Date and Date Ranges in Rails 3 - ruby-on-rails-3

Question

I have a Rails 3 application with a prescription model. The model has a number of fields, two of them are to calculate and display the duration of a prescription.
At the moment the user enters a value in a text field such as '3 Months' and then manually changes a datetime input to three months from now. This seems like a perfect form to automate for the user.
Currently the fields are like this:
Duration of Treatment
<%= f.text_field :duration, :class => "input-text" %>
Date of Expiry
<%= f.datetime_select :expiry, :order => [:day, :month, :year], :class => "input-text" %>
So, my question. How can I create two dropdown lists for the duration field such as:
[1] [Day]
The user can select the number from the first list and in the second they can choose Day, Week or Month.
The value they pick using the duration select boxes would be saved as a text string e.g. "1 month" and the value of the Time.now in 1 month would be saved as a datetime value in the expiry column.
Is something like this possible to do? If so, how?

Answer 1

I'll provide an example of how you'd use the chronic gem, since it seems tailor-made for this purpose:
require 'chronic'
duration = "3 months" # => "3 months"
Time.now # => 2012-07-09 18:43:50 -0700
Chronic.parse(duration + " from now") # => 2012-10-09 18:43:55 -0700
If I understand your use case correctly, you can then just get rid of the datetime select entirely. Ask the user for the text duration and assign that to the text attribute. Then use chronic to determine the time value from the text parameter and assign that to the datetime attribute. For extra credit get the parsed time value asynchronously and display it on the page before they submit the form so they can see that what they are submitting makes sense.

Answer 2

You can just do something easy like:
Time.now + 10.days
Source: How to add 10 days to current time in Rails
And how to do drop-downs?
Drop down box in Rails
Assuming the prescription is valid at the time of object creation, you can store the start date in the database as the current time Time.now (may want to convert to a datetime) and then based on the drop-down, add the amount of time until it expires like off the top of my head:
eval "Time.now + #{params[:prescription][:amount].#{params[:prescription][:time_type]}"
Hope that made sense. I would look up a better way to add the time though that maybe doesn't use eval. Heres the time reference: http://api.rubyonrails.org/classes/Time.html

Answer 3

First, change your duration field to a select menu with 1-30, or whatever numbers you want.
Then in the controller action that handles your form:
#prescription = Prescription.new(params[:prescrption])
#prescription.duration = "#{pluralize(params[:prescription][:duration], params[:prescription][:expiry])}"
if params[:prescription][:expiry] == "Day"
#prescription.expiry = Time.now + params[:prescription][:duration].days
elsif params[:prescription][:expiry] == "Week"
# Put week logic here
elsif params[:prescription][:expiry] == "Month"
# Put month logic here
end
# Put the rest of the #prescription.save stuff here.
It's a little verbose, but I think that's kind of the way it is with the way time is set up in Ruby...