Ruby solution to Merchant's Guide to the Galaxy problem

You decided to give up on earth after the latest financial collapse left 99.99% of the earth's population with 0.01% of the wealth. Luckily, with the scant sum of money that is left in your account, you are able to afford to rent a spaceship, leave earth, and fly all over the galaxy to sell common metals and dirt (which apparently is worth a lot).

Buying and selling over the galaxy requires you to convert numbers and units, and you decided to write a program to help you.

The numbers used for intergalactic transactions follows similar convention to the roman numerals and you have painstakingly collected the appropriate translation between them.

Numbers are formed by combining symbols together and adding the values. For example, MMVI is 1000 + 1000 + 5 + 1 = 2006. Generally, symbols are placed in order of value, starting with the largest values. When smaller values precede larger values, the smaller values are subtracted from the larger values, and the result is added to the total. For example MCMXLIV = 1000 + (1000 − 100) + (50 − 10) + (5 − 1) = 1944.

The symbols "I", "X", "C", and "M" can be repeated three times in succession, but no more. (They may appear four times if the third and fourth are separated by a smaller value, such as XXXIX.) "D", "L", and "V" can never be repeated. "I" can be subtracted from "V" and "X" only. "X" can be subtracted from "L" and "C" only. "C" can be subtracted from "D" and "M" only. "V", "L", and "D" can never be subtracted. Only one small-value symbol may be subtracted from any large-value symbol.

A number written in [16]Arabic numerals can be broken into digits. For example, 1903 is composed of 1, 9, 0, and 3. To write the Roman numeral, each of the non-zero digits should be treated separately. Inthe above example, 1,000 = M, 900 = CM, and 3 = III. Therefore, 1903 = MCMIII.

Input to your program consists of lines of text detailing your notes on the conversion between intergalactic units and roman numerals. You are expected to handle invalid queries appropriately.

glob is I

prok is V

pish is X

tegj is L

glob glob Silver is 34 Credits

glob prok Gold is 57800 Credits

pish pish Iron is 3910 Credits

how much is pish tegj glob glob ?

how many Credits is glob prok Silver ?

how many Credits is glob prok Gold ?

how many Credits is glob prok Iron ?

how much wood could a woodchuck chuck if a woodchuck could chuck wood ?

pish tegj glob glob is 42

glob prok Silver is 68 Credits

glob prok Gold is 57800 Credits

glob prok Iron is 782 Credits

I have no idea what you are talking about

It will output an error message when the resulting Roman numeral is invalid.

Example:

how much is pish pish pish pish pish ? will result in: That's not even a real unit!

It consists of InputParser, Galaxy, Metal and Roman classes.

• InputParser parses each line and performs the corresponding action (like adding galactic units or coversions).
• Galaxy is responsible of managing galactic units and their conversion to integer.
• Metal handles metal units like Silver and Iron, allowing us to either add new units or convert existing ones to Credits.
• Roman performs the conversion between Roman numerals and integers.

InputParser depends on Galaxy and Metal, which are both injected parameters. Galaxy for instance depends on Roman, a direct dependency. At last, Metal depends on Galaxy, which is also injected.

This ships with a "helper" script merchant_galaxy.rb. It reads from input.txt file by default. Modify this file at your will :)

ruby merchant_galaxy.rb

ruby merchant_galaxy.rb different-file.txt

Tests are written using rspec and can be run by using rspec or rspec spec/test_file commands.

There are both unit and integration specs and they can be found in spec/ and spec/integration directories respectively.

• rspec >= 3.7
• ruby >= 2.4