepares for getUpdates polling.
func (a *Adapter) Connect(ctx context.Context) error {
	a.mu.Lock()
	if a.connected {
		a.mu.Unlock()
		return nil
	}
	if a.closed {
		a.mu.Unlock()
		return fmt.Errorf("telegram: %w", adapter.ErrClosed)
	}
	if a.cfg.BotToken == "" {
		a.mu.Unlock()
		return fmt.Errorf("telegram: %w", ErrMissingToken)
	}
	token := a.cfg.BotToken
	webhookURL := a.cfg.WebhookURL
	a.mu.Unlock()

	webhookMode := false
	if webhookURL != "" {
		if err := a.setWebhook(ctx, webhookURL); err != nil {
			return fmt.Errorf("telegram: register webhook: %w", err)
		}
		webhookMode = true
	}
	a.log.Info("connected", "webhook", webhookMode, "token_len", len(token))

	a.mu.Lock()
	a.connected = true
	a.webhook = webhookMode
	a.offset = 0
	a.mu.Unlock()
	return nil
}

// Disconnect tears down the session and stops an in-flight poll loop. It is
// idempotent.
func (a *Adapter) Disconnect(ctx context.Context) error {
	a.mu.Lock()
	if !a.connected {
		a.mu.Unlock()
		return nil
	}
	a.connected = false
	cancel := a.pollCancel
	a.mu.Unlock()
	if cancel != nil {
		cancel()
	}
	a.log.Info("disconnected")
	return nil
}

// Close permanently shuts the adapter down, stopping any polling loop and
// marking it closed. It is idempotent; subsequent operations fail with
// adapter.ErrClosed.
func (a *Adapter) Close() error {
	a.mu.Lock()
	if a.closed {
		a.mu.Unlock()
		return nil
	}
	a.closed = true
	a.connected = false
	cancel := a.pollCancel
	a.mu.Unlock()
	if cancel != nil {
		cancel()
	}
	a.log.Info("closed")
	return nil
}

// IsConnected reports whether the session is currently live.
func (a *Adapter) IsConnected() bool {
	a.mu.RLock()
	defer a.mu.RUnlock()
	return a.connected
}

// HealthCheck verifies the session is usable by calling getMe against the Bot
// API. It returns an error wrapping adapter.ErrNotConnected when not connected.
func (a *Adapter) HealthCheck(ctx context.Context) error {
	if err := a.requireConnected(); err != nil {
		return err
	}
	bot, err := a.getMe(ctx)
	if err != nil {
		return fmt.Errorf("telegram: health check: %w", err)
	}
	a.log.Debug("health check ok", "bot", bot)
	return nil
}

// Capabilities declares what the Telegram platform supports. Proactive push is
// enabled because Telegram permits arbitrary outbound messages.
func (a *Adapter) Capabilities() adapter.Capabilities {
	return adapter.Capabilities{
		MaxMessageLength:  maxMessageLen,
		Markdown:          true,
		Image:             true,
		Voice:             true,
		Reaction:          false,
		TypingHint:        false,
		RecommendBurstMax: 1,
		Proactive:         true,
	}.Normalize()
}

// SetMessageHandler installs the push-style inbound callback used by the webhook
// delivery path (see ProcessUpdate). A nil fn clears the handler.
func (a *Adapter) SetMessageHandler(fn adapter.MessageHandler) {
	a.mu.Lock()
	defer a.mu.Unlock()
	a.handler = fn
}

// ListChannels returns the conversations observed so far, ordered by ChannelID.
func (a *Adapter) ListChannels(ctx context.Context) ([]adapter.ChannelInfo, error) {
	a.mu.RLock()
	defer a.mu.RUnlock()
	out := make([]adapter.ChannelInfo, 0, len(a.chats))
	for _, c := range a.chats {
		out = append(out, c)
	}
	sort.Slice(out, func(i, j int) bool { return out[i].ChannelID < out[j].ChannelID })
	return out, nil
}

// ProcessUpdate decodes a raw webhook payload (a single Telegram Update) and
// delivers the normalized message through the installed message handler. It is
// the push-side counterpart to ReadMessages and returns the number of messages
// delivered. Non-message updates (for example callback queries) are ignored.
func (a *Adapter) ProcessUpdate(ctx context.Context, raw []byte) (int, error) {
	var update telegramUpdate
	if err := json.Unmarshal(raw, &update); err != nil {
		return 0, fmt.Errorf("telegram: decode webhook update: %w", err)
	}
	msg, ok := a.toUnifiedMessage(update)
	if !ok {
		return 0, nil
	}
	if err := msg.Validate(); err != nil {
		return 0, fmt.Errorf("telegram: validate webhook update: %w", err)
	}
	a.mu.RLock()
	handler := a.handler
	a.mu.RUnlock()
	if handler != nil {
		handler(ctx, msg)
	}
	return 1, nil
}

// requireConnected guards operations that need a live session.
func (a *Adapter) requireConnected() error {
	a.mu.RLock()
	defer a.mu.RUnlock()
	if a.closed {
		return fmt.Errorf("telegram: %w", adapter.ErrClosed)
	}
	if !a.connected {
		return fmt.Errorf("telegram: %w", adapter.ErrNotConnected)
	}
	return nil
}

// isWebhookMode reports whether the adapter is serving via webhook rather than
// polling.
func (a *Adapter) isWebhookMode() bool {
	a.mu.RLock()
	defer a.mu.RUnlock()
	return a.webhook
}