#407 Activity Feed from Scratch pro

rails g resource activity user:belongs_to action trackable:belongs_to trackable_type
rake db:migrate

def track_activity(trackable, action = params[:action])
  current_user.activities.create! action: action, trackable: trackable
end

track_activity @recipe

track_activity @comment

def index
  @activities = Activity.order("created_at desc")
end

class ActivityPresenter < SimpleDelegator
  attr_reader :activity
  
  def initialize(activity, view)
    super(view)
    @activity = activity
  end
  
  def render_activity
    div_for activity do
      link_to(activity.user.name, activity.user) + " " + render_partial
    end
  end
  
  def render_partial
    locals = {activity: activity, presenter: self}
    locals[activity.trackable_type.underscore.to_sym] = activity.trackable
    render partial_path, locals
  end
  
  def partial_path
    partial_paths.detect do |path|
      lookup_context.template_exists? path, nil, true
    end || raise("No partial found for activity in #{partial_paths}")
  end
  
  def partial_paths
    [
      "activities/#{activity.trackable_type.underscore}/#{activity.action}",
      "activities/#{activity.trackable_type.underscore}",
      "activities/activity"
    ]
  end
end

<% @activities.each do |activity| %>
  <%= ActivityPresenter.new(activity, self).render_activity %>
<% end %>

<%= activity.action.sub(/e?$/, "ed") %> recipe
<%= link_to recipe.name, recipe if recipe %>

<% if comment %>
  commented on <%= link_to comment.recipe.name, comment.recipe %>
<% else %>
  added a comment which has since been removed
<% end %>