(function () {
    'use strict';

    var script = document.currentScript || (function () {
        var scripts = document.getElementsByTagName('script');
        return scripts[scripts.length - 1] || null;
    })();
    var service = script && script.dataset ? script.dataset.service : '';
    var endpoint = script && script.dataset && script.dataset.endpoint
        ? script.dataset.endpoint
        : new URL('../asset-version.php', script ? script.src : window.location.href).toString();
    var interval = script && script.dataset && script.dataset.interval ? Number(script.dataset.interval) : 30000;

    if (!service || window.__assetReloadStarted) return;

    window.__assetReloadStarted = true;
    interval = Math.max(15000, Number.isFinite(interval) ? interval : 30000);

    var storageKey = 'assetVersion:' + service;
    var reloadKey = 'assetReload:' + service;
    var running = false;

    function addQuery(url, key, value) {
        var parsed = new URL(url, window.location.href);
        parsed.searchParams.set(key, value);
        return parsed.toString();
    }

    function deleteCaches() {
        if (!window.caches || !window.caches.keys) return Promise.resolve();

        return window.caches.keys().then(function (keys) {
            return Promise.all(keys.map(function (key) {
                return window.caches.delete(key);
            }));
        }).catch(function () {});
    }

    function reloadWith(version) {
        var token = version.slice(0, 12);
        var marker = token + ':' + Math.floor(Date.now() / 10000);

        if (sessionStorage.getItem(reloadKey) === marker) return;

        sessionStorage.setItem(reloadKey, marker);
        deleteCaches().then(function () {
            window.location.replace(addQuery(window.location.href, 'assetReload', token));
        });
    }

    function check(force) {
        if (running || (!force && document.hidden)) return;

        running = true;
        fetch(addQuery(endpoint, '_', String(Date.now())), {
            cache: 'no-store',
            credentials: 'same-origin',
            headers: {
                'Cache-Control': 'no-cache',
                'Pragma': 'no-cache'
            }
        }).then(function (response) {
            if (!response.ok) throw new Error('asset version request failed');
            return response.json();
        }).then(function (data) {
            if (!data || data.result !== 'ok' || !data.version) return;

            var previous = localStorage.getItem(storageKey);
            localStorage.setItem(storageKey, data.version);

            if (previous && previous !== data.version) {
                reloadWith(data.version);
            }
        }).catch(function () {}).finally(function () {
            running = false;
        });
    }

    window.addEventListener('pageshow', function () {
        check(true);
    });
    window.addEventListener('focus', function () {
        check(true);
    });
    document.addEventListener('visibilitychange', function () {
        if (!document.hidden) check(true);
    });

    setInterval(function () {
        check(false);
    }, interval);
    check(true);
})();