{#
  Version picker sidebar block.

  The list is fetched at page load from versions.json at the site root rather
  than baked in at build time. Each version's docs are built once, when its tag
  is pushed, and never rebuilt -- so a list baked into 0.2.0's pages would
  forever omit every version released after it. Fetching at runtime keeps every
  published version's picker current without a rebuild.

  Renders nothing when versions.json is unreachable, which is the case for a
  plain local `make docs` build.
#}
<div id="ember-versions" hidden>
    <h3>Versions</h3>
    <select id="ember-version-select" aria-label="Documentation version"></select>
</div>
<script>
(function () {
    // pathto('', 1) is the relative path to this version's root, so one more
    // level up is the site root holding versions.json and the version dirs.
    var root = "{{ pathto('', 1) }}" + "../";
    var current = "{{ ember_version_slug }}";
    var page = "{{ pagename }}.html";
    var box = document.getElementById("ember-versions");
    var select = document.getElementById("ember-version-select");

    function go() {
        var base = root + select.value;
        // Prefer the same page in the target version, but fall back to its
        // index: pages come and go between releases.
        fetch(base + page, {method: "HEAD"}).then(function (response) {
            window.location.href = response.ok ? base + page : base;
        }).catch(function () {
            window.location.href = base;
        });
    }

    fetch(root + "versions.json").then(function (response) {
        if (!response.ok) {
            throw new Error("versions.json: " + response.status);
        }
        return response.json();
    }).then(function (data) {
        data.versions.forEach(function (version) {
            var option = document.createElement("option");
            option.value = version.url;
            option.textContent = version.name;
            option.selected = version.name === current;
            select.appendChild(option);
        });
        select.addEventListener("change", go);
        box.hidden = false;
    }).catch(function () {
        // Single-version or local build; leave the picker hidden.
    });
})();
</script>