// Landing "notify me", the enhanced path. The form posts to /notify on its
// own with JS off; this submits the same route and the same encoding over
// fetch so the visitor keeps their place on the page instead of reloading it.
// Posting the form verbatim also means the CSRF token rides along without
// being read out and re-attached by hand.
function submitNotify(e) {
    e.preventDefault();
    var form = document.getElementById('notify-form');
    var status = document.getElementById('notify-status');
    var btn = form.querySelector('button');
    btn.disabled = true;
    btn.textContent = 'Sending...';
    status.textContent = '';
    status.className = 'notify-status';
    fetch(form.action, {
        method: 'POST',
        headers: {'Accept': 'application/json'},
        body: new URLSearchParams(new FormData(form))
    }).then(function(r) {
        // The route answers a redirect to /?notify=ok or /?notify=invalid.
        // fetch follows it, so the landed URL is what says which happened.
        if (!r.ok) throw new Error('Something went wrong');
        if (r.url.indexOf('notify=invalid') !== -1) {
            throw new Error('That address didn\'t look right.');
        }
        status.textContent = 'You\'re on the list.';
        status.className = 'notify-status success';
        form.querySelector('input[name="email"]').value = '';
    }).catch(function(err) {
        status.textContent = err.message;
        status.className = 'notify-status error';
    }).finally(function() {
        btn.disabled = false;
        btn.textContent = 'Notify Me';
    });
    return false;
}