Problem statement

**Develop a service that simulates basic banking operations in a programming language of your choice. This service will manage accounts, process deposits, withdrawals, and transfers between accounts.**

### The system should be designed reflecting real-world constraints of a bank.

## Requirements:

1. A class or set of functions that allow:
○ Account creation: Allow users to create an account with an initial deposit.
○ Deposit: Enable users to deposit money into their account.
○ Withdrawal: Allow users to withdraw money from their account, ensuring that overdrafts are not allowed.
○ Transfer: Enable transferring funds between accounts.
○ Account balance: Provide the ability to check the account balance.
2. Database:
○ In-memory data storage will suffice, no need to have a database alongside the project, but you can add one at your discretion

The word “service” here is used in a “software component/module” rather “deployable unit with an API” sense, no need to provide API for it.

Goals

Develop a service that simulates basic banking operations in a programming language of your choice. This service will manage accounts, process deposits, withdrawals, and transfers between accounts

Non-Goals (Out of Scope)

• Functional
  • Transaction History
  • Transfer History
  • Fees, Charges, Tax
  • Overdraft
  • Multi Currency
  • Balance Hold
• Technical
  • Frontend Build
  • APIs
  • Observability

Tech Stack

• NodeJS (Express) with Typescript
• Postgres
• Docker

Assumption and Clarification

• Double-Entry Bookkeeping Ledger will be used as a principle design of this service.
  • Note : This might not be in the scope and might be considered as over-engineering, however in real world, on each money movement, ledger is the only source of truth. Therefore, just consider to scope this in to show high level surface to illustrate the business and operation impact. If this is not needed, it can be taken out as well.
• Amount is in BigInt
  • All monetary amounts are stored as bigint in cents (smallest currency unit)
  • This avoids floating-point precision issues when dealing with currency.

• Bank will have ledger account (Liability)
• Each users will have ledger accounts created upon user creation (Asset)
• Each user will only have one ledger accounts with type [SAVING]
• Balance of any ledger account cannot go negative.