Table of Contents
PayIt API Documentation
- Endpoints
  - Accounts
  - Transfers
Unit Tests
In-Memory Data
Concurrency

PayIt API Documentation

This document provides information about the endpoints available in the PayIt API, as well as the data models/entities used in the API.

Endpoints

Accounts

Get Account by ID

HTTP Method: GET
Endpoint: /accounts/:id
Description: Retrieve an account by its ID.

Response (JSON):
```
{
  "id": "812f2e44-6b34-4e26-a418-9affc416c032",
  "name": "John Doe",
  "balance": 1000.0
}
```
- Note: The balance field in the request body is of type string, but in the response, it will be of type float. (Why? Example data is supplied with Balance as a string, but to facilitate transfers it was changed to float)

Get All Accounts

HTTP Method: GET
Endpoint: /accounts
Description: Retrieve a list of all accounts.

Create Account

HTTP Method: POST
Endpoint: /accounts

Description: Create a new account.

Request Body (JSON):

{
  "name": "John Doe",
  "balance": "1000.00"
}

Update Account by ID

HTTP Method: PUT
Endpoint: /accounts/:id
Description: Update an account by its ID.

Request Body (JSON):
```
{
  "name": "Updated Name",
  "balance": "1500.00"
}
```
- Note: The id field in the request URL specifies the account to update.

Transfers

Get Transfer by ID

HTTP Method: GET
Endpoint: /transfers/:id

Description: Retrieve a transfer by its ID.

Response (JSON):

{
  "id": "33f47cae-580f-11ee-8c99-0242ac120002",
  "senderID": "7d4b886d-dd4d-4133-9bc7-26f0c6233e8c",
  "receiverID": "53f30a2e-f9c8-4442-a278-b622a42e4054",
  "amount": 500.0,
  "succeeded": true
}

Get All Transfers

HTTP Method: GET
Endpoint: /transfers
Description: Retrieve a list of all transfers.

Create Transfer

HTTP Method: POST
Endpoint: /transfers

Description: Make a new transfer.

Request Body (JSON):

{
  "id": "33f47cae-580f-11ee-8c99-0242ac120002",
  "senderID": "7d4b886d-dd4d-4133-9bc7-26f0c6233e8c",
  "receiverID": "53f30a2e-f9c8-4442-a278-b622a42e4054",
  "amount": 500.0,
}

API Test

A collection of requests is provided.
For Postman
For ThunderClient

Running PayIt

To run the PayIt program, follow these steps:

Using source code
```
go run main.go
```
Build and run executable
```
go build -o payit
./payit
```
Server starts on port 8080

Note: The application loads accounts.json data into the memory, if successful this message will be logged: Ready to receive requests.
Note: Optionally replace accounts.json with your own accounts.json file, but it should follow the same format, before running.

Unit Tests

To run unit tests run:

go test ./...

In-Memory Data

Go's sync.Map is used as the main structure for holding Accounts & Transfers entities.

There is a separate for each kind of entity.

sync.Map facilitates concurrent read and write access to the data .

Concurrency

The transfer must carefully modify the sender and receiver accounts.

This is done by introducing a mutex.Lock for each account. This means that the locking granularity is on the row level.

Transfers include locking the sender's account, inspecting their balance, and then deducting the transfer amount, and finally and unlocking the sender's account.

As for the receiver, their account is locked until their balance is updated, to ensure that there are no write after write issues, and finally ublocking the receiver's account.

As for fetching and creating accounts and transfers, the concurrency is handled by the sync.Map

marwansalem/payit

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