(function (scope) {
  'use strict';

  var TITLE_RE = /<title>([\s\S]*?)<\/title>/i;
  var TEMPLATE_RE = /data-template="([a-z0-9_-]+)"/i;

  var TEMPLATES = './templates/';

  var NAMES = [
    'base.njk',
    'page.njk',
    'book.njk',
    'index.njk',
    'version.njk',
    'notice.njk'
  ];

  scope.TEMPLATE_URLS = NAMES.map(function (name) { return TEMPLATES + name; });

  scope.createRenderer = function (readText) {
    function Loader() {}
    Loader.prototype.async = true;
    Loader.prototype.getSource = function (name, callback) {
      readText(TEMPLATES + name).then(
        function (src) { callback(null, { src: src, path: name, noCache: false }); },
        function (err) { callback(err); });
    };

    var env = new nunjucks.Environment(new Loader(), { autoescape: true });

    var loaded = null;

    // Nunjucks resolves {% include %} asynchronously. A template that is not
    // compiled yet when the render reaches it is skipped, taking the rest of
    // the block it sits in with it, and the render still succeeds.
    function loadAll() {
      if (!loaded) {
        loaded = Promise.all(NAMES.map(function (name) {
          return new Promise(function (resolve) {
            env.getTemplate(name, true, null, false, function () { resolve(); });
          });
        }));
      }
      return loaded;
    }

    function render(name, context) {
      return loadAll().then(function () {
        return new Promise(function (resolve, reject) {
          env.render(name, context, function (err, out) {
            return err ? reject(err) : resolve(out);
          });
        });
      });
    }

    return {
      render: render,

      compose: function (fragment) {
        var title = (TITLE_RE.exec(fragment) || ['', ''])[1].trim();
        var content = fragment.replace(TITLE_RE, '');
        var name = (TEMPLATE_RE.exec(content) || ['', 'page'])[1] + '.njk';
        return render(name, { title: title, content: content });
      },

      notice: function (heading, text) {
        return render('notice.njk', { heading: heading, text: text });
      }
    };
  };
})(self);