script/plugin install git://github.com/cdunn/has_activity.git

  class Feed < ActiveRecord::Base
    # Defaults to created_at
    has_activity
    
    ...
  end

  class Feed < ActiveRecord::Base
    # Change the timestamp DB field to something custom
    has_activity :by => "published_at"
    
    ...
  end

  # Get all activity since 1 week ago grouped by day (default) 
  Feed.activity_since(1.week.ago)
  => [{:activity=>0, :offset=>7, :created_at=>Mon Mar 09 10:27:34 -0700 2009}, {:activity=>0, :offset=>6, :created_at=>Tue Mar 10 10:27:34 -0700 2009}, {:activity=>8, :offset=>5, :created_at=>Wed Mar 11 01:19:09 -0700 2009}, {:activity=>2, :offset=>4, :created_at=>Thu Mar 12 04:26:09 -0700 2009}, {:activity=>0, :offset=>3, :created_at=>Fri Mar 13 10:27:34 -0700 2009}, {:activity=>0, :offset=>2, :created_at=>Sat Mar 14 10:27:34 -0700 2009}, {:activity=>0, :offset=>1, :created_at=>Sun Mar 15 10:27:34 -0700 2009}, {:activity=>0, :offset=>0, :created_at=>Mon Mar 16 10:27:34 -0700 2009}]

SELECT
 published_at AS timestamp,
 COUNT(*) AS activity_count,
 DATEDIFF(now(), published_at) as days_ago
 FROM feeds
 WHERE 1=1 AND published_at > '2009-03-09 17:27:33'
 GROUP BY days_ago
 ORDER BY published_at ASC

  # Get all activity since 1 day ago grouped by hour scoped to a certain user
  Feed.activity_since(1.week.ago, :conditions => ["user_id = ?", current_user.id], :group_by => :hour)
  => [{:activity=>0, :offset=>24, :created_at=>Sun Mar 15 10:29:47 -0700 2009}, {:activity=>0, :offset=>23, :created_at=>Sun Mar 15 11:29:47 -0700 2009}, {:activity=>0, :offset=>22, :created_at=>Sun Mar 15 12:29:47 -0700 2009}, {:activity=>0, :offset=>21, :created_at=>Sun Mar 15 13:29:47 -0700 2009}, {:activity=>0, :offset=>20, :created_at=>Sun Mar 15 14:29:47 -0700 2009}, {:activity=>0, :offset=>19, :created_at=>Sun Mar 15 15:29:47 -0700 2009}, {:activity=>0, :offset=>18, :created_at=>Sun Mar 15 16:29:47 -0700 2009}, {:activity=>0, :offset=>17, :created_at=>Sun Mar 15 17:29:47 -0700 2009}, {:activity=>0, :offset=>16, :created_at=>Sun Mar 15 18:29:47 -0700 2009}, {:activity=>0, :offset=>15, :created_at=>Sun Mar 15 19:29:47 -0700 2009}, {:activity=>0, :offset=>14, :created_at=>Sun Mar 15 20:29:47 -0700 2009}, {:activity=>0, :offset=>13, :created_at=>Sun Mar 15 21:29:47 -0700 2009}, {:activity=>0, :offset=>12, :created_at=>Sun Mar 15 22:29:47 -0700 2009}, {:activity=>0, :offset=>11, :created_at=>Sun Mar 15 23:29:47 -0700 2009}, {:activity=>0, :offset=>10, :created_at=>Mon Mar 16 00:29:47 -0700 2009}, {:activity=>0, :offset=>9, :created_at=>Mon Mar 16 01:29:47 -0700 2009}, {:activity=>0, :offset=>8, :created_at=>Mon Mar 16 02:29:47 -0700 2009}, {:activity=>0, :offset=>7, :created_at=>Mon Mar 16 03:29:47 -0700 2009}, {:activity=>0, :offset=>6, :created_at=>Mon Mar 16 04:29:47 -0700 2009}, {:activity=>0, :offset=>5, :created_at=>Mon Mar 16 05:29:47 -0700 2009}, {:activity=>0, :offset=>4, :created_at=>Mon Mar 16 06:29:47 -0700 2009}, {:activity=>0, :offset=>3, :created_at=>Mon Mar 16 07:29:47 -0700 2009}, {:activity=>0, :offset=>2, :created_at=>Mon Mar 16 08:29:47 -0700 2009}, {:activity=>0, :offset=>1, :created_at=>Mon Mar 16 09:29:47 -0700 2009}, {:activity=>0, :offset=>0, :created_at=>Mon Mar 16 10:29:47 -0700 2009}]\

SELECT
 published_at AS timestamp,
 COUNT(*) AS activity_count,
 ((((YEAR(now()) - YEAR(published_at))*365) (DAYOFYEAR(now())-DAYOFYEAR(published_at)))*24) (HOUR(now())-HOUR(published_at)) as hours_ago,
 CONCAT(YEAR(published_at), CONCAT(DAYOFYEAR(published_at), HOUR(published_at))) AS unique_hour
 FROM feeds
 WHERE user_id = 1 AND published_at > '2009-03-15 17:29:47'
 GROUP BY unique_hour
 ORDER BY published_at ASC

  # Get all activity since 2 months ago grouped by week and order it from current week to oldest week
  Feed.activity_since(2.months.ago, :group_by => :week, :order => :desc)
  => [{:activity=>0, :offset=>0, :created_at=>Mon Mar 16 10:34:28 -0700 2009}, {:activity=>0, :offset=>1, :created_at=>Mon Mar 09 10:34:28 -0700 2009}, {:activity=>0, :offset=>2, :created_at=>Mon Mar 02 10:34:28 -0800 2009}, {:activity=>0, :offset=>3, :created_at=>Mon Feb 23 10:34:28 -0800 2009}, {:activity=>0, :offset=>4, :created_at=>Mon Feb 16 10:34:28 -0800 2009}, {:activity=>0, :offset=>5, :created_at=>Mon Feb 09 10:34:28 -0800 2009}, {:activity=>0, :offset=>6, :created_at=>Mon Feb 02 10:34:28 -0800 2009}, {:activity=>0, :offset=>7, :created_at=>Mon Jan 26 10:34:28 -0800 2009}, {:activity=>0, :offset=>8, :created_at=>Mon Jan 19 10:34:28 -0800 2009}]

  SELECT
   published_at AS timestamp,
   COUNT(*) AS activity_count,
   ((YEAR(now()) - YEAR(published_at))*52) (WEEK(now())-WEEK(published_at)) as weeks_ago,
   YEARWEEK(published_at) AS unique_week
   FROM feeds
   WHERE 1=1 AND published_at > '2009-01-16 17:34:28'
   GROUP BY unique_week
   ORDER BY published_at ASC

Feed.activity_since(6.months.ago, :group_by => :week, :order => :desc).to_activity_gchart
=> "http://chart.apis.google.com/chart?cht=bvs&chs=200x50&chd=t:0,10,15,3,8,4,0,3,2,3,0,11,4,23,14,0,0,0,13,0,4,8,19,10,12,21,1&chco=336699&chbh=a,2&chds=0,23&chf=bg,s,EFEFEF&"

  # Grabs a hash of the activity since <time ago> grouped by <hour/day/week>
  # 
  #   * :conditions
  #       same as the standard Rails finder. Used to scope your activity to a particular user, etc.
  #   * :padding
  #       true/false
  #   * :group_by
  #       :hour, :day, :week
  # 
  def activity_since(since=1.week.ago, options={})

  # Returns a URL to a simple google chart the represents the activity returned by the plugin
  # 
  #   * :type => :bar/:line
  #   * :size => "200x50"
  #   * :bgcolor => "EFEFEF"
  #   * :chart_color => "336699"
  #   * :area_color => "DFEBFF" (only for :line)
  #   * :line_color => "0077CC" (only for :line)
  #   * :line_width => "2" (only for :line)
  # 
  def to_activity_gchart(options={})

add_index :model, [:created_at]