import { Component } from 'react'
import { createStore, combineReducers } from 'redux'
import parseLinkHeader from 'parse-link-header'

const START = 'start'
const SUCCEED = 'succeed'
const ERROR = 'error'

const inflight = (state={}, action) => (
  ((state) => (
    action.type === START ? (
      (state[action.pathname] = true, state)
    ) : action.type === SUCCEED || action.type === ERROR ? (
      (delete state[action.pathname], state)
    ) : state
  ))({ ...state })
)

const links = (state={}, action) => (
  ((state) => (
    action.type === SUCCEED ? (
      (state[action.pathname] = action.link, state)
    ) : action.type === ERROR ? (
      (delete state[action.pathname], state)
    ) : state
  ))({ ...state })
)

const data = (state={}, action) => (
  ((state) => (
    action.type === SUCCEED ? (
      (state[action.pathname] = action.data, state)
    ) : action.type === ERROR ? (
      (delete state[action.pathname], state)
    ) : state
  ))({ ...state })
)

const errors = (state={}, action) => (
  ((state) => (
    action.type === ERROR ? (
      (state[action.pathname] = action.error)
    ) : action.type === START ? (
      (delete state[action.pathname], state)
    ) : state
  ))({ ...state })
)

const store = createStore(combineReducers({
  inflight,
  data,
  errors,
  links
}))

const stringify = (obj) => (
  Object.keys(obj).map((key) => (
    `${key}=${obj[key]}`
  )).join('&')
)

class Fetch extends Component {

  state = {
    error: null,
    data: null,
    loading: null
  }

  componentWillUnmount() {
    this.unmounted = true
  }

  componentDidMount() {
    store.subscribe(() => {
      if (!this.unmounted) {
        const { errors, inflight, data, links } = store.getState()
        const pathname = this.getPathname()
        this.setState({
          error: errors[pathname] || null,
          data: data[pathname] || null,
          loading: inflight[pathname] || null,
          links: links[pathname] || null
        })
      }
    })
    this.fetch()
  }

  componentWillReceiveProps(nextProps) {
    const nextPathname = this.getPathname(nextProps)
    const currentPathname = this.getPathname()
    if (nextPathname !== currentPathname) {
      this.fetch(nextProps)
    }
  }

  getPathname(props) {
    const { url, query } = props || this.props
    let pathname = url
    if (query)
      pathname += '?'+stringify(query)
    return pathname
  }

  fetch(props) {
    const pathname = this.getPathname(props)
    const { inflight, data } = store.getState()
    const alreadyCached = data[pathname]
    const alreadyInFlight = inflight[pathname]
    if (!alreadyCached && !alreadyInFlight) {
      store.dispatch({ type: START, pathname })
      fetch(pathname).then(res => {
        const link = res.headers.get('Link')
        const json = res.json()
        return Promise.all([ json, link ? parseLinkHeader(link) : null ])
      }).then(([ data, link ]) => {
        store.dispatch({ type: SUCCEED, pathname, data, link })
      }, (error) => (
        store.dispatch({ type: ERROR, pathname, error })
      ))
    }
  }

  render() {
    return this.props.children(this.state)
  }
}

export default Fetch