I was asked to work out a case for VCN. In this project, I say how I went to work and how I have thought it out.

There is an interface that can only be used for authorized (paying) customers to allow currency conversion. A few resources can be used for the conversion, the former being less reliable and possibly slower.

Available resources:

• https://free.currencyconverterapi.com/
• http://currencyconverter.kowabunga.net/converter.asmx

• All services must be able to be used and others should be able to be plugged into it with ease.
• Other requirements received on paper.

• Guzzle: HTTP client that is versatile, well documented and almost a global default.
• PHP Soap: This is to interface with currencyvonverter.kowabunga.net.
• Laravel: This will hold the base endpoints. This because it is easily securable and fast also supports all other functionality that is required.
• BootstrapCSS: This is because I am not that great with CSS and will take some pain away.
• jQuery: This will handle all user input, used because it is cross-platform compatible.
• TypeScript: Because we will work in bigger teams and the type definitions are a blessing in that regard.
• Select2: This is a clean, well-supported dropdown with autocomplete.
• WebPack: To make everything as small as possible and not include more javascript than needed.
• NodeJS + SocketIO: This to allow for real-time communication of the new conversion rates when available.[^1]
• (The Laravel application will send information to Nodejs, so a web server on Nodejs is also required).

1. First I checked out the provided paper & screenshot and started thinking about what we needed.

   1. By interface, I decided that select2, bootstrap, and jQuery are needed to provide for a clean interface.
   2. An API is also needed for the AJAX calls that will be sent to the server.
   3. Based on the requirements I decided that caching for the currencies is in order, this will be stored in the database.
   4. Because the currencies are current for one day, a cronjob will be added to sync the currencies and cache the new data, historic data will be saved in another database.
   5. An adapter pattern will be used for the separate resources to receive the currencies.

2. Check out the provided resources, I decided that adapters are in place for this.

   1. The adapters will receive a static variable to give a priority for ordering.
   2. Based on this ordering the requests will be done, initiated by the cronjob.
   3. Add Unit tests for the "interface".
   4. An abstract adapter will be created and will serve by default a guzzle client, which method can be overwritten to support another client (SOAP for example).
   5. The following methods will be defined:
      1. getClient
      2. getRate
      3. getHistory

3. Interface information

   1. AJAX will be used to retrieve all the information from the server, this will provide for smooth user experience.
   2. As information will become available at some time, sockets will be used to distribute new information to all the users when available.[^1]
   3. A check for online status will also be given [^1]
   4. Based on the currency conversion the historic data will be retrieved, this will also be done with AJAX.

4. Cronjobs 1.

5. User registration

   1. This will be a manual task for how this might be automated by giving an authorization based on Ideal or PayPal.
   2. Because this is manual a command-line command will be created to create a new account. The account will need an email address. The password will be mailed to the user so he can log in.

6. Endpoints

   1. /login: Show the login
   2. /: This will be the currency converter
   3. /api/rate/{currency}: Get the conversion rates of the initially selected currency.
   4. /api/history/{currency_from}/{currency_to}: Get the historic data of the currency conversion.

• Although far-fetched when a user is offline the currency converter doesn't work.