ayonymus / cryptomarket

Simple Android app to display a couple of trading pairs

CryptoMarkets

Features

This app getting a list of crypto trade pairs from an end point and polls every 5 seconds. Displays basic information about the tokens. User can filter the list of tokens.

Main	Filter	Error

Tech used

I was following CleanArchitecture principles so that the code isn't tightly coupled. On the view layer I have used MVI for producing predictable view states.

I have used the following libraries:

• Compose for defining the UI
• Coroutintes and Flow for asynchronous data
• Koin for dependency injection
• Room for storing info on tokens
• Retrofit for network access

I have also added unit tests for a couple of critical paths, but not everything is covered.

Implementation challenges

The biggest challenge was Bitfinex endpoints. I have created a Postman collection for probing the different calls. I haven't found an endpoint that would serve simple data on Tokens, e.g. assets that I could display and names. Designs provided had this kind of data, so I decided to dig in.

Bitfinex endpoint issues

You will use the Bitfinex API (https://docs.bitfinex.com/reference#rest-public-tickers )

I have found the following issues with the end point:

• LUNA still seem to refer to the (now defunct) classic Terra, which now has new symbol: LUNC
• Endpoint doesn't seem to return 24 hour relative price change properly, so I disabled in the ui
• Endpoint documentation is out of date. Data fields have to be guessed
• Bitfinex APIs lack a "Token details" endpoint (symbol, token name, token url, description, etc.)

CoinMarketCap for Token Details

I have turned to Coingecko and CoinMarketCap. CoinGecko is free, but the returned data is excessive.

I decided to take basic token information from CoinMarketCap, even though they require an api key. Number of queries are limited. Therefore, TokenDetails are stored in a local Room database in order to limit CMC queries

Improvements in the future

Currently there are no UI tests. Some compionents are not covered by regular unit tests.

Bitfinex has a websocket, which could be better suited for getting the most up to date results than polling every 5 sends. Therefore, market data access is designed in a way so that only the FlowingMarketRepository has to be reimplemented

Currently the ticker pairs are hard coded. However, the TradingPairPreferences interface and the TickerPair data class makes it possible to change this to a user modifiable list.

The BitfinexTradeSymbolSource implementation is also static. This could be connected to the Bitfinex configs endpoint, and retrieve dynamic pairs

it would be nice to add a preferences screen so that user can change/select Tickers. Navigation is already added.

Modularization would also be nice.

Token Repository should be refreshed every now and then.

Styling could be massively improved.

Setting up ktlint or Detekt would improve code formatting issues.