Builder Pattern

- Part of Creational design pattern since it deals with creation of objects
- Useful for creating complex objects
	- When object creation needs to be separate from its assembly
	- When different representations neeeds to be created with finer control

- For this example
	- InventoryReport 
		- Complex object we want to build
			- Contains Properties
				- TitleSection
				- DimensionsSection;
				- LogisticsSection;
	- IFurnitureInventoryBuilder
		- Builder interface that has method that would help concrete implementation build the actual object
			- Contains methods
				- AddTitle()
				- AddLogistics()
				- AddDimensions()
				- Build()
	- DailyReportBuilder
		- Concrete builder responsible for building InventoryReportObject
			- Contains field that stores the instance of InventoryReport
	- InventoryBuildDirector
		- Class responsible for executing whatever concrete builder is requested for execution
	

- Approach#1 - Using Director class
	- From Program.cs, 
		- Create instance of Concrete Builder (DailyReportBuilder)
		- Create instance of director class and pass in reference of concrete builder that will be used by the director class to build object
		- Call Build method responsible for building actual object

	- Less practically used since it has a lot of abstractions
- Approach#2 - Fluent Builder approach
	- From Program.cs
		- Create instance of Concrete Builder (DailyReportBuilder)
		- Start Building the object directly

- Use cases
	- Not for everything - It is actually an overkill for most classes where subclassing, refactoring or abstract interfaces would be better solution
	- To be used where we see Bloated class constructors
	- When we know of finite number of related classes performing similar functions with different representations

- Implication
	- Lets us vary product internal representation
	- Isolates code for construction and representation
	- Finer control over construction process
	- Shares similarities with Factory pattern. Difference is Builder responsible for creation of a single object whereas Factory responsible for creation of factories of similar objects




//Concrete class
public class AuditMessage
{
	public string OrganizationId{get;set;}
	public string Service{get;set;}
	public string Endpoint{get;set;}
	public string Payload{get;set;}
	public string Timestamp{get;set;}
}

//Builder interface
public interface IAuditMessageBuilder
{
	IAuditMessageBuilder SetOrg(string org);
	IAuditMessageBuilder SetService(string svc);
	IAuditMessageBuilder SetEndpoint(string endpoint);
	IAuditMessageBuilder SetPayload(string payload);
	AuditMessage Build();
}

//Concrete builder
public class AuditMessageBuilder : IAuditMessageBuilder
{
	private readonly AuditMessage _auditMessage;
	public AuditMessageBuilder()
	{
		_auditMessage = new();
	}

	public IAuditMessageBuilder SetOrg(string org)
	{
		_auditMessage.OrganizationId = org;
		return this;
	}
	public IAuditMessageBuilder SetService(string svc)
	{
		_auditMessage.Service = svc;
		return this;
	}
	public IAuditMessageBuilder SetEndpoint(string endpoint)
	{
		_auditMessage.Endpoint = endpoint;
		return this;
	}
	public IAuditMessageBuilder SetPayload(string payload)
	{
		_auditMessage.Payload = payload;
		return this;
	}
	public AuditMessage Build()
	{
		_auditMessage.Timestamp = DateTime.UtcNow;
		return _auditMessage;
	}
}

//DI-Wireup
services.AddScoped<IAuditMessageBuilder, AuditMessageBuilder>();

//Consumer
public class HomeController : ControllerBase
{
	private readonly IAuditMessageBuilder _auditMessageBuilder;

	public HomeController(IAuditMessageBuilder auditMessageBuilder)
	{
		_auditMessageBuilder = auditMessageBuilder;
	}

	[HttpGet, Route("/get")]
	public IActionResult Get(CancellationToken cancellationToken)
	{
		//Get audit message
		var auditMessage = _auditMessageBuilder.SetOrg("SetOrg)
		.SetService("Svc")
		.SetEndpoint("endpoint")
		.SetPayload("payload")
		.Build();
	}
}