Refactoring a controller action

after.rb

class CommentsController
  def create
    result = CreateComment.call(params, @user)
    if result.ok?
      render :partial => "comments/postedreply", :layout => false,
        :content_type => "text/html", :locals => { :comment => result.value }
    else
      case result.error.name
      when :story_not_found
        render :plain => "can't find story", :status => 400
      when :parent_comment_not_found
        render :json => { :error => "invalid parent comment", :status => 400 }
      when :duplicate_comment
        comment = result.error.comment
        comment.errors.add(:comment, "^You have already posted a comment here recently.")
        render :partial => "commentbox", :layout => false,
          :content_type => "text/html", :locals => { :comment => comment }
      else #:didnt_save
        preview result.error.comment
      end
    end
  end
end

module CreateComment
  extend self
  extend Resonad::Mixin

  Error = Struct.new(:name, :comment)

  def call(params, user)
    is_preview = params[:preview].present?

    find_story(params[:story_id])
      .and_then { |story| build_comment(params, story, user) }
      .and_then { |comment| prevent_duplicates(comment, is_preview) }
      .and_then { |comment| save_comment(comment, is_preview) }
  end

  private

  def find_story(story_id)
    story = Story.where(:short_id => story_id).first
    if story && !story.is_gone?
      Success(story)
    else
      Failure(Error.new(:story_not_found, nil))
    end
  end

  def build_comment(params, story, user)
    comment = story.comments.build
    comment.comment = params[:comment].to_s
    comment.user = user

    if params[:hat_id] && user.hats.where(:id => params[:hat_id])
      comment.hat_id = params[:hat_id]
    end

    if params[:parent_comment_short_id].present?
      parent = Comment.where(story_id: story.id, short_id: params[:parent_comment_short_id]).first
      if parent
        comment.parent_comment = parent
      else
        return Failure(Error.new(:parent_comment_not_found, comment))
      end
    end

    Success(comment)
  end

  def prevent_duplicates(comment, is_preview)
    unless is_preview
      doubled_comment = Comment.where(
        story_id: comment.story_id,
        user_id: comment.user_id,
        parent_comment_id: comment.parent_comment_id
      ).first

      if doubled_comment && (Time.now - doubled_comment.created_at) < 5.minutes
        return Failure(Error.new(:duplicate_comment, comment))
      end
    end

    Success(comment)
  end

  def save_comment(comment, is_preview)
    if comment.valid? && is_preview && comment.save
      comment.current_vote = { :vote => 1 }
      Success(comment)
    else
      comment.upvotes = 1
      comment.current_vote = { :vote => 1 }
      Failure(Error.new(:didnt_save, comment))
    end
  end
end

before.rb

class CommentsController
  def create
    if !(story = Story.where(:short_id => params[:story_id]).first) ||
    story.is_gone?
      return render :plain => "can't find story", :status => 400
    end

    comment = story.comments.build
    comment.comment = params[:comment].to_s
    comment.user = @user

    if params[:hat_id] && @user.hats.where(:id => params[:hat_id])
      comment.hat_id = params[:hat_id]
    end

    if params[:parent_comment_short_id].present?
      if pc = Comment.where(:story_id => story.id, :short_id =>
      params[:parent_comment_short_id]).first
        comment.parent_comment = pc
      else
        return render :json => { :error => "invalid parent comment",
          :status => 400 }
      end
    end

    # prevent double-clicks of the post button
    if params[:preview].blank? &&
    (pc = Comment.where(:story_id => story.id, :user_id => @user.id,
      :parent_comment_id => comment.parent_comment_id).first)
      if (Time.now - pc.created_at) < 5.minutes
        comment.errors.add(:comment, "^You have already posted a comment " <<
          "here recently.")

        return render :partial => "commentbox", :layout => false,
          :content_type => "text/html", :locals => { :comment => comment }
      end
    end

    if comment.valid? && params[:preview].blank? && comment.save
      comment.current_vote = { :vote => 1 }

      render :partial => "comments/postedreply", :layout => false,
        :content_type => "text/html", :locals => { :comment => comment }
    else
      comment.upvotes = 1
      comment.current_vote = { :vote => 1 }

      preview comment
    end
  end
end

refactor2.rb

class CommentsController
  def create
    begin
      comment = CreateComment.call(params, @user)
      render :partial => "comments/postedreply", :layout => false,
        :content_type => "text/html", :locals => { :comment => comment }
    rescue CreateComment::StoryNotFound
      render :plain => "can't find story", :status => 400
    rescue CreateComment::ParentNotFound
      render :json => { :error => "invalid parent comment", :status => 400 }
    rescue CreateComment::DuplicateComment => ex
      ex.comment.errors.add(:comment, "^You have already posted a comment here recently.")
      render :partial => "commentbox", :layout => false,
        :content_type => "text/html", :locals => { :comment => ex.comment }
    rescue CreateComment::DidntSave => ex
      preview ex.comment
    end
  end
end

class CreateComment
  class StoryNotFound < StandardError; end
  class ParentNotFound < StandardError; end
  class DuplicateComment < StandardError
    attr_reader :comment

    def initialize(comment)
      @comment = comment
      super()
    end
  end
  class DidntSave < StandardError
    attr_reader :comment

    def initialize(comment)
      @comment = comment
      super()
    end
  end

  def self.call(*args)
    new(*args).call
  end

  def initialize(params, user)
    @params = params
    @user = user
  end

  def call
    story = find_story!(params[:story_id])
    comment = build_comment!(story)
    prevent_duplicates!(comment)
    save_comment!(comment)

    comment
  end

  private

  attr_reader :params, :user

  def find_story!(story_id)
    story = Story.where(:short_id => story_id).first
    if story && !story.is_gone?
      story
    else
      raise StoryNotFound
    end
  end

  def build_comment!(story)
    comment = story.comments.build
    comment.comment = comment_params[:comment].to_s
    comment.user = user

    if comment_params[:hat_id] && user.hats.where(:id => comment_params[:hat_id])
      comment.hat_id = comment_params[:hat_id]
    end

    if comment_params[:parent_comment_short_id].present?
      parent = Comment.where(story_id: story.id, short_id: comment_params[:parent_comment_short_id]).first
      if parent
        comment.parent_comment = parent
      else
        raise ParentNotFound
      end
    end

    comment
  end

  def prevent_duplicates!(comment)
    if !preview? && duplicate?(comment)
      raise DuplicateComment.new(comment)
    end
  end

  def save_comment!(comment)
    if comment.valid? && preview? && comment.save
      comment.current_vote = { :vote => 1 }
    else
      comment.upvotes = 1
      comment.current_vote = { :vote => 1 }
      raise DidntSave.new(comment)
    end
  end

  def comment_params
    @comment_params ||= params.slice(:comment, :hat_id, :parent_comment_short_id)
  end

  def preview?
    params[:preview].present?
  end

  def duplicate?(comment)
    duplicate = Comment.where(
      story_id: comment.story_id,
      user_id: comment.user_id,
      parent_comment_id: comment.parent_comment_id
    ).first

    duplicate && (Time.now - duplicate.created_at) < 5.minutes
  end
end