/* @flow */

import * as React from 'react';
import deepmerge from 'deepmerge';
import createThemeProvider from './createThemeProvider';
import createWithTheme from './createWithTheme';
import type { WithThemeType } from './createWithTheme';
import type { ThemeProviderType } from './createThemeProvider';
import type { $DeepShape } from './types';

export type ThemingType<T> = {
  ThemeProvider: ThemeProviderType<T>,
  withTheme: WithThemeType<T>,
};

export default function createTheming<T: Object>(
  defaultTheme: T
): ThemingType<T> {
  const ThemeContext: React.Context<T> = React.createContext(defaultTheme);

  const ThemeProvider: ThemeProviderType<T> = createThemeProvider(
    defaultTheme,
    ThemeContext
  );

  const withTheme: WithThemeType<T> = createWithTheme(
    ThemeProvider,
    ThemeContext
  );

  const useTheme = (overrides?: $DeepShape<T>): T => {
    const theme = React.useContext(ThemeContext);
    const result = React.useMemo(
      () =>
        theme && overrides ? deepmerge(theme, overrides) : theme || overrides,
      [theme, overrides]
    );

    return result;
  };

  return {
    ThemeProvider,
    withTheme,
    useTheme,
  };
}