document.addEventListener('DOMContentLoaded', () => {
    const papersGrid = document.getElementById('papersGrid');
    const searchInput = document.getElementById('searchInput');
    const dateFrom = document.getElementById('dateFrom');
    const dateTo = document.getElementById('dateTo');
    const searchBtn = document.getElementById('searchBtn');
    const loader = document.getElementById('loader');
    const noResults = document.getElementById('noResults');
    const resultCount = document.getElementById('resultCount');

    // Default query for AI papers
    const DEFAULT_QUERY = 'cat:cs.AI OR cat:cs.LG OR cat:cs.CL';
    
    // Initial Fetch
    fetchPapers(DEFAULT_QUERY);

    // Event Listeners
    searchBtn.addEventListener('click', () => {
        const query = searchInput.value.trim();
        fetchPapers(query ? `all:${query}` : DEFAULT_QUERY);
    });

    searchInput.addEventListener('keypress', (e) => {
        if (e.key === 'Enter') {
            searchBtn.click();
        }
    });

    // Date Filter Listener (Client-side filter on loaded data)
    // For simplicity in this demo, we re-fetch or filter if data is present. 
    // Here we'll re-trigger the search logic to apply filters if data exists, 
    // but for a robust app, we'd store the 'allPapers' array.
    let allPapersData = [];

    dateFrom.addEventListener('change', applyClientFilters);
    dateTo.addEventListener('change', applyClientFilters);

    async function fetchPapers(searchQuery) {
        showLoader(true);
        noResults.classList.add('hidden');
        papersGrid.innerHTML = '';
        
        try {
            // ArXiv API endpoint
            const baseUrl = 'http://export.arxiv.org/api/query?';
            const params = new URLSearchParams({
                search_query: searchQuery,
                start: 0,
                max_results: 50, // Fetch a good amount to filter by date
                sortBy: 'submittedDate',
                sortOrder: 'descending'
            });

            const response = await fetch(baseUrl + params.toString());
            if (!response.ok) throw new Error('Network response was not ok');
            
            const xmlText = await response.text();
            const papers = parseArxivXml(xmlText);
            
            allPapersData = papers;
            applyClientFilters(); // Apply any existing date filters immediately

        } catch (error) {
            console.error('Error fetching papers:', error);
            resultCount.textContent = 'Error fetching data';
            noResults.classList.remove('hidden');
            showLoader(false);
        }
    }

    function parseArxivXml(xmlString) {
        const parser = new DOMParser();
        const xmlDoc = parser.parseFromString(xmlString, "text/xml");
        const entries = xmlDoc.getElementsByTagName("entry");
        const papers = [];

        for (let i = 0; i < entries.length; i++) {
            const entry = entries[i];
            
            // Title
            const title = entry.getElementsByTagName("title")[0].textContent;
            
            // Summary (Abstract) - Remove newlines and trim
            const summary = entry.getElementsByTagName("summary")[0].textContent.replace(/\s+/g, ' ').trim();
            
            // Published Date
            const published = entry.getElementsByTagName("published")[0].textContent;
            
            // Authors
            const authors = [];
            const authorNodes = entry.getElementsByTagName("author");
            for (let j = 0; j < authorNodes.length; j++) {
                authors.push(authorNodes[j].getElementsByTagName("name")[0].textContent);
            }
            
            // Link (PDF)
            const links = entry.getElementsByTagName("link");
            let pdfLink = "";
            for(let k=0; k<links.length; k++) {
                if(links[k].getAttribute("type") === "application/pdf") {
                    pdfLink = links[k].getAttribute("href");
                    break;
                }
            }
            // Arxiv ID Link
            const idLink = entry.getElementsByTagName("id")[0].textContent;

            papers.push({
                title,
                summary,
                published,
                authors,
                pdfLink,
                idLink
            });
        }
        return papers;
    }

    function applyClientFilters() {
        papersGrid.innerHTML = '';
        
        const fromVal = dateFrom.value ? new Date(dateFrom.value) : null;
        const toVal = dateTo.value ? new Date(dateTo.value) : null;
        
        // Set time to end of day for 'to' filter to be inclusive
        if (toVal) toVal.setHours(23, 59, 59, 999);

        const filteredPapers = allPapersData.filter(paper => {
            const paperDate = new Date(paper.published);
            
            let isValid = true;

            if (fromVal && paperDate < fromVal) isValid = false;
            if (toVal && paperDate > toVal) isValid = false;

            return isValid;
        });

        displayPapers(filteredPapers);
    }

    function displayPapers(papers) {
        showLoader(false);
        resultCount.textContent = `Found ${papers.length} papers`;

        if (papers.length === 0) {
            noResults.classList.remove('hidden');
            return;
        }

        papers.forEach(paper => {
            // Create Web Component
            const card = document.createElement('paper-card');
            
            // Pass data to component
            card.setAttribute('title', paper.title);
            card.setAttribute('summary', paper.summary);
            card.setAttribute('authors', paper.authors.join(', '));
            card.setAttribute('date', new Date(paper.published).toLocaleDateString());
            card.setAttribute('pdf-link', paper.pdfLink);
            card.setAttribute('abs-link', paper.idLink);
            
            papersGrid.appendChild(card);
        });
    }

    function showLoader(show) {
        if (show) {
            loader.classList.remove('hidden');
            papersGrid.classList.add('hidden');
            resultCount.textContent = 'Searching...';
        } else {
            loader.classList.add('hidden');
            papersGrid.classList.remove('hidden');
        }
    }
});