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Commission Fees App

Wholly developed by Valentyn Grekulov.

Prerequisites: node v20.12.2, npm 10.6.0

This project contains only the dev dependencies, so run npm i if needed to run lint, prettier, or test scripts

Available Scripts

In the project directory, you can run:

npm run execute

Runs the App, and the output is displayed in the terminal. It is possible to modify the src/input.json to verify the accuracy of the logic. It is not only displaying the fees, but also various informative warning messages, is case if input is not valid.

npm run lint

Checks all project according to ESLint rules, which are extended from the Airbnb config

npm run lint:fix

Trying to fix all possible places according to the ESLint rules

npm run prettier:write

Checks the code matching with the style rules defined by Prettier

npm run prettier:write

Format your code to match the style rules defined by Prettier

npm run test

Runs all tests

npm run prepare

Initialises the husky. It is needed only for further work with this repository. Needs to run only once -- establish pre-commit and pre-push hooks

Project Structure

~ src/app.js --> root file which is running from npm run execute. It is reading and parsing file by path provided as a second argument of the execute script. For each operation it fires the proceedOperation function with the operation's data as an argument. The result (a fee or a bunch of operation errors) is logged into a terminal.

~ src/input.json --> data from what fees are calculated and displayed.

~ src/constants/feeRuleDetails.js --> consolidated presentation of the fee calculation rule details. Also this structure defines which calculation rule from the feesCalculationEngine will be applied to an operation. It is organised by operationType and by operationUserType. Resulting rule details object has always the same interface:

interface FeeRuleDetails {
  percents: number;
  ruleName: string;
  criteria: { amount: number; currency: string };
}

Acceptable operationType:

type OperationType = 'cash_in' | 'cash_out';

Acceptable operationUserType:

type OperationType = 'natural' | 'juridical';

feeRuleDetails can be extended with various operationType and operationUserType

~ src/utils/feesCalculationEngine.js --> core place which contains the calculating fees logic based on the ruleName. Each rule-based method don't know anything about operationType or operationUserType and as a result it is FeeRuleDetails agnostic, it receives them as arguments altogether with the operation data. This class can be extended with any additional calculation rules.

~ src/utils/checkOperationErrors.js --> as there is no TS, I've decided to add such input validation layer. It simply validates an operation input and returns an array of errors, or empty array is all is fine.

~ src/utils/proceedOperation.js --> this function is running for each operation. It checks the operation validity with checkOperationErrors. If there are resulting errors, it returns them and don't proceed further. If the operation is valid it is retrieving the needed ruleName from the feeRuleDetails based on the operationType and operationUserType. It runs the feesCalculationEngine instance method with the name equal to ruleName value and passing there as argument an object with correspondent feeRuleDetails and operation data. The fee output is rounded to 2 decimals and returned.