/*
 * Gallery archive builder — the admin's "Rebuild now" button.
 *
 * The archive normally rebuilds itself in the background, but the photographer
 * often wants it finished before sending the link out. Building a multi-gigabyte
 * ZIP cannot happen in one request on a 60 s execution limit, so this loops:
 * POST step, get back {done, total, finished}, repeat until finished.
 *
 * Every piece of state lives on the server, so this loop is disposable — closing
 * the tab pauses the build, "Resume" picks it up at the photo it stopped on, and
 * the background worker would eventually finish it regardless.
 */
(function () {
    'use strict';

    var card = document.getElementById('archive-card');
    if (!card) return;

    var api = card.dataset.api;
    var slug = card.dataset.slug;
    var csrf = card.dataset.csrf;

    var buildBtn = document.getElementById('archive-build');
    var cancelBtn = document.getElementById('archive-cancel');
    var bar = document.getElementById('archive-bar');
    var fill = bar.querySelector('span');
    var status = document.getElementById('archive-status');

    var running = false;
    var stopped = false;
    var startedAt = 0;
    var startedFrom = 0;

    function post(action) {
        var body = new FormData();
        body.append('slug', slug);
        body.append('action', action);
        return fetch(api, {
            method: 'POST',
            headers: { 'X-CSRF-Token': csrf },
            body: body
        }).then(function (response) {
            return response.json().catch(function () {
                return { error: 'Server returned a non-JSON response (HTTP ' + response.status + ')' };
            });
        });
    }

    /* Rough finish time from the rate this run has actually achieved. */
    function eta(done, total) {
        var elapsed = (Date.now() - startedAt) / 1000;
        var processed = done - startedFrom;
        if (processed < 1 || elapsed < 1) return '';
        var remaining = Math.round((total - done) * (elapsed / processed));
        if (remaining < 60) return ' · about a minute left';
        return ' · about ' + Math.round(remaining / 60) + ' min left';
    }

    function show(done, total, suffix) {
        bar.hidden = false;
        fill.style.width = (total ? Math.round((done / total) * 100) : 0) + '%';
        status.textContent = done + ' of ' + total + ' photos' + (suffix || '');
    }

    function fail(message, done, total) {
        running = false;
        bar.hidden = total > 0 ? false : true;
        status.innerHTML = '';
        status.appendChild(document.createTextNode(message + ' '));
        var resume = document.createElement('button');
        resume.className = 'btn-ghost';
        resume.style.margin = '0';
        resume.textContent = 'Resume';
        resume.addEventListener('click', function () { run('step'); });
        status.appendChild(resume);
        buildBtn.disabled = false;
        cancelBtn.hidden = true;
    }

    function run(action) {
        running = true;
        stopped = false;
        buildBtn.disabled = true;
        cancelBtn.hidden = false;
        startedAt = Date.now();
        startedFrom = -1;

        var retried = false;

        function step(which) {
            post(which).then(function (result) {
                if (stopped) return;

                if (result.error && !result.total) {
                    // A transient S3 hiccup is worth one silent retry; anything
                    // else needs the photographer to see it.
                    if (!retried) {
                        retried = true;
                        step('step');
                        return;
                    }
                    fail(result.error, 0, 0);
                    return;
                }
                retried = false;
                if (startedFrom < 0) startedFrom = result.done;

                if (result.finished) {
                    running = false;
                    show(result.total, result.total, ' · done');
                    // Reload so the status line, size and share-side button all
                    // reflect the archive that now exists.
                    window.location.reload();
                    return;
                }

                if (result.error) {
                    show(result.done, result.total, '');
                    fail(result.error, result.done, result.total);
                    return;
                }

                show(result.done, result.total, eta(result.done, result.total));
                step('step');
            }).catch(function (err) {
                if (!stopped) fail('Network error: ' + err.message, 0, 0);
            });
        }

        step(action);
    }

    buildBtn.addEventListener('click', function () {
        if (running) return;
        // "start" discards any half-finished attempt and opens a fresh upload.
        run(buildBtn.dataset.resume ? 'step' : 'start');
    });

    cancelBtn.addEventListener('click', function () {
        stopped = true;
        running = false;
        post('cancel').then(function () { window.location.reload(); });
    });
})();