//go:build linux || windows || darwin

package tun

import (
	"errors"
	"sync"
	"time"

	"github.com/sagernet/sing/common/atomic"
	"github.com/sagernet/sing/common/control"
	"github.com/sagernet/sing/common/logger"
	"github.com/sagernet/sing/common/x/list"
)

func (m *networkUpdateMonitor) RegisterCallback(callback NetworkUpdateCallback) *list.Element[NetworkUpdateCallback] {
	m.access.Lock()
	defer m.access.Unlock()
	return m.callbacks.PushBack(callback)
}

func (m *networkUpdateMonitor) UnregisterCallback(element *list.Element[NetworkUpdateCallback]) {
	m.access.Lock()
	defer m.access.Unlock()
	m.callbacks.Remove(element)
}

func (m *networkUpdateMonitor) emit() {
	m.access.Lock()
	callbacks := m.callbacks.Array()
	m.access.Unlock()
	for _, callback := range callbacks {
		callback()
	}
}

type defaultInterfaceMonitor struct {
	interfaceFinder       control.InterfaceFinder
	overrideAndroidVPN    bool
	underNetworkExtension bool
	defaultInterface      atomic.Pointer[control.Interface]
	androidVPNEnabled     bool
	noRoute               bool
	networkMonitor        NetworkUpdateMonitor
	checkUpdateTimer      *time.Timer
	element               *list.Element[NetworkUpdateCallback]
	access                sync.Mutex
	callbacks             list.List[DefaultInterfaceUpdateCallback]
	logger                logger.Logger
}

func NewDefaultInterfaceMonitor(networkMonitor NetworkUpdateMonitor, logger logger.Logger, options DefaultInterfaceMonitorOptions) (DefaultInterfaceMonitor, error) {
	return &defaultInterfaceMonitor{
		interfaceFinder:       options.InterfaceFinder,
		overrideAndroidVPN:    options.OverrideAndroidVPN,
		underNetworkExtension: options.UnderNetworkExtension,
		networkMonitor:        networkMonitor,
		logger:                logger,
	}, nil
}

func (m *defaultInterfaceMonitor) Start() error {
	m.postCheckUpdate()
	m.element = m.networkMonitor.RegisterCallback(m.delayCheckUpdate)
	return nil
}

func (m *defaultInterfaceMonitor) delayCheckUpdate() {
	if m.checkUpdateTimer == nil {
		m.checkUpdateTimer = time.AfterFunc(time.Second, m.postCheckUpdate)
	} else {
		m.checkUpdateTimer.Reset(time.Second)
	}
}

func (m *defaultInterfaceMonitor) postCheckUpdate() {
	err := m.interfaceFinder.Update()
	if err != nil {
		m.logger.Error("update interface: ", err)
		return
	}
	err = m.checkUpdate()
	if errors.Is(err, ErrNoRoute) {
		if !m.noRoute {
			m.noRoute = true
			m.defaultInterface.Store(nil)
			m.emit(nil, 0)
		}
	} else if err != nil {
		m.logger.Error("check interface: ", err)
	} else {
		m.noRoute = false
	}
}

func (m *defaultInterfaceMonitor) Close() error {
	if m.element != nil {
		m.networkMonitor.UnregisterCallback(m.element)
	}
	return nil
}

func (m *defaultInterfaceMonitor) DefaultInterface() *control.Interface {
	return m.defaultInterface.Load()
}

func (m *defaultInterfaceMonitor) OverrideAndroidVPN() bool {
	return m.overrideAndroidVPN
}

func (m *defaultInterfaceMonitor) AndroidVPNEnabled() bool {
	return m.androidVPNEnabled
}

func (m *defaultInterfaceMonitor) RegisterCallback(callback DefaultInterfaceUpdateCallback) *list.Element[DefaultInterfaceUpdateCallback] {
	m.access.Lock()
	defer m.access.Unlock()
	return m.callbacks.PushBack(callback)
}

func (m *defaultInterfaceMonitor) UnregisterCallback(element *list.Element[DefaultInterfaceUpdateCallback]) {
	m.access.Lock()
	defer m.access.Unlock()
	m.callbacks.Remove(element)
}

func (m *defaultInterfaceMonitor) emit(defaultInterface *control.Interface, flags int) {
	m.access.Lock()
	callbacks := m.callbacks.Array()
	m.access.Unlock()
	for _, callback := range callbacks {
		callback(defaultInterface, flags)
	}
}