Rails How to give options in date time select - ruby-on-rails

Question

I am trying to implement a datetime_select option for a form. I was using a simple date selector like below before hand but the requirements have changed.
<%= f.datetime_select :ends_at, :start_year => Date.current.year %>
What I want to implement instead is to give users only three options as: "One hour", "Two hours", "Three hours" for selection. The corresponding values for the chosen option sent as POST through the form would be calculated from the time the submit button is pressed.
How can I give these options for the users for a datetime data type ?

Answer 1

Okay you can do something like that:
In your Model define:
TIMER = [{"time"=>"One Hour", "val"=>"1"}, {"time"=>"Two Hours", "val"=>"2"}, {"time"=>"Three Hours", "val"=>"3"}]
In your form use a different select field:
<%= f.select :time_to_end, options_for_select(Model::TIMER.map { |obj| [obj['time'], obj['val']] }) %>
Then in the model allow time_to_end parameter as a attr_accesible.
attr_accessible :time_to_end
Also, add a before save callback to change the ends_at field:
before_save :update_ends_at_field
private
def update_ends_at_field
self.ends_at = Time.now + time_to_end.to_i.hours
end
I didn't tested the code above. Hope you got the idea.

Answer 2

I ended up using
<%= f.select :ends_at, options_for_select(ApplicationHelper::TIMER.map { |obj| [obj['time'], obj['val']] })%>
in the form itself.
Where Timer is defined as:
module ApplicationHelper
TIMENOW = DateTime.now
TIMER = [{"time"=>"Half Hour", "val"=> TIMENOW + 0.5.hour},{"time"=>"One Hour", "val"=> TIMENOW + 1.hour}, {"time"=>"One Day", "val"=> TIMENOW + 24.hour}, {"time"=>"Three Days", "val"=> TIMENOW + 3.day}, {"time"=>"Seven Days", "val"=> TIMENOW + 7.day}]
end
in the ApplicationHelper