HTML5 Video Voting backend

vote.rb

class Vote < ActiveRecord::Base
  belongs_to :video
  belongs_to :user
  has_one :comment
  validates :vote_is_not_in_same_bar, :presence => {:on => :create}

  def self.time_intervals(params)
    bars = params[:bars].to_i
    groups = Array.new(bars, 0)
    vote = Vote.where(:video_id => params[:video_id]).first
    interval = 1 if vote.nil?
    interval ||= vote.duration / bars
    sql = <<-QUERY
      SELECT time_interval, COUNT(*) AS cnt
      FROM (SELECT FLOOR(time / #{interval}) AS time_interval
      FROM votes
      WHERE video_id = #{params[:video_id]}) AS vote
      GROUP BY time_interval
    QUERY
    find_by_sql(sql).each do |time|
      groups[time.time_interval] = time.cnt
    end
    groups
  end
  
  def vote_is_not_in_same_bar
    bars = Video.find(self.video_id).bars
    last_vote = Vote.where(:ip_address => self.ip_address).last
    interval = self.duration / bars.to_i
    created_at = 0 if last_vote.blank?
    created_at ||= last_vote['created_at'].to_time.to_i
    now = Time.now.to_time.to_i
    diff = now - created_at
    if diff > interval
      return true
    else
      errors.add_to_base('You just voted!')
    end
  end
end

votes_controller.rb

class VotesController < ApplicationController
  before_filter :authenticate_user!, :except => [:create, :show, :new, :index]
  respond_to :html, :json
  
  def index
    respond_with(@votes = Vote.all)
  end

  def show
    @votes = Vote.time_intervals(params)
    if params[:callback]
      output = params[:callback] + '("' + @votes.to_json + '");'
    else
      output = @votes
    end
    respond_with do |format|
      format.html {}
      format.json  { render :json => output }
    end
  end

  def new
    respond_with(@vote = Vote.new)
  end

  def edit
    @vote = Vote.find params[:id]
  end

  def create
    if params[:callback]
      @vote = Vote.new(params[:data][:vote])
      output = params[:callback] + '()'
    else
      @vote = Vote.new params[:vote]
      output = @vote
    end
    @vote.user_id = current_user.id if current_user
    respond_with do |format|
      if @vote.save
        format.json  { render :json => output , :status => :created }
      else
        format.json  { render :json => @vote.errors, :status => :unprocessable_entity }
      end
    end
  end

  def update
    @vote = Vote.find params[:id]

    respond_with do |format|
      if @vote.update_attributes params[:vote]
        format.html { redirect_to @vote, :notice => 'Vote was successfully updated.' }
        format.json  { head :ok }
      else
        format.html { render :action => "edit" }
        format.json  { render :xml => @vote.errors, :status => :unprocessable_entity }
      end
    end
  end
  
  def destroy
    Vote.destroy params[:id]

    respond_to do |format|
      format.html { redirect_to votes_url }
      format.json  { head :ok }
    end
  end
  
  def destroy_all
    Vote.destroy_all(:video_id => params[:video_id])
    
    respond_to do |format|
      format.html { redirect_to votes_url }
      format.json  { head :ok }
    end
  end
end