implement category subscriptions

app/controllers/categories_controller.rb

@@ -1,10 +1,36 @@
 class CategoriesController < ApplicationController
+  before_action :authenticate_user!, only: [:subscribe, :unsubscribe]
+  before_action :find_category, only: [:show, :subscribe, :unsubscribe]
+
   def index
     @categories = Category.order(:name)
   end
 
   def show
-    @category  = Category.find_by_permalink! params[:permalink]
     @questions = @category.questions.includes(:answers, :author).recent.page(params[:page]).per(20)
   end
+
+  def subscribe
+    current_user.subscribe_to @category
+
+    respond_to do |format|
+      format.html { redirect_to @category }
+      format.js
+    end
+  end
+
+  def unsubscribe
+    current_user.unsubscribe_from @category
+
+    respond_to do |format|
+      format.html { redirect_to @category }
+      format.js
+    end
+  end
+
+  private
+
+  def find_category
+    @category = Category.find_by_permalink! params[:permalink]
+  end
 end

app/helpers/categories_helper.rb

@@ -0,0 +1,15 @@
+module CategoriesHelper
+  def link_to_category_subscription(category)
+    return link_to('subscribe', new_user_session_path) unless user_signed_in?
+
+    if current_user.subscribed_to? category
+      title = 'unsubscribe'
+      path = unsubscribe_category_path(category)
+    else
+      title = 'subscribe'
+      path = subscribe_category_path(category)
+    end
+
+    link_to title, path, method: :post, remote: true, class: 'btn btn-primary', data: { category_id: category.id }
+  end
+end

app/models/category.rb

@@ -2,6 +2,7 @@ class Category < ActiveRecord::Base
   acts_as_url :name, url_attribute: :permalink
 
   has_many :questions, dependent: :destroy
+  has_many :subscriptions, as: :subscribable, dependent: :destroy
 
   validates :name, presence: true
 

app/models/user.rb

@@ -24,6 +24,24 @@ def to_param
     username
   end
 
+  def subscribe_to(subscribable)
+    subscriptions.create(subscribable: subscribable) unless subscribed_to?(subscribable)
+  end
+
+  def unsubscribe_from(subscribable)
+    subscriptions.where(
+      subscribable_id: subscribable.id,
+      subscribable_type: subscribable.class
+    ).destroy_all if subscribed_to?(subscribable)
+  end
+
+  def subscribed_to?(subscribable)
+    subscriptions.where(
+      subscribable_id: subscribable.id,
+      subscribable_type: subscribable.class
+    ).any?
+  end
+
   private
 
   def self.find_for_database_authentication(warden_conditions)

app/views/categories/show.html.slim

@@ -6,9 +6,12 @@
       h2 = link_to @category.name, @category
       p No questions in this category.
     - else
-      h2
-        ' Recent questions in
-        = link_to @category.name, @category
+      .clearfix
+        h2.pull-left
+          ' Recent questions in
+          = link_to @category.name, @category
+        .pull-right
+          = link_to_category_subscription(@category)
 
       .question-list
         = render partial: 'questions/question', collection: @questions

app/views/categories/subscribe.js.erb

@@ -0,0 +1 @@
+$('a[data-category-id=<%= @category.id %>]').replaceWith('<%= escape_javascript(link_to_category_subscription @category) %>');

app/views/categories/unsubscribe.js.erb

@@ -0,0 +1 @@
+$('a[data-category-id=<%= @category.id %>]').replaceWith('<%= escape_javascript(link_to_category_subscription @category) %>');

config/routes.rb

@@ -17,6 +17,13 @@
     end
   end
 
+  concern :subscribable do
+    member do
+      post :subscribe
+      post :unsubscribe
+    end
+  end
+
   get '/ask', to: redirect('/questions/new')
   get '/q/:id', to: redirect('/questions/%{id}'), as: :question_short
   get '/settings', to: redirect('/settings/profile')
@@ -33,7 +40,7 @@
   end
 
   resources :tags, only: [:show], param: :name
-  resources :categories, only: [:index, :show], param: :permalink
+  resources :categories, only: [:index, :show], param: :permalink, concerns: :subscribable
   resources :users, only: [:show], param: :username do
     member do
       get :answers

spec/controllers/categories_controller_spec.rb

@@ -2,6 +2,7 @@
 
 RSpec.describe CategoriesController, type: :controller do
   let(:category) { create :category }
+  let(:user)     { create :confirmed_user }
 
   describe "GET #index" do
     it "returns http success" do
@@ -16,4 +17,57 @@
       expect(response).to be_success
     end
   end
+
+  describe "POST #subscribe" do
+    context "when not signed in" do
+      it "redirects to sign in page" do
+        post :subscribe, permalink: category.permalink
+        expect(response).to redirect_to(new_user_session_path)
+      end
+    end
+
+    context "when signed in" do
+      before { sign_in user }
+
+      it "subscribes user to category and redirects to category page" do
+        expect {
+          post :subscribe, permalink: category.permalink
+        }.to change(category.subscriptions, :count).by(1)
+        expect(response).to redirect_to(category)
+      end
+
+      it "returns http success for remote request" do
+        xhr :post, :subscribe, permalink: category.permalink
+        expect(response).to be_success
+      end
+    end
+  end
+
+  describe "POST #unsubscribe" do
+    context "when not signed in" do
+      it "redirects to sign in page" do
+        post :unsubscribe, permalink: category.permalink
+        expect(response).to redirect_to(new_user_session_path)
+      end
+    end
+
+    context "when signed in" do
+      before do
+        sign_in user
+        user.subscriptions.create subscribable: category
+      end
+
+      it "unsubscribes user from category and redirects to category page" do
+        expect {
+          post :unsubscribe, permalink: category.permalink
+        }.to change(category.subscriptions, :count).by(-1)
+        expect(response).to redirect_to(category)
+      end
+
+      it "returns http success for remote request" do
+        xhr :post, :unsubscribe, permalink: category.permalink
+        expect(response).to be_success
+      end
+    end
+  end
 end

spec/factories/subscriptions.rb

@@ -1,6 +1,9 @@
 FactoryGirl.define do
   factory :subscription do
     subscriber
-    # association :subscribable, factory: :category
+  end
+
+  factory :category_subscription, parent: :subscription do
+    association :subscribable, factory: :category
   end
 end

spec/models/user_spec.rb

@@ -1,6 +1,9 @@
 require 'rails_helper'
 
 RSpec.describe User, type: :model do
+  let(:user)     { create :confirmed_user }
+  let(:category) { create :category }
+
   describe "relations" do
     it { should have_many(:answers).conditions(anonymous: false).
       with_foreign_key('author_id').dependent(:destroy) }
@@ -19,4 +22,35 @@
     it { should allow_value('', nil).for(:fullname) }
     it { should validate_length_of(:bio).is_at_most(400) }
   end
+
+  describe "#subscribe_to" do
+    it "subscribes user to subscribable" do
+      subscribable = category
+      expect { user.subscribe_to(subscribable) }.to change(user.subscriptions, :count).by(1)
+
+      subscription = user.subscriptions.last
+      expect(subscription.subscribable_id).to eq(subscribable.id)
+      expect(subscription.subscribable_type).to eq(subscribable.class.to_s)
+      expect(subscription.subscriber_id).to eq(user.id)
+    end
+  end
+
+  describe "#unsubscribe_from" do
+    it "unsubscribes user from subscribable" do
+      subscribable = category
+      create :subscription, subscribable: subscribable, subscriber: user
+
+      expect { user.unsubscribe_from(subscribable) }.to change(user.subscriptions, :count).by(-1)
+    end
+  end
+
+  describe "#subscribed_to?" do
+    it "checks if user subscribed to subscribable" do
+      create :subscription, subscribable: category, subscriber: user
+      category2 = create :category
+
+      expect(user.subscribed_to?(category)).to be true
+      expect(user.subscribed_to?(category2)).to be false
+    end
+  end
 end