const puppeteer = require('puppeteer');
const { decrypt } = require('../utils/crypto');

/**
 * Scrapes the Moodle LMS dashboard for deadlines.
 * @param {string} username - The plaintext LMS username.
 * @param {string} encryptedPassword - The AES-encrypted password from DB.
 * @param {string} iv - The initialization vector for decryption.
 * @returns {Promise<Array>} - Array of deadline objects.
 */
async function scrapeDeadlines(username, encryptedPassword, iv) {
    let browser;
    try {
        // Decrypt the password
        const plaintextPassword = decrypt(encryptedPassword, iv);

        // Launch an invisible Chrome browser
        console.log(`[Scraper] Launching browser for user: ${username}...`);
        browser = await puppeteer.launch({
            headless: 'new',
            executablePath: process.env.CHROME_BIN || null,
            args: [
                '--no-sandbox', 
                '--disable-setuid-sandbox',
                '--disable-dev-shm-usage',
                '--disable-gpu'
            ]
        });

        const page = await browser.newPage();
        
        // --- BOOYAH: Fast Puppeteer (Block heavy assets) ---
        await page.setRequestInterception(true);
        page.on('request', (req) => {
            if (['image', 'stylesheet', 'font', 'media'].includes(req.resourceType())) {
                req.abort(); // Drops page load time from ~30s to ~5s!
            } else {
                req.continue();
            }
        });

        // Bulletproof timeouts to prevent hanging indefinitely
        page.setDefaultNavigationTimeout(45000);
        page.setDefaultTimeout(45000);

        // Navigate to the Moodle login page
        // If they visit /my/, it automatically redirects to the login screen
        await page.goto('https://lms.nust.edu.pk/portal/my/', { waitUntil: 'networkidle2' });

        // Wait for the login fields to appear (standard Moodle selectors)
        await page.waitForSelector('#username', { timeout: 10000 });
        await page.waitForSelector('#password', { timeout: 10000 });

        // Type credentials and login
        await page.type('#username', username);
        await page.type('#password', plaintextPassword);
        
        console.log(`[Scraper] Credentials entered for ${username}. Logging in...`);
        
        // Click the login button and wait for navigation back to the dashboard
        await Promise.all([
            page.waitForNavigation({ waitUntil: 'networkidle2' }),
            page.click('#loginbtn') // the standard Moodle login button ID
        ]);

        console.log(`[Scraper] Successfully logged into dashboard for ${username}. Waiting for timeline...`);

        // Wait for the timeline block to load
        // Note: Moodle 4.x Timeline items usually have 'data-region="event-item"'
        let hasItems = true;
        await page.waitForSelector('[data-region="event-list-item"]', { timeout: 15000 }).catch(async () => {
            // VERIFICATION: Check if timeline is officially empty, or if this is a Moodle crash/timeout
            const bodyText = await page.evaluate(() => document.body.innerText);
            if (bodyText.includes("No upcoming activities due") || bodyText.includes("No activities require action")) {
                console.log(`[Scraper] Verified officially empty timeline for ${username}.`);
                hasItems = false;
            } else {
                throw new Error("Timeline failed to load completely. Suspected Moodle outage. Aborting scrape.");
            }
        });

        if (!hasItems) {
            return []; // Completely safe to return empty, student has no assignments!
        }

        // Extract assignments from the Timeline block
        const deadlines = await page.evaluate(() => {
            const results = [];
            
            // This selects the standard Moodle Timeline event container
            const eventItems = document.querySelectorAll('[data-region="event-list-item"]');
            
            eventItems.forEach(item => {
                try {
                    // Extracting course name (Usually in a small badge or link inside the item)
                    const courseEl = item.querySelector('.text-truncate'); 
                    let courseName = courseEl ? courseEl.innerText.trim() : 'Unknown Course';

                    // Extracting assignment title
                    const titleEl = item.querySelector('.text-truncate a') || item.querySelector('.event-name-container a');
                    let assignmentTitle = titleEl ? titleEl.innerText.trim() : 'Unknown Assignment';

                    // Check for that pesky emoji and "is due" that might be injected.
                    // We let stringFormatter handle most of it, but ensure we don't pass massive objects.

                    // Find the date by looking at the parent DOM structure
                    // Moodle groups items under a parent <div> which is preceded by an <h5> containing the date
                    let dateHeader = null;
                    let parent = item.parentElement;
                    if (parent && parent.previousElementSibling && parent.previousElementSibling.tagName === 'H5') {
                        dateHeader = parent.previousElementSibling.innerText.trim();
                    }

                    // Extract the time from inside the item
                    const timeEl = item.querySelector('.text-right') || item.querySelector('.date');
                    const timeString = timeEl ? timeEl.innerText.trim() : '';

                    // Combine date and time
                    const dateString = dateHeader && timeString ? `${dateHeader}, ${timeString}` : timeString;

                    // DEBUG: Grab the raw HTML of the item so we can inspect it in the terminal later if needed
                    const rawHtml = item.innerHTML;

                    if (assignmentTitle && dateString) {
                        results.push({
                            courseName,
                            assignmentTitle,
                            dateString,
                            rawHtml: results.length === 0 ? rawHtml : undefined // only save html for the first item to avoid returning massive strings
                        });
                    }
                } catch (err) {
                    // Skip malformed items
                }
            });
            
            return results;
        });

        console.log(`[Scraper] Extracted ${deadlines.length} raw deadlines for ${username}.`);
        
        return deadlines;

    } catch (error) {
        console.error(`[Scraper] Error scraping for ${username}:`, error.message);
        return [];
    } finally {
        if (browser) {
            try {
                await browser.close();
                console.log(`[Scraper] Browser closed for ${username}.`);
            } catch (closeErr) {
                console.error(`[Scraper] Error closing browser gracefully for ${username}, forcefully killing process...`, closeErr.message);
                if (browser.process() != null) {
                    browser.process().kill('SIGKILL');
                }
            }
        }
    }
}

module.exports = { scrapeDeadlines };