ICEYE Developer Assignment - Poker LARVIS

author: Zoltán Domahidi
date: November 10, 2022

Introduction

The goal of this assignment is to test your familiarity with Go, or provide a small project to start getting into it.

Requirements:
• A Go project, described below, using go modules for any dependencies
• Using any libraries of your choice, except for the poker logic. Please justify your choices on the README.md :)
• It should follow best practices
• It should run via docker

We expect you to return a .zip file with:
• All source files needed to run your project, including a Dockerfile
• A README.md markdown file with instructions on how to build and run your project, with and without docker, and any comments you might want to add

Background

   Drip...
Ugh...
   ...drip...
Came on...
   ...drip...
LARVIS , did you seal the water tank properly?
   Of course I did, I know how important it is for you to keep our water reserves, human.
   ...drip...
LARVISSSS !!!! Ok fine, you go to the tank seal and press the lever a bit more securely. Dripping seems to stop.
   Water seal closed at 105%
LARVIS , recalibrate water seal, this is the 100% now...
   Water seal recalibration... Done.
Well, at least LARVIS has stopped imitating the speech of cat video commenters, like the last time it ”learned” from the media database, so you take this as progress. However, you are still incredibly bored in this station, even when nothing is threatening to kill you.
   You need a break from consuming Earth’s early internet media on your ample free time, and no more chess with LARVIS , it wasn’t ever fun anyway, so... What about Poker?
LARVIS , do you play poker?
   I’m sorry human, I know what it is from my knowledge database, but Space Command added a limitation to play it for some reason. Something about ”gambling” and ”bad idea in an isolated space station”
Right. Well, that doesn’t apply when I’m alone here and getting nuts. You better learn to play it, lets have a poker night!
   I’m sorry, I can’t learn it on my own due to the limit in my programming. You could perhaps add it as an extension module? Yesss!!! That would do. You remember you can program LARVIS to do pretty much whatever, provided you add the module yourself. Poker night time!!!

Program a Poker LARVIS module

One of the issues of having to do this yourself is that you don’t really remember all the Poker rules, so a simplified version will have to do. You write down the rules you remember:

Cards:
• Each player gets a hand of 5 cards
• Available symbols are 23456789TJQKA, in order of value ( A being the more valuable)

Combinations in order of value:
• Four of a kind, like 77377
• Full house, means 3 of a kind, and 2 of a kind, in the same hand, like KK2K2
• Triple, like 32666
• Two pairs, like 77332
• A pair, like 43K9K
• High card, when there’s none of the above, like 297QJ

When two hands have the same combination value, the combination with the higher cards wins. When there are two pairs, the higher pair is compared first, so 99662 wins against 88776 . When comparing full houses, triples go first, then pairs, so 88822 defeats QQ777 . If the combinations are identical, then the other cards are compared, highest to lowest, so 7T2T6 wins against TT753 , because TT = TT , 7 = 7 , but 6 > 5 .

With these rules in mind, you write a quick command line program to pass two hands and output which one is the winner, the first or the second one. From there, LARVIS should be able to evaluate hands and you would get your poker night!

Dockerize your LARVIS module

Huh, you just remembered, in order for LARVIS to load your little program, you have to provide it with a docker image, so you quickly write a Dockerfile and build it. Good to go!

Appendix: Hand examples

Some examples of hands and what the result should be.

Hand 1	Hand 2	Winner
AAAQQ	QQAAA	Tie
53QQ2	Q53Q2	Tie
53888	88385	Tie
QQAAA	AAAQQ	Tie
Q53Q2	53QQ2	Tie
88385	53888	Tie
AAAQQ	QQQAA	Hand 1
Q53Q4	53QQ2	Hand 1
53888	88375	Hand 1
33337	QQAAA	Hand 1
22333	AAA58	Hand 1
33389	AAKK4	Hand 1
44223	AA892	Hand 1
22456	AKQJT	Hand 1
99977	77799	Hand 1
99922	88866	Hand 1
9922A	9922K	Hand 1
99975	99965	Hand 1
99975	99974	Hand 1
99752	99652	Hand 1
99752	99742	Hand 1
99753	99752	Hand 1
QQQAA	AAAQQ	Hand 2
53QQ2	Q53Q4	Hand 2
88375	53888	Hand 2
QQAAA	33337	Hand 2
AAA58	22333	Hand 2
AAKK4	33389	Hand 2
AA892	44223	Hand 2
AKQJT	22456	Hand 2
77799	99977	Hand 2
88866	99922	Hand 2
9922K	9922A	Hand 2
99965	99975	Hand 2
99974	99975	Hand 2
99652	99752	Hand 2
99742	99752	Hand 2
99752	99753	Hand 2

---

Running the module

With the help of make commands it is possible to build the module:

• make install - installs the dependencies
• make build - runs the tests and build the poker binary
• make package - creates the Docker image.

In case make is not installed the commands could be run from the Makefile instead.

Running the module is possible by three ways:

1. build the module with make build and run the bin/poker [hand1] [hand2] command (where [hand1] and [hand2] must be replaced with the actual card values, i.e. 476KA)
2. simply run the go application with go run main.go [hand1] [hand2]
3. package the module with make package and run the container with docker run iceye/poker [hand1] [hand2]

Code explanation

The solution could have been much shorter but I used multiple files to have better modularity and testability.

The internal folder contains most of the logic. The cards are tokenized into a Combinations struct which will help to compare the cards by their value and strength of combination. Two combinations could be compared where we evaluate in order all the rule comparators having the CompareRuleFunc function. Each rule is evaluated independently and in case of equality the comparator calls the next rule. This means the order of the rules are important.

The internal modules have no knowledge about the actual rule orders and because of this it is easy to change their order or to implement new rules (if needed). The rules are instantiated and passed to the comparator in the pkg folder where the validations, game rules and game evaluation are defined.

The pokerlarvis_test.go acts as an integration test and it contains all the tests scenarios attached to the assignment.

The cmd folder contains the command part of the game.

Used libraries

Only a two modules were used:

• github.com/spf13/cobra to make a simple CLI interface with argument validation and help functionality
• github.com/stretchr/testify for testing which has some nice features over the built-in go testing library like asserts, mocks, test preparation and clean up