post_vote.rb: determine vote magnitude from voter, not CurrentUser.

Bug: when moving favorites, the parent is given an upvote for each gold+
favoriter, but the magnitude of these upvotes was based on the
CurrentUser, rather than the upvoter. This meant that upvotes for
supervoter favorites weren't given correctly.

To fix this, `magnitude` is changed to use the voting `user` instead of
CurrentUser.

New problem: when setting the score, `score=` calls `magnitude`, but
`user` isn't initialized yet. So we also refactor so that

    1. `initialize_attributes` initializes `user` before setting `score`
    2. the vote direction is given by `vote`, so it's separate from `score`
    3. updating the score on the post happens in a callback instead of
       directly in `score=`.

app/models/post.rb

@@ -1063,7 +1063,7 @@ class Post < ActiveRecord::Base
       !PostVote.exists?(:user_id => user.id, :post_id => id)
     end
 
-    def vote!(score, voter = CurrentUser.user)
+    def vote!(vote, voter = CurrentUser.user)
       unless voter.is_voter?
         raise PostVote::Error.new("You do not have permission to vote")
       end
@@ -1072,7 +1072,7 @@ class Post < ActiveRecord::Base
         raise PostVote::Error.new("You have already voted for this post")
       end
 
-      votes.create!(user: voter, score: vote)
+      votes.create!(user: voter, vote: vote)
       reload # PostVote.create modifies our score. Reload to get the new score.
     end
 

app/models/post_vote.rb

@@ -2,10 +2,14 @@ class PostVote < ActiveRecord::Base
   class Error < Exception ; end
 
   belongs_to :post
-  before_validation :initialize_user, :on => :create
+  belongs_to :user
+  attr_accessor :vote
+  attr_accessible :post, :post_id, :user, :user_id, :score, :vote
+
+  after_initialize :initialize_attributes, if: :new_record?
   validates_presence_of :post_id, :user_id, :score
   validates_inclusion_of :score, :in => [SuperVoter::MAGNITUDE, 1, -1, -SuperVoter::MAGNITUDE]
-  attr_accessible :post_id, :user_id, :score
+  after_create :update_post_on_create
   after_destroy :update_post_on_destroy
 
   def self.prune!
@@ -24,18 +28,22 @@ class PostVote < ActiveRecord::Base
     select_values_sql("select post_id from post_votes where score > 0 and user_id = ?", user_id)
   end
 
-  def score=(x)
-    if x == "up"
-      Post.where(:id => post_id).update_all("score = score + #{magnitude}, up_score = up_score + #{magnitude}")
-      write_attribute(:score, magnitude)
-    elsif x == "down"
-      Post.where(:id => post_id).update_all("score = score - #{magnitude}, down_score = down_score - #{magnitude}")
-      write_attribute(:score, -magnitude)
+  def initialize_attributes
+    self.user_id ||= CurrentUser.user.id
+
+    if vote == "up"
+      self.score = magnitude
+    elsif vote == "down"
+      self.score = -magnitude
     end
   end
 
-  def initialize_user
-    self.user_id ||= CurrentUser.user.id
+  def update_post_on_create
+    if score > 0
+      Post.where(:id => post_id).update_all("score = score + #{score}, up_score = up_score + #{score}")
+    else
+      Post.where(:id => post_id).update_all("score = score + #{score}, down_score = down_score + #{score}")
+    end
   end
 
   def update_post_on_destroy
@@ -47,7 +55,7 @@ class PostVote < ActiveRecord::Base
   end
 
   def magnitude
-    if CurrentUser.is_super_voter?
+    if user.is_super_voter?
       SuperVoter::MAGNITUDE
     else
       1

test/unit/post_vote_test.rb

@@ -14,17 +14,17 @@ class PostVoteTest < ActiveSupport::TestCase
 
   context "Voting for a post" do
     should "interpret up as +1 score" do
-      vote = PostVote.create(:post_id => @post.id, :score => "up")
+      vote = PostVote.create(:post_id => @post.id, :vote => "up")
       assert_equal(1, vote.score)
     end
 
     should "interpret down as -1 score" do
-      vote = PostVote.create(:post_id => @post.id, :score => "down")
+      vote = PostVote.create(:post_id => @post.id, :vote => "down")
       assert_equal(-1, vote.score)
     end
 
     should "not accept any other scores" do
-      vote = PostVote.create(:post_id => @post.id, :score => "xxx")
+      vote = PostVote.create(:post_id => @post.id, :vote => "xxx")
       assert(vote.errors.any?)
     end
   end