class ViewPagerAdapter(manager: FragmentManager) :
        FragmentStatePagerAdapter(manager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {

        var productsHome: ProductsFragment? = null
        var productsCategories: ProductsFragment? = null
        var categories: CategoriesFragment? = null
        var home: HomeFragment? = null

        override fun getItem(pos: Int): Fragment {
            return when (pos) {
                CurrentFragment.PROFILE -> ProfileFragment()
                CurrentFragment.CATEGORIES -> {
                    if (categoriesProductsMode) {
                        if (productsCategories == null) {
                            productsCategories = ProductsFragment()
                        }
                        productsHome as Fragment
                    } else {
                        if (categories == null) {
                            categories = CategoriesFragment()
                        }
                        categories as Fragment
                    }
                }
                CurrentFragment.FAVORITES -> FavoritesFragment()
                else -> {
                    if (homeProductsMode) {
                        if (productsHome == null) {
                            productsHome = ProductsFragment()
                        }
                        productsHome as Fragment
                    } else {
                        if (home == null) {
                            home = HomeFragment()
                        }
                        home as Fragment
                    }
                }
            }
        }

        override fun getCount(): Int {
            return 4
        }

        override fun getItemPosition(obj: Any): Int {
            return if (obj is HomeFragment || obj is ProductsFragment) {
                PagerAdapter.POSITION_NONE
            } else {
                super.getItemPosition(obj)
            }
        }

        override fun instantiateItem(container: ViewGroup, position: Int): Any {
            val fragment = super.instantiateItem(container, position)
            if (fragment is HomeFragment) {
                home = fragment
                fragment.callback = this@MainActivity
            }
            if(fragment is CategoriesFragment) {
                categories = fragment
                fragment.callback = this@MainActivity
            }
            if(fragment is ProductsFragment) {
                fragment.callback = this@MainActivity
                if(position == 0) {
                    productsHome = fragment
                    homeProductsMode = true
                }
                else {
                    productsCategories = fragment
                    categoriesProductsMode = true
                }
            }
            return fragment
        }
    }