StoneHengeBank

StoneHengeBank is a SAMPLE application desgined to do fast investment calculations, with friendly verbose responses, allowing the user to understand better what an investment can provide.

(WIP) An easy-to-use command-line interface runs a calculation on values of an investment, such as: interest rate, future and present values, regular parcels, return periods.

Via a Domain-Specific Language, it's possible to have results returned for a client application using this gem.

Installation

(WIP) This gem is not yet published on RubyGems, so it's necessary to clone/fork this repo to use it, for now.

Add this line to your application's Gemfile:

  gem 'stonehenge_bank'

And then execute:

$ bundle

Or install it yourself as:

$ gem install stonehenge_bank

Usage

Command-Line Interface:

To use the command-line interface, the gem provides several commands.

Future value:

$ stonehenge_bank future_value --present_value=1000 --rate='3.89% monthly' --period=2 --periodicity='year'
# This command calculates a future value of an investment with present value of 1000, with interest rate of 3.89% monthly, in a return period of 2 year.
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help future_value

Present value:

$ stonehenge_bank present_value --future_value=1000 --rate='3.89% monthly' --period=2 --periodicity='year'
# This command calculates a present value of an investment with future value of 1000, with interest rate of 3.89% monthly, in a return period of 2 year.
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help present_value

Investment period:

$ stonehenge_bank investment_period --present_value=100 --future_value=1000 --rate='3.89% monthly' --periodicity=year
# This command calculates the investment return period, in years, of an investment with present value of 100, future value of 1000, and interest rate of 3.89% monthly.
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help investment_period

Investment rate:

$ stonehenge_bank investment_rate --present_value=100 --future_value=1000 --period=20
# This command calculates the investment rate of an investment with present value of 100, future value of 1000 in a period of 20 (months).
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help investment_rate

Investment regular parcel:

$ stonehenge_bank regular_parcel --present_value=100 --future_value=1000 --rate '1.25% annually' --period=20 --periodicity=month
# This command calculates the regular parcel paid by an investment with present value of 100, future value of 1000 in a period of 20 months, rating 1.25% annually.
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help regular_parcel

Net present value:

$ stonehenge_bank net_present_value --init_cost=30000 --returns 20000 45000 30000 --rate '1.25% annually' --periodicity=month
# This command calculates net present value for an investment with initial cost of 30000, returns of 20000, 45000 and 30000 monthly, rating 1.25% annually.
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help net_present_value

Simple payback:

$ stonehenge_bank simple_payback --init_cost=30000 --returns 20000 45000 30000
# This command calculates simple payback for an investment with initial cost of 30000 and returns of 20000, 45000 and 30000.
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help simple_payback

Discounted payback:

$ stonehenge_bank discounted_payback --init_cost=30000 --returns 20000 45000 30000 --rate '1.25% annually' --periodicity=month
# This command calculates the discounted payback for an investment with initial cost of 30000, returns of 20000, 45000 and 30000 monthly, rating 1.25% annually.
# You can use abbreviated flags for this command. Check via:
$ stonehenge_bank help discounted_payback

Domain-Specific Language inside applications:

StoneHengeBank provides an easy and clarified DSL to be used on applications that depend upon it.

Although it's possible to use the verbosity level with it (set :verbose argument to true), most cases will only need to run numeric results.

Future value:

          StonehengeBank::DSL::Interface.simple_calculations do
            an_investment      with_present_value: 100.0
            with_interest_rate "3.89% monthly"
            return_on          period_of: 2, as: "year"
            future_value       verbose: false
          end

Present value:

          StonehengeBank::DSL::Interface.simple_calculations do
            an_investment      with_future_value: 1500.0
            with_interest_rate "3.89% monthly"
            return_on          period_of: 2, as: "year"
            present_value       verbose: false
          end

Investment period:

          StonehengeBank::DSL::Interface.simple_calculations do
            an_investment with_present_value: 100.0, with_future_value: 4780.0
            with_interest_rate "1.7% annually"
            return_on as: "year"
            investment_period verbose: false
          end

Investment rate:

          StonehengeBank::DSL::Interface.simple_calculations do
            an_investment with_present_value: 1200.99, with_future_value: 130_470.99
            return_on period_of: 36
            investment_rate verbose: false
          end

Investment regular parcel:

          StonehengeBank::DSL::Interface.simple_calculations do
            an_investment with_present_value: 159.70, with_future_value: 1300.0
            with_interest_rate "0.079% monthly"
            return_on period_of: 12, as: "month"
            regular_parcel verbose: false
          end

Net present value:

          StonehengeBank::DSL::Interface.cash_flow_calculations do
            an_investment with_initial_cost: 450000.00
            with_interest_rate "0.079% monthly"
            has_returns_of 30_000.89, 550_730.82, 899_720.32
            return_on as: :year
            net_present_value
          end

Simple payback:

          StonehengeBank::DSL::Interface.cash_flow_calculations do
            an_investment with_initial_cost: 450000.00
            has_returns_of 30_000.89, 550_730.82, 899_720.32
            simple_payback
          end

Discounted payback:

          StonehengeBank::DSL::Interface.cash_flow_calculations do
            an_investment with_initial_cost: 450000.00
            with_interest_rate "0.079% monthly"
            has_returns_of 30_000.89, 550_730.82, 899_720.32
            return_on as: :year
            discounted_payback
          end

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment. Run bundle exec stonehenge_bank to use the gem in this directory, ignoring other installed copies of this gem.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Testing

StoneHengeBank has a test suite based on integration tests for CLI commands and unit tests. In order to run the test suite, just run:

$ rspec

or

$ bundle exec rspec

Contributing

Bug reports and pull requests are welcome. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

License

The gem is available as open source under the terms of the MIT License.