import React, { useState } from 'react';
import ReactDOM from 'react-dom';

import { createContext, useContextSelector } from 'use-context-selector';

const context = createContext(null);

const Counter1 = () => {
  const count1 = useContextSelector(context, v => v[0].count1);
  const setState = useContextSelector(context, v => v[1]);
  const increment = () => setState(s => ({
    ...s,
    count1: s.count1 + 1,
  }));
  return (
    <div>
      {Math.random()}
      <span>Count1: {count1}</span>
      <button type="button" onClick={increment}>+1</button>
    </div>
  );
};

const Counter2 = () => {
  const count2 = useContextSelector(context, v => v[0].count2);
  const setState = useContextSelector(context, v => v[1]);
  const increment = () => setState(s => ({
    ...s,
    count2: s.count2 + 1,
  }));
  return (
    <div>
      {Math.random()}
      <span>Count2: {count2}</span>
      <button type="button" onClick={increment}>+1</button>
    </div>
  );
};

const StateProvider = ({ children }) => {
  const [state, setState] = useState({ count1: 0, count2: 0 });
  return (
    <context.Provider value={[state, setState]}>
      {children}
    </context.Provider>
  );
};

const App = () => (
  <StateProvider>
    <Counter1 />
    <Counter2 />
  </StateProvider>
);

ReactDOM.render(<App />, document.getElementById('app'));