stocks forwarding kata
The goal of this kata is to improve your skills when it comes to testing http services in golang. The application to be build will calculate the daily percentage-wise change in stock prices for a particular stock and forward this result to another service. You may implement the receiving endpoint in whichever way you see fit. However, it should receive JSON in the following format:
{
"msf": [
["2020-02-20", 120],
["2020-02-21", 100],
["2020-02-22", 110],
["2020-02-23", 130]
],
"goog": [
["2020-02-20", 220],
["2020-02-21", 250],
["2020-02-22", 210],
["2020-02-23", 180]
]
}This means the stock msf was worth 120$ on 2020-02-20 and 100$ on 2020-02-21 etc. Note that there can be more than one stock item (in this example msf and goog).
The endpoint for the other service is POST http://foo.invalid/changes/{Symbol} where {Symbol} is a ticker symbol (for example MSF for microsoft). It must receive a list of changes in percentages per day. Example: POST http://foo.invalid/changes/MSF Body:
[
["2020-02-21", -16.67],
["2020-02-22", 10.00],
["2020-02-23", 18.18]
]The first value means that from the 2020-02-20 to 2020-02-21 the stock went down by -16.67 percent. The second value means that the stock went up by 10 percent from 2020-02-21 to 2020-02-22. Note that 2020-02-20 is missing. This is because there is no value before that so we cannot calculate a change in percentage.
This solution
Even though the business logic of this service is extremely simple I would like to implement this service using a hexagonal architecture. This has the benefit that the business logic can be developed independently from the infrastructure (maybe we want this functionality as a command line utility later). (^1)
(1) One should note that it is questionable why this piece of business logic deserves its own service. Following DDD this service and the other service should most likely be combined as they (more than likely) share a common language in terms of the business logic.