package main

import (
	"bytes"
	"context"
	"encoding/base64"
	"fmt"
	"log"
	"math"
	"net/http"
	"os"
	"regexp"
	"strings"

	"github.com/gotd/td/session"
	"github.com/gotd/td/telegram"
	"github.com/gotd/td/telegram/auth"
	"github.com/gotd/td/telegram/message"
	"github.com/gotd/td/telegram/message/html"
	"github.com/gotd/td/telegram/updates"
	"github.com/gotd/td/tg"
	"golang.org/x/term"
	"gopkg.in/yaml.v3"
)

type YAMLScamPattern struct {
	Name    string  `yaml:"name"`
	Pattern string  `yaml:"pattern"`
	Weight  float64 `yaml:"weight"`
}

type Config struct {
	APIId         int               `yaml:"api_id"`
	APIHash       string            `yaml:"api_hash"`
	MonitoredChat int64             `yaml:"monitored_chat"`
	AlertChat     int64             `yaml:"alert_chat"`
	NtfyHost      string            `yaml:"ntfy_host"`
	NtfyToken     string            `yaml:"ntfy_token"`
	NtfyTopic     string            `yaml:"ntfy_topic"`
	SessionPath   string            `yaml:"session_path"`
	YAMLPatterns  []YAMLScamPattern `yaml:"scam_patterns"`
	Patterns      []scamPattern     `yaml:"-"` // Compiled patterns, not from YAML
}

func loadConfig(path string) (*Config, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			// Create default config file
			defaultConfig := `api_id: 0
api_hash: ""
monitored_chat: 0
alert_chat: 0
ntfy_host: "https://ntfy.sh/"
ntfy_token: ""
ntfy_topic: ""
session_path: "antiscam.session"
scam_patterns: []
`
			if err := os.WriteFile(path, []byte(defaultConfig), 0644); err != nil {
				return nil, fmt.Errorf("creating default config file: %w", err)
			}
			log.Printf("Created default config file at %s. Please fill in the required values.", path)
			data = []byte(defaultConfig)
		} else {
			return nil, fmt.Errorf("reading config file: %w", err)
		}
	}

	var cfg Config
	if err := yaml.Unmarshal(data, &cfg); err != nil {
		return nil, fmt.Errorf("parsing config: %w", err)
	}

	// Validate required fields
	if cfg.APIId == 0 {
		return nil, fmt.Errorf("api_id is not set in config")
	}
	if cfg.APIHash == "" {
		return nil, fmt.Errorf("api_hash is not set in config")
	}
	if cfg.MonitoredChat == 0 {
		return nil, fmt.Errorf("monitored_chat is not set in config")
	}
	if cfg.SessionPath == "" {
		return nil, fmt.Errorf("session_path is not set in config")
	}

	// Compile patterns from YAML
	if len(cfg.YAMLPatterns) > 0 {
		cfg.Patterns = make([]scamPattern, len(cfg.YAMLPatterns))
		for i, p := range cfg.YAMLPatterns {
			re, err := regexp.Compile(p.Pattern)
			if err != nil {
				return nil, fmt.Errorf("compiling pattern %q: %w", p.Name, err)
			}
			cfg.Patterns[i] = scamPattern{
				name:   p.Name,
				re:     re,
				weight: p.Weight,
			}
		}
		log.Printf("✓ Loaded %d scam patterns from YAML config:", len(cfg.Patterns))
		for _, p := range cfg.Patterns {
			log.Printf("  - %s (%s) (weight: %.1f)", p.name, p.re, p.weight)
		}
	}

	return &cfg, nil
}

type scamPattern struct {
	name   string
	re     *regexp.Regexp
	weight float64
}

type matchResult struct {
	score           float64
	matchedKeywords map[string][]string
}

var scamPatterns = []scamPattern{
	{
		name:   "seeking",
		re:     regexp.MustCompile(`(?i)(?:(?:several\s+people|seeking|looking\s+for)\s+(?:partner|(\d+\s*[-–]\s*\d+|\d+)|two)?)|(new\s+project)`),
		weight: 0.5,
	},
	{
		name:   "job_opportunity",
		re:     regexp.MustCompile(`(?i)(?:remote|earning|in\s+a)\s+(?:collaboration|growing\s+field|opportunity|work)`),
		weight: 0.4,
	},
	{
		name:   "money",
		re:     regexp.MustCompile(`(?i)(?:\d+[\s,]*(?:\$|€|₹|£)|(?:\$|€|₹|£)\s*\d+,?\d+)(\s+per\s+(week|day))?`),
		weight: 0.6,
	},
	{
		name:   "contact",
		re:     regexp.MustCompile(`(?i)(?:\bdm\b|(send|write).*(?:private)?\s+.?\+.?|get\s+in\s+touch)|@\w+`),
		weight: 0.5,
	},
	{
		name:   "links",
		re:     regexp.MustCompile(`https://t\.me/\+\S+|https://t\.me/[a-z0-9_]+`),
		weight: 0.5,
	},
	{
		name:   "call_to_action",
		re:     regexp.MustCompile(`(?i)[⬇👇👆⬆💬🪂🎯⤵⤴📍]+|(?:click|tap|join|link|check)\s+(?:here|now|below|out)`),
		weight: 0.5,
	},
	{
		name:   "extended_latin",
		re:     regexp.MustCompile(`(?i)[äöüß]+`),
		weight: 0.2,
	},
}

func keywordMatchScore(input string, patterns []scamPattern) matchResult {
	matched := make(map[string][]string)
	totalScore := 0.0

	for _, p := range patterns {
		var matches []string
		for _, m := range p.re.FindAllString(input, -1) {
			m = strings.TrimSpace(m)
			if m != "" {
				matches = append(matches, m)
			}
		}
		if len(matches) > 0 {
			matched[p.name] = matches
			totalScore += p.weight
		}
	}

	score := math.Min(totalScore, 1.0)
	// Round to 2 decimal places
	score = math.Round(score*100) / 100

	return matchResult{score: score, matchedKeywords: matched}
}

func escapeMarkdown(text string) string {
	escapeChars := `\_*[]()~` + "`" + `>#+-=|{}.!`
	var result strings.Builder
	for _, r := range text {
		if strings.ContainsRune(escapeChars, r) {
			result.WriteRune('\\')
		}
		result.WriteRune(r)
	}
	return result.String()
}

func escapeHTML(text string) string {
	var result strings.Builder
	for _, r := range text {
		switch r {
		case '&':
			result.WriteString("&")
		case '<':
			result.WriteString("&lt;")
		case '>':
			result.WriteString("&gt;")
		case '"':
			result.WriteString("&quot;")
		case '\'':
			result.WriteString("&#39;")
		default:
			result.WriteRune(r)
		}
	}
	return result.String()
}

func notify(message, host, topic, title string, priority int, token string) {
	if !strings.HasSuffix(host, "/") {
		host = host + "/"
	}
	url := host + topic
	req, err := http.NewRequest("POST", url, bytes.NewBufferString(message))
	if err != nil {
		log.Printf("notify: creating request: %v", err)
		return
	}
	if title != "" {
		req.Header.Set("Title", title)
	}
	req.Header.Set("Priority", fmt.Sprintf("%d", priority))
	req.Header.Set("Markdown", "yes")
	if token != "" {
		// ntfy uses basic auth with empty username and token as password
		encoded := base64.StdEncoding.EncodeToString([]byte(":" + token))
		req.Header.Set("Authorization", "Basic "+encoded)
	}
	resp, err := http.DefaultClient.Do(req)
	if err != nil {
		log.Printf("notify: sending request: %v", err)
		return
	}
	defer resp.Body.Close()
}

func resolveAlertPeer(ctx context.Context, api *tg.Client, cfg *Config) (*tg.InputPeerChannel, error) {
	result, err := api.MessagesGetDialogs(ctx, &tg.MessagesGetDialogsRequest{
		OffsetPeer: &tg.InputPeerEmpty{},
		Limit:      100,
	})
	if err != nil {
		return nil, err
	}

	var chats []tg.ChatClass

	switch v := result.(type) {
	case *tg.MessagesDialogs:
		chats = v.Chats
	case *tg.MessagesDialogsSlice:
		chats = v.Chats
	case *tg.MessagesDialogsNotModified:
		return nil, fmt.Errorf("dialogs not modified")
	default:
		return nil, fmt.Errorf("unexpected dialogs type: %T", result)
	}

	for _, chat := range chats {
		if channel, ok := chat.(*tg.Channel); ok {
			if channel.ID == cfg.AlertChat {
				return &tg.InputPeerChannel{
					ChannelID:  channel.ID,
					AccessHash: channel.AccessHash,
				}, nil
			}
		}
	}

	return nil, fmt.Errorf("alert channel %d not found", cfg.AlertChat)
}

func handleNewMessage(ctx context.Context, api *tg.Client, alertPeer *tg.InputPeerChannel, cfg *Config, entities tg.Entities, update any) error {
	// Extract message from either UpdateNewMessage or UpdateNewChannelMessage
	var msg *tg.Message
	switch u := update.(type) {
	case *tg.UpdateNewMessage:
		m, ok := u.Message.(*tg.Message)
		if !ok {
			return nil
		}
		msg = m
	case *tg.UpdateNewChannelMessage:
		m, ok := u.Message.(*tg.Message)
		if !ok {
			return nil
		}
		msg = m
	default:
		log.Printf("DEBUG: unknown update type %T", update)
		return nil
	}

	// Only process messages sent by the bot (Out=true)
	if msg.Out {
		return nil
	}

	// Check if from monitored supergroup (channels in gotd terminology)
	peerChannel, ok := msg.PeerID.(*tg.PeerChannel)
	if !ok || int64(peerChannel.ChannelID) != cfg.MonitoredChat {
		return nil
	}
	log.Printf("✓ Processing message in chat %v: %s", msg.PeerID, msg.Message)
	chatID := int64(peerChannel.ChannelID)

	// Use YAML patterns if available, otherwise use defaults
	patterns := cfg.Patterns
	if len(patterns) == 0 {
		patterns = scamPatterns
		log.Printf("Using hardcoded scam patterns (%d patterns)", len(patterns))
	} else {
		log.Printf("Using YAML-loaded scam patterns (%d patterns)", len(patterns))
	}

	// Score the message
	result := keywordMatchScore(msg.Message, patterns)

	if extended_latin, ok := result.matchedKeywords["extended_latin"]; ok {
		for range extended_latin {
			result.score += 0.1
			if result.score >= 1.0 {
				result.score = 1.0
				break
			}
		}
	}

	if result.score < 1.0 {
		return nil
	}

	if result.score == 1.0 ||
		(result.score == 1.0 &&
			result.matchedKeywords["extended_latin"] != nil &&
			len(result.matchedKeywords["links"]) > 0) {

		log.Printf("Matched message with score %.2f", result.score)
		for key, values := range result.matchedKeywords {
			for _, value := range values {
				log.Printf("  %s: %s", key, value)
			}
		}

		// Delete the message from supergroup
		channel, ok := entities.Channels[chatID]
		if !ok {
			return fmt.Errorf("channel %d not found in entities", chatID)
		}
		_, err := api.ChannelsDeleteMessages(ctx, &tg.ChannelsDeleteMessagesRequest{
			Channel: &tg.InputChannel{
				ChannelID:  chatID,
				AccessHash: channel.AccessHash,
			},
			ID: []int{msg.ID},
		})
		if err != nil {
			log.Printf("Failed to delete message: %v", err)
		}

		// Get sender info
		var senderID int64
		if fromID, ok := msg.FromID.(*tg.PeerUser); ok {
			senderID = int64(fromID.UserID)
		} else {
			return fmt.Errorf("could not determine sender")
		}

		user, ok := entities.Users[senderID]
		if !ok {
			return fmt.Errorf("user %d not found in entities", senderID)
		}

		displayName := user.FirstName
		if user.LastName != "" {
			displayName += " " + user.LastName
		}
		displayName = strings.TrimSpace(displayName)

		username := "no username"
		if user.Username != "" {
			username = "@" + user.Username
		}

		// Restrict sender in supergroup
		_, err = api.ChannelsEditBanned(ctx, &tg.ChannelsEditBannedRequest{
			Channel: &tg.InputChannel{
				ChannelID:  chatID,
				AccessHash: channel.AccessHash,
			},
			Participant: &tg.InputPeerUser{
				UserID:     senderID,
				AccessHash: user.AccessHash,
			},
			BannedRights: tg.ChatBannedRights{
				SendMessages: true,
				SendMedia:    true,
				SendStickers: true,
				SendGifs:     true,
				UntilDate:    0,
			},
		})
		if err != nil {
			log.Printf("Failed to restrict user %d: %v", senderID, err)
		}

		// Get supergroup name
		chatName := channel.Title

		// Build alert message with HTML formatting for markdown v2
		matchMessageHTML := fmt.Sprintf("🚨 Matched\n<b>Score</b>: %.2f\n<b>Chat</b>: %s (ID: %d)\n<b>User</b>: %s (ID: %d)\n",
			result.score, escapeMarkdown(chatName), chatID, displayName+" ("+username+")", senderID)

		// Send ntfy notification if config set (use plain text for ntfy)
		if cfg.NtfyToken != "" || cfg.NtfyTopic != "" {
			plainMessage := fmt.Sprintf("🚨 Matched\nScore: %.2f\nChat: %s (ID: %d)\nUser: %s (ID: %d)\n\n%s",
				result.score, escapeMarkdown(chatName), chatID, escapeMarkdown(displayName+" ("+username+")"), senderID, escapeMarkdown(msg.Message))
			notify(plainMessage, cfg.NtfyHost, cfg.NtfyTopic, fmt.Sprintf("Scam Alert: %s", chatName), 5, cfg.NtfyToken)
		}

		// Create a resolver for user mentions (not needed for this message, but required by html.String)
		userResolver := func(id int64) (tg.InputUserClass, error) {
			return &tg.InputUserFromMessage{
				Peer:   alertPeer,
				MsgID:  0,
				UserID: id,
			}, nil
		}

		// Send alert message to alert chat using StyledText with HTML
		sender := message.NewSender(api)
		_, err = sender.To(alertPeer).StyledText(ctx, html.String(userResolver, matchMessageHTML))
		if err != nil {
			log.Printf("Failed to send alert message: %v", err)
		}
	}

	return nil
}

func main() {
	ctx := context.Background()

	// Load configuration
	configPath := "config.yaml"
	if len(os.Args) > 1 {
		configPath = os.Args[1]
	}

	cfg, err := loadConfig(configPath)
	if err != nil {
		log.Fatalf("Failed to load config: %v", err)
	}

	dispatcher := tg.NewUpdateDispatcher()
	gapManager := updates.New(updates.Config{Handler: dispatcher})

	client := telegram.NewClient(cfg.APIId, cfg.APIHash, telegram.Options{
		UpdateHandler:  gapManager,
		SessionStorage: &session.FileStorage{Path: cfg.SessionPath},
	})

	err = client.Run(ctx, func(ctx context.Context) error {
		// Check if session exists; if not, authenticate
		_, err := os.Stat(cfg.SessionPath)
		if err != nil {
			// Session doesn't exist, prompt for credentials
			fmt.Print("Enter phone number: ")
			var phone string
			fmt.Scanln(&phone)

			fmt.Print("Enter 2FA password: ")
			pwBytes, err := term.ReadPassword(0)
			if err != nil {
				return fmt.Errorf("reading password: %w", err)
			}
			fmt.Println()
			password := string(pwBytes)

			flow := auth.NewFlow(
				auth.Constant(
					phone,
					password,
					auth.CodeAuthenticatorFunc(func(ctx context.Context, sentCode *tg.AuthSentCode) (string, error) {
						fmt.Print("Enter code: ")
						var code string
						fmt.Scanln(&code)
						return code, nil
					}),
				),
				auth.SendCodeOptions{},
			)

			if err := client.Auth().IfNecessary(ctx, flow); err != nil {
				return err
			}
		}

		api := client.API()

		// Resolve alert channel peer at startup
		alertPeer, err := resolveAlertPeer(ctx, api, cfg)
		if err != nil {
			return fmt.Errorf("resolving alert peer: %w", err)
		}

		// Register message handler for private/group messages
		dispatcher.OnNewMessage(func(ctx context.Context, entities tg.Entities, update *tg.UpdateNewMessage) error {
			return handleNewMessage(ctx, api, alertPeer, cfg, entities, update)
		})

		// Register handler for channel messages (supergroups)
		dispatcher.OnNewChannelMessage(func(ctx context.Context, entities tg.Entities, update *tg.UpdateNewChannelMessage) error {
			return handleNewMessage(ctx, api, alertPeer, cfg, entities, update)
		})

		// Get self ID for updates manager
		status, err := client.Auth().Status(ctx)
		if err != nil {
			return err
		}

		user := status.User
		username := ""
		if user.Username != "" {
			username = " (@" + user.Username + ")"
		}
		displayName := user.FirstName
		if user.LastName != "" {
			displayName += " " + user.LastName
		}
		log.Printf("✓ Logged in as: %s%s (ID: %d)", displayName, username, user.ID)
		log.Printf("✓ Bot running, monitoring chat %d", cfg.MonitoredChat)
		return gapManager.Run(ctx, api, status.User.ID, updates.AuthOptions{})
	})

	if err != nil {
		log.Fatal(err)
	}
}