discourse/app/controllers/groups_controller.rb

class GroupsController < ApplicationController

  def show
    render_serialized(find_group(:id), BasicGroupSerializer)
  end

  def counts
    group = find_group(:group_id)
    render json: {counts: { posts: group.posts_for(guardian).count,
                            members: group.users.count } }
  end

  def posts
    group = find_group(:group_id)
    posts = group.posts_for(guardian, params[:before_post_id]).limit(20)
    render_serialized posts.to_a, GroupPostSerializer
  end

  def members
    group = find_group(:group_id)
    render_serialized(group.users.order('username_lower asc').limit(200).to_a, GroupUserSerializer)
  end

  private

  def find_group(param_name)
    name = params.require(param_name)
    group = Group.find_by("lower(name) = ?", name.downcase)
    guardian.ensure_can_see!(group)
    group
  end

end