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#Cabify Backend Challenge This my solution for the Cabify Backend challenge.

Client application can be found here.

Considerations

This set of applications have been developed using the Java programming language, Spring Boot framework, Spring Shell library and Spring Boot Admin library. I have also used docker and docker compose in order to provide some facilities to make extremely easy to run the system.

I have use the OOP paradigm for the development and also have followed the hexagonal architecture in order to provide a clean architecture with the business logic decoupled from infrastructure concerns. The system has a pretty high code coverage and I can tell that it is almost bug-free (you can never be 100% that your code is bug free).

The system is composed by three different applications:

  • Cabify Store Server: It is the core of the system, consist of a Spring Boot app implementing a REST API with several endpoints that allow to perform the different required operations. Here I used a ConcurrentHashMap as data structure to store the shopping carts so operations over carts are thread safe. In addition, I have implemented an additional synchronization mechanism through a read/write lock in the cart class to ensure that concurrent operations over the same cart are executed consistently. I haven't used any concurrent collection for the item repository since operations over items are read only (I have made the assumption that items cannot be added while the application is running). I would like to have added some tests to ensure that concurrent operations run consistently but unfortunately I run out of time. I have also added a correlation ID feature in order to allow the traceability of requests. Available items in the repository are configured through a Spring Boot property and are loaded when the application starts. Available discounts are also loaded on application start but they are not configurable via properties, I would have liked to add this feature but it is not straightforward due to the heterogeneous nature of the discounts configuration, and finally I didn't have time to investigate and implement that feature. I have also made the assumption that there is just one applicable discount per cart entry.

  • Cabify Store Client: This is a CLI application that implements a client that allows the interaction with the server. This app is developed using Spring Boot + Spring Shell. It provides several commands that allow to perform all required operations against the server. The shell contains several commodities like autocompletion and help. I would have liked to add some integration tests for the commands but I finally did not get the time to do it.

  • Spring Boot Admin Server: This is a Spring Boot app implementing the Spring Boot Admin which provides a UI over Spring Boot Actuators allowing to admin one or several spring boot apps remotely from a central server. I have added this app in order to provide visibility and observability for the server application. Only the server application is connected to the admin server.

I have developed the system in two different repositories:

  • Cabify Store Server: A multi-module maven project that contains the cabify store server and the admin server bootapps. I know that I should have developed this two applications in two different repositories, but I took this decision in order to ease the development at the beginning and I finally did not find the moment to split it. I would like to point out also that I have developed each layer of the hexagonal architecture in a different module, I don't usually apply this technique in my daily basis but I considered interesting to do it here to make clearer the layer separation and to make me more conscious of the dependencies between layers. However, in hindsight, I can tell that I would not take the same decision again if I had to repeat the exercise, since it add more pain than value.

  • Cabify Store Client: A single module maven project implementing the client application.

Running

In order to run the applications you need to have installed the Java 8 SDK. I have added docker files to build each application in a docker image, and docker compose file to ease the orchestration of the application startup, but you still need to have Java installed in order to generate the jar files. Docker images generations is automated through maven, although you can still build the images without using maven, that is up to you.

Manual Running

You can easily run the system manually without docker, I have added a maven wrapper on each repository and module in order to ease the build and run. You can run each app using the spring boot maven plugin ./mvnw spring-boot:run or executing the jar file generated after a ./mvnw package.

Store Server and Admin Server

  1. Run ./mvnw install from the repository's root directory in order to build the whole application and make sure that all tests pass.
cd /path/to/cabify-store-server
./mvnw install
  1. Run Admin Server:
cd /path/to/cabify-store-server/spring-boot-admin-server
./mvnw spring-boot:run
  1. Run Store Server:
cd /path/to/cabify-store-server/infrastructure
./mvnw spring-boot:run
  1. You can access the admin server through http://localhost:10011/ (it listens on port 10011 by default), there you can see the store server application status which should be UP. Store server listens on port 8080 by default.

Store Client

  1. Run ./mvnw install from the repository's root directory in order to build the whole application and make sure that all tests pass.
cd /path/to/cabify-store-client
./mvnw install
  1. Run the client shell application:
cd /path/to/cabify-store-client
./mvnw spring-boot:run
  1. You can start entering commands to work with the application. First, I recommend to to type help in order to get help on the different commands use.

Run with Docker and Docker compose

Each image docker file is located under /docker directory on each repository, although the docker-compose.yml located in the cabify store server repository contains the configuration to start up the whole system (store client included).

  1. Build the image for the Admin Server:
cd /path/to/cabify-store-server/spring-boot-admin-server
./mvnw package
  1. Build the image for the Store Server:
cd /path/to/cabify-store-server/cabify-store-server
./mvnw package
  1. Build the image for the Store Client:
cd /path/to/cabify-store-client
./mvnw package
  1. Start the container and attach to client shell:
cd /path/to/cabify-store-server/docker
docker-compose run storeclient

The previous command should start the three containers and attach to the client application shell, so you can start working right after. It's possible that it takes a little bit of time for docker to establish the connections between containers, so if you get an error at the very first command you enter, please wait a moment and try again.

Cabify Store Server REST API

The server REST API is made by the following endpoints:

  • POST /cart Creates a new cart.
  • POST /cart/{cartId}/item Add an item to the cart.
{ "itemCode": "TSHIRT", "quantity": 1 }
  • GET /cart/{cartId} Get total amount for given cart.
  • DELETE /cart/{cartId} Remove given cart.

Cabify Store Client CLI application

The shell application provides the following commands

  • add, add-item: Add an item to an existent cart
NAME
	add - Add an item to an existent cart

SYNOPSYS
	add [-cart] string  [-item] string  [[-quantity] int]

OPTIONS
	-cart or -cartId  string
		Id of the cart to add the item to
		[Mandatory]

	-item or -itemCode or -code  string
		Code of the item to be added to the cart (VOUCHER|TSHIRT|MUG)
		[Mandatory]

	-quantity  int
		Id of the cart to add the item to
		[Optional, default = 1]

ALSO KNOWN AS
	add-item
  • add-bulk, add-several-items: Add several items to an existent cart (just one unit per item)
NAME
	add-bulk - Add several items to an existent cart (just one unit per item)

SYNOPSYS
	add-bulk [-cart] string  [-items] string

OPTIONS
	-cart or -cartId  string
		Id of the cart to add the items to
		[Mandatory]

	-items or -itemCodes or -codes  string
		Comma-separated list of item-codes to be added to the cart (VOUCHER,TSHIRT,MUG,TSHIRT)
		[Mandatory]

ALSO KNOWN AS
	add-several-items
  • create, create-cart: Create a new shopping cart
NAME
	create - Create a new shopping cart

SYNOPSYS
	create

ALSO KNOWN AS
	create-cart
  • delete, delete-cart: Delete the given cart
NAME
	delete - Delete the given cart

SYNOPSYS
	delete [-cart] string

OPTIONS
	-cart or -cartId  string
		Id of the cart to be deleted
		[Mandatory]

ALSO KNOWN AS
	delete-cart
  • get-cart-total, total: Return the total amount for the given cart
NAME
	get-cart-total - Return the total amount for the given cart

SYNOPSYS
	get-cart-total [-cart] string

OPTIONS
	-cart or -cartId  string
		Id of the cart
		[Mandatory]

ALSO KNOWN AS
	total

TODO

  • Load available discounts via configuration properties.
  • Remove domain entities tests and test them in a transitive way via application services tests.
  • Add tests to ensure that concurrent operations on server behaves consistently.
  • Refactor server application's Price class to make it receive a simple float or double value (maybe a string) through its constructor instead of receive a BigDecimal which is its inner value. I think the code would be clearer this way.
  • Add correlation ID for command executions in client application, and propagate it through request to server application, so full system traceability is possible.
  • Add integration tests for client commands.
  • Connect client application to admin server.