portfolio-calculator

NodeJS command line app to find portfolio details based on the given parameters. The parameters include token and date.

Prerequisites

This app uses :-

• NodeJS 14.17.0.
• Free Crypto API from CryptoCompareAPI to fetch the latest currency value.
• Mocha/Chai/Sinon for unit tests.

Installation

• git clone [email protected]:murtaza-bagwala/portfolio-calculator.git

• Download transactions.csv file and put it in root folder.

• Rename .env.example to .env and replace CRYPTO_COMPARE_API_KEY with the generated key.

• npm install.

• npm install -g . to install the script globally.

• portfolioCalculatorInCurrency -t "BTC" -d "2022-11-02" to run the command line script to fetch the portfolios converted in USD.

• npm run test to run the tests.

Application Design

I am using yargs to fetch the command line arguments and then validating the received arguments in .bin/start.js. for example if date is not valid then it throws an error and shows you the exact format which is YYYY-MM-DD. Also, currently as our transactions.csv only contains 3 types of cryptocurrencies BTC, ETH and XRP, thats why I am validating that too but we can remove that validation if we need to support any other cryptocurrencies in future. For now currency is set as USD by default but in future we can take it as an argument too, rest of the code is generalized with default set as USD.

Model

I have created plain javascript class Portfolio to store portfolio details like token and amount and some of the methods which operates on the amount attribute.

Currency

I am using currency.js for the monetary operations as there are floating point issues with the representation of the decimals in binary. Added the precision upto 6 digits after decimal. Having currency.js making application little bit slower as each time we add or subtract, it creates new currency object in memory but I think for application like this which deals with monetary assets correctness is more important than performance.

Strategies

Now once the arguments are validated I use them to create strategy as I am using strategy pattern to invoke strategies/algorithm based on the received parameters, for that I have created various strategies in ./strategies folder. These strategies parses received record from CSV and performs the buisness logic accordingly.

So we have 4 types of strategies :-

allPortfolios

If no option is passed then this strategy will be called to calculate the portfolio values converted to the USD for all the tokens.

allPortfoliosByDate

If date option is passed then this strategy will be called to calculate the portfolio values converted to the USD for the given date.

portfolioByToken

If token option is passed then this strategy will be called to calculate the portfolio value converted to the latest USD for the given token.

portfolioByDateAndToken

If token and date both options are passed then this strategy will be called to calculate the portfolio value converted to the USD for the given date and token.

CSV Parser

To parse this kind of big CSV file I am using Reactive approach using NodeJS streams API. Generally reactive/event-driven approaches work on 3 events data, error and close and I am passing strategy as a callback function to CSVParser for data event. Code can be found in ./parsers/CSVParser.js.

External Services

Once we compute the portfolio values for tokens then we call the external service to fetch the latest conversion rate.

I am using NodeJS https module to call an external API because, I prefer to use built-in libraries instead of adding external dependencies to keep application light and avoid dependencies hell.

I am using CryptoCompareAPI APIs to fetch the latest currency rate and currency rate based on the timestamp.

Code for this can be found in services/CryptoAPI.js, I have created a generalized function called as getCryptoToCurrencyConversionRate which takes options={token: "BTC", timestamp: 153649404}} and currency=USD type as arguments and returns currency value. we can pass any currency symbol but currently it defaults to USD.

Utils

There are various pure utility functions I have created like :-

• DateValidator to validate the date and its format.
• DateToTimestampConvertor converts date to timestamp in epoch, So basically from commandline we get dateString and then we convert it to timestamp and add 86399 seconds to it to get a last timestamp of particluar day for example if dateString is 2022-11-03 then in timestamp it will be 1667556454 equals to 2022-11-03:T23:59:59. This is done to ensure we get correct conversion rate from external service for that day.
• PortfolioCalculator adds or subtracts the amount based on the transaction type.
• PortfolioCreator it creates or updates a portfoliosByToken map based on the received token, so if token is present it updates the value otherwise it creates new token as a key and adds portfolio details as a value.

Testcases

I have written testcases for all the modules, used expect for assertions and sinon stub to stub external API calls.

Tests can be found in ./test.

Formatting

Added eslint and prettier for formattng and conventions.