Design/implement a system to manage car pooling.
At Cabify we provide the service of taking people from point A to point B. So far we have done it without sharing cars with multiple groups of people. This is an opportunity to optimize the use of resources by introducing car pooling.
You have been assigned to build the car availability service that will be used to track the available seats in cars.
Cars have a different amount of seats available, they can accommodate groups of up to 4, 5 or 6 people.
People requests cars in groups of 1 to 6. People in the same group want to ride on the same car. You can take any group at any car that has enough empty seats for them. If it's not possible to accommodate them, they're willing to wait until there's a car available for them. Once a car is available for a group that is waiting, they should ride.
Once they get a car assigned, they will journey until the drop off, you cannot ask them to take another car (i.e. you cannot swap them to another car to make space for another group).
In terms of fairness of trip order: groups should be served as fast as possible, but the arrival order should be kept when possible. If group B arrives later than group A, it can only be served before group A if no car can serve group A.
For example: a group of 6 is waiting for a car and there are 4 empty seats at a car for 6; if a group of 2 requests a car you may take them in the car. This may mean that the group of 6 waits a long time, possibly until they become frustrated and leave.
This challenge has a partially automated scoring system. This means that before it is seen by the evaluators, it needs to pass a series of automated checks and scoring.
All checks need to pass in order for the challenge to be reviewed.
- The
acceptancetest step in the.gitlab-ci.ymlmust pass in master before you submit your solution. We will not accept any solutions that do not pass or omit this step. This is a public check that can be used to assert that other tests will run successfully on your solution. This step needs to run without modification - "further tests" will be used to prove that the solution works correctly. These are not visible to you as a candidate and will be run once you submit the solution
There is a number of scoring systems being run on your solution after it is submitted. It is ok if these do not pass, but they add information for the reviewers.
To simplify the challenge and remove language restrictions, this service must provide a REST API which will be used to interact with it.
This API must comply with the following contract:
Indicate the service has started up correctly and is ready to accept requests.
Responses:
- 200 OK When the service is ready to receive requests.
Load the list of available cars in the service and remove all previous data (reset the application state). This method may be called more than once during the life cycle of the service.
Body required The list of cars to load.
Content Type application/json
Sample:
[
{
"id": 1,
"seats": 4
},
{
"id": 2,
"seats": 6
}
]Responses:
- 200 OK When the list is registered correctly.
- 400 Bad Request When there is a failure in the request format, expected headers, or the payload can't be unmarshalled.
A group of people requests to perform a journey.
Body required The group of people that wants to perform the journey
Content Type application/json
Sample:
{
"id": 1,
"people": 4
}Responses:
- 200 OK or 202 Accepted When the group is registered correctly
- 400 Bad Request When there is a failure in the request format or the payload can't be unmarshalled.
A group of people requests to be dropped off. Whether they traveled or not.
Body required A form with the group ID, such that ID=X
Content Type application/x-www-form-urlencoded
Responses:
- 200 OK or 204 No Content When the group is unregistered correctly.
- 404 Not Found When the group is not to be found.
- 400 Bad Request When there is a failure in the request format or the payload can't be unmarshalled.
Given a group ID such that ID=X, return the car the group is traveling
with, or no car if they are still waiting to be served.
Body required A url encoded form with the group ID such that ID=X
Content Type application/x-www-form-urlencoded
Accept application/json
Responses:
- 200 OK With the car as the payload when the group is assigned to a car. See below for the expected car representation
{
"id": 1,
"seats": 4
}- 204 No Content When the group is waiting to be assigned to a car.
- 404 Not Found When the group is not to be found.
- 400 Bad Request When there is a failure in the request format or the payload can't be unmarshalled.
At Cabify, we use Gitlab and Gitlab CI for our backend development work. In this repo you may find a .gitlab-ci.yml file which contains some tooling that would simplify the setup and testing of the deliverable. This testing can be enabled by simply uncommenting the final acceptance stage. Note that the image build should be reproducible within the CI environment.
Additionally, you will find a basic Dockerfile which you could use a baseline, be sure to modify it as much as needed, but keep the exposed port as is to simplify the testing.
acceptance step of .gitlab-ci.yml, such as
docker-compose
You are free to use whatever programming language you deem is best to solve the problem but please bear in mind we want to see your best!
You can ignore the Gitlab warning "Cabify Challenge has exceeded its pipeline minutes quota," it will not affect your test or the ability to run pipelines on Gitlab.
- The service should be as efficient as possible.
It should be able to work reasonably well with at least
$10^4$ /$10^5$ cars / waiting groups. Explain how you did achieve this requirement. - You are free to modify the repository as much as necessary to include or remove dependencies, subject to tooling limitations above.
- Document your decisions using MRs or in this very README adding sections to it, the same way you would be generating documentation for any other deliverable. We want to see how you operate in a quasi real work environment.
In Cabify, we really appreciate your interest and your time. We are highly interested on improving our Challenge and the way we evaluate our candidates. Hence, we would like to beg five more minutes of your time to fill the following survey:
Your participation is really important. Thanks for your contribution!
The REST API application is created with Ruby 3.3.3 and Rails 7.1.4.
The solution meets the challenge's requirements of being self-contained and not using a database.
Key Design Choices
- Cars and groups are stored in hash maps, allowing fast lookups and in-memory data modifications. This is essential for efficiently handling large numbers of elements.
- The controller
CarPoolingControllerdelegates operations to the serviceCarPoolingService, stored as a class variable to ensure data consistency across requests. - To handle concurrent requests, all operations use a semaphore
Mutexto manage access to shared data.
Development Tools
- I have used Apipie gem to describe endpoints and validate parameters.
The documentation is available in
/apipieroute. - I have used SimpleCov gem to gather code coverage data. I have created 10 tests with 42 assertions in total, each targeting different workflows for comprehensive validation.
- Dockerfile has been fully modified to install dependencies and run the Rails server on port 9091.
$ /harness --address http://pooling:9091 acceptance
Running suite 1/1: "Acceptance" with 17 assertions
1/17: "Accepts valid PUT cars request"
2/17: "Rejects invalid JSON cars request"
3/17: "Rejects invalid content type cars request"
4/17: "Rejects invalid method cars request"
5/17: "Accepts valid POST journey request"
6/17: "Rejects invalid JSON journey request"
7/17: "Rejects invalid content type journey request"
8/17: "Rejects invalid method journey request"
9/17: "Accepts valid POST dropoff request"
10/17: "Rejects invalid form dropoff request"
11/17: "Rejects invalid content type dropoff request"
12/17: "Rejects invalid method dropoff request"
13/17: "Accepts valid POST locate request"
14/17: "Returns valid payload for POST locate request"
15/17: "Rejects invalid form locate request"
16/17: "Rejects invalid content type locate request"
17/17: "Rejects invalid method locate request"
Job succeeded