Write a Hello World program

1. The program has 1 current business requirement write Hello World to the console/screen.

- To Run
    - Set the startup project to 'Exercise'
        - This is a common console applicatiton project
    - Run the app and it will display 'Hello World' in a console app
  	    - Default application behavior
    - The following line will appear above 'Hello World'
        - Loading: ToConsoleModule
            - I am using AutoFac for the IoC/Dependency Injection pattern (more details to come)
            - This is the injection bindings module that is being used (shown for clarity)
          	    - https://en.wikipedia.org/wiki/Inversion_of_control
          	    - https://www.nuget.org/packages/Autofac/
          	    - https://www.nuget.org/packages/Autofac.Configuration/ 	         

2. The program should have an API that is separated from the program logic to eventually support mobile applications, web applications, console applications or windows services.

- All abstract details of the app and api (interfaces) are located in 'Exercise.Domain'
	- These interfaces define the behavior of the application and api
	- Any concrete implementation of these interfaces do so by implementing the interfaces explicitly
		- This ensures complete adherence and testability 
		- https://docs.microsoft.com/en-us/dotnet/csharp/programming-guide/interfaces/explicit-interface-implementation
- The concrete implementation of the api is in the following project:
	- Exercise.Api
- The concrete application details are coded in the following projects
	- Exercise.ToConsole	 
	- Exercise.ToFile
	- Exercise.ToTrace
	- Each one of these define a different way to write 'Hello World'
	- None of the these projects reference the Exercise.Api project
		- The api to use is determined at runtime (although there is only one api definition) 
		- This ensure total separation of concerns
- The only projects that have direct references to concrete implementations of the app or api are:
	- Exercise.Bindings
		- Define what concrete object to use at runtime
	- Exercise.Tests
		- NUnit & Moq unit tests
 - Other api deatils
 	- I separated the api into 2 layers to create a hypothetical separation of concerns
 		- MessageService
 			- This is the common area and the 1st layer for all api calls
 			- This could handle all authorization, parameter validation, then call to the 2nd layer 'Provider' to carry out the business rule
 			- This creates a nice separation of concerns and makes the business code cleaner in my opinion
 			- This service can be added a any top level api layer such as a Web Api
 		- MessageProvider
 			- For this exercise MessageProvider returns the string 'HelloWorld'; but that could just as easily have come from a database, file, etc.
 			- The MessageService takes in the IMessageProvider in the constructor so it can be injected with the IoC container
 				- This also makes testing of the MessageService possible without testing it with a specific implentation of the IMessageProvider 
 					- This is where unit testing mocking comes into play (more details later) 	    	 

3. The program should support future enhancements for writing to a database, console application, etc.

Use common design patterns (inheritance, e.g.) to account for these future concerns.

- I chose to use IoC/Dependency injection to support future changes
- Everything is defined first as an interface and I used AutoFac as the IoC Container to assign concrete classes at runtime

Use configuration files or another industry standard mechanism for determining where to write the information to.

- Use the 'App.config' in Exercise project to do the following
	- Decide what variation of the application to run by uncommenting the module you want (see autofac-> modules xml element)
		- Exercise.App.ToConsoleModule (default)
			- Writes 'Hello World' from api to Console
		- Exercise.App.ToFile
			- Writes 'Hello World' from api to file in bin directory 'Exercise.txt'
			- You will see additional information in the console app when running this variation 	 	  
		- Exercise.App.ToTrace
			- Writes 'Hello World' from api to System.Diagnostics.Trace.WriteLine("") 
			- There are 2 trace listeners setup in the App.config you can use with this app choice
				- ConsoleTraceListener (default)
				- TextWriterTracelistener
					- This one was setup to write to file in bin directory: 'Exercise.log' 	  	 	               

4. Write unit tests to support the API.

- I'm using NUnit and Moq (mocking) for unit testing
	- https://www.nuget.org/packages/NUnit/
	- https://www.nuget.org/packages/Moq/	 
- I wrote complete unit tests for the following
	- Exercise.Api
	- Exercise.App.Console 

5. Feel free to use a github program to store the coding exercise as I know that’s typically easier to use.