// Command topdeck serves a personal, self-hosted collection of ranked
// favorites.
package main

import (
	"context"
	"crypto/rand"
	"errors"
	"fmt"
	"log/slog"
	"math/big"
	"net/http"
	"os"
	"os/signal"
	"strings"
	"syscall"
	"time"

	"github.com/cdnutter/topdeck/internal/auth"
	"github.com/cdnutter/topdeck/internal/config"
	"github.com/cdnutter/topdeck/internal/imgcache"
	"github.com/cdnutter/topdeck/internal/providers"
	"github.com/cdnutter/topdeck/internal/server"
	"github.com/cdnutter/topdeck/internal/store"
)

// version is set at build time with -ldflags "-X main.version=…".
var version = "dev"

func main() {
	level := slog.LevelInfo
	if strings.EqualFold(os.Getenv("TOPDECK_LOG_LEVEL"), "debug") {
		level = slog.LevelDebug
	}
	log := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: level}))
	if err := run(log); err != nil {
		log.Error("fatal", "err", err)
		os.Exit(1)
	}
}

func run(log *slog.Logger) error {
	cfg := config.Load()
	if err := os.MkdirAll(cfg.DataDir, 0o755); err != nil {
		return fmt.Errorf("creating data dir: %w", err)
	}
	st, err := store.Open(cfg.DataDir)
	if err != nil {
		return fmt.Errorf("opening database: %w", err)
	}
	defer st.Close()
	images, err := imgcache.New(cfg.DataDir, providers.UserAgent)
	if err != nil {
		return fmt.Errorf("image cache: %w", err)
	}
	ver := version
	if ver == "dev" {
		ver = fmt.Sprintf("dev-%d", time.Now().Unix())
	}
	srv, err := server.New(cfg, st, images, log, ver)
	if err != nil {
		return err
	}

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

	if err := bootstrapAdmin(ctx, cfg, st, srv, log); err != nil {
		return err
	}

	go func() {
		t := time.NewTicker(6 * time.Hour)
		defer t.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-t.C:
				if err := st.PruneSessions(ctx); err != nil {
					log.Warn("pruning sessions", "err", err)
				}
			}
		}
	}()

	httpSrv := &http.Server{
		Addr:              cfg.ListenAddr,
		Handler:           srv.Handler(),
		ReadHeaderTimeout: 10 * time.Second,
		IdleTimeout:       120 * time.Second,
	}
	errc := make(chan error, 1)
	go func() {
		log.Info("TopDeck is running", "addr", cfg.ListenAddr, "data", cfg.DataDir, "version", version)
		errc <- httpSrv.ListenAndServe()
	}()
	select {
	case err := <-errc:
		if !errors.Is(err, http.ErrServerClosed) {
			return err
		}
	case <-ctx.Done():
		log.Info("shutting down")
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
		defer cancel()
		return httpSrv.Shutdown(shutdownCtx)
	}
	return nil
}

// bootstrapAdmin creates the owner account from the environment, or else
// prints a one-time code that's required to claim the instance in the
// browser, so a stranger can't get there first.
func bootstrapAdmin(ctx context.Context, cfg config.Config, st *store.Store, srv *server.Server, log *slog.Logger) error {
	n, err := st.UserCount(ctx)
	if err != nil || n > 0 {
		return err
	}
	if cfg.AdminUsername != "" && cfg.AdminPassword != "" {
		if len(cfg.AdminPassword) < auth.MinPasswordLength {
			return fmt.Errorf("TOPDECK_ADMIN_PASSWORD must be at least %d characters", auth.MinPasswordLength)
		}
		hash, err := auth.HashPassword(cfg.AdminPassword)
		if err != nil {
			return err
		}
		if err := st.CreateUser(ctx, cfg.AdminUsername, hash); err != nil {
			return err
		}
		log.Info("created admin account from environment", "username", cfg.AdminUsername)
		return nil
	}
	code := setupCode()
	srv.SetSetupCode(code)
	log.Info("no admin account yet: open /setup in your browser and enter this setup code", "code", code)
	return nil
}

func setupCode() string {
	const alphabet = "ABCDEFGHJKLMNPQRSTUVWXYZ23456789"
	b := make([]byte, 8)
	for i := range b {
		n, err := rand.Int(rand.Reader, big.NewInt(int64(len(alphabet))))
		if err != nil {
			panic(err)
		}
		b[i] = alphabet[n.Int64()]
	}
	return string(b[:4]) + "-" + string(b[4:])
}