import * as React from 'react';
import { ConsumerProps, Context, ProviderProps } from 'create-react-context';

function onlyChild(children: any): any {
  return Array.isArray(children) ? children[0] : children;
}

export function combineContext<In extends { [key: string]: any }>(
  contexts: { [K in keyof In]: Context<In[K]> }
): Context<{ [K in keyof In]: In[K] }> {
  class Provider extends React.Component<ProviderProps<{ [K in keyof In]: In[K] }>> {
    render() {
      const init = this.props.children;
      return Object.keys(contexts).reduce((acc, contextName) => {
        const TheContext = contexts[contextName];
        return <TheContext.Provider value={this.props.value[contextName]}>{acc}</TheContext.Provider>;
      }, init);
    }
  }

  class Consumer extends React.Component<ConsumerProps<{ [K in keyof In]: In[K] }>> {
    render() {
      const init = (value: { [K in keyof In]: In[K] }) => onlyChild(this.props.children)(value);
      const renderer = Object.keys(contexts).reduce<(value: { [K in keyof In]: In[K] }) => any>((acc, contextName) => {
        const TheContext = contexts[contextName];
        return (value: { [K in keyof In]: In[K] }) => (
          <TheContext.Consumer>
            {contextValue => {
              return acc({
                ...(value as any),
                [contextName]: contextValue,
              });
            }}
          </TheContext.Consumer>
        );
      }, init);
      return renderer({} as any);
    }
  }

  return {
    Consumer,
    Provider,
  };
}