//go:build linux

package notify

import (
	"context"
	"fmt"
	"slices"
	"sync"
	"time"

	"github.com/godbus/dbus/v5"
)

// The freedesktop Notifications service on the session bus. One connection
// per process, made lazily on first use and kept: the daemon notifies on
// every announcement and must see the ActionInvoked signals for the Cancel
// button, which only works on a connection that stays open.
const (
	notifDest  = "org.freedesktop.Notifications"
	notifPath  = "/org/freedesktop/Notifications"
	notifIface = "org.freedesktop.Notifications"

	// dbusCallTimeout bounds every call: a hanging notification service
	// must never hold up an announcement.
	dbusCallTimeout = 2 * time.Second
)

var bus struct {
	once     sync.Once
	conn     *dbus.Conn
	err      error
	caps     []string
	server   string
	mu       sync.Mutex
	handlers map[uint32]func(action string) // by notification id
}

// connect opens the session bus once, subscribes to the service's signals
// and starts the dispatcher. A missing bus (DBUS_SESSION_BUS_ADDRESS unset:
// servers, SSH, WinRM-style sessions) is a normal, remembered failure.
func connect() (*dbus.Conn, error) {
	bus.once.Do(func() {
		conn, err := dbus.SessionBus()
		if err != nil {
			bus.err = fmt.Errorf("session bus: %w", err)
			return
		}
		ctx, cancel := context.WithTimeout(context.Background(), dbusCallTimeout)
		defer cancel()
		obj := conn.Object(notifDest, notifPath)
		var name, vendor, version, spec string
		if err := obj.CallWithContext(ctx, notifIface+".GetServerInformation", 0).Store(&name, &vendor, &version, &spec); err != nil {
			bus.err = fmt.Errorf("no notification service on the session bus: %w", err)
			return
		}
		bus.server = name
		if version != "" {
			bus.server += " " + version
		}
		if err := obj.CallWithContext(ctx, notifIface+".GetCapabilities", 0).Store(&bus.caps); err != nil {
			bus.caps = nil
		}
		if err := conn.AddMatchSignal(dbus.WithMatchObjectPath(notifPath), dbus.WithMatchInterface(notifIface)); err != nil {
			bus.err = fmt.Errorf("subscribing to notification signals: %w", err)
			return
		}
		bus.handlers = map[uint32]func(string){}
		ch := make(chan *dbus.Signal, 32)
		conn.Signal(ch)
		go dispatch(ch)
		bus.conn = conn
	})
	return bus.conn, bus.err
}

// dispatch routes ActionInvoked to the notification's handler and drops the
// handler on NotificationClosed.
func dispatch(ch <-chan *dbus.Signal) {
	for sig := range ch {
		if len(sig.Body) == 0 {
			continue
		}
		id, ok := sig.Body[0].(uint32)
		if !ok {
			continue
		}
		switch sig.Name {
		case notifIface + ".ActionInvoked":
			action, _ := sig.Body[1].(string)
			bus.mu.Lock()
			h := bus.handlers[id]
			bus.mu.Unlock()
			if h != nil {
				h(action)
			}
		case notifIface + ".NotificationClosed":
			bus.mu.Lock()
			delete(bus.handlers, id)
			bus.mu.Unlock()
		}
	}
}

// dbusAvailable reports whether a notification service answers on the bus.
func dbusAvailable() bool {
	_, err := connect()
	return err == nil
}

// dbusSupportsActions reports the "actions" capability of the service.
func dbusSupportsActions() bool {
	if _, err := connect(); err != nil {
		return false
	}
	return slices.Contains(bus.caps, "actions")
}

// dbusDescribe names the service for `talk doctor`.
func dbusDescribe() (string, bool) {
	if _, err := connect(); err != nil {
		return "", false
	}
	s := "notification service " + bus.server + " via D-Bus"
	if slices.Contains(bus.caps, "actions") {
		return s + " (cancel button supported)", true
	}
	return s + " (no actions: no cancel button)", true
}

// dbusNotify shows a notification and returns its id. actions is the flat
// freedesktop list [key, label, …]; onAction receives the key when the user
// clicks. expire_timeout 0 keeps the notification until talk closes it, so
// the Cancel button stays for the whole announcement.
func dbusNotify(ctx context.Context, text string, actions []string, onAction func(action string)) (uint32, error) {
	conn, err := connect()
	if err != nil {
		return 0, err
	}
	if actions == nil {
		actions = []string{}
	}
	expire := int32(-1) // server default for plain toasts
	if len(actions) > 0 {
		expire = 0
	}
	ctx, cancel := context.WithTimeout(ctx, dbusCallTimeout)
	defer cancel()
	hints := map[string]dbus.Variant{
		"urgency":       dbus.MakeVariant(byte(1)),
		"desktop-entry": dbus.MakeVariant(Title),
	}
	var id uint32
	err = conn.Object(notifDest, notifPath).CallWithContext(ctx, notifIface+".Notify", 0,
		Title, uint32(0), "audio-speakers", Title, text, actions, hints, expire).Store(&id)
	if err != nil {
		return 0, fmt.Errorf("notify: %w", err)
	}
	if onAction != nil {
		bus.mu.Lock()
		bus.handlers[id] = onAction
		bus.mu.Unlock()
	}
	return id, nil
}

// dbusClose dismisses a notification (best effort).
func dbusClose(id uint32) {
	conn, err := connect()
	if err != nil {
		return
	}
	bus.mu.Lock()
	delete(bus.handlers, id)
	bus.mu.Unlock()
	ctx, cancel := context.WithTimeout(context.Background(), dbusCallTimeout)
	defer cancel()
	_ = conn.Object(notifDest, notifPath).CallWithContext(ctx, notifIface+".CloseNotification", 0, id).Err
}