$(document).ready(function () {
  var isHeaderEnable = CONFIG.header && CONFIG.header.enable
  var isShowHeaderOnPost = isHeaderEnable && CONFIG.header.showOnPost
  // The previous distance from the page to the top.
  var prevScrollTop = 0
  var isNavFix = false
  var isAnimation = true

  function headerNavScroll () {
    var isPostPage = !!$('#is-post').length
    var isNoHeader = !isHeaderEnable || (isPostPage && !isShowHeaderOnPost)
    var $headerNav = $('.header-nav')
    var scrollTop = Math.floor($(window).scrollTop())
    var delta = Math.floor(scrollTop - prevScrollTop)

    if (scrollTop === 0) {
      if (isNoHeader) {
        setTimeout(function () {
          $headerNav.addClass('slider--clear')
          isAnimation = false
        }, 200)
      }
      $headerNav.removeClass('header-nav--sticky')
      $headerNav.removeClass('slider--up')
      $headerNav.addClass('slider--down')
    } else {
      if (isNoHeader && scrollTop < $headerNav.height()) {
        return false
      }

      var MIN_SCROLL_TO_CHANGE_NAV = 5
      // Make the state of nav bar not change due to tiny scrolling.
      if (Math.abs(delta) > MIN_SCROLL_TO_CHANGE_NAV) {
        if (isNoHeader) {
          if (!isAnimation) {
            isAnimation = true
          } else {
            $headerNav.removeClass('slider--clear')
          }
        }
        if (!isNavFix) {
          isNavFix = true
        } else {
          $headerNav.addClass('header-nav--sticky')
        }
        if (delta > 0) {
          $headerNav.removeClass('slider--down')
          $headerNav.addClass('slider--up')
        } else {
          $headerNav.removeClass('slider--up')
          $headerNav.addClass('slider--down')
        }
      } else {
        $headerNav.addClass('header-nav--sticky')
      }
    }
    prevScrollTop = scrollTop
  }

  var isBack2topEnable = CONFIG.back2top && CONFIG.back2top.enable
  var isBack2topShow = false

  // Back the page to top.
  function back2top () {
    var $back2top = $('#back2top')
    var scrollTop = $(window).scrollTop()

    if (scrollTop !== 0) {
      if (!isBack2topShow) {
        $back2top.addClass('back2top--show')
        $back2top.removeClass('back2top--hide')
        isBack2topShow = true
      }
    } else {
      $back2top.addClass('back2top--hide')
      $back2top.removeClass('back2top--show')
      isBack2topShow = false
    }
  }

  if (isBack2topEnable) {
    // Initializaiton
    back2top()

    $('#back2top').on('click', function () {
      $('body')
        .velocity('stop')
        .velocity('scroll')
    })
  }

  // Initializaiton
  headerNavScroll()

  $(window).on(
    'scroll',
    Stun.utils.throttle(function () {
      headerNavScroll()

      if (isBack2topEnable) {
        back2top()
      }
    }, 100)
  )
})