(function () {
  function normalizePrefix(prefix) {
    if (!prefix) {
      return "/";
    }

    var normalized = prefix;
    if (!normalized.startsWith("/")) {
      normalized = "/" + normalized;
    }
    if (!normalized.endsWith("/")) {
      normalized += "/";
    }
    return normalized.replace(/\/{2,}/g, "/");
  }

  function joinPath(prefix, suffix) {
    var cleanSuffix = (suffix || "").replace(/^\/+/, "");
    return normalizePrefix(prefix) + cleanSuffix;
  }

  function samePageTarget(currentPrefix, targetPrefix) {
    var currentPath = window.location.pathname;
    var normalizedCurrent = normalizePrefix(currentPrefix);
    var normalizedTarget = normalizePrefix(targetPrefix);

    if (currentPath.indexOf(normalizedCurrent) === 0) {
      return joinPath(normalizedTarget, currentPath.slice(normalizedCurrent.length));
    }

    return normalizedTarget;
  }

  function setStatus(node, message, isError) {
    if (!node) {
      return;
    }

    node.textContent = message;
    node.classList.toggle("is-error", Boolean(isError));
  }

  document.addEventListener("DOMContentLoaded", function () {
    var container = document.querySelector(".doc-version-selector");
    if (!container) {
      return;
    }

    var select = container.querySelector(".js-version-select");
    var status = container.querySelector(".js-version-status");
    var currentVersion = container.dataset.currentVersion || "latest";
    var versionsUrl = container.dataset.versionsUrl;

    if (!select || !versionsUrl) {
      return;
    }

    fetch(versionsUrl, { credentials: "same-origin" })
      .then(function (response) {
        if (!response.ok) {
          throw new Error("Unable to load versions");
        }
        return response.json();
      })
      .then(function (manifest) {
        var versions = Array.isArray(manifest.versions) ? manifest.versions : [];
        if (!versions.length) {
          throw new Error("No versions defined");
        }

        var activeVersion = manifest.current || currentVersion;
        var activeEntry = versions.find(function (item) {
          return item.slug === activeVersion;
        }) || versions.find(function (item) {
          return item.slug === currentVersion;
        }) || versions[0];

        select.innerHTML = "";

        versions.forEach(function (item) {
          var option = document.createElement("option");
          option.value = item.slug;
          option.textContent = item.label || item.slug;
          option.dataset.prefix = item.prefix || "/" + item.slug + "/";
          if (item.slug === activeEntry.slug) {
            option.selected = true;
          }
          select.appendChild(option);
        });

        setStatus(status, manifest.description || "Switch versions without leaving the current page.");

        select.addEventListener("change", function (event) {
          var chosen = versions.find(function (item) {
            return item.slug === event.target.value;
          });

          if (!chosen) {
            return;
          }

          var targetPath = samePageTarget(activeEntry.prefix, chosen.prefix);
          var nextUrl = targetPath + window.location.search + window.location.hash;
          window.location.assign(nextUrl);
        });
      })
      .catch(function () {
        setStatus(status, "versions.json could not be loaded.", true);
      });
  });
})();