Extending NX generate component

In my Monorepo, there are two types of components that i am using.

1. Is a standard component for applications, and nx g c foo works fine here.
2. Is a library component for a library. Here, I exclusively use secondary entry points. So a component always has an index.ts, a public_api.ts, a bar.module.ts and a package.json file.

My question is, how could I extend the standard functionality of the nx g c foo, so that it automatically creates these files?

You probably want to write your own schematics collection.
Please check documentation, some nice articles and sources.
Basically your extending code from new component schematic will look like this:

import { chain, externalSchematic, Rule } from '@angular-devkit/schematics';

export default function(schema: any): Rule {
    // add your custom code here

    return chain([
        externalSchematic('@nrwl/schematics', 'module', {
          ...module options
        }),
        externalSchematic('@nrwl/schematics', 'component', {
          ...component options
        }),

        // and here
    ]);
}

UPD

The same written using nx generators API:

import { wrapAngularDevkitSchematic } from '@nrwl/devkit/ngcli-adapter';
import {
  Tree,
  formatFiles,
  generateFiles,
  joinPathFragments,
  names,
} from '@nrwl/devkit';
// this is your custom generator schema
import { Schema } from './models/schema.model';

export default async function (tree: Tree, schema: Schema) {
  const moduleGenerator = wrapAngularDevkitSchematic(
    '@schematics/angular',
    'module'
  );
  const componentGenerator = wrapAngularDevkitSchematic(
    '@schematics/angular',
    'component'
  );

  // it will create a custom module for you
  await moduleGenerator(tree, {
    name: ...module name,
    project: ...project to add module,
    path: ...path to add module file,
  });

  // it will create a custom component for you
  await componentGenerator(tree, {
    name: ...your name,
    project: ...project to add component,
  });

  // it's a branch where you can add your package.json and index.ts
  // you should create template files for them in ./files folder
  generateFiles(
    tree, // the virtual file system
    joinPathFragments(__dirname, './files'), // path to the file templates
    joinPathFragments('libs/'), // destination path of the files
    {
      ...schema,
      ...names(schema.name),
      tmpl: '',
    } // config object to replace variable in file templates
  );


  return tree;
}

See their tests for more examples.