(function () {
    // Configuration
    const ENDPOINT_ORIGIN = 'https://lltracking.fly.dev'; // Change this to production URL later
    const SCRIPT_ID = 'lltracking-script';

    // Get Account ID from script attribute
    const scriptTag = document.getElementById(SCRIPT_ID);
    const ACCOUNT_ID = scriptTag ? scriptTag.getAttribute('data-account-id') : null;

    if (!ACCOUNT_ID) {
        console.error('LLTracking: Account ID not found. ensure script has id="lltracking-script" and data-account-id attribute.');
        return;
    }

    // Utilities
    function generateUUID() {
        return 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g, function (c) {
            var r = Math.random() * 16 | 0, v = c == 'x' ? r : (r & 0x3 | 0x8);
            return v.toString(16);
        });
    }

    function getCookie(name) {
        const value = `; ${document.cookie}`;
        const parts = value.split(`; ${name}=`);
        if (parts.length === 2) return parts.pop().split(';').shift();
    }

    function setCookie(name, value, days) {
        let expires = "";
        if (days) {
            const date = new Date();
            date.setTime(date.getTime() + (days * 24 * 60 * 60 * 1000));
            expires = "; expires=" + date.toUTCString();
        }
        document.cookie = name + "=" + (value || "") + expires + "; path=/";
    }

    // Session Management
    // Requirement: Session ID in cookie, persists across pages/restarts, 90 day expiry.
    let sessionId = getCookie('ll_session_id');
    if (!sessionId) {
        sessionId = generateUUID();
        // Set cookie for 90 days
        setCookie('ll_session_id', sessionId, 90);
    } else {
        // Refresh cookie expiry on each visit to ensure 90 days from LAST visit?
        // User said "reset after 90 days, if it still exists". Usually this means rolling window.
        setCookie('ll_session_id', sessionId, 90);
    }

    let visitorId = getCookie('ll_visitor_id');
    if (!visitorId) {
        visitorId = generateUUID();
        setCookie('ll_visitor_id', visitorId, 365);
    } else {
        setCookie('ll_visitor_id', visitorId, 365);
    }

    // Collect Data
    const visitData = {
        account_id: ACCOUNT_ID,
        session_id: sessionId,
        visitor_id: visitorId,
        page_url: window.location.href,
        referrer: document.referrer,
        utm_source: new URLSearchParams(window.location.search).get('utm_source') || '',
        utm_medium: new URLSearchParams(window.location.search).get('utm_medium') || '',
        utm_campaign: new URLSearchParams(window.location.search).get('utm_campaign') || '',
        utm_term: new URLSearchParams(window.location.search).get('utm_term') || '',
        utm_content: new URLSearchParams(window.location.search).get('utm_content') || '',
        gclid: new URLSearchParams(window.location.search).get('gclid') || '',
        user_agent: navigator.userAgent,
        screen_width: window.screen.width,
        screen_height: window.screen.height,
        device_pixel_ratio: window.devicePixelRatio || 1
    };

    let visitId = null;

    // Send Visit Data
    fetch(`${ENDPOINT_ORIGIN}/api/track/visit`, {
        method: 'POST',
        headers: { 'Content-Type': 'application/json' },
        body: JSON.stringify(visitData)
    })
        .then(res => res.json())
        .then(data => {
            if (data.visit_id) {
                visitId = data.visit_id;
                startHeartbeat();
            }
        })
        .catch(err => console.error('LLTracking: Failed to send visit', err));

    // Event Tracking
    window.lltrack = {
        trackEvent: function (eventName, eventData) {
            if (!visitId) return; // Wait for visit init or queue? For now drop.

            const payload = {
                account_id: ACCOUNT_ID,
                session_id: sessionId,
                visit_id: visitId,
                event_name: eventName,
                event_data: JSON.stringify(eventData)
            };

            fetch(`${ENDPOINT_ORIGIN}/api/track/event`, {
                method: 'POST',
                headers: { 'Content-Type': 'application/json' }, // keepalive not always supported with json body in old browsers, but mostly ok
                keepalive: true,
                body: JSON.stringify(payload)
            }).catch(e => console.error('LLTracking event error', e));
        }
    };

    // Heartbeat & Scroll Tracking
    let maxScroll = 0;
    let timeOnPage = 0;

    function updateScroll() {
        const docHeight = document.documentElement.scrollHeight - document.documentElement.clientHeight;
        const scrollTop = document.documentElement.scrollTop;
        const percentage = Math.round((scrollTop / docHeight) * 100);
        if (percentage > maxScroll) maxScroll = percentage;
    }

    window.addEventListener('scroll', () => {
        requestAnimationFrame(updateScroll);
    });

    function sendHeartbeat() {
        if (!visitId) return;

        const payload = {
            visit_id: visitId,
            time_on_page: timeOnPage,
            scroll_depth: maxScroll
        };

        // Use sendBeacon if possible for reliability on unload, but JSON requirement makes fetch easier
        fetch(`${ENDPOINT_ORIGIN}/api/track/heartbeat`, {
            method: 'POST',
            body: JSON.stringify(payload),
            headers: { 'Content-Type': 'application/json' },
            keepalive: true
        }).catch(() => { });
    }

    function startHeartbeat() {
        setInterval(() => {
            timeOnPage += 5; // 5 seconds
            sendHeartbeat();
        }, 5000);

        window.addEventListener('beforeunload', () => {
            sendHeartbeat();
        });
    }

})();