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subscription_counter.rb

This annotated codebase is meant to serve as Practicing Ruby Issue 2.13. While the typical Practicing Ruby issue is published in article format, the subject matter for this issue seemed to fit a literate-programming format better.

 

      		
    

    

      
        

          
        

        
In this issue, I’ll discuss how I implemented the code necessary to generate
this PDF report.
Business reporting can be tricky in Ruby, and even modest reporting
tasks demand a non-trivial amount of software design consideration.

      		
      
        

      		
    

    

      
        

          
        

        
Rather than trying to come up with some general guidelines for how to approach
reporting problems in Ruby, I decided it might be interesting to attack a real
problem of mine, clean up my code as much as possible, and share the results.
Please be sure to let me know what you think!

      		
      
        

      		
    

    

      
        

          
        

        
The subcription_counter.rb file you’re looking at now is the entry point 
into this project, and it’s where I’ve stacked all the necessary requires to 
get a fully running application. Typically I break things out starting with 
the standard libraries I’m using, followed by the third party libraries, 
then lastly my project files. This gives me a nice way to see the 
dependencies of the entire project at glance.

      		
      
        

      		
    

    

      
        

          
        

        

      		
      
        

      		
    

    

      
        

          
        

        
While my external dependencies almost certainly load more stdlibs, this report 
only explicitly depend on the date and tempfile libraries.

      		
      
        
require "date"
require "tempfile"

      		
    

    

      
        

          
        

        

      		
      
        

      		
    

    

      
        

          
        

        
As for external dependencies: I make use of RSRuby 
to integrate with the R programming language for graphing 
and basic stats computations, Hominid 
for integrating with the MailChimp API, and 
Prawn for PDF generation.

      		
      
        
require "rsruby"
require "hominid"
require "prawn"

      		
    

    

      
        

          
        

        

      		
      
        

      		
    

    

      
        

          
        

        
I define some values in the mailchimp_settings.rb file and 
reference them later via the 
SubscriptionCounter::MAILCHIMP_SETTINGS constant. Because this
is just a boring hash of API keys and other database ids, you can
safely treat it as a black box.

      		
      
        
require_relative "../config/mailchimp_settings"

      		
    

    

      
        

          
        

        

      		
      
        

      		
    

    

      
        

          
        

        
I did what I could to make this code as modular as possible. The list below
outlines the different objects this system is made up of, and what their
respective jobs are.



    

  • Campaign integrates
with MailChimp to pull down subscriber counts and dates for each campaign.
    • 

  • DataSeries and
DataPoint are
the data structures that I normalize the MailChimp data into. The goal in
creating them was to make it possible for the report to be reasonably
decoupled from SubscriptionCounter::Campaign so that I could load this
same data from a different representation down the line (such as a CSV
file).
    • 

  • Graph is a simple singleton object that
wraps the R plotting functions I use. 
    • 

  • Statistics is another singleton 
object which uses R to implement an adjusted average computation that
I use in this report.
    • 

  • Report is an adapter object which
transforms a DataSeries object into data that is convenient to work
with in formatted output.
    • 

  • Report::PDF generates a nicely
formatted representation of the data contained in the Report
    • 


      		
      
        
require_relative "subscription_counter/campaign"
require_relative "subscription_counter/data_point"
require_relative "subscription_counter/data_series"
require_relative "subscription_counter/graph"
require_relative "subscription_counter/statistics"
require_relative "subscription_counter/report"
require_relative "subscription_counter/report/pdf"

      		
    

    

      
        

          
        

        



NOTE: If you start with the Campaign
object and follow the breadcrumbs at the end of each page, you should be able
to get a nice comprehensive walkthrough of this codebase.