git ssb

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const nest = require('depnest')
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const { h } = require('mutant')
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exports.gives = nest('app.html.scroller')
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exports.create = function (api) {
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  return nest('app.html.scroller', Scroller)
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  function Scroller (opts = {}) {
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    const { prepend, content = null, append, classList = [], className = '', title = '', scrollIntoView } = opts
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    const contentSection = h('section.content', { title: '' }, content)
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    const container = h('Scroller',
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      {
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        classList,
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        className,
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        title,
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        style: { 'overflow-y': 'scroll', 'overflow-x': 'auto' },
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        intersectionBindingViewport: { rootMargin: '1000px' } // mutant magic
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        // TODO (watch for breaks e.g. stuff stops updating after scrolling)
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      },
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      [
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        prepend ? h('section.top', prepend) : null,
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        contentSection,
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        append ? h('section.bottom', append) : null
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      ]
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    )
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    container.scroll = keyscroll(contentSection, scrollIntoView)
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    return {
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      content: contentSection,
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      container
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    }
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  }
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}
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function keyscroll (content, scrollIntoView = false) {
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  var curMsgEl
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  if (!content) return () => {}
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  content.addEventListener('click', onActivateChild, false)
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  content.addEventListener('focus', onActivateChild, true)
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  function onActivateChild (ev) {
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    for (var el = ev.target; el; el = el.parentNode) {
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      if (el.parentNode === content) {
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        curMsgEl = el
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        return
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      }
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    }
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  }
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  return function scroll (d) {
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    const child = (!curMsgEl || d === 'first') ? content.firstChild
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      : (!curMsgEl || d === 'last') ? content.lastChild
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        : d < 0 ? curMsgEl.previousElementSibling || content.firstChild
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          : d > 0 ? curMsgEl.nextElementSibling || content.lastChild
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            : curMsgEl
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    selectChild(child)
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    return curMsgEl
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  }
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  function selectChild (el) {
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    if (!el) { return }
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    if (scrollIntoView) {
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      if (!el.scrollIntoViewIfNeeded && !el.scrollIntoView) return
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      ;(el.scrollIntoViewIfNeeded || el.scrollIntoView).call(el)
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    } else {
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      content.parentElement.scrollTop = el.offsetTop - content.parentElement.offsetTop - 10
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    }
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    if (el.focus) el.focus()
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    curMsgEl = el
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  }
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}
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