package app

import (
	"context"
	"errors"
	"fmt"
	"log"
	"net"
	"net/http"
	"sort"
	"time"

	"supervisor/internal/config"
	"supervisor/internal/httpserver"
	"supervisor/internal/session"
	"supervisor/internal/store/memory"
	"supervisor/internal/supervisor"
	"supervisor/internal/util"
)

type App struct {
	cfg            config.Config
	logger         *log.Logger
	httpServer     *http.Server
	SessionManager *session.Manager
	Supervisor     *supervisor.Manager
}

func New(cfg config.Config) (*App, error) {
	logger := util.NewLogger()
	memStore := memory.NewStore()
	sessionManager := session.NewManager(memStore, nil)
	supervisorManager := supervisor.NewManager()

	router, err := httpserver.NewRouter(httpserver.Dependencies{
		Logger:  logger,
		Manager: sessionManager,
	})
	if err != nil {
		return nil, fmt.Errorf("build router: %w", err)
	}

	srv := &http.Server{
		Addr:              cfg.Addr,
		Handler:           router,
		ReadHeaderTimeout: 10 * time.Second,
	}

	return &App{
		cfg:            cfg,
		logger:         logger,
		httpServer:     srv,
		SessionManager: sessionManager,
		Supervisor:     supervisorManager,
	}, nil
}

func (a *App) Run(ctx context.Context) error {
	errCh := make(chan error, 1)
	go func() {
		a.logServerURLs()
		errCh <- a.httpServer.ListenAndServe()
	}()

	select {
	case <-ctx.Done():
		shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
		defer cancel()
		_ = a.httpServer.Shutdown(shutdownCtx)
		return nil
	case err := <-errCh:
		if errors.Is(err, http.ErrServerClosed) {
			return nil
		}
		return err
	}
}

func (a *App) logServerURLs() {
	urls, err := serverURLs(a.cfg.Addr)
	if err != nil {
		a.logger.Printf("warning: determine local server URLs: %v", err)
	}
	if len(urls) == 0 {
		a.logger.Printf("HTTP server listening on %s", a.cfg.Addr)
		return
	}

	a.logger.Print("HTTP server available at:")
	for _, url := range urls {
		a.logger.Printf("  %s", url)
	}
}

func serverURLs(addr string) ([]string, error) {
	return serverURLsWithLocalIPv4Addrs(addr, discoverLocalIPv4Addrs)
}

func serverURLsWithLocalIPv4Addrs(addr string, localIPv4Addrs func() ([]string, error)) ([]string, error) {
	host, port, err := net.SplitHostPort(addr)
	if err != nil {
		return nil, err
	}

	urls := make([]string, 0, 4)
	seen := make(map[string]struct{})
	addURL := func(host string) {
		if host == "" {
			return
		}
		url := "http://" + net.JoinHostPort(host, port)
		if _, ok := seen[url]; ok {
			return
		}
		seen[url] = struct{}{}
		urls = append(urls, url)
	}

	if isWildcardHost(host) {
		addURL("localhost")
		addURL("127.0.0.1")

		addrs, err := localIPv4Addrs()
		for _, addr := range addrs {
			ip := net.ParseIP(addr)
			if !isUsableLocalIPv4(ip) {
				continue
			}
			addURL(ip.String())
		}
		return urls, err
	}

	ip := net.ParseIP(host)
	if ip == nil {
		addURL(host)
		return urls, nil
	}
	if ip4 := ip.To4(); ip4 != nil && !ip4.IsUnspecified() {
		addURL(ip4.String())
	}
	return urls, nil
}

func isWildcardHost(host string) bool {
	return host == "" || host == "0.0.0.0" || host == "::"
}

func discoverLocalIPv4Addrs() ([]string, error) {
	interfaces, err := net.Interfaces()
	if err != nil {
		return nil, err
	}

	addrs := make([]string, 0)
	seen := make(map[string]struct{})
	for _, iface := range interfaces {
		if iface.Flags&net.FlagUp == 0 || iface.Flags&net.FlagLoopback != 0 {
			continue
		}

		ifaceAddrs, err := iface.Addrs()
		if err != nil {
			return addrs, err
		}
		for _, ifaceAddr := range ifaceAddrs {
			ip := ipFromAddr(ifaceAddr)
			if !isUsableLocalIPv4(ip) {
				continue
			}

			addr := ip.To4().String()
			if _, ok := seen[addr]; ok {
				continue
			}
			seen[addr] = struct{}{}
			addrs = append(addrs, addr)
		}
	}

	sort.Strings(addrs)
	return addrs, nil
}

func ipFromAddr(addr net.Addr) net.IP {
	switch v := addr.(type) {
	case *net.IPNet:
		return v.IP
	case *net.IPAddr:
		return v.IP
	default:
		return nil
	}
}

func isUsableLocalIPv4(ip net.IP) bool {
	if ip == nil {
		return false
	}
	ip4 := ip.To4()
	if ip4 == nil {
		return false
	}
	return !ip4.IsUnspecified() &&
		!ip4.IsLoopback() &&
		!ip4.IsMulticast() &&
		!ip4.IsLinkLocalUnicast()
}