Technical Assignment

The candidate is asked to build a small project consisting of two Go processes:

The API server accepts trade submissions via POST /trades and writes them to a queue table.
The worker process continuously reads new trades, validates them, stores them, and instantly updates the account's profit.

Your code must compile, pass go vet and go test -race, and run via docker-compose up.

Purpose of This Task

We want to assess your ability to write clean HTTP code, work with SQL, and reason about concurrency.

What You Should Build

Components and Architecture

┌──────────────┐ POST /trades       ┌───────────────┐
│  API Server  │ ─────────────────► │  Queue Table  │
│  cmd/server  │                    └───────────────┘
└──────────────┘                         ▲
                                         │ SELECT … FOR UPDATE
┌──────────────┐            UPDATE stats │
│  Worker      │ ◄───────────────────────┘
│  cmd/worker  │
└──────────────┘

API (HTTP) — exposes one POST endpoint and one GET endpoint.
Queue — an SQLite table trades_q used by the API to enqueue trades, and by the worker to mark them as processed.
Worker — a separate process that polls the queue every 100ms, calculates profit, and updates account_stats.

Trade Input Format

Field	Type	Validation Rule
`account`	string	must not be empty
`symbol`	string	`^[A-Z]{6}$` (e.g. EURUSD)
`volume`	float64	must be > 0
`open`	float64	must be > 0
`close`	float64	must be > 0
`side`	string	either "buy" or "sell"

Profit calculation (performed by the worker):

lot := 100000.0
profit := (close - open) * volume * lot
if side == "sell" { profit = -profit }

HTTP Contracts

Method	URL	Request / Response	Expected Behavior
POST	`/trades`	JSON trade payload	Enqueue trade; respond with 200 OK or 400 on errors
GET	`/stats/{acc}`	`{"account":"123","trades":37,"profit":1234.56}`	Return current statistics for the given account
GET	`/healthz`	plain text OK	Health check endpoint (for Kubernetes liveness probe)

How to Run

# Terminal 1
go run ./cmd/server.go --db data.db --listen 8080

# Terminal 2
go run ./cmd/worker.go --db data.db --poll 100ms

Sample request:

curl -X POST http://localhost:8080/trades \
     -H 'Content-Type: application/json' \
     -d '{"account":"123","symbol":"EURUSD","volume":1.0,
          "open":1.1000,"close":1.1050,"side":"buy"}'

curl http://localhost:8080/stats/123
# {"account":"123","trades":1,"profit":500.0}

What We Expect from Your Code

Requirement	Minimum / Bonus
Go 1.24+, only stdlib + light libs	sqlx / chi / validator OK
`go vet` and `go test -race` pass	required
Test coverage	≥ 60%
Dockerfile + docker-compose.yml	bonus (+1)
README: how to run + curl examples	required

How We Will Evaluate

CI script (GitLab CI) will:

Run go vet and go test -race -covermode=atomic.
Launch both API and worker processes in the background.
Send one invalid and one valid POST request.
Fetch and validate the response from /stats.

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