import $ from 'jquery';

import { event } from '../utils';
import toTopButton from '../components/shared/to-top-button.vue';

/**
 * Add a "infinite scroll" functionality to any component using this mixin.
 * Such a component should have a `scrolling` method bound to `scroll` event on
 * the wrapper element: @scroll="scrolling"
 */
export default {
    components: { toTopButton },

    data() {
        return {
            numOfItems: 30, // Number of currently loaded and displayed items
            perPage: 30,    // Number of items to be loaded per "page"
            showBackToTop: false,
        };
    },

    methods: {
        scrolling(e) {
            // Here we check if the user has scrolled to the end of the wrapper (or 32px to the end).
            // If that's true, load more items.
            if (e.target.scrollTop + e.target.clientHeight >= e.target.scrollHeight - 32) {
                this.displayMore();
            }

            this.showBackToTop = e.target.scrollTop > 64;
        },

        /**
         * Load and display more items into the scrollable area.
         */
        displayMore() {
            this.numOfItems += this.perPage;
        },

        /**
         * Scroll to top fo the wrapper.
         */
        scrollToTop() {
            $(this.$refs.wrapper).animate({ scrollTop: 0}, 500);
            this.showBackToTop = false;
        },
    },

    created() {
        event.on('koel:teardown', () => {
            this.numOfItems = 30;
            this.showBackToTop = false;
        });
    },
};