Payment service

Features

• Account creation with the initial balance
• Payment creation which leads to money transfer between accounts (multicurrency support)
• Review current exchange rates
• Review payment history per account
• Review list of all accounts in the system

Requirements

To start application or run integration tests you need only docker.

• Docker 18.09+ - everything else is optional
• Postgresql 11+ - optional with docker
• Golang 1.11+ - optional with docker
• dep 0.5.0 - optional because all dependencies are vendored

Installation

To start application you can run: docker-compose up.
It will listen on port 9090.

Application run required database migrations on startup. Migrations are stored in migrations folder.

Configuration

Application configured via ENV variables:

• POSTGRESQL_HOST - database host
• POSTGRESQL_PORT - database port
• POSTGRESQL_USER - database user
• POSTGRESQL_PASSWORD - database password
• POSTGRESQL_DATABASE - database name
• HTTP_HOST - host listen on (default=0.0.0.0)
• HTTP_PORT - port listen on (default=80)

Integration testing

To run integration tests, which are located in integration_tests folder, run ./scripts/integration_tests.sh.

External dependencies

• https://github.com/satori/go.uuid - stable and popular (2.7k stars) library for UUID. Used it multiple times before.
• https://github.com/vrischmann/envconfig - small library to fill configuration struct with ENV variables. Used it multiple times before.
• https://github.com/go-kit/kit - it is go-kit!
• https://github.com/stretchr/testify - very popular and stable test assertions. Used it multiple times before.
• https://github.com/go-chi/chi - small, stable and popular (5k stars) http router. Used it multiple times before.
• https://github.com/go-pg/pg - native golang postgresql driver
• https://github.com/shopspring/decimal - arbitrary-precision fixed-point decimal numbers in go. Very convinient API. Used it multiple times before.

Possible improvements

I was very limited in time. So I had to sacrifice some features, good practices, etc.

• Add sctructured logging with https://github.com/sirupsen/logrus
• API error rendering, might be better, need to dig dipper in go-kit
• Store in payment history how much money was withdrawed/credited in account's currency.
• Integration with some online exchange service to update exchange rates on the flight. For example via https://github.com/me-io/go-swap
• Extend current exchange rates database. It is only USD to UAH,BYN,RYB,EUR. And, for example, when UAH converted to BYN it uses USD to BYN and USD to UAH rates to calculate UAH to BYN rate.
• Add methods to create and modify exchage rates and currencies.

API

Errors

codes	messages
1	INVALID_CURRENCY_CODE
2	INVALID_ACCOUNT_ID
3	NEGATIVE_BALANCE
4	NEGATIVE_PAYMENT_AMOUNT
5	NOT_ENOUGH_MONEY
6	SAME_ACCOUNT_TRANSFER
100	INTERNAL_ERROR
101	INVALID_OFFSET_VALUE
102	INVALID_LIMIT_VALUE

Content example

{
  "code": 1,
  "msg": "INVALID_CURRENCY_CODE"
}

Accounts

List of accounts

Get list of all accounts with balance and currency code. Limit and offset are optional, by default offset=0 and limit=100

URL: /accounts?offset=0&limit=20

Method: GET

Response

Code: 200 OK

Content example

[
  {
    "id": "6cd061e4-4a0c-4991-85fd-4825702f873b",
    "currency_numeric_code": 980,
    "balance": "10000.5"
  }
]

Account by ID

Get account by ID.

URL: /accounts/6cd061e4-4a0c-4991-85fd-4825702f873b

Method: GET

Response

Code: 200 OK

Content example

{
  "id": "6cd061e4-4a0c-4991-85fd-4825702f873b",
  "currency_numeric_code": 980,
  "balance": "10000.5"
}

Create account

Create new account with positive balance

URL: /accounts

Method: POST

Request

Content example

{
  "currency_numeric_code": 980,
  "balance": "1500.50"
}

Response

Code: 201 CREATED

Content example

{
  "id": "6cd061e4-4a0c-4991-85fd-4825702f873b",
}

Currencies

List of currencies

URL: /currencies

Method: GET

Response

Code: 200 OK

Content example

[
  {
    "numeric_code": 643,
    "alpha_code": "RUB",
    "minor": 2
  },
  {
    "numeric_code": 840,
    "alpha_code": "USD",
    "minor": 2
  },
  {
    "numeric_code": 933,
    "alpha_code": "BYN",
    "minor": 2
  },
  {
    "numeric_code": 978,
    "alpha_code": "EUR",
    "minor": 2
  },
  {
    "numeric_code": 980,
    "alpha_code": "UAH",
    "minor": 2
  }
]

Payments

List of payments per account

Get list of payment history per account. Limit and offset are optional, by default offset=0 and limit=100

URL: /accounts/6cd061e4-4a0c-4991-85fd-4825702f873b/payments?offset=0&limit=20

Method: GET

Response

Code: 200 OK

Content example

[
  {
    "id": "6cd061e4-4a0c-4991-85fd-4825702f873b",
    "currency_numeric_code": 980,
    "balance": "10000.5"
  }
]

Create payment

Create new payment and tranfer money between accounts.

URL: /payments

Method: POST

Request

Content example

{
  "from_account": "6a261c31-7009-4082-80c4-6abde77082bb",
  "to_account": "2d47cfa8-d092-4bc3-a30c-93e8c9aaf6d6",
  "currency_numeric_code": 980,
  "amount": "950.55"
}

Response

Code: 201 CREATED

Content example

{
  "id": "6cd061e4-4a0c-4991-85fd-4825702f873b",
}