comments: allow swapping votes.

Allow users to upvote a comment, then downvote it, without raising an
error or having to manually remove the upvote first. The upvote is
automatically removed and replaced by the downvote.

Changes to the /comment_votes API:

* `POST /comment_votes` and `DELETE /comment_votes` now return a comment
  vote instead of a comment.
* The `score` param in `POST /comment_votes` is now 1 or -1, not
  `up` or `down.`

app/components/comment_component/comment_component.html.erb

@@ -51,7 +51,7 @@
           <% elsif upvoted? %>
             <%= link_to "🡹", comment_comment_votes_path(comment_id: comment.id), class: "comment-upvote-link comment-unvote-link", method: :delete, remote: true %>
           <% else %>
-            <%= link_to "🡹", comment_comment_votes_path(comment_id: comment.id, score: "up"), class: "comment-upvote-link", method: :post, remote: true %>
+            <%= link_to "🡹", comment_comment_votes_path(comment_id: comment.id, score: "1"), class: "comment-upvote-link", method: :post, remote: true %>
           <% end %>
 
           <span class="comment-score"><%= comment.score %></span>
@@ -61,7 +61,7 @@
           <% elsif downvoted? %>
             <%= link_to "🡻",  comment_comment_votes_path(comment_id: comment.id), class: "comment-downvote-link comment-unvote-link", method: :delete, remote: true %>
           <% else %>
-            <%= link_to "🡻",  comment_comment_votes_path(comment_id: comment.id, score: "down"), class: "comment-downvote-link", method: :post, remote: true %>
+            <%= link_to "🡻",  comment_comment_votes_path(comment_id: comment.id, score: "-1"), class: "comment-downvote-link", method: :post, remote: true %>
           <% end %>
         </li>
       <% end %>

app/controllers/comment_votes_controller.rb

@@ -1,23 +1,31 @@
 class CommentVotesController < ApplicationController
   skip_before_action :api_check
   respond_to :js, :json, :xml, :html
-  rescue_with CommentVote::Error, ActiveRecord::RecordInvalid, status: 422
 
   def index
     @comment_votes = authorize CommentVote.visible(CurrentUser.user).paginated_search(params, count_pages: true)
     @comment_votes = @comment_votes.includes(:user, comment: [:creator, post: [:uploader]]) if request.format.html?
+
     respond_with(@comment_votes)
   end
 
   def create
-    @comment = authorize Comment.find(params[:comment_id]), policy_class: CommentVotePolicy
-    @comment_vote = @comment.vote!(params[:score])
-    respond_with(@comment)
+    @comment = Comment.find(params[:comment_id])
+
+    @comment.with_lock do
+      @comment_vote = authorize CommentVote.new(comment: @comment, score: params[:score], user: CurrentUser.user)
+      CommentVote.where(comment: @comment, user: CurrentUser.user).destroy_all
+      @comment_vote.save
+    end
+
+    flash.now[:notice] = @comment_vote.errors.full_messages.join("; ") if @comment_vote.errors.present?
+    respond_with(@comment_vote)
   end
 
   def destroy
-    @comment = authorize Comment.find(params[:comment_id]), policy_class: CommentVotePolicy
-    @comment.unvote!
-    respond_with(@comment)
+    @comment_vote = authorize CommentVote.find_by!(comment_id: params[:comment_id], user: CurrentUser.user)
+    @comment_vote.destroy
+
+    respond_with(@comment_vote)
   end
 end

app/models/comment.rb

@@ -44,39 +44,7 @@ class Comment < ApplicationRecord
     end
   end
 
-  module VoteMethods
-    def vote!(val, voter = CurrentUser.user)
-      numerical_score = (val == "up") ? 1 : -1
-      vote = votes.create!(user: voter, score: numerical_score)
-
-      if vote.is_positive?
-        update_column(:score, score + 1)
-      elsif vote.is_negative?
-        update_column(:score, score - 1)
-      end
-
-      return vote
-    end
-
-    def unvote!
-      vote = votes.where("user_id = ?", CurrentUser.user.id).first
-
-      if vote
-        if vote.is_positive?
-          update_column(:score, score - 1)
-        else
-          update_column(:score, score + 1)
-        end
-
-        vote.destroy
-      else
-        raise CommentVote::Error.new("You have not voted for this comment")
-      end
-    end
-  end
-
   extend SearchMethods
-  include VoteMethods
 
   def validate_creator_is_not_limited
     if creator.is_comment_limited? && !do_not_bump_post?

app/models/comment_vote.rb

@@ -1,13 +1,15 @@
 class CommentVote < ApplicationRecord
-  class Error < StandardError; end
-
   belongs_to :comment
   belongs_to :user
+
   validates_presence_of :score
   validates_uniqueness_of :user_id, :scope => :comment_id, :message => "have already voted for this comment"
   validate :validate_comment_can_be_down_voted
   validates_inclusion_of :score, :in => [-1, 1], :message => "must be 1 or -1"
 
+  after_create :update_score_after_create
+  after_destroy :update_score_after_destroy
+
   def self.visible(user)
     if user.is_moderator?
       all
@@ -37,6 +39,18 @@ class CommentVote < ApplicationRecord
     score == -1
   end
 
+  def update_score_after_create
+    comment.with_lock do
+      comment.update_columns(score: comment.score + score)
+    end
+  end
+
+  def update_score_after_destroy
+    comment.with_lock do
+      comment.update_columns(score: comment.score - score)
+    end
+  end
+
   def self.available_includes
     [:comment, :user]
   end

app/policies/comment_vote_policy.rb

@@ -1,7 +1,10 @@
 class CommentVotePolicy < ApplicationPolicy
+  def create?
+    unbanned? && !record.comment.is_deleted?
+  end
+
   def destroy?
-    # XXX permissions are checked in Comment#unvote!
-    true
+    record.user_id == user.id
   end
 
   def can_see_votes?

app/views/comment_votes/create.js.erb

@@ -1,2 +1,6 @@
-var $comment = $("article#comment_<%= @comment.id %>");
-$comment.replaceWith("<%= j render_comment(@comment, current_user: CurrentUser.user) %>");
+<% if flash[:notice] %>
+  Danbooru.Utility.notice("<%= j flash[:notice] %>");
+<% end %>
+
+var $comment = $("article#comment_<%= @comment_vote.comment_id %>");
+$comment.replaceWith("<%= j render_comment(@comment_vote.comment, current_user: CurrentUser.user) %>");

app/views/comment_votes/destroy.js.erb

@@ -1,2 +0,0 @@
-var $comment = $("article#comment_<%= @comment.id %>");
-$comment.replaceWith("<%= j render_comment(@comment, current_user: CurrentUser.user) %>");

app/views/comment_votes/destroy.js.erb

@@ -0,0 +1 @@
+create.js.erb