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https://github.com/alvarogarcia7/bank-kata-kotlin

Bank pet project, in kotlin. See interests as topics
https://github.com/alvarogarcia7/bank-kata-kotlin

api-first api-standard bank-kata blackbox-testing etude finite-state-machine gradle gradlew hateoas junit junit5 kata kotlin multimodule paypal-rest-api practice spark sparkjava trikitrok with-client

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Bank pet project, in kotlin. See interests as topics

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README 

        
# Bank kata



I've practiced the [bank kata](https://github.com/sandromancuso/Bank-kata) by [Sandro Mancuso](https://twitter.com/sandromancuso)



My goals where to practice a mix of outside-in + classicist mix of TDD (an idea by [Manuel Rivero](https://twitter.com/trikitrok)) 



Keeping track of the time using git commits.



## Feedback



  - The ability to refactor without breaking the tests is quite good, satisfying even

  - Testing at the almost-boundaries does not cover all the cases, but it's a step in the good direction



## Development notes



### Variants for Safe transfers (ACID)



I've implemented the feature of safe transfers: the account can be

configured to request a code (e.g., OTP) to verify the wire transfer,

both outgoing (e.g., most banks have this) as incoming.



I've investigated ways to conserve the ACID properties, rather than choosing

an eventually consistent system.



#### Parameters



As parameters of the Account class: [Code](https://github.com/alvarogarcia7/bank-kata-kotlin/tree/variant/control-safe-transfers-as-parameters)



This is the simplest approach: depend on the type of the parameter to

decide the behaviour of the class.



#### State machine



As a state machine: [Code](https://github.com/alvarogarcia7/bank-kata-kotlin/tree/variant/control-safe-transfers-as-state-machine)



Configure the states and the transitions as an internal/external part of

the Transfer class, therefore making it more generic and future-proof (YAGNI?)



This can be represented using inheritance from a common class (in this

case, Transfer) or using a wrapper (State<>) to signify the current state.

For the former, there's the production code. For the latter, a side étude

implementing a state machine library (using a Car + its factory as the domain)



In the implementation, it is less type-safe, less comfortable to work

with this implementation, as the method signatures are quite ambiguous:

any state is representable under the Transfer object.



#### Either



As Either (i.e., failed computation): [Code](https://github.com/alvarogarcia7/bank-kata-kotlin/tree/variant/control-safe-transfers-as-either)



Either allows you to represent two explicit computation results. Left has

been used to mean blocked/safe transfer and Right to mean unblocked transfer.



This only allows for representing two values, in an implicit way: the

team consensus indicates left and right for these meanings.



Also, it's strage to see an `Either` where both `T` are the same.

It's possible that this is caused by having the state machine implicitly

(inheriting from a common class) + the Either.



#### Thunks



As thunks (i.e., delayed computations): [Code](https://github.com/alvarogarcia7/bank-kata-kotlin/tree/variant/control-safe-transfers-as-thunks)



A thunk has been passed as a parameter and executed when it is necessary.

This system does not allow for easy persistance/storage, as functions can't

be serialized/deserialized.



### Workflow



As a workflow (i.e., a set of predefined steps): [Code][https://github.com/alvarogarcia7/bank-kata-kotlin/tree/variant/control-safe-transfers-as-workflow]



This workflow has a set of steps (that can be validated or not), and at the

end there is a set of actions.



Based on the way it has been implemented (only data is passed around, but

not behaviour), this could be serialized / exposed over ReST.



## Clock



`f log --format="%s;%ct"|grep CLOCK|cut -d";" -f1` gives the messages

`f log --format="%s;%ct"|grep CLOCK|cut -d";" -f2` gives the times in millis



Then copy to a spreadsheet and calculate the difference when it is STOP