package main

import (
	"context"
	"errors"
	"log"
	"net/http"
	"os"
	"os/signal"
	"strconv"
	"strings"
	"syscall"
	"time"

	"mangabm/backend/internal/api"
	"mangabm/backend/internal/httpmw"
	"mangabm/backend/internal/latest"
	"mangabm/backend/internal/store"
	"mangabm/backend/internal/userscript"
	"mangabm/backend/internal/web"
)

// Config holds all runtime settings, sourced from environment variables.
type Config struct {
	Token          string
	AllowedOrigins []string
	DBPath         string
	Port           string
	// WebPassword gates the browser UI. Empty disables the web routes entirely.
	WebPassword string
	// UserscriptPath is the file served at /u/{token}/manga-bookmark.user.js.
	// Supplied by a bindmount so the script can be edited without a rebuild.
	UserscriptPath string
	// LatestPoll configures the background latest-chapter fetcher.
	LatestPoll LatestPoll
}

// LatestPoll configures the background latest-chapter poller.
//
// Sizing: batch x (cooldown / interval) is how many series hold a true cooldown
// cadence — 14 x (1h / 10m) = 84 with these defaults, which covers this
// deployment. Past that nothing breaks; the effective cadence stretches to
// N x interval / batch and the oldest-checked-first ordering keeps it uniform.
type LatestPoll struct {
	Enabled  bool
	Cooldown time.Duration
	Interval time.Duration
	Stagger  time.Duration
	Batch    int
}

const (
	defaultPollCooldown = time.Hour
	defaultPollInterval = 10 * time.Minute
	defaultPollStagger  = 20 * time.Second
	defaultPollBatch    = 14
	// minPollCooldown keeps a typo from turning a polite background check into
	// a hammer against sites that are already bot-scoring us.
	minPollCooldown = 15 * time.Minute
)

func envOr(key, def string) string {
	if v := os.Getenv(key); v != "" {
		return v
	}
	return def
}

// envBool reads a boolean env var. Anything unrecognised falls back to def.
func envBool(key string, def bool) bool {
	switch v := strings.ToLower(strings.TrimSpace(os.Getenv(key))); v {
	case "":
		return def
	case "0", "false", "no", "off":
		return false
	case "1", "true", "yes", "on":
		return true
	default:
		log.Printf("config: %s=%q is not a boolean, using %v", key, v, def)
		return def
	}
}

// envDuration reads a duration env var. An unparseable or non-positive value
// falls back to def and logs rather than failing startup: the poller is an
// enhancement, and a typo in one of its knobs must not stop bookmark sync.
func envDuration(key string, def time.Duration) time.Duration {
	raw := strings.TrimSpace(os.Getenv(key))
	if raw == "" {
		return def
	}
	d, err := time.ParseDuration(raw)
	if err != nil || d <= 0 {
		log.Printf("config: %s=%q is not a positive duration, using %s", key, raw, def)
		return def
	}
	return d
}

// envInt reads a positive integer env var, with the same fallback policy.
func envInt(key string, def int) int {
	raw := strings.TrimSpace(os.Getenv(key))
	if raw == "" {
		return def
	}
	n, err := strconv.Atoi(raw)
	if err != nil || n <= 0 {
		log.Printf("config: %s=%q is not a positive integer, using %d", key, raw, def)
		return def
	}
	return n
}

// loadLatestPoll reads the poller's settings, clamping anything that would make
// it antisocial.
func loadLatestPoll() LatestPoll {
	p := LatestPoll{
		Enabled:  envBool("LATEST_CHAPTER_POLL_ENABLED", true),
		Cooldown: envDuration("LATEST_CHAPTER_POLL_COOLDOWN", defaultPollCooldown),
		Interval: envDuration("LATEST_CHAPTER_POLL_INTERVAL", defaultPollInterval),
		Stagger:  envDuration("LATEST_CHAPTER_POLL_STAGGER", defaultPollStagger),
		Batch:    envInt("LATEST_CHAPTER_POLL_BATCH", defaultPollBatch),
	}
	if p.Cooldown < minPollCooldown {
		log.Printf("config: cooldown %s is below the %s floor, clamping", p.Cooldown, minPollCooldown)
		p.Cooldown = minPollCooldown
	}
	// batch x stagger has to fit inside one tick or a batch is still running
	// when the next one is due. Run() serialises them, so this degrades to a
	// slower cadence rather than to overlapping fetches — worth a warning, not
	// a failure.
	if span := time.Duration(p.Batch) * p.Stagger; span > p.Interval {
		log.Printf("config: batch(%d) x stagger(%s) = %s exceeds interval %s; batches will overrun their tick",
			p.Batch, p.Stagger, span, p.Interval)
	}
	return p
}

func loadConfig() Config {
	c := Config{
		Token:          os.Getenv("API_TOKEN"),
		DBPath:         envOr("DB_PATH", "/data/bookmarks.db"),
		Port:           envOr("PORT", "8080"),
		WebPassword:    os.Getenv("WEB_PASSWORD"),
		UserscriptPath: envOr("USERSCRIPT_PATH", "/userscript/manga-bookmark.user.js"),
		LatestPoll:     loadLatestPoll(),
	}
	for _, o := range strings.Split(os.Getenv("ALLOWED_ORIGINS"), ",") {
		if o = strings.TrimSpace(o); o != "" {
			c.AllowedOrigins = append(c.AllowedOrigins, o)
		}
	}
	return c
}

// newRouter wires routes and middleware. CORS is the outermost layer so
// preflight OPTIONS short-circuits before auth; /bookmarks* is auth-protected,
// /healthz is public.
func newRouter(s *store.Store, cfg Config) http.Handler {
	mux := http.NewServeMux()
	mux.HandleFunc("GET /healthz", api.Healthz)

	// Outside httpmw.Auth (the updater sends no Authorization header) and
	// outside the WEB_PASSWORD gate (the script must be installable either
	// way). The path segment carries the token instead.
	mux.HandleFunc("GET /u/{token}/manga-bookmark.user.js", userscript.Handler(cfg.Token, cfg.UserscriptPath))

	h := &api.Handler{Store: s}
	protected := http.NewServeMux()
	protected.HandleFunc("GET /bookmarks", h.List)
	protected.HandleFunc("PUT /bookmarks/{key}", h.Put)
	protected.HandleFunc("DELETE /bookmarks/{key}", h.Delete)

	auth := httpmw.Auth(cfg.Token, protected)
	mux.Handle("/bookmarks", auth)
	mux.Handle("/bookmarks/", auth)

	// The browser UI is registered only when a password is configured, so a
	// deployment that forgets WEB_PASSWORD exposes nothing rather than
	// exposing an unprotected list.
	if cfg.WebPassword != "" {
		wh, err := web.New(s, cfg.Token, cfg.WebPassword)
		if err != nil {
			log.Fatalf("web handler: %v", err)
		}
		wh.Register(mux)
	}

	return httpmw.CORS(cfg.AllowedOrigins, httpmw.Gzip(guardEmptyUserscriptToken(mux)))
}

// guardEmptyUserscriptToken heads off ServeMux's own path-cleaning redirect:
// an empty {token} segment makes the request path "/u//manga-bookmark.user.js",
// and ServeMux 307s that to "/u/manga-bookmark.user.js" before pattern
// matching ever runs. The endpoint's contract is 404 for any wrong token,
// including this one, so catch it ahead of the mux.
func guardEmptyUserscriptToken(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if strings.HasPrefix(r.URL.Path, "/u//") {
			http.NotFound(w, r)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func main() {
	cfg := loadConfig()
	if cfg.Token == "" {
		log.Fatal("API_TOKEN is required")
	}

	s, err := store.Open(cfg.DBPath)
	if err != nil {
		log.Fatalf("open store: %v", err)
	}
	defer s.Close()

	// The poller is off the request path entirely: if it cannot start, the
	// service still serves bookmarks and the userscript still captures latest
	// chapters on its own.
	pollCtx, stopPoll := context.WithCancel(context.Background())
	defer stopPoll()
	startLatestPoller(pollCtx, s, cfg.LatestPoll)

	srv := &http.Server{
		Addr:              ":" + cfg.Port,
		Handler:           newRouter(s, cfg),
		ReadHeaderTimeout: 10 * time.Second,
	}

	go func() {
		log.Printf("listening on :%s (db=%s, origins=%v)", cfg.Port, cfg.DBPath, cfg.AllowedOrigins)
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			log.Fatalf("serve: %v", err)
		}
	}()

	stop := make(chan os.Signal, 1)
	signal.Notify(stop, syscall.SIGINT, syscall.SIGTERM)
	<-stop

	log.Println("shutting down")
	// Stop polling before draining requests, so an in-flight series fetch does
	// not hold the process open past the shutdown deadline.
	stopPoll()
	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	if err := srv.Shutdown(ctx); err != nil {
		log.Printf("shutdown: %v", err)
	}
}

// startLatestPoller launches the background poller unless it is disabled or its
// HTTP client cannot be built. Any problem here is logged and skipped: this
// feature going missing degrades the service to userscript-only latest-chapter
// tracking, which is exactly how it behaved before.
func startLatestPoller(ctx context.Context, s *store.Store, cfg LatestPoll) {
	if !cfg.Enabled {
		log.Println("latest-chapter poller: disabled by config")
		return
	}
	f, err := latest.NewTLSFetcher()
	if err != nil {
		log.Printf("latest-chapter poller: disabled, cannot build client: %v", err)
		return
	}
	p := &latest.Poller{
		Store:    s,
		Fetch:    f,
		Now:      time.Now,
		Cooldown: cfg.Cooldown,
		Interval: cfg.Interval,
		Stagger:  cfg.Stagger,
		Batch:    cfg.Batch,
	}
	go p.Run(ctx)
}