src/core/event/scroll.js

import { isMobile } from '../util/env';
import * as dom from '../util/dom';
import config from '../config';
import Tweezer from 'tweezer.js';

const nav = {};
let hoverOver = false;
let scroller = null;
let enableScrollEvent = true;
let coverHeight = 0;

function scrollTo(el, offset = 0) {
  if (scroller) {
    scroller.stop();
  }

  enableScrollEvent = false;
  scroller = new Tweezer({
    start: window.pageYOffset,
    end: el.getBoundingClientRect().top + window.pageYOffset - offset,
    duration: 500,
  })
    .on('tick', v => window.scrollTo(0, v))
    .on('done', () => {
      enableScrollEvent = true;
      scroller = null;
    })
    .begin();
}

function highlight(path) {
  if (!enableScrollEvent) {
    return;
  }

  const sidebar = dom.getNode('.sidebar');
  const anchors = dom.findAll('.anchor');
  const wrap = dom.find(sidebar, '.sidebar-nav');
  let active = dom.find(sidebar, 'li.active');
  const doc = document.documentElement;
  const top = ((doc && doc.scrollTop) || document.body.scrollTop) - coverHeight;
  let last;

  for (let i = 0, len = anchors.length; i < len; i += 1) {
    const node = anchors[i];

    if (node.offsetTop > top) {
      if (!last) {
        last = node;
      }

      break;
    } else {
      last = node;
    }
  }

  if (!last) {
    return;
  }

  const li =
    nav[getNavKey(decodeURIComponent(path), last.getAttribute('data-id'))];

  if (!li || li === active) {
    return;
  }

  active && active.classList.remove('active');
  li.classList.add('active');
  active = li;

  // Scroll into view
  // https://github.com/vuejs/vuejs.org/blob/master/themes/vue/source/js/common.js#L282-L297
  if (!hoverOver && dom.body.classList.contains('sticky')) {
    const height = sidebar.clientHeight;
    const curOffset = 0;
    const cur = active.offsetTop + active.clientHeight + 40;
    const isInView =
      active.offsetTop >= wrap.scrollTop && cur <= wrap.scrollTop + height;
    const notThan = cur - curOffset < height;
    const top = isInView ? wrap.scrollTop : notThan ? curOffset : cur - height;

    sidebar.scrollTop = top;
  }
}

function getNavKey(path, id) {
  return `${path}?id=${id}`;
}

export function scrollActiveSidebar(router) {
  const cover = dom.find('.cover.show');
  coverHeight = cover ? cover.offsetHeight : 0;

  const sidebar = dom.getNode('.sidebar');
  let lis = [];
  if (sidebar !== null && sidebar !== undefined) {
    lis = dom.findAll(sidebar, 'li');
  }

  for (let i = 0, len = lis.length; i < len; i += 1) {
    const li = lis[i];
    const a = li.querySelector('a');
    if (!a) {
      continue;
    }

    let href = a.getAttribute('href');

    if (href !== '/') {
      const {
        query: { id },
        path,
      } = router.parse(href);
      if (id) {
        href = getNavKey(path, id);
      }
    }

    if (href) {
      nav[decodeURIComponent(href)] = li;
    }
  }

  if (isMobile) {
    return;
  }

  const path = router.getCurrentPath();
  dom.off('scroll', () => highlight(path));
  dom.on('scroll', () => highlight(path));
  dom.on(sidebar, 'mouseover', () => {
    hoverOver = true;
  });
  dom.on(sidebar, 'mouseleave', () => {
    hoverOver = false;
  });
}

export function scrollIntoView(path, id) {
  if (!id) {
    return;
  }
  const topMargin = config().topMargin;
  const section = dom.find('#' + id);
  section && scrollTo(section, topMargin);

  const li = nav[getNavKey(path, id)];
  const sidebar = dom.getNode('.sidebar');
  const active = dom.find(sidebar, 'li.active');
  active && active.classList.remove('active');
  li && li.classList.add('active');
}

const scrollEl = dom.$.scrollingElement || dom.$.documentElement;

export function scroll2Top(offset = 0) {
  scrollEl.scrollTop = offset === true ? 0 : Number(offset);
}