Deal with bad internet

Topics: resilience, Schedule, circuit breaker, caching

The given implementation of Poké-Fun works fine... if the internet connection is fine (extra points for irony if the room where you are working on this tasks has bad internet). Any realistic application that accesses other services must protect itself against potential disconnections, lags, or services which are down. We refer with the term resilience to all those techniques which help in providing a better experience in problematic scenarios.

This topic is well documented in the official Arrow documentation, we suggest the reader to check the Resilience section, both the introduction and the pages describing Schedule and CircuitBreaker.

Retry if fails

The task here is to create a wrapper that adds retry capabilities to an inner PokemonTcgApi instance. Explore different variations of the Schedule, from a simple fixed repetition, to exponential backoff policies.

Use a circuit breaker

Improve the previous soltuion with a circuit breaker, which ensures that we do not overload the service or the client in case the (transient) failure takes a long time to recover.

As described in the documentation, the best option for resilience is to combine both approaches.

A common pattern to make resilient systems is to compose a circuit breaker with a backing-off policy that prevents the resource from overloading. Schedule is insufficient to make your system resilient because you also have to consider parallel calls to your functions. In contrast, a circuit breaker track failures of every function call or even different functions to the same resource or service.

Introduce a cache

The given implementation queries the Pokémon TCG API service for every search and every card. However, cards with an existing identifier almost never change (except for errata), so there is no need to get them over and over. Searches also change rarely: new sets with additional cards only appear every 3 months, and we do not expect our users to stay that long in the application.

Introducing a cache improves performance, and also makes our application more resilient, since fewer calls need to communicate outside. Your task is to introduce Cache4k, a nice Kotlin Multiplatform option for this matter.