Turning a calendar into a form using Rails?

Question: How do I turn a calendar into a form where the dateselect is rendered to match the calendar day instead of the current date?

What I'm trying to do: I'd like to create a calendar that displays the cyclist's workouts.

Create workouts within each calendar day, automatically rendering the workoutdate that matches the given day in the form

Each workout has many intervals. Each calendar day has one workout.

Plugins: Extracted the table_builder.rb and calendar_helper.rb from https://github.com/p8/table_builder (both gem and plugin do not deploy with rails 3.1)

class WorkoutsController.rb

  def new
    @workout = Workout.new
    @date = params[:month] ? Date.parse(params[:month].gsub('-', '/')) : Date.today
    3.times do
      @workout.intervals.build
    end
  end

Workout.rb

  attr_accessible :workoutdate, :intervals_attributes
  has_many :intervals, :dependent => :destroy
  accepts_nested_attributes_for :intervals, :reject_if => lambda { |a| a[:interval_name].blank? }, :allow_destroy => true

Interval.rb

attr_accessible :interval_name, :workout_id
belongs_to :workout

views/workouts/new.html.erb

<div id ="calendar">
  <%= calendar_for @workouts, :year => @date.year, :month => @date.month do |calendar| %>
    <%= calendar.head('Sunday', 'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday') %>
    <% calendar.day(:day_method => :workoutdate) do |date, workouts| %>
      <%= date.day %>
      <%= render 'form' %>
    <% end %>
  <% end %>
</div>

views/workouts/_form.html.erb

<%= nested_form_for @workout do |f| %>
  <%= f.error_messages %>
  <p>
    <%= f.label :workoutdate %><br />
    <%= f.date_select :workoutdate %>
  </p>
  <%= f.fields_for :intervals %>
  <p><%= f.link_to_add "Add interval", :intervals %></p>
  <p><%= f.submit "Submit" %></p>
<% end %>

views/workouts/_interval_fields.html.erb

<p>
  <%= f.label :interval_name, "Interval" %>
  <%= f.text_field :interval_name %>
  <%= f.link_to_remove "remove" %>
</p>

currently up on heroku http://billeee.herokuapp.com/workouts

Since you have the date available in the block of the day method, you should be able to pass it on to the partial like so:

<% calendar.day(:day_method => :workoutdate) do |date, workouts| %>
  <%= date.day %>
  <%= render 'form', :date => date %>
<% end %>

Then you can make use of it within the form partial and set the date of the date select via the local variable you have just passed in:

<%= f.date_select :workoutdate, :default => date %>

As a note: this method seems a bit funny, since you're rendering this form always for a particular day anyways. Why not send the date e.g. via a hidden input field? Is the user supposed to change the date? And if so, doesn't that break the UI logic?