git ssb

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const { h, Value, Dict, dictToCollection, map, computed, resolve, watch } = require('mutant')
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module.exports = function (renderPage, defaultViews) {
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  const views = Dict({})
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  const forwardHistory = []
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  const backHistory = []
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  // if defaultViews changes, load them!
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  watch(defaultViews, (defaultViews) => {
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    if (defaultViews) {
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      defaultViews.forEach((view) => {
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        if (!views.has(view)) {
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          views.put(view, renderPage(view))
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        }
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      })
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    }
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  })
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  const lastViewed = {}
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  // delete cached view after 5 mins of last seeing
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  setInterval(() => {
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    views.keys().forEach((view) => {
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      if (!(resolve(defaultViews) || []).includes(view)) {
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        if (lastViewed[view] !== true && Date.now() - lastViewed[view] > (5 * 60e3) && view !== currentView()) {
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          views.delete(view)
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        }
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      }
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    })
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  }, 60e3)
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  const canGoForward = Value(false)
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  const canGoBack = Value(false)
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  const currentView = Value((resolve(defaultViews) || [])[0] || null)
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  const viewCollection = dictToCollection(views)
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  const html = h('div.main', map(viewCollection, (item) => {
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    return h('div.view', {
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      attributes: {
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        'data-href': item.key
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      },
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      hidden: computed([item.key, currentView], (a, b) => a !== b)
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    }, [item.value])
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  }))
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  return {
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    get: views.get,
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    defaultViews,
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    canGoForward,
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    canGoBack,
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    currentView,
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    setView,
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    goBack,
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    goForward,
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    html
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  }
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  // scoped
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  function goBack () {
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    if (backHistory.length) {
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      canGoForward.set(true)
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      forwardHistory.push(currentView())
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      const view = backHistory.pop()
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      loadView(view)
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      currentView.set(view)
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      canGoBack.set(backHistory.length > 0)
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    }
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  }
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  function goForward () {
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    if (forwardHistory.length) {
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      backHistory.push(currentView())
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      const view = forwardHistory.pop()
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      loadView(view)
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      currentView.set(view)
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      canGoForward.set(forwardHistory.length > 0)
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      canGoBack.set(true)
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    }
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  }
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  function loadView (view) {
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    if (!views.has(view)) {
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      const page = renderPage(view)
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      if (page) {
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        if (page.uniqueKey) {
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          views.keys().forEach(k => {
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            if (views.get(k).uniqueKey === page.uniqueKey) {
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              views.delete(k)
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            }
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          })
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        }
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        views.put(view, page)
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      }
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    }
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  }
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  function setView (view, anchor) {
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    loadView(view)
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    if (views.has(view)) {
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      if (lastViewed[view] !== true) {
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        lastViewed[view] = Date.now()
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      }
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      if (currentView() && lastViewed[currentView()] !== true) {
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        lastViewed[currentView()] = Date.now()
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      }
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      const viewElement = views.get(view)
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      if (viewElement && typeof viewElement.setAnchor === 'function') {
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        viewElement.setAnchor(anchor)
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      }
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      if (view !== currentView()) {
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        canGoForward.set(false)
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        canGoBack.set(true)
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        forwardHistory.length = 0
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        backHistory.push(currentView())
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        currentView.set(view)
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      }
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    }
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  }
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}
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