const history = require('sheet-router/history')
const sheetRouter = require('sheet-router')
const document = require('global/document')
const href = require('sheet-router/href')
const sendAction = require('send-action')
const assert = require('assert')
const xtend = require('xtend')
const yo = require('yo-yo')

choo.view = yo
module.exports = choo

// framework for creating sturdy web applications
// null -> fn
function choo () {
  const _models = []
  var _router = null

  start.toString = toString
  start.router = router
  start.model = model
  start.start = start

  return start

  // render the application to a string
  // (str, obj) -> str
  function toString (route, state) {
    const initialState = {}

    _models.forEach(function (model) {
      if (model.state) apply(model.name, model.state, initialState)
    })

    const tree = _router(route, xtend(initialState, state), function () {
      throw new Error('send() cannot be called on the server')
    })

    return tree.toString()
  }

  // start the application
  // obj -> DOMNode
  function start (opts) {
    opts = opts || {}
    const name = opts.name || 'choo'
    const initialState = {}
    const reducers = {}
    const effects = {}

    _models.push(appInit(opts))
    _models.forEach(function (model) {
      if (model.state) apply(model.namespace, model.state, initialState)
      if (model.reducers) apply(model.namespace, model.reducers, reducers)
      if (model.effects) apply(model.namespace, model.effects, effects)
    })

    // send() is used to trigger actions inside
    // views, effects and subscriptions
    const send = sendAction({
      onaction: handleAction,
      onchange: onchange,
      state: initialState
    })

    // subscriptions are loaded after sendAction() is called
    // because they both need access to send() and can't
    // react to actions (read-only)
    _models.forEach(function (model) {
      if (model.subscriptions) {
        assert.ok(Array.isArray(model.subscriptions, 'subs must be an array'))
        model.subscriptions.forEach(function (sub) {
          sub(send)
        })
      }
    })

    // the rootId is determined to find the application root
    // on update. Since the DOM nodes change between updates,
    // we must call document.querySelector() to find the root.
    // Use different names when loading multiple choo applications
    // on the same page
    const rootId = name + '-root'
    const tree = _router(send.state().app.location, send.state(), send)
    tree.setAttribute('id', rootId)
    return tree

    // handle an action by either reducers, effects
    // or both - return the new state when done
    // (obj, obj, fn) -> obj
    function handleAction (action, state, send) {
      var reducersCalled = false
      var effectsCalled = false

      // validate if a namespace exists. Namespaces
      // are delimited by the first ':'. Perhaps
      // we'll allow recursive namespaces in the
      // future - who knows
      if (/:/.test(action.type)) {
        const arr = action.type.split(':')
        var ns = arr.shift()
        action.type = arr.join(':')
      }

      const _reducers = ns ? reducers[ns] : reducers
      if (_reducers && _reducers[action.type]) {
        if (ns) {
          const newState = _reducers[action.type](action, state[ns])
          state[ns] = xtend(state[ns], newState)
        } else state = xtend(state, reducers[action.type](action, state))
        reducersCalled = true
      }

      const _effects = ns ? effects[ns] : effects
      if (_effects && _effects[action.type]) {
        if (ns) _effects[action.type](action, state[ns], send)
        else _effects[action.type](action, state, send)
        effectsCalled = true
      }

      if (!reducersCalled && !effectsCalled) {
        throw new Error('Could not find action ' + action.type)
      }

      return state
    }

    // update the DOM after every state mutation
    // (obj, obj) -> null
    function onchange (action, state) {
      const oldTree = document.querySelector('#' + rootId)
      const newTree = _router(state.app.location, state, send)
      newTree.setAttribute('id', rootId)
      yo.update(oldTree, newTree)
    }
  }

  // register all routes on the router
  // [obj|fn] -> null
  function router (cb) {
    _router = sheetRouter(cb)
    return _router
  }

  // create a new model
  // (str?, obj) -> null
  function model (model) {
    _models.push(model)
  }
}

// initial application state model
// obj -> obj
function appInit (opts) {
  const model = {
    namespace: 'app',
    state: { location: document.location.href },
    subscriptions: [],
    reducers: {
      // handle href links
      location: function setLocation (action, state) {
        return {
          location: action.location.replace(/#.*/, '')
        }
      }
    }
  }

  // enable catching <href a=""></href> links
  // enable HTML5 history API
  if (opts.history !== false) pushLocationSub(href)
  if (opts.history !== false) pushLocationSub(history)

  return model

  // create a new subscription that modifies
  // 'app:location' and push it to be loaded
  // fn -> null
  function pushLocationSub (cb) {
    model.subscriptions.push(function (send) {
      cb(function (href) {
        send('app:location', { location: href })
      })
    })
  }
}

// compose an object conditionally
// optionally contains a namespace
// which is used to nest properties.
// (str, obj, obj) -> null
function apply (ns, source, target) {
  Object.keys(source).forEach(function (key) {
    if (ns) {
      if (!target[ns]) target[ns] = {}
      target[ns][key] = source[key]
    } else target[key] = source[key]
  })
}