Saturday, January 16, 2016

RSStockFighter Framework

In this post I will talk about the StockFighter framework that I crated for the Swift language named RSStockFighter.  If you have not heard about StockFighter, it is a really nice (and free) online coding challenge where you need to solve a series of problems by using your coding skills.   You can read about StockFigher here.  The GitHub repository for RSStockFighter is here.  I am currently finishing up my third book on the Swift programming language so I have not had a lot of time to play the StockFighter game (yet) but I have used RSStockFighter to make it though level 4. 

I first read about StockFighter on DZone.  The idea behind StockFighter is you are a developer that has been tasked to create an automated trading system designed to automate stock trading for your firm.  The game has several levels that progressively get harder.  The first few levels are designed to get you familiar with the API while later levels require you to incorporate logic to determine when to buy and when to sell your stocks.  Don’t worry if you do not have any stock market experience, the game teaches you everything you need to know to complete each level. 

All of the APIs are REST based which means you can use any language you want to complete the levels.  I obviously chose to use the Swift language.  Why?  Because I really like programming with the Swift language.  RSStockFighter is designed to make it very easy to interact with the StockFighter API so you can focus on solving the levels rather than the backend network code. 

When I started looking at the StockFighter API, my first thought was I needed to create a framework for the API so I would not need to keep creating or cutting/pasting the code to perform the network requests in each challenge.  In this post I will explain how I designed RSStockFighter and how you can use it in your code.

At the time I am writing this document, StockFighter has ten documented API calls (I have currently implemented seven of the calls in RSStockFighter). One of my biggest concerns is the StockFighter challenge has not been around very long therefore I suspect they will be changing and/or adding to the API.  This means that it needs to be easy to add new API calls to RSStockFighter.  When I have a design problem like this I usually start off by pulling out one of my design pattern books and look through it to see if any of the patterns may solve my problem.  In this case the command pattern was perfectly suited for my needs.

The command pattern falls under the behavioral patter group.  In this pattern we encapsulate the logic of our actions into types that conforms to a command protocol.  We can then provide instances of the command types for use by an invoker.  The invoker will use the interface provided by the protocol to invoke the actions on the types that conform to that protocol.  What this means is we will create a separate command type for each one of our API calls.   We will then submit instances of these types to our invoker which will make the call to the StockFighter API.
The class structure to make our API calls will look like this:
The StockFighter request types will encapsulate the information needed to make the individual requests.  The RSStockFighterTransaction type will contain an instance of a StockFighter request type and also the information to make the network request.  Finally the RSStockFighterTransactionRequest will contain methods to make the actual network request to the StockFighter API.

I created a type named StockFighterHelper which implements the Façade pattern to hide the underlying RSStockFighterTransaction and RSStockFighterTransactionRequest types.  I did this for two reasons.  The first is to hide the complexity of the types and the second is to make it easy to change the interfaces of these types if needed.

In addition to the seven StockFighter request types we also have seven StockFighter response types.  These response types will encapsulate the logic needed to parse the response.  This will make it easy to pull the information from the response, as we need it. 

Enough about the design of RSStockFighter, lets see how we would use it.  We will start off by seeing if the StockFighter API is up.  The following code will make a request to check the status of the stockFighter API.
func apiStatus() {
    let request = StockFighterAPIStatus()
    StockFighterHelper.sendStockFighterTransaction(request, success: {
       (dict:NSDictionary!) -> Void in
        }, failure: {
            (str: String) -> Void in
            print("Error:  \(str)")
In this function we begin by creating an instance of the StockFighterAPIStatus type.  We then call the static sendStockFighterTransaction() method from the StockFighterHelper protocol.  The sendStockFighterTransaction() method takes three parameters which are:
  • transType:  An instance of a type that conforms to the StockFigherRequestType type which contains the information for our request. 
  • success:   A completion handler that will be called if the StockFighter API call was successful
  • failure:  A completion handler that will be called if the StockFigher API call failed.
In this example we set the transType parameter to an instance of the StockFighterAPIStatus type.  In the success completion handler we call a method named checkStatusResponse() and in the failure completion handler we print the error message to the console.
The checkStatusResponse() method called if the API call was successful looks like this:

func checkStatusResponse(dict: NSDictionary) {
    let response = StockFighterAPIStatusResponse(dict: dict)
    print("StockFighter is up:  \(response.ok)")
In this method we use the StockfighterAPIStatusResponse type to parse the response.  We then print a message to the console letting us know if the Stock Fighter API is up or not.

That was pretty easy but lets look at a more difficult API call like placing a new order.  The following code demonstrates how to do this:

let order = StockFighterOrder(symbol:SF_STOCK_SYMBOL, price:95.00,qty: 100,direction:SF_OrderDirection.Buy,orderType:SF_OrderTypes.Limit.rawValue)
StockFighterHelper.sendStockFighterTransaction(order, success: {
    (dict:NSDictionary!) -> Void in
}, failure: {(str: String) -> Void in
In this example we create an instance of the StockFighterOrder type.  The initializer for this type takes five parameters which are:
  • symbol:  The stock symbol for the stock to place the order for
  • price:  The maximum price to buy or minimum price to sell the stock at
  • qty:  The quantity to buy or sell
  • direction:  Specifies if this is a buy or a sell order
  • orderType:  The order type
We then pass the instance of the StockFighterOrder type to the static sendStockFighterTransaction() method, just like we did with the API status example, to make the request to the StockFighter API.

If the API call was successful we would parse the response using the StockFighterOrderResponse type like this:

let response = StockFighterOrderResponse(dict: order)

Pretty easy, don’t you think?  The seven StockFighter request types that I have implemented in RSStockFighter are:
  • StockFighterAPIStatus
  • StockFighterVenueStatus
  • StockFighterStocksOnVenue
  • StockFighterOrder
  • StockFighterOrderBook
  • StockFighterQueryOrder
  • StockFighterCancelOrder
For each of these request types I also implemented a response parser type which are:
  • StockFighterAPIStatusResponse
  • StockFighterVenueStatusResponse
  • StockFighterStocksOnVenueResponse
  • StockFighterOrderResponse
  • StockFighterOrderBookResponse
  • StockFighterQueryOrderResponse
  • StockFighterCancelOrderResponse

There are two enumerations defined in this framework that you will be working with.  These are the SF_OrderTypes and SF_OrderDirection enumerations.  The SF_OrderTypes enumeration defines the type of order we are placing (You can read more about order types in the StockFighter help pages) and has the following values:
  • Limit - Immediately matches any order on the books that has an offer price as good or better than the one listed on the order.  This order type is good until cancelled
  • Market - Immediately matches any order.  Do not use this type.
  • FOK - Fill or Kill:  Immediately fills the whole order.  If it cannot fill the whole order immediately then the whole order is killed
  • IOC - Immediate or Cancel:  Immediately fills or partially fills the whole order and then cancels any shares that remains.
The SF_OrderDirection is used to define if the order is a buy or sell order and have the following values:
  • Buy - The order is a purchase shares
  • Sell - The order is to sell shares
Before you can use the API, you do need to make changes to a couple global constants.  These constants are in the StockFighterInfo.swift file.
  • SF_API_KEY – Your API ley
  • SF_VENUE – The venue you are using for this challenge
  • SF_ACCOUNT – The account you are using for this challenge
  • SF_STOCK_SYMBOL – The symbol of the stock you are using for this challenge

Overall the framework consists of six files that you will need to download and include in your project.  These files are:
  • StockFighterInfo
  • StockFighterKeys
  • StockFighterRequestTypes
  • StockFighterResponseTypes
  • RSStockFighterTransactionRequest
  • RSStockFighterTransaction

The GitHub repository for RSStockFighter is located here: 

So why am I releasing this framework?  I would like to see how many Swift Developers can complete this challenge.  As you go though the levels using RSStockFighter, post a comment to this blog posting telling us how far you have advanced (please no hints on how to complete a level).

Is using RSStockFighter cheating at the challenge?  Personally I do not think so.  I see using RSStockFighter like using any other third party framework (like the Alamofire framework) in our applications.  We use third party frameworks in our day to day development work to make our lives easier so we can focus on the business logic, why not use them to make challenges like this easier so we can focus on the business logic.

Good luck and happy coding.

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