Welcome to the Moonpig engineering test. Here at Moonpig we really value quality code, and this test has been designed to allow you to show us how you think quality code should be written.
To allow you to focus on the design and implementation of the code we have added all the use cases we expect you to implement to the bottom of the instructions. In return we ask that you make sure your implementation follows all the best practices you are aware of, and that at the end of it, the code you submit, is code you are proud of.
We have not set a timelimit, we prefer that you spend some extra time to get it right and write the highest quality code you can. Please feel free to make any changes you want to the solution, add classes, remove projects etc. If you change the request or response please update the example in the section below.
For bonus points, commit regularly and include the .git folder in your submission. This will allow us to follow the evolution of your solution.
When complete please upload your solution and answers in a .zip to the google drive link provided to you by the recruiter.
You have been tasked with creating a service that calculates the estimated despatch dates of customers' orders.
An order consists of an order date and a collection of products that a customer has added to their shopping basket.
Each of these products is supplied to Moonpig on demand through a number of 3rd party suppliers.
As soon as an order is received by a supplier, the supplier will start processing the order. The supplier has an agreed lead time in which to process the order before delivering it to the Moonpig Post Office.
Once the Moonpig Post Office has received all products in an order it is despatched to the customer.
Assumptions:
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Suppliers start processing an order on the same day that the order is received. For example, a supplier with a lead time of one day, receiving an order today will send it to Moonpig tomorrow.
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For the purposes of this exercise we are ignoring time i.e. if a supplier has a lead time of 1 day then an order received any time on Tuesday would arrive at Moonpig on the Wednesday.
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Once all products for an order have arrived at Moonpig from the suppliers, they will be despatched to the customer on the same day.
When the /api/DespatchDate endpoint is hit return the despatch date of that order.
Moonpig Post Office staff are getting complaints from customers expecting packages to be delivered on the weekend. You find out that the Moonpig post office is shut over the weekend. Packages received from a supplier on a weekend will be despatched the following Monday.
Modify the existing code to ensure that any orders received from a supplier on the weekend are despatched on the following Monday.
The Moonpig post office is still getting complaints... It turns out suppliers don't work during the weekend as well, i.e. if an order is received on the Friday with a lead time of 2 days, Moonpig would receive and dispatch on the Tuesday.
Modify the existing code to ensure that any orders that would have been processed during the weekend resume processing on Monday.
Parts 1 & 2 have already been completed albeit lacking in quality. Please review the code, document the problems you find (see question 1), and refactor into what you would consider quality code.
Once you have completed the refactoring, extend your solution to capture the requirements listed in part 3.
Please note, the provided DbContext is a stubbed class which provides test data. Please feel free to use this in your implementation and tests but do keep in mind that it would be switched for something like an EntityFramework DBContext backed by a real database in production.
While completing the exercise please answer the questions listed below. We are not looking for essay length answers. You can add the answers in this document.
Q1. What 'code smells' / anti-patterns did you find in the existing implemention of part 1 & 2?
- I have detailed all of my findings within this Change Log. The main issues here were
-- Naming conventions - Use of acronyms and name formats not applicable to the type of object (property, field, private variable...)
-- Public variable which should have been a variable local to a method
-- Mix of procedures belonging to different application layers within a single code file (e.g. presentation, data access and business logic).
-- Class named DbContext would have the same name as EF DbContext
-- No business exceptions were raised by any of the code. I have added 2 exceptions to perfrom some basic validation. I would expand upon this if I had more time.
-- Unit tests did not have any structure
-- Dependency injeciton was not being used
-- Loop getting single records from the database. This should have been a single call to the database or a maximum of 2 calls if accessing tables individually (as I have because I wanted to perform some validation)
Q2. What best pracices have you used while implementing your solution?
- I have split my code by layer, allowing business logic to be handled separately to data access and presentation code. As mentioned previously, I would move the data access code from DespatchDatecontroller if I had more time.
- I have implemented some basic validation to assure requests
- Limited database calls
- I have tested all of my code using a combination of unit and behaviour tests. Achieving 100% code coverage within the classes that I created and 94% within the controller.
- I have followed SOLID principles while developing this change.
Q3. What further steps would you take to improve the solution given more time?
- Move the data access element to another file / project
- Consider moving the business logic that I have move to another project. This would enable the code to be reused by other projects, for example when migrating this functioanlity to a new technology.
- If I had more time then I would investigate the remaining 6% test coverage.
- I would consider whether other technologies could be used to provider further performance benefits
Q4. What's a technology that you're excited about and where do you see this being applicable? (Your answer does not have to be related to this problem)
- The ability to develop app services on Azure using gRPC has been high on my list for some time. I am now aware that gRPC is already supported by App Mesh on AWS, which is of great interest to me. This could be applicable to Moonpig as the payload being sent is generally much smaller than that sent to REST services because it is serailised to binary. It also makes use of http2 providing that it is communicating over a secure connection.
Please see examples for how to make requests and the expected response below.
The service is setup as a Web API and takes a request in the following format
GET /api/DespatchDate?ProductIds={product_id}&orderDate={order_date}
e.g.
GET /api/DespatchDate?ProductIds=1&orderDate=2018-01-29T00:00:00
GET /api/DespatchDate?ProductIds=2&ProductIds=3&orderDate=2018-01-29T00:00:00
The response will be a JSON object with a date property set to the resulting Despatch Date
{
"date" : "2018-01-30T00:00:00"
}
Given an order contains a product from a supplier with a lead time of 1 day
And the order is place on a Monday - 01/01/2018
When the despatch date is calculated
Then the despatch date is Tuesday - 02/01/2018
Given an order contains a product from a supplier with a lead time of 2 days
And the order is place on a Monday - 01/01/2018
When the despatch date is calculated
Then the despatch date is Wednesday - 03/01/2018
Given an order contains a product from a supplier with a lead time of 1 day
And the order also contains a product from a different supplier with a lead time of 2 days
And the order is place on a Monday - 01/01/2018
When the despatch date is calculated
Then the despatch date is Wednesday - 03/01/2018
Given an order contains a product from a supplier with a lead time of 1 day
And the order is place on a Friday - 05/01/2018
When the despatch date is calculated
Then the despatch date is Monday - 08/01/2018
Given an order contains a product from a supplier with a lead time of 1 day
And the order is place on a Saturday - 06/01/18
When the despatch date is calculated
Then the despatch date is Tuesday - 09/01/2018
Given an order contains a product from a supplier with a lead time of 1 days
And the order is place on a Sunday - 07/01/2018
When the despatch date is calculated
Then the despatch date is Tuesday - 09/01/2018
Given an order contains a product from a supplier with a lead time of 6 days
And the order is place on a Friday - 05/01/2018
When the despatch date is calculated
Then the despatch date is Monday - 15/01/2018
Given an order contains a product from a supplier with a lead time of 11 days
And the order is place on a Friday - 05/01/2018
When the despatch date is calculated
Then the despatch date is Monday - 22/01/2018