window.App = window.App || {};
App.version = App.version || {};

(function() {
    const VERSION_URL = '/api/version';
    const POLL_INTERVAL_MS = 60000;

    // Baseline manifest captured on startup: { version, files: { rel: hash } }.
    let baseline = null;
    let timer = null;
    // Set once a JS/HTML change is detected; the page reloads at a safe moment.
    let reloadPending = false;
    let checking = false;

    async function fetchVersion() {
        const resp = await fetch(VERSION_URL, { cache: 'no-store' });
        if (!resp.ok) throw new Error('version fetch failed: ' + resp.status);
        return resp.json();
    }

    // Swap a stylesheet <link> in place using a cache-busted href so updated CSS
    // applies instantly. The old link is removed only after the new one loads to
    // avoid a flash of unstyled content.
    function hotReloadCss(relPath, hash) {
        const links = Array.from(document.querySelectorAll('link[rel="stylesheet"]'));
        const match = links.find((l) => {
            const href = (l.getAttribute('href') || '').split('?')[0];
            return href.endsWith(relPath) || href.endsWith('/' + relPath);
        });
        if (!match) return false;
        const base = (match.getAttribute('href') || '').split('?')[0];
        const fresh = match.cloneNode(false);
        fresh.setAttribute('href', base + '?v=' + hash);
        fresh.addEventListener('load', () => { if (match.parentNode) match.remove(); });
        fresh.addEventListener('error', () => { if (fresh.parentNode) fresh.remove(); });
        match.parentNode.insertBefore(fresh, match.nextSibling);
        return true;
    }

    function diffFiles(oldFiles, newFiles) {
        const changed = [];
        const keys = new Set([
            ...Object.keys(oldFiles || {}),
            ...Object.keys(newFiles || {})
        ]);
        keys.forEach((k) => {
            if ((oldFiles || {})[k] !== (newFiles || {})[k]) changed.push(k);
        });
        return changed;
    }

    // A reload is "safe" when the user isn't mid-playback: no open video modal,
    // no active reels feed, and no playing <video>. App state survives a reload
    // because it is restored from localStorage on boot.
    function isSafeToReload() {
        if (App.state && App.state.feedOpen) return false;
        const modal = document.getElementById('video-modal');
        if (modal && modal.style.display && modal.style.display !== 'none') return false;
        const player = document.getElementById('player');
        if (player && !player.paused && !player.ended) return false;
        return true;
    }

    function showUpdateBanner() {
        const banner = document.getElementById('update-banner');
        if (!banner) return;
        banner.classList.add('show');
        const btn = document.getElementById('update-banner-btn');
        if (btn) btn.onclick = () => window.location.reload();
    }

    function tryReloadWhenSafe() {
        if (!reloadPending) return;
        if (isSafeToReload()) {
            window.location.reload();
        } else {
            showUpdateBanner();
        }
    }

    function apply(latest) {
        const changed = diffFiles(baseline.files, latest.files);
        if (!changed.length) return;

        let needsReload = false;
        changed.forEach((file) => {
            if (file.endsWith('.css') && hotReloadCss(file, latest.files[file])) {
                return; // hot-swapped without reload
            }
            // JS and HTML can't be safely live-patched; they require a reload.
            needsReload = true;
        });

        // Adopt the new manifest so we don't re-trigger on the same change.
        baseline = latest;

        if (needsReload) {
            reloadPending = true;
            tryReloadWhenSafe();
        }
    }

    async function check() {
        if (checking || !baseline) return;
        checking = true;
        try {
            const latest = await fetchVersion();
            apply(latest);
        } catch (e) {
            // Network blips are non-fatal; we retry on the next tick.
        } finally {
            checking = false;
        }
    }

    App.version.start = async function() {
        try {
            baseline = await fetchVersion();
        } catch (e) {
            return; // endpoint unavailable; skip version checking entirely
        }
        timer = setInterval(check, POLL_INTERVAL_MS);
        // Check promptly when the user returns to the tab so updates land while
        // they were away, and retry a pending reload once playback stops.
        document.addEventListener('visibilitychange', () => {
            if (document.visibilityState === 'visible') {
                tryReloadWhenSafe();
                check();
            }
        });
        // Re-attempt a deferred reload whenever a video finishes/pauses.
        const player = document.getElementById('player');
        if (player) {
            player.addEventListener('pause', tryReloadWhenSafe);
            player.addEventListener('ended', tryReloadWhenSafe);
        }
    };
})();