const { h, Value, Dict, dictToCollection, map, computed, resolve, watch } = require('mutant')

module.exports = function (renderPage, defaultViews) {
  const views = Dict({})

  const forwardHistory = []
  const backHistory = []

  // if defaultViews changes, load them!
  watch(defaultViews, (defaultViews) => {
    if (defaultViews) {
      defaultViews.forEach((view) => {
        if (!views.has(view)) {
          views.put(view, renderPage(view))
        }
      })
    }
  })

  const lastViewed = {}

  // delete cached view after 5 mins of last seeing
  setInterval(() => {
    views.keys().forEach((view) => {
      if (!(resolve(defaultViews) || []).includes(view)) {
        if (lastViewed[view] !== true && Date.now() - lastViewed[view] > (5 * 60e3) && view !== currentView()) {
          views.delete(view)
        }
      }
    })
  }, 60e3)

  const canGoForward = Value(false)
  const canGoBack = Value(false)
  const currentView = Value((resolve(defaultViews) || [])[0] || null)

  const viewCollection = dictToCollection(views)
  const html = h('div.main', map(viewCollection, (item) => {
    return h('div.view', {
      attributes: {
        'data-href': item.key
      },
      hidden: computed([item.key, currentView], (a, b) => a !== b)
    }, [item.value])
  }))

  return {
    get: views.get,
    defaultViews,
    canGoForward,
    canGoBack,
    currentView,
    setView,
    goBack,
    goForward,
    html
  }

  // scoped

  function goBack () {
    if (backHistory.length) {
      canGoForward.set(true)
      forwardHistory.push(currentView())

      const view = backHistory.pop()
      loadView(view)

      currentView.set(view)
      canGoBack.set(backHistory.length > 0)
    }
  }

  function goForward () {
    if (forwardHistory.length) {
      backHistory.push(currentView())

      const view = forwardHistory.pop()
      loadView(view)

      currentView.set(view)
      canGoForward.set(forwardHistory.length > 0)
      canGoBack.set(true)
    }
  }

  function loadView (view) {
    if (!views.has(view)) {
      const page = renderPage(view)
      if (page) {
        if (page.uniqueKey) {
          views.keys().forEach(k => {
            if (views.get(k).uniqueKey === page.uniqueKey) {
              views.delete(k)
            }
          })
        }
        views.put(view, page)
      }
    }
  }

  function setView (view, anchor) {
    loadView(view)

    if (views.has(view)) {
      if (lastViewed[view] !== true) {
        lastViewed[view] = Date.now()
      }

      if (currentView() && lastViewed[currentView()] !== true) {
        lastViewed[currentView()] = Date.now()
      }

      const viewElement = views.get(view)

      if (viewElement && typeof viewElement.setAnchor === 'function') {
        viewElement.setAnchor(anchor)
      }

      if (view !== currentView()) {
        canGoForward.set(false)
        canGoBack.set(true)
        forwardHistory.length = 0
        backHistory.push(currentView())
        currentView.set(view)
      }
    }
  }
}