import React, { createContext, useContext, useMemo, useReducer } from 'react'

/** Takes options that fully define a store and turns it into a more potent reducer */
export const usePotentReducer = options => {
  const { reducer = {}, thunks = {}, initialState } = options
  const { onUpdate, logging } = options
  const reducerFn = useMemo(
    () => makeReducerFn(reducer, { onUpdate, logging }),
    [reducer, onUpdate, logging]
  )
  const [state, dispatch] = useReducer(reducerFn, initialState)
  const _thunks = useMemo(() => bindThunks(thunks, dispatch), [
    thunks,
    dispatch
  ])
  return [state, _thunks]
}

/** A ReducerStore Factory that uses React.context
 * Used to make a Store accessible through multiple components
 */
export const createStore = options => {
  const context = createContext(null)
  const Provider = ({ children }) => {
    const store = usePotentReducer(options)
    return React.createElement(context.Provider, { value: store }, children)
  }
  const useStore = () => useContext(context)
  const useSelector = selector => selector(useContext(context)[0])
  return { Provider, Consumer: context.Consumer, useStore, useSelector }
}

/** Turn a reducer definition object to a function
 * @param {Object} reducer: Object definition of a reducer: {<type>: (state, payload) => <newState>}
 * @returns {Function}: Proper reducer
 */
function makeReducerFn(reducer, { onUpdate, logging }) {
  const noop = state => state
  return (prevState, action) => {
    const { type, ...payload } = action
    const reducerBranch = reducer[type] || reducer['default'] || noop
    const nextState = reducerBranch(prevState, payload)
    const stats = { prevState, nextState, action }
    typeof onUpdate === 'function' && onUpdate(stats)
    if (logging) logger(stats)
    return nextState
  }
}

/** Returns a set of actions that are bound to the store
 * @param {Object} actions: {<name>: payload => ({dispatch, type}) => }
 */
function bindThunks(thunks, dispatch) {
  const _thunks = {}
  for (let name of Object.keys(thunks)) {
    const defaultType = camelToSnakeCase(name).toUpperCase()
    _thunks[name] = (...args) =>
      thunks[name](...args)(patchDispatch(dispatch, defaultType))
  }
  return _thunks
}

const camelToSnakeCase = str =>
  str.replace(/[A-Z]/g, letter => `_${letter.toLowerCase()}`)

/** Returns a dispatch function that fills in a default type if none is given */
function patchDispatch(dispatch, type) {
  return action => {
    dispatch({ type, ...action })
  }
}

/** Log action inspired by redux-logger */
const logger = ({ prevState, action, nextState }) => {
  const css = color => `color: ${color}; font-weight: bold;`
  console.groupCollapsed(`%c action`, 'color: #9E9E9E', action.type)
  console.log('%c prevState ', css('#9E9E9E'), prevState)
  console.log('%c action    ', css('#03A9F4'), action)
  console.log('%c nextState ', css('#4CAF50'), nextState)
  console.groupEnd()
}