Coding Challenge

For this prompt we want to build a tool together that lets us analyze a file of JSON data.

Imagine we're tasked to write a script that will be run a couple times a year by an engineer on your team. It should be readable/maintainable, but doesn't need to be extremely robust. We're more interested in just getting to the solution quickly then on making it scalable, extensible, 100% tested, etc.

Some Background

Our customers are primarily doctors offices, which we call a "Practice". Our doctors make money by selling monthly memberships to their patients.

We track how these memberships change over time in our system as "events". This lets us report ons how their memberships changes over time.

There are 4 types of events. Each has a created_at, type, and membership field, but the other attributes vary, depending on the type of event. The events are:

1. membership.started A membership started

{
  created_at: String, # i.e. "2022-01-03 14:02:06"
  type: "membership.started",
  start_date: String, # i.e. "2022-01-02",
  plan: String,
  price: Integer,
  membership: String,
  patient: String,
}

2. membership.ended A membership ended

{
  created_at: String, # i.e. "2022-01-03 14:02:06"
  type: "membership.ended",
  end_date: String, # i.e. "2022-01-02",
  plan: String,
  price: Integer,
  membership: String,
  patient: String,
}

3. membership.price_changed The cost of a membership changed

{
  created_at: String, # i.e. "2022-01-03 14:02:06"
  type: "membership.price_changed",
  from_price: Integer,
  to_price: Integer,
  membership: String,
}

4. membership.plan_changed The plan of a membership changed

{
  created_at: String, # i.e. "2022-01-03 14:02:06"
  type: "membership.plan_changed",
  from_plan: String,
  to_plan: String,
  membership: String,
}

The full event data for this year for a practice is provided as a json file in data/patients.json

Challenge / Goals

We want to write a script that can answer the following questions. How it does this is up to you - as long as it would be usable to a developer tasked with running it.

1. How many events are in the file?
2. What's the total change in revenue for the year?
3. What's the change of revenue in April? For instance...

A membership starts with price $100.00
A membership ends with price $50.00
A membership price changes from $10.00 to $20.00

We'd expect the revenue change to be $60.00

4. What is the total revenue each month assuming the practice finished 2021 with a revenue of $10,000.00
5. What's the % change in revenue month over month? For instance, if April's revenue was $100.00 and May's was $150.00, the month over month change is 50%.
6. How many active members does the practice have at the end of each month, assuming it ended 2021 with 500 members

Extra Credit / If we have time:

We have a patient's DB, for this exercise is also provided as json.

A patient has the following format:

{
  id: String,
  name: String,
  date_of_birth: String, # ie "2002-09-28"
}

1. We want to know the average age of new members month over month?
2. What about the median?

Even more questions:

• How would you implement a system that does this?
• How will you generate the data?
• How will you store it?