package app

import (
	"context"
	"reflect"

	"v2ray.com/core/common"
	"v2ray.com/core/common/errors"
	"v2ray.com/core/common/log"
)

type Application interface {
	Interface() interface{}
}

type InitializationCallback func() error

func CreateAppFromConfig(ctx context.Context, config interface{}) (Application, error) {
	application, err := common.CreateObject(ctx, config)
	if err != nil {
		return nil, err
	}
	switch a := application.(type) {
	case Application:
		return a, nil
	default:
		return nil, errors.New("App: Not an application.")
	}
}

// A Space contains all apps that may be available in a V2Ray runtime.
// Caller must check the availability of an app by calling HasXXX before getting its instance.
type Space interface {
	GetApplication(appInterface interface{}) Application
	AddApplication(application Application) error
	Initialize() error
	OnInitialize(InitializationCallback)
}

type spaceImpl struct {
	initialized bool
	cache       map[reflect.Type]Application
	appInit     []InitializationCallback
}

func NewSpace() Space {
	return &spaceImpl{
		cache:   make(map[reflect.Type]Application),
		appInit: make([]InitializationCallback, 0, 32),
	}
}

func (v *spaceImpl) OnInitialize(f InitializationCallback) {
	if v.initialized {
		if err := f(); err != nil {
			log.Error("Space: error after space initialization: ", err)
		}
	} else {
		v.appInit = append(v.appInit, f)
	}
}

func (v *spaceImpl) Initialize() error {
	for _, f := range v.appInit {
		if err := f(); err != nil {
			return err
		}
	}
	v.appInit = nil
	v.initialized = true
	return nil
}

func (v *spaceImpl) GetApplication(appInterface interface{}) Application {
	if v == nil {
		return nil
	}
	appType := reflect.TypeOf(appInterface)
	return v.cache[appType]
}

func (v *spaceImpl) AddApplication(app Application) error {
	if v == nil {
		return errors.New("App: Nil space.")
	}
	appType := reflect.TypeOf(app.Interface())
	v.cache[appType] = app
	return nil
}

type contextKey int

const (
	spaceKey = contextKey(0)
)

func AddApplicationToSpace(ctx context.Context, appConfig interface{}) error {
	space := SpaceFromContext(ctx)
	if space == nil {
		return errors.New("App: No space in context.")
	}
	application, err := CreateAppFromConfig(ctx, appConfig)
	if err != nil {
		return err
	}
	return space.AddApplication(application)
}

func SpaceFromContext(ctx context.Context) Space {
	return ctx.Value(spaceKey).(Space)
}

func ContextWithSpace(ctx context.Context, space Space) context.Context {
	return context.WithValue(ctx, spaceKey, space)
}