diff --git a/app/controllers/application_controller.rb b/app/controllers/application_controller.rb
index d83690e..9cffe66 100644
--- a/app/controllers/application_controller.rb
+++ b/app/controllers/application_controller.rb
@@ -2,4 +2,65 @@ class ApplicationController < ActionController::Base
   # Prevent CSRF attacks by raising an exception.
   # For APIs, you may want to use :null_session instead.
   protect_from_forgery with: :exception
+  helper_method :current_user, :is_logined?, :current_user_is_admin?, :get_categories_options, :current_user_can_star?,
+                :current_user_can_edit_comment?, :markdown_parser
+
+  rescue_from Exception, with: :error_500 unless Rails.env.development?
+  rescue_from ActiveRecord::RecordNotFound, with: :error_404 unless Rails.env.development?
+
+  before_filter :current_user
+
+  def current_user
+    @current_user = nil
+    if session[:user_id].present?
+      @current_user = User.find(session[:user_id])
+      redirect_to logout_path(referer) unless @current_user
+    end
+    @current_user
+  end
+
+  def current_user_is_admin?
+    @current_user && @current_user.admin
+  end
+
+  def current_user_can_star?(article)
+    return false unless @current_user
+    !article.article_stars.find_by(user_id: @current_user.id).present?
+  end
+
+  def current_user_can_edit_comment?(comment)
+    return false unless @current_user
+    comment.user_id == @current_user.id
+  end
+
+  def get_categories_options
+    options = []
+    Category.order('articles_count desc').each {|c| options << [c.name, c.id]}
+    options
+  end
+
+  def markdown_parser(content)
+    markdown = Redcarpet::Markdown.new Redcarpet::Render::HTML, autolink: true, tables: true
+    markdown.render content
+  end
+
+  def referer
+    request.env['HTTP_REFERER'] || root_path
+  end
+
+  def is_logined?
+    session[:user_id].present? && session[:user_id]
+  end
+
+  def require_login
+    redirect_to root_path unless is_logined?
+  end
+
+  def error_500
+    render file: File.join(Rails.root, 'public/500.html'), status: 500, layout: false
+  end
+
+  def error_404
+    render file: File.join(Rails.root, 'public/404.html'), status: 404, layout: false
+  end
 end
diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index de6be79..dbabfe6 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -1,2 +1,27 @@
 module ApplicationHelper
+  def avatar(user)
+    user.avatar.present? ? image_tag(user.avatar) : (gravatar_image_tag user.email, alt: user.username)
+  end
+
+  def avatar_url(user)
+    user.avatar.present? ? user.avatar : (gravatar_image_url user.email, alt: user.username)
+  end
+
+  def get_categories
+    Category.order('articles_count desc')
+  end
+
+  def get_tags(article)
+    tags = article.tags || ''
+    tags.split(',')
+  end
+
+  def get_articles_count
+    Article.count
+  end
+
+  def blog_title
+    blog = BlogInfo.first
+    blog.present? ? blog.blog_title : 'Blog'
+  end
 end