Hi Candidate!

Description of main task

We've implemented this simple transaction service, it's able to add, get, list and delete transactions. After playing around with the transaction service we discovered that we really wanted to know the balance of given accounts over time, so we created a protobuf specification for a new service. This balance service may serve as a datasource for a graph, plotting the balance of an account over time. We hope you can help us implement the service and some CLI for querying the service.

We envisioned a CLI looking something like this:

Here we query to balance service to return balance for accounts/1, period is specified and the size of each bucket (720h, 30 days) is specified. We expect that the service would figure out when these buckets start and stop and also what the balance is at that given period.

$ bin/candidate balance --duration 720h accounts/1 2016-01-01 2016-01-31
from: 2016-01-01 to: 2016-02-01 amount: 1234
from: 2016-02-01 to: 2016-03-01 amount: 4321
from: 2016-03-01 to: 2016-04-01 amount: -1234.5
...
from: 2016-12-01 to: 2016-12-31 amount: 1

Another way to query the balance service should be to specify the number of buckets we want, for example:

$ bin/candidate balance --buckets 365 accounts/1 2016-01-01 2016-12-31
from: 2016-01-01 to: 2016-01-02 amount: 123
...
from: 2016-12-30 to: 2016-12-31 amount: 1

This command should probably return the daily balance of that account.

The specification for the balance service is defined in api/balance.proto, feel free to modify it if you come up with something better. An empty service implementation is added in pkg/balance/service.go, add meat and bones to it.

Current implementation

We've provided a transaction service, it's able to get, add, remove and list transactions. You can build the project by doing:

$ go get github.com/smblab/candidate
$ cd $GOPATH/src/github.com/smblab/candidate
$ go build -o bin/candidate ./cmd/candidate
$ # or alternatively
$ make build

You can start the transaction service by running:

$ bin/candidate serve transactionservice

After the transaction service is up and running you can utilize other commands to get, add, remove and list transactions:

$ bin/candidate add ...
$ bin/candidate delete ...
$ bin/candidate list ...
$ bin/candidate get ...

We've also added a balance service, but the required handlers are left unimplemented. You can launch the balance service by:

$ bin/candidate serve balanceservice

After the balance and transaction service is up and running you can issue the command:

$ bin/candidate balance ...

This command is also not implemented, only the basics are in place.

Tasks

1. Implement the missing balance service
2. Add required support in CLI (for getting balance results)
3. Add tests for newly added functionality

Bonus tasks

• Add better parameter support in CLI (listen address, transaction endpoint etc)
• Implement balance service or client in another language
• Improve the non-existing test coverage
• Improve error handling
• Add HTTP REST endpoints for balance service
• Add REST gateway to service launch code
• Add kubernetes deployment configuration

Frontend

If you don't feel like a backend or fullstack guy, create a frontend for these services and submit that instead. We're looking for developers in general - fullstack, backend, frontend and SRE.

Be creative, feel free

Looking forward for your submissions,

Sincerely, SMB LAB geeks

(PS: You can tarball your solution and ship it to Torkel [torkel at smblab.no])