(function() {
    const root = $(`link[type='root']`).attr('href');
    const incrementalLoadingParams = {
        start: 0,
        count: viewPortToCount()
    };
    const filterTypes = ['lang', 'category', 'q'];
    const bookMap = new Map();
    let iso;
    let isFetching = false;
    let noResultInjected = false;
    let params = new URLSearchParams(window.location.search);
    let timer;

    function queryUrlBuilder() {
        let url = `${root}/catalog/search?`;
        url += Object.keys(incrementalLoadingParams).map(key => `${key}=${incrementalLoadingParams[key]}`).join("&");
        params.forEach((value, key) => {url+= value ? `&${key}=${value}` : ''});
        return (url);
    }

    function htmlEncode(str) {
        return str.replace(/[\u00A0-\u9999<>\&]/gim, (i) => `&#${i.charCodeAt(0)};`);
    }

    function viewPortToCount(){
        return Math.floor(window.innerHeight/100 + 1)*(window.innerWidth>1000 ? 3 : 2);
    }

    function getInnerHtml(node, query) {
        return node.querySelector(query).innerHTML;
    }

    function generateBookHtml(book, sort = false) {
        const link = book.querySelector('link').getAttribute('href');
        const title =  getInnerHtml(book, 'title');
        const description = getInnerHtml(book, 'summary');
        const id = getInnerHtml(book, 'id');
        const iconUrl = getInnerHtml(book, 'icon');
        const articleCount = getInnerHtml(book, 'articleCount');
        const mediaCount = getInnerHtml(book, 'mediaCount');

        const linkTag = document.createElement('a');
        linkTag.setAttribute('class', 'book');
        linkTag.setAttribute('data-id', id);
        linkTag.setAttribute('href', link);
        if (sort) {
            linkTag.setAttribute('data-idx', bookMap[id]);
        }
        linkTag.innerHTML = `<div class='book__background' style="background-image: url('${iconUrl}');">
            <div class='book__title' title='${title}'>${title}</div>
            <div class='book__description' title='${description}'>${description}</div>
            <div class='book__info'>${articleCount} articles, ${mediaCount} medias</div>
        </div>`;
        return linkTag;
    }

    function toggleFooter(show=false) {
        const footer = document.getElementById('kiwixfooter');
        const fadeOutDiv = document.getElementsByClassName('fadeOut')[0];
        if (footer.style.display === 'none' && show) {
            footer.style.display = 'block';
            fadeOutDiv.style.display = 'none';
        } else if (footer.style.display !== 'none' && !show) {
            footer.style.display = 'none';
            fadeOutDiv.style.display = 'block';
        }
    }

    async function loadBooks() {
        const loader = document.querySelector('.loader');
        loader.style.display = 'block';
        return await fetch(queryUrlBuilder()).then(async (resp) => {
            const data = new window.DOMParser().parseFromString(await resp.text(), 'application/xml');
            const books = data.querySelectorAll('entry');
            books.forEach((book, idx) => {
                bookMap.set(getInnerHtml(book, 'id'), idx);
            });
            incrementalLoadingParams.start += books.length;
            if (parseInt(data.querySelector('totalResults').innerHTML) === bookMap.size) {
                incrementalLoadingParams.count = 0;
                toggleFooter(true);
            } else {
                toggleFooter();
            }
            loader.style.display = 'none';
            return books;
        });
    }

    async function loadAndDisplayOptions(nodeQuery, query) {
        // currently taking an object in place of query, will replace it with query while fetching data from backend later on.
        document.querySelector(nodeQuery).innerHTML += Object.keys(query)
            .map((option) => {return `<option value='${option}'>${htmlEncode(query[option])}</option>`})
        .join('');
    }

    function checkAndInjectEmptyMessage() {
        const kiwixBodyDiv = document.getElementsByClassName('kiwixHomeBody')[0];
        if (!bookMap.size) {
            if (!noResultInjected) {
                noResultInjected = true;
                iso.remove(document.getElementsByClassName('book__list')[0].getElementsByTagName('a'));
                iso.layout();
                const spanTag = document.createElement('span');
                spanTag.setAttribute('class', 'noResults');
                spanTag.innerHTML = `No result. Would you like to <a href="/?lang=">reset filter?</a>`;
                kiwixBodyDiv.append(spanTag);
                spanTag.getElementsByTagName('a')[0].onclick = (event) => {
                    event.preventDefault();
                    window.history.pushState({}, null, `${window.location.href.split('?')[0]}?lang=`);
                    resetAndFilter();
                    filterTypes.forEach(key => {document.getElementsByName(key)[0].value = params.get(key) || ''});
                };
            }
            return true;
        } else if (noResultInjected) {
            noResultInjected = false;
            kiwixBodyDiv.getElementsByClassName('noResults')[0].remove();
        }
        return false;
    }

    async function loadAndDisplayBooks(sort = false) {
        if (isFetching) return;
        isFetching = true;
        await loadAndDisplayBooksUnguarded(sort);
        isFetching = false;
    }

    async function loadAndDisplayBooksUnguarded(sort) {
        let books = await loadBooks();
        if (checkAndInjectEmptyMessage()) {return}
        const booksToFilter = new Set();
        const booksToDelete = new Set();
        iso.arrange({
            filter: function (idx, elem) {
                const id = elem.getAttribute('data-id');
                const retVal = bookMap.has(id);
                if (retVal) {
                    booksToFilter.add(id);
                    if (sort) {
                        elem.setAttribute('data-idx', bookMap[id]);
                        iso.updateSortData(elem);
                    }
                } else {
                    booksToDelete.add(elem);
                }
                return retVal;
            }
        });
        books = [...books].filter((book) => {return !booksToFilter.has(getInnerHtml(book, 'id'))});
        booksToDelete.forEach(book => {iso.remove(book);});
        books.forEach((book) => {iso.insert(generateBookHtml(book, sort))});
    }

    async function resetAndFilter(filterType = '', filterValue = '') {
        isFetching = false;
        incrementalLoadingParams.start = 0;
        incrementalLoadingParams.count = viewPortToCount();
        bookMap.clear();
        params = new URLSearchParams(window.location.search);
        if (filterType) {
            if (!filterValue) {
                params.delete(filterType);
            } else {
                params.set(filterType, filterValue);
            }
            window.history.pushState({}, null, `${window.location.href.split('?')[0]}?${params.toString()}`);
        }
        await loadAndDisplayBooks(true);
    }

    window.addEventListener('popstate', async () => {
        await resetAndFilter();
        filterTypes.forEach(key => {document.getElementsByName(key)[0].value = params.get(key) || ''});
    });

    async function loadSubset() {
        if (incrementalLoadingParams.count && window.innerHeight + window.scrollY >= document.body.offsetHeight) {
            loadAndDisplayBooks();
        }
    }

    window.addEventListener('resize', (event) => {
        if (timer) {clearTimeout(timer)}
        timer = setTimeout(() => {
            incrementalLoadingParams.count = incrementalLoadingParams.count && viewPortToCount();
            loadSubset();
        }, 100, event);
    });

    window.addEventListener('scroll', loadSubset);

    window.onload = async () => {
            iso = new Isotope( '.book__list', {
                itemSelector: '.book',
                getSortData:{
                    weight: function( itemElem ) {
                        const index = itemElem.getAttribute('data-idx');
                        return index ? parseInt(index) : Infinity;
                    }
                },
                sortBy: 'weight'
        });
        await loadAndDisplayBooks();
        await loadAndDisplayOptions('#languageFilter', langList);
        await loadAndDisplayOptions('#categoryFilter', categoryList);
        filterTypes.forEach((filter) => {
            const filterTag = document.getElementsByName(filter)[0];
            filterTag.addEventListener('change', () => {resetAndFilter(filterTag.name, filterTag.value)});
        });
        params.forEach((value, key) => {document.getElementsByName(key)[0].value = value});
        document.getElementById('kiwixSearchForm').onsubmit = (event) => {event.preventDefault()};
        if (!window.location.search) {
            const browserLang = navigator.language.split('-')[0];
            if (browserLang.length === 3) {
                document.getElementById('languageFilter').value = browserLang;
                langFilter.dispatchEvent(new Event('change'));
            } else {
                const langFilter = document.getElementById('languageFilter');
                langFilter.value = iso6391To3[browserLang];
                langFilter.dispatchEvent(new Event('change'));
            }
        }
    }
})();