import invariant from 'fbjs/lib/invariant';

/**
 * Make sure the config passed e.g. to StackRouter, TabRouter has
 * the correct format, and throw a clear error if it doesn't.
 */
function validateRouteConfigMap(routeConfigs: NavigationRouteConfigMap) {
  const routeNames = Object.keys(routeConfigs);
  invariant(
    routeNames.length > 0,
    'Please specify at least one route when configuring a navigator.'
  );

  routeNames.forEach((routeName: string) => {
    const routeConfig = routeConfigs[routeName];

    invariant(
      routeConfig.screen || routeConfig.getScreen,
      `Route '${routeName}' should declare a screen. ` +
      'For example:\n\n' +
      'import MyScreen from \'./MyScreen\';\n' +
      '...\n' +
      `${routeName}: {\n` +
      '  screen: MyScreen,\n' +
      '}'
    );

    if (routeConfig.screen && routeConfig.getScreen) {
      invariant(false,
        `Route '${routeName}' should declare a screen or ` +
        'a getScreen, not both.'
      );
    }

    if (routeConfig.screen) {
      invariant(
        typeof (routeConfig.screen) === 'function',
        `The component for route '${routeName}' must be a ` +
        'a React component. For example:\n\n' +
        'import MyScreen from \'./MyScreen\';\n' +
        '...\n' +
        `${routeName}: {\n` +
        '  screen: MyScreen,\n' +
        '}\n\n' +
        'You can also use a navigator:\n\n' +
        'import MyNavigator from \'./MyNavigator\';\n' +
        '...\n' +
        `${routeName}: {\n` +
        '  screen: MyNavigator,\n' +
        '}'
      );
    }
  });
}

export default validateRouteConfigMap;