/transaction-manager

Primary LanguageRustMIT LicenseMIT

transaction-manager

Linters

An application that authorizes a transaction for a specific account following a set of predefined rules.

Operations

The program handles two kinds of operations, deciding on which one according to the line that is being processed:

  1. Account creation
  2. Transaction authorization

Your program is going to be provided json lines as input in the stdin, and should provide a json line output for each one — imagine this as a stream of events arriving at the authorizer.

$ cat operations
{"account": {"active-card": true, "available-limit": 100}}
{"transaction": {"merchant": "Burger King", "amount": 20, "time": "2019-02-13T10:00:00.000Z"}}
{"transaction": {"merchant": "Habbib's", "amount": 90, "time": "2019-02-13T11:00:00.000Z"}}

$ authorize < operations

{"account": {"active-card": true, "available-limit": 100}, "violations": []}
{"account": {"active-card": true, "available-limit": 80}, "violations": []}
{"account": {"active-card": true, "available-limit": 80}, "violations": ["insufficient-limit"]}

State

The program should not rely on any external database. Internal state should be handled by an explicit in-memory structure. State is to be reset at application start.

Operations

The program handles two kinds of operations, deciding on which one according to the line that is being processed:

  1. Account creation
  2. Transaction authorization

For the sake of simplicity, you can assume all monetary values are positive integers using a currency without cents.

1. Account creation

Input

Creates the account with available-limit and active-card set. For simplicity sake, we will assume the application will deal with just one account.

Output

The created account's current state + any business logic violations.

Business rules

  • Once created, the account should not be updated or recreated: account-already-initialized.

Examples

input
    {"account": {"active-card": true, "available-limit": 100}}
    ...
    {"account": {"active-card": true, "available-limit": 350}}


output
    {"account": {"active-card": true, "available-limit": 100}, "violations": []}
    ...
    {"account": {"active-card": true, "available-limit": 100}, "violations": ["account-already-initialized" ]}

2. Transaction authorization

Input

Tries to authorize a transaction for a particular merchant, amount and time given the account's state and last authorized transactions.

Output

The account's current state + any business logic violations.

Business rules

You should implement the following rules, keeping in mind new rules will appear in the future:

  • No transaction should be accepted without a properly initialized account: account-not-initialized

  • No transaction should be accepted when the card is not active: card-not-active

  • The transaction amount should not exceed available limit: insufficient-limit

  • There should not be more than 3 transactions on a 2 minute interval: high-frequency-small-interval (the input order cannot be relied upon, since transactions can eventually be out of order respectively to their times)

  • There should not be more than 1 similar transactions (same amount and merchant) in a 2 minutes interval: doubled-transaction

Examples

Given there is an account with active-card: true and available-limit: 100:
input
    {"transaction": {"merchant": "Burger King", "amount": 20, "time": "2019-02-13T10:00:00.000Z"}}

output
    {"account": {"active-card": true, "available-limit": 80}, "violations": []}
Given there is an account with active-card: true and available-limit: 80:
input
    {"transaction": {"merchant": "Habbib's", "amount": 90, "time": "2019-02-13T11:00:00.000Z"}}

output
    {"account": {"active-card": true, "available-limit": 80}, "violations": ["insufficient-limit"]}

Test

To run the tests:

make test

Usage

Documentation

$ cargo doc --no-deps

License

mit