import $ from 'jquery';

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 the parent DOM element defined as "wrapper": v-el:wrapper
 * - have a `scrolling` method bound to `scroll` event on such element: @scroll="scrolling"
 * - have the array of all objects named as `items`, either as data, computed, or a prop
 */
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) {
            const $wrapper = $(this.$els.wrapper);

            // 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 ($wrapper.scrollTop() + $wrapper.innerHeight() >= $wrapper[0].scrollHeight - 32) {
                this.displayMore();
            }

            this.showBackToTop = $wrapper.scrollTop() > 64;
        },

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

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

    events: {
        'koel:teardown': function () {
            this.numOfItems = 30;
            this.showBackToTop = false;
        },
    },
};