Mobile.js

import {getSet, indexOf, viewOf} from './utils.js'

export function Mobile(){
  return {
    view: v => {
      Promise.resolve().then(reconcile)

      return viewOf(v)(Unit)
    }
  }

  const arriving = new Map
  const removing = new Map
  const ranges   = new Map
  const states   = new Set

  function reconcile(){
    if(!arriving.size)
      return 

    const moving = new Map(
      Array.from(arriving).filter(([key]) => 
        removing.has(key)
      )
    )

    arriving.clear()
    removing.clear()
  }

  function Unit({key, state}){
    states.add(states)

    return {
      view: v => 
        v.instance || m.fragment(['']),

      onupdate: v => {
        state.index  = indexOf(v.dom) 
      },

      oncreate: v => {
        state.index  = indexOf(v.dom)
        state.parent = v.dom.parentNode
        state.range  = getSet(ranges, parent, () => 
          Array(index + 1),
        )
      },


      onbeforeremove: v => {
        removing.set(key, v)

        return Promise.resolve()
      },
    }
  }
}