function normalizeGithubUrl(url) {
  if (!url) { return null }

  var isAlias = !/\/\//.test(url) // no protocol in the url, we assume it's an alias
  url = isAlias
    ? 'https://github.com/' + url + '/edit/master/docs/'
    : url.replace(/^git\+/, '')

  return url
}

function install(hook, vm) {
  var editLinkConfig = vm.config.editLink || {}
  var text = editLinkConfig.text || 'Edit this page'
  var cssClass = editLinkConfig.cssClass || 'edit-link'
  var repoUrl = normalizeGithubUrl(editLinkConfig.repo || vm.config.repo)

  if (!repoUrl) { throw Error('$docsify.editLink.repo is required. Fix your config.') }

  hook.afterEach(function (html) {
    var editLink = '<p class="' + cssClass + '" style="text-align: right;">' +
      '<a href="' + repoUrl + vm.route.file + '" target="_blank">' + text + '</a></p>'

    return editLink + html
  });
}

$docsify.plugins = [].concat(install, $docsify.plugins)