Mailspring/app/internal_packages/thread-list/lib/message-list-toolbar.jsx

import React from 'react';
import PropTypes from 'prop-types';
import ReactCSSTransitionGroup from 'react-addons-css-transition-group';
import { Rx, FocusedContentStore } from 'nylas-exports';
import ThreadListStore from './thread-list-store';
import InjectsToolbarButtons, { ToolbarRole } from './injects-toolbar-buttons';

function getObservable() {
  return Rx.Observable
    .combineLatest(
      Rx.Observable.fromStore(FocusedContentStore),
      ThreadListStore.selectionObservable(),
      (store, items) => ({ focusedThread: store.focused('thread'), items })
    )
    .map(({ focusedThread, items }) => {
      if (focusedThread) {
        return [focusedThread];
      }
      return items;
    });
}

const MessageListToolbar = ({ items, injectedButtons }) => {
  const shouldRender = items.length > 0;

  return (
    <ReactCSSTransitionGroup
      className="message-toolbar-items"
      transitionLeaveTimeout={125}
      transitionEnterTimeout={125}
      transitionName="opacity-125ms"
    >
      {shouldRender ? injectedButtons : undefined}
    </ReactCSSTransitionGroup>
  );
};
MessageListToolbar.displayName = 'MessageListToolbar';
MessageListToolbar.propTypes = {
  items: PropTypes.array,
  injectedButtons: PropTypes.element,
};

const toolbarProps = {
  getObservable,
  extraRoles: [`MessageList:${ToolbarRole}`],
};

export default InjectsToolbarButtons(MessageListToolbar, toolbarProps);