articles_controller.rb

class ArticlesController < ApplicationController
  before_action :authorized, only: [:new, :create, :upvote, :downvote]
  helper_method :article

  def index
    @articles = Article.order(created_at: :desc).page(params[:page]).per(20)
    @user_votes = Vote.where(user: current_user, votable: @articles.to_a).index_by(&:votable_id)
  end

  def show
    @comments = article.comments.without_parent.order(created_at: :desc)
    @comment = Comment.new
  end

  def upvote
    vote(1)
    respond_to do |format|
      format.json { render json: {new_score: article.score} }
    end
  end

  def downvote
    vote(-1)
    respond_to do |format|
      format.json { render json: {new_score: article.score} }
    end
  end

  def new
    @article = Article.new
  end

  def create
    @article = Article.new(article_params)
    article.user = current_user

    if article.save
      redirect_to article
    else
      render :new, status: :unprocessable_entity
    end
  end

  private

  def article
    @article ||= Article.find(params[:id])
  end

  def article_params
    params.require(:article).permit(:title, :link)
  end

  def vote(value)
    vote = article.votes.find_or_initialize_by(user: current_user)
    if vote.value == value
      vote.update(value: 0)
    else
      vote.update(value: value)
    end
  end
end