I started by dividing up the problem into four major components/responsibilities:

1. A server to receive and route API requests to a controller
2. A controller that forms requests into a domain-specific query for the business logic layer
3. A business logic layer that does the heavy lifting of the problem: interpreting the query and performing the filtering and sorting
4. A CSV reader that turns the flat file into domain objects for the business logic layer to work with

The business logic layer is where the challenging problem lies; all the rest is wiring. So I decided to focus on that as the center of the design. It was critical that the interfaces on either side of it were sensible and easy to drop into a test harness. I spent the majority of my time deciding on how to lay out the interfaces and crafting the unit tests. When it could stand on its own, I set up the server in server.ts and resolved the dependencies, making a basic controller and shopping for a decent CSV reader.

• Tests for server
• Clean up controller test
• Come up with a better name for the business logic layer (OrganizationData)
• Refactor the OrganizationData tests for clarity

It's a Node.js project, so we'll need to start with the typical Node.js prep. First, either install the latest Node.js runtime or have nvm get it for you, using the .nvmrc file:

nvm install

Now that we have the correct Node.js version, install the project's dependencies:

npm install

Run the Jest tests as you would for any other Node.js project:

npm test

Since this is a TypeScript project, the start script will also do a build prior to starting the server with node:

npm start

You can reach the API via localhost:3000. For example: http://localhost:3000/organizations?category=Greek&city=Washington.