Introduction

Hello engineering candidate! This is Hologram's take-home exercise for software engineers with a backend or full-stack focus. The challenge will be to implement a “usage parser” class to handle several types of incoming data strings, differentiated by id, and parse their constituent data. To facilitate this, we’ve done the TDD part for you: you have a set of tests that should pass when the class is complete!

Setup

The tests require RSpec to run. There is a basic Gemfile that should install it via bundle install. To run the tests, just enter the command rspec. To see more detailed output from the tests, run rspec --format d.

Evaluation

We'll be evaluating each submission based on the following criteria:

Passing Tests - Your code should fulfill the basic requirements of the challenge. We’ll expect to see the original tests passing for your code.

Readability / Maintainability - This isn’t full production code, but the results of your solution should be well-organized and readable. We value long-term maintainability of code.

Requirements

Parser Class

The skeleton parser class has been provided in the repository. The parse method should accept a usage string or an array of strings. It should perform the parsing and return an array of objects containing the id and the available values as depicted below. Values not present in the parsing strings should be included in the returned object as null/nil.

ID Parsing

All strings will have at least two comma-separated values. The first value will always be the id.

• IDs ending with 4 should use the “extended” string parsing scheme to store the data
• IDs ending with 6 should use the “hex” string parsing scheme
• All other IDs should use the “basic” string parsing scheme

Basic String Parsing

Basic strings are comma separated with just two values, the id and the bytes used, both integers.

<id>,<bytes_used>

Extended String Parsing

Extended strings are comma separated with values for multiple fields. All values are integers except dmcc which is a string. Fields are always in the same order.

<id>,<dmcc>,<mnc>,<bytes_used>,<cellid>

Hex String Parsing

<id>,<hex>

Hex strings consist of two comma separate values: the id, and a string of hex bytes representing more rich data. To access the values, the hex string will have to be parsed.

The hex string is a 24-character (12-byte) non-separated string with fixed position elements noted below. Each byte of the string (two characters, e.g. a0) is part of a value. Hex values should be converted to appropriate types when they parsed into fields. All values are integers (e.g. 3a09 would be 14857) except for ip which is a string.

• Bytes 1-2 → mnc
• Bytes 3-4 > bytes_used
• Bytes 5-8 → cellid
• Bytes 9-12 → ip
  • String
  • Each byte is one segment of the ip, separated by a period: e.g. c0a80001 would be '192.168.0.1'

Example parsed objects:

[
  {
    id: 7294,
	mnc: 182,
	bytes_used: 293451,
	dmcc: nil,
	cellid: 31194,
	ip: '192.168.0.1'
  },
  {
	id: 3,
	mnc: 9523,
	bytes_used: 1024,
	dmcc: 'a03',
	cellid: 193955,
	ip: nil
  }
]

Submitting your exercise

When you have something you're happy with, please respond with the URL of your repo, and we'll take a look. While it’s intended to be possible to do very well in only a couple of hours, time pressure is not intended to be a factor, so feel free to take a week to find time to work on it, or longer if your schedule requires.