'use strict'

import {
  EventEmitter
} from 'events'


const keyRegExp = /\{(\w+)\}/g
const sep = '.'

function resolveParam(keyPath, payload){
  return keyPath
          .replace(
            keyRegExp
          , (_,$1) => payload[$1]
          )
          .split(sep)
}
function walk(cur, tiers, lvl = 0){
  if(tiers.length === 0){
    return cur
  }
  let prop = cur[tiers[0]]
  let tails = tiers.slice(1)
  if(tails.length === 0){
    return prop
  }else if(prop === undefined || prop === null){
    throw new Error(` {lvl} `)
  }else{
    return walk(prop, tails, lvl + 1)
  }
}

const evName = 'change'

function deepMerge(tiers, source, patch){
  //FIXME Immutable!
  let target = source
  let locationTiers = tiers.slice(0,tiers.length - 1)
  let patchKey = tiers[tiers.length - 1]
  walk(target, locationTiers)[patchKey] = patch
  return target
}

export default function Effector(initialState = {}){
  let currentState = initialState
  let broadcastMap = {}
  const emitter = new EventEmitter()
  const getState = () => currentState
  const subscribe = (fn) => {
    let cb = (nextState) => fn(nextState)
    emitter.addListener(evName, cb)
    return () => emitter.removeListener(evName, cb)
  }
  const createAction = (keyPath, fn, deps = []) => {
    let action = (payload, options = {}) => {

      let tiers = resolveParam(keyPath, payload)
      let source = walk(currentState, tiers)
      let args = [payload, source].concat(deps.map((dp) => {
        return walk(currentState, resolveParam(dp, payload))
      }))
      args.push(function resolve(target){

        currentState = deepMerge(tiers, currentState, target)
        Object.keys(broadcastMap).forEach((path) => {
          if(keyPath.indexOf(path) > 0){
            broadcastMap[path].forEach((subcriber) => {
              subcriber(payload, {trigger:false})
            })
          }
        })
        if(options.trigger !== false){
          emitter.emit(evName, currentState)
        }
      })
      return fn.apply(null, args)
    }
    action.listenTo = (path) => {
      var subcribers;
      if(!broadcastMap[path]){
        subcribers = broadcastMap[path] = [action]
      }else{
        subcribers = broadcastMap[path]
      }
      return action
    }

    return action
  }
  return {
    createAction,
    subscribe,
    getState
  }
}