jquense · November 1, 2018 18:39 · Nov 1, 2018
diff --git a/createStore.js b/createStore.js
@@ -0,0 +1,105 @@
+import React, { useReducer, useContext, useMemo } from 'react'
+import get from 'lodash/get'
+import invariant from 'invariant'
+
+const INIT = {
+  type: `INIT${Math.random()
+    .toString(36)
+    .substring(7)
+    .split('')
+    .join('.')}`,
+}
+
+function compose(funcs) {
+  if (funcs.length === 0) return arg => arg
+  if (funcs.length === 1) return funcs[0]
+  return funcs.reduce((a, b) => (...args) => a(b(...args)))
+}
+
+export function bindActionCreators(actionCreators, dispatch) {
+  if (typeof actionCreators === 'function')
+    return (...args) => dispatch(actionCreators(...args))
+
+  const boundActionCreators = {}
+  for (const [key, actionCreator] of Object.entries(actionCreators)) {
+    if (typeof actionCreator === 'function')
+      boundActionCreators[key] = (...args) => dispatch(actionCreator(...args))
+  }
+
+  return boundActionCreators
+}
+
+export const combineReducers = reducers => {
+  const entries = Object.entries(reducers)
+
+  return (state = {}, action, parentPath = 'root') => {
+    let hasChanged = false
+
+    const nextState = {}
+    for (let [key, reducer] of entries) {
+      const path = `${parentPath}.${key}`
+      const prevStateKey = state[key]
+      const nextStateKey = reducer(prevStateKey, action, __DEV__ && path)
+      invariant(
+        nextStateKey !== undefined,
+        action.type === INIT.type
+          ? `Could not initialize state for reducer key: '${path}', return an initial state value or null for an empty state`
+          : `Reducer at '${path}' did not return a state value, use null for an empty state`
+      )
+      nextState[key] = nextStateKey
+      hasChanged = hasChanged || nextStateKey !== prevStateKey
+    }
+
+    return hasChanged ? nextState : state
+  }
+}
+
+const applyMiddleware = (middlewares, dispatch) => {
+  return compose(middlewares.map(m => m(dispatch)))(dispatch)
+}
+
+export default (reducers, initialState = {}, middleware) => {
+  const StateContext = React.createContext({})
+  const DispatchContext = React.createContext()
+
+  const reducer = combineReducers(reducers)
+
+  initialState = reducer(initialState, INIT)
+
+  function useStoreDispatch() {
+    return useContext(DispatchContext)
+  }
+
+  function useBoundActions(actionsToBind) {
+    const dispatch = useStoreDispatch()
+    return useMemo(() => bindActionCreators(actionsToBind, dispatch), [
+      actionsToBind,
+    ])
+  }
+
+  function useStoreState(key) {
+    const state = useContext(StateContext)
+    return key ? get(state, key) : state
+  }
+
+  function Provider({ children }) {
+    const [state, baseDispatch] = useReducer(reducer, initialState)
+
+    const dispatch = useMemo(() => applyMiddleware(middleware, baseDispatch), [
+      baseDispatch,
+    ])
+
+    return (
+      <DispatchContext.Provider value={dispatch}>
+        <StateContext.Provider value={state}>{children}</StateContext.Provider>
+      </DispatchContext.Provider>
+    )
+  }
+
+  return {
+    useBoundActions,
+    useStoreDispatch,
+    useStoreState,
+    Provider,
+  }
+}