package main

import (
	"context"
	"crypto/sha1"
	"encoding/hex"
	"errors"
	"flag"
	"fmt"
	"io"
	"log"
	"net/http"
	"net/url"
	"os"
	"os/signal"
	"path/filepath"
	"sort"
	"strings"
	"sync"
	"syscall"
	"time"

	toml "github.com/pelletier/go-toml/v2"
)

type Config struct {
	Port         int      `toml:"port"`
	PollInterval string   `toml:"poll_interval"`
	CacheDir     string   `toml:"cache_dir"`
	Sources      []string `toml:"sources"`
}

func loadConfig(path string) (Config, time.Duration, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return Config{}, 0, fmt.Errorf("read config: %w", err)
	}

	var cfg Config
	if err := toml.Unmarshal(data, &cfg); err != nil {
		return Config{}, 0, fmt.Errorf("parse config: %w", err)
	}

	if cfg.Port == 0 {
		cfg.Port = 8080
	}
	if cfg.CacheDir == "" {
		cfg.CacheDir = "cache"
	}
	intervalText := cfg.PollInterval
	if intervalText == "" {
		intervalText = "60m"
	}

	interval, err := time.ParseDuration(intervalText)
	if err != nil {
		return Config{}, 0, fmt.Errorf("parse poll_interval: %w", err)
	}
	if interval <= 0 {
		return Config{}, 0, errors.New("poll_interval must be positive")
	}

	if len(cfg.Sources) == 0 {
		return Config{}, 0, errors.New("no sources configured")
	}

	return cfg, interval, nil
}

type Aggregator struct {
	mu        sync.RWMutex
	perSource map[string]map[string]struct{}
}

func NewAggregator() *Aggregator {
	return &Aggregator{perSource: make(map[string]map[string]struct{})}
}

func (a *Aggregator) Update(source string, links []string) {
	set := make(map[string]struct{}, len(links))
	for _, link := range links {
		set[link] = struct{}{}
	}

	a.mu.Lock()
	a.perSource[source] = set
	a.mu.Unlock()
}

func (a *Aggregator) List() []string {
	a.mu.RLock()
	defer a.mu.RUnlock()

	combined := make(map[string]struct{})
	for _, set := range a.perSource {
		for link := range set {
			combined[link] = struct{}{}
		}
	}

	list := make([]string, 0, len(combined))
	for link := range combined {
		list = append(list, link)
	}

	sort.Strings(list)
	return list
}

func main() {
	configPath := flag.String("config", "config.toml", "path to config file")
	flag.Parse()

	cfg, interval, err := loadConfig(*configPath)
	if err != nil {
		log.Fatalf("config error: %v", err)
	}

	if err := os.MkdirAll(cfg.CacheDir, 0o755); err != nil {
		log.Fatalf("cache dir: %v", err)
	}

	agg := NewAggregator()

	client := &http.Client{Timeout: 15 * time.Second}

	for _, source := range cfg.Sources {
		cached, err := loadCachedLinks(cfg.CacheDir, source)
		if err != nil {
			log.Printf("load cache for %s: %v", source, err)
		}
		if len(cached) > 0 {
			agg.Update(source, cached)
		}
	}

	ctx, stop := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
	defer stop()

	for _, source := range cfg.Sources {
		go pollSource(ctx, source, interval, cfg.CacheDir, agg, client)
	}

	mux := http.NewServeMux()
	mux.HandleFunc("/list", func(w http.ResponseWriter, r *http.Request) {
		links := agg.List()
		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
		for i, link := range links {
			if i > 0 {
				_, _ = w.Write([]byte("\n"))
			}
			_, _ = w.Write([]byte(link))
		}
	})

	server := &http.Server{
		Addr:              fmt.Sprintf(":%d", cfg.Port),
		Handler:           mux,
		ReadHeaderTimeout: 5 * time.Second,
		ReadTimeout:       10 * time.Second,
		WriteTimeout:      10 * time.Second,
	}

	go func() {
		<-ctx.Done()
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
		defer cancel()
		if err := server.Shutdown(shutdownCtx); err != nil {
			log.Printf("server shutdown: %v", err)
		}
	}()

	log.Printf("listening on :%d", cfg.Port)
	if err := server.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
		log.Fatalf("server error: %v", err)
	}
}

func pollSource(ctx context.Context, source string, interval time.Duration, cacheDir string, agg *Aggregator, client *http.Client) {
	ticker := time.NewTicker(interval)
	defer ticker.Stop()

	runOnce(ctx, source, cacheDir, agg, client)

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			runOnce(ctx, source, cacheDir, agg, client)
		}
	}
}

func runOnce(ctx context.Context, source string, cacheDir string, agg *Aggregator, client *http.Client) {
	links, err := fetchSource(ctx, source, client)
	if err != nil {
		log.Printf("poll %s: %v", source, err)
		return
	}
	if len(links) == 0 {
		agg.Update(source, nil)
		if err := writeCache(cacheDir, source, nil); err != nil {
			log.Printf("write cache %s: %v", source, err)
		}
		return
	}

	agg.Update(source, links)
	if err := writeCache(cacheDir, source, links); err != nil {
		log.Printf("write cache %s: %v", source, err)
	}
}

func fetchSource(ctx context.Context, source string, client *http.Client) ([]string, error) {
	u, err := url.Parse(source)
	if err != nil {
		return nil, fmt.Errorf("invalid source url: %w", err)
	}

	switch u.Scheme {
	case "http", "https":
		req, err := http.NewRequestWithContext(ctx, http.MethodGet, source, nil)
		if err != nil {
			return nil, fmt.Errorf("build request: %w", err)
		}
		resp, err := client.Do(req)
		if err != nil {
			return nil, fmt.Errorf("request failed: %w", err)
		}
		defer resp.Body.Close()
		if resp.StatusCode < 200 || resp.StatusCode >= 300 {
			return nil, fmt.Errorf("unexpected status: %s", resp.Status)
		}
		body, err := io.ReadAll(resp.Body)
		if err != nil {
			return nil, fmt.Errorf("read body: %w", err)
		}
		return normalizeLinks(string(body)), nil
	case "file":
		path := u.Path
		if path == "" {
			return nil, errors.New("file source path is empty")
		}
		data, err := os.ReadFile(path)
		if err != nil {
			return nil, fmt.Errorf("read file: %w", err)
		}
		return normalizeLinks(string(data)), nil
	default:
		return nil, fmt.Errorf("unsupported source scheme: %s", u.Scheme)
	}
}

func normalizeLinks(content string) []string {
	rawLines := strings.Split(content, "\n")
	set := make(map[string]struct{})

	for _, line := range rawLines {
		link := strings.TrimSpace(line)
		if link == "" {
			continue
		}
		if !isValidTrackerLink(link) {
			continue
		}
		set[link] = struct{}{}
	}

	result := make([]string, 0, len(set))
	for link := range set {
		result = append(result, link)
	}
	sort.Strings(result)
	return result
}

func isValidTrackerLink(link string) bool {
	u, err := url.Parse(link)
	if err != nil {
		return false
	}

	switch u.Scheme {
	case "http", "https", "udp", "ws", "wss":
	default:
		return false
	}

	if u.Hostname() == "" {
		return false
	}

	return true
}

func cacheFilePath(cacheDir, source string) string {
	sum := sha1.Sum([]byte(source))
	filename := hex.EncodeToString(sum[:]) + ".txt"
	return filepath.Join(cacheDir, filename)
}

func writeCache(cacheDir, source string, links []string) error {
	path := cacheFilePath(cacheDir, source)
	data := strings.Join(links, "\n")
	return os.WriteFile(path, []byte(data), 0o644)
}

func loadCachedLinks(cacheDir, source string) ([]string, error) {
	path := cacheFilePath(cacheDir, source)
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	return normalizeLinks(string(data)), nil
}