Wave Software Development Challenge

Applicants for the Full-stack Developer role at Wave must complete the following challenge, and submit a solution prior to the onsite interview.

The purpose of this exercise is to create something that we can work on together during the onsite. We do this so that you get a chance to collaborate with Wavers during the interview in a situation where you know something better than us (it's your code, after all!)

There isn't a hard deadline for this exercise; take as long as you need to complete it. However, in terms of total time spent actively working on the challenge, we ask that you not spend more than a few hours, as we value your time and are happy to leave things open to discussion in the on-site interview.

Please use whatever programming language and framework you feel the most comfortable with.

Feel free to email dev.careers@waveapps.com if you have any questions.

Project Description

Imagine that this is the early days of Wave's history, and that we are prototyping a new payroll system API. A front end (that hasn't been developed yet, but will likely be a single page application) is going to use our API to achieve two goals:

1. Upload a CSV file containing data on the number of hours worked per day per employee
2. Retrieve a report detailing how much each employee should be paid in each pay period

All employees are paid by the hour (there are no salaried employees.) Employees belong to one of two job groups which determine their wages; job group A is paid $20/hr, and job group B is paid $30/hr. Each employee is identified by a string called an "employee id" that is globally unique in our system.

Hours are tracked per employee, per day in comma-separated value files (CSV). Each individual CSV file is known as a "time report", and will contain:

1. A header, denoting the columns in the sheet (date, hours worked, employee id, job group)
2. 0 or more data rows

In addition, the file name should be of the format time-report-x.csv, where x is the ID of the time report represented as an integer. For example, time-report-42.csv would represent a report with an ID of 42.

You can assume that:

1. Columns will always be in that order.
2. There will always be data in each column and the number of hours worked will always be greater than 0.
3. There will always be a well-formed header line.
4. There will always be a well-formed file name.

A sample input file named time-report-42.csv is included in this repo.

What your API must do:

We've agreed to build an API with the following endpoints to serve HTTP requests:

1. An endpoint for uploading a file.

   • This file will conform to the CSV specifications outlined in the previous section.
   • Upon upload, the timekeeping information within the file must be stored to a database for archival purposes.
   • If an attempt is made to upload a file with the same report ID as a previously uploaded file, this upload should fail with an error message indicating that this is not allowed.

2. An endpoint for retrieving a payroll report structured in the following way:

   NOTE: It is not the responsibility of the API to return HTML, as we will delegate the visual layout and redering to the front end. The expectation is that this API will only return JSON data.

   • Return a JSON object payrollReport.
   • payrollReport will have a single field, employeeReports, containing a list of objects with fields employeeId, payPeriod, and amountPaid.
   • The payPeriod field is an object containing a date interval that is roughly biweekly. Each month has two pay periods; the first half is from the 1st to the 15th inclusive, and the second half is from the 16th to the end of the month, inclusive. payPeriod will have two fields to represent this interval: startDate and endDate.
   • Each employee should have a single object in employeeReports for each pay period that they have recorded hours worked. The amountPaid field should contain the sum of the hours worked in that pay period multiplied by the hourly rate for their job group.
   • If an employee was not paid in a specific pay period, there should not be an object in employeeReports for that employee + pay period combination.
   • The report should be sorted in some sensical order (e.g. sorted by employee id and then pay period start.)
   • The report should be based on all of the data across all of the uploaded time reports, for all time.

   As an example, given the upload of a sample file with the following data:

   date	hours worked	employee id	job group
   2020-01-04	10	1	A
   2020-01-14	5	1	A
   2020-01-20	3	2	B
   2020-01-20	4	1	A

   A request to the report endpoint should return the following JSON response:

   {
     payrollReport: {
       employeeReports: [
         {
           employeeId: 1,
           payPeriod: {
             startDate: "2020-01-01",
             endDate: "2020-01-15"
           },
           amountPaid: "$300.00"
         },
         {
           employeeId: 1,
           payPeriod: {
             startDate: "2020-01-16",
             endDate: "2020-01-31"
           },
           amountPaid: "$80.00"
         },
         {
           employeeId: 2,
           payPeriod: {
             startDate: "2020-01-16",
             endDate: "2020-01-31"
           },
           amountPaid: "$90.00"
         }
       ];
     }
   }

We consider ourselves to be language agnostic here at Wave, so feel free to use any combination of technologies you see fit to both meet the requirements and showcase your skills. We only ask that your submission:

• Is easy to set up
• Can run on either a Linux or Mac OS X developer machine
• Does not require any non open-source software

Documentation:

Please commit the following to this README.md:

1. Instructions on how to build/run your application
2. Answers to the following questions:
   • How did you test that your implementation was correct?
   • If this application was destined for a production environment, what would you add or change?
   • What compromises did you have to make as a result of the time constraints of this challenge?

Submission Instructions

1. Clone the repository.
2. Complete your project as described above within your local repository.
3. Ensure everything you want to commit is committed.
4. Create a git bundle: git bundle create your_name.bundle --all
5. Email the bundle file to dev.careers@waveapps.com and CC the recruiter you have been in contact with.

Evaluation

Evaluation of your submission will be based on the following criteria.

1. Did you follow the instructions for submission?
2. Did you complete the steps outlined in the Documentation section?
3. Were models/entities and other components easily identifiable to the reviewer?
4. What design decisions did you make when designing your models/entities? Are they explained?
5. Did you separate any concerns in your application? Why or why not?
6. Does your solution use appropriate data types for the problem as described?

Jeff Documentation

Installation instructions

used ruby version 2.7.1 to develop, uses sqlite for relational database prerequisites: requires rbenv/rvm for installing ruby and gem install bundler

1. run bundle install
2. run migrations: a) rails db:setup b) RAILS_ENV=test rails db:setup
3. for unit tests: rspec
4. to run the server: rails s (will be available at localhost:3000 by default)

available routes

1. /time_report - POST request ex: curl -F 'file=@"time-report-42.csv"' localhost:3000/time_report while in project root directory

2. /payroll_report - GET returns the report of all EmployeeTime from all imported csv files so far, ex: localhost:3000/payroll_report

High level design

Helper Libraries

• time_report_csv_importer - responsible for taking csv file path and saving EmployeeTime records plus extra data (pay period start and end date for easier report generation)
• pay_roll_report_generator - run SQL to generate the payroll report

Models

• EmployeeTime - represents each line in the imported csv + additional information (used for generating payroll report)
• TimeReport - response each csv file uploaded and related info

Non database models

EmployeePeriodPayrollReport - represents each line in the generated report (hold data and help with displaying)

Questions

1. How did you test that your implementation was correct?

• having unit tests
• running it locally (upload the csv file and hitting the payroll report to see the generated report + some spot checks from the csv to generated report)

2. If this application was destined for a production environment, what would you add or change?

• use PostgreSQL or MySQL for the relational database since sqlite is for prototyping only (will need to added indices for the group by query I am using)
• link each EmployeeTime to TimeReport (for debugging purposes: which records came from which files)
• handle more edge cases for file upload (requires more discussion)
• add a linting program like Rubocop (easier to add it now than later where there could be very different code style across the files)
• add a CI pipeline (something that will run all the unit tests when a commit or PR is merged to master)

3. What compromises did you have to make as a result of the time constraints of this challenge?

• handling edge cases for csv imports, assuming best case scenario only, filename checking and only upload same report once edge case ex: -if two csv files import the same record, what happens? -if duplicate records happen in a same file, what happens?
• handling the csv import asynchronously via a background worker like Sidekiq (probably not needed, depends if the csv file will be big)

payroll report output for only time-report-42.csv

{"payrollReport":{"employeeReports":[{"employeeId":"1","payPeriod":{"startDate":"2016-11-01","endDate":"2016-11-15"},"amountPaid":"$150.00"},{"employeeId":"1","payPeriod":{"startDate":"2016-11-16","endDate":"2016-11-30"},"amountPaid":"$220.00"},{"employeeId":"1","payPeriod":{"startDate":"2016-12-01","endDate":"2016-12-15"},"amountPaid":"$150.00"},{"employeeId":"1","payPeriod":{"startDate":"2016-12-16","endDate":"2016-12-31"},"amountPaid":"$220.00"},{"employeeId":"2","payPeriod":{"startDate":"2016-11-01","endDate":"2016-11-15"},"amountPaid":"$930.00"},{"employeeId":"2","payPeriod":{"startDate":"2016-12-01","endDate":"2016-12-15"},"amountPaid":"$930.00"},{"employeeId":"3","payPeriod":{"startDate":"2016-11-01","endDate":"2016-11-15"},"amountPaid":"$590.00"},{"employeeId":"3","payPeriod":{"startDate":"2016-12-01","endDate":"2016-12-15"},"amountPaid":"$470.00"},{"employeeId":"4","payPeriod":{"startDate":"2015-02-16","endDate":"2015-02-28"},"amountPaid":"$100.00"},{"employeeId":"4","payPeriod":{"startDate":"2016-02-16","endDate":"2016-02-29"},"amountPaid":"$150.00"},{"employeeId":"4","payPeriod":{"startDate":"2016-11-01","endDate":"2016-11-15"},"amountPaid":"$150.00"},{"employeeId":"4","payPeriod":{"startDate":"2016-11-16","endDate":"2016-11-30"},"amountPaid":"$450.00"},{"employeeId":"4","payPeriod":{"startDate":"2016-12-01","endDate":"2016-12-15"},"amountPaid":"$150.00"},{"employeeId":"4","payPeriod":{"startDate":"2016-12-16","endDate":"2016-12-31"},"amountPaid":"$450.00"}]}}