class CreateComments < ActiveRecord::Migration
  def change
    create_table :comments do |t|
      t.text :content
      t.references :commentable, polymorphic: true, index: true
      t.references :author, index: true

      t.timestamps null: false
    end

    add_foreign_key :comments, :users, column: :author_id
  end
end

class Comment < ActiveRecord::Base
  belongs_to :author, class_name: "User"
  belongs_to :commentable, polymorphic: true

  validates :text, presence: true

  default_scope -> { order(created_at: "desc") }
  scope :persisted, lambda { where.not(id: nil) }

end

class CommentsController < ApplicationController
  before_action :set_post

  def create
    @comment = @commentable.comments.new(comment_params)
    @comment.author = current_user
    authorize @comment, :create?

    if @comment.save
     flash[:notice] = "Comment has been created."
     redirect_to @commentable
    else
     flash.now[:alert] = "Comment has not been created."
     render "posts/show"
    end
 end


  private

  def set_post
    @post = Post.find(params[:post_id])
  end

  def comment_params
    params.require(:comment).permit(:text)
  end
end

.
.
.
#comments
  = render partial: "comments/form", locals: {commentable: @post}

  - if @post.comments.persisted.any?
    h4
      = t(:available_comments, count: @post.comments.count)
    = render partial: "comments/comments", locals: {commentable: @post}
  - else
    p
      There are no comments for this post.

.header
      h3 New Comment

    = simple_form_for [commentable, Comment.new] do |f|
      .form-group
        = f.input :content, label: "Comment", placeholder: "Add a comment", input_html: { rows: 6 }
      = f.submit class: "btn btn-primary"
    <br>

resources :posts, only: [:index, :show, :edit, :update]

  resources :posts, only: [] do
    resources :comments, only: [:create], module: :posts
  end

class Posts::CommentsController < CommentsController
  before_action :set_commentable

  private

  def set_commentable
    @commentable = Post.find(params[:post_id])
  end
end

class Role < ActiveRecord::Base
  belongs_to :user
  belongs_to :post

  def self.available_roles
    %w(manager editor viewer)
  end
end

FactoryGirl.define do
  factory :comment do
    content { "A comment!" }

    trait :post_comment do
      association :commentable, factory: :post
      #commentable_type 'Post'
      association :author_id, factory: :user
    end
  end
end

class CommentPolicy < ApplicationPolicy
  class Scope < Scope
   def resolve
     scope
   end
  end

 def create?
    user.try(:admin?) || record.commentable.has_manager?(user)
 end
end

require 'rails_helper'
    RSpec.describe CommentPolicy do
      context "permissions" do
        subject { CommentPolicy.new(user, comment) }

        let(:user) { create(:user) }
        let(:post) { create(:post)}
        let(:post_comment) { create(:comment, :post_comment)}

        context "for anonymous users" do
          let(:user) { nil }
          it { should_not permit_action :create }
        end

        context "for viewers of the post_comment" do
          before { assign_role!(user, :viewer, post) }
          it { should_not permit_action :create }
        end

        context "for editors of the post" do
          before { assign_role!(user, :editor, post) }
          it { should permit_action :create }
        end

        context "for managers of the post" do
          before { assign_role!(user, :manager, post) }
          it { should permit_action :create }
        end

        context "for managers of other post" do
          before do
            assign_role!(user, :manager, create(:post))
          end
          it { should_not permit_action :create }
        end

        context "for administrators" do
          let(:user) { create(:user, :admin) }
          it { should permit_action :create }
        end
      end

    end

`rspec spec/policies/comment_policy_spec.rb`
Run options: exclude {:slow=>true}
FFFFFF

Failure/Error: subject { CommentPolicy.new(user, comment) }

     NameError:
       undefined local variable or method `comment' for #<RSpec::ExampleGroups::CommentPolicy::Permissions::.....

Run options: exclude {:slow=>true}
FFFFF.
Failure/Error: user.try(:admin?) || record.commentable.has_manager?(user)

     NoMethodError:
       undefined method `commentable' for #<Post:0x007f9cc3dba328>
       Did you mean?  comments

class Comment < ActiveRecord::Base
  belongs_to :commentable, polymorphic: true
  #etc...
end

class Post < ActiveRecord::Base
  has_many :comments, as: :commentable, dependent: :destroy
  #etc...
end

belongs_to :post
belongs_to :commentable, polymorphic: true

@post.comments.build
#this will set comment.commentable_id = @post.id, and comment.commentable_type = "Post"
#but will not set comment.post_id

scope.joins(:roles).where(roles: {user_id: user}

scope.joins(:roles).where(roles: {user_id: user.id}