add Facade pattern

tk-codes · tk-codes · commit d1aedcebcfda · 2017-10-28T22:10:36.000+02:00
diff --git a/README.md b/README.md
@@ -4,7 +4,7 @@ Design Patterns in C# / .NET
 [![Build Status](https://travis-ci.org/tk-codes/DesignPatterns.NET.svg?branch=master)](https://travis-ci.org/tk-codes/DesignPatterns.NET)
 ![Language C#](https://img.shields.io/badge/language-c%23-blue.svg)
 ![status in progress](https://img.shields.io/badge/status-in%20progress-brightgreen.svg)
-![number of patterns](https://img.shields.io/badge/patterns-11-red.svg)
+![number of patterns](https://img.shields.io/badge/patterns-12-red.svg)
 
 ## Creational Patterns
 
@@ -25,7 +25,7 @@ Design Patterns in C# / .NET
 | | Bridge |
 |:heavy_check_mark: | [Composite](/StructuralPatterns/Composite) | 
 |:heavy_check_mark:| [Decorator](/StructuralPatterns/Decorator) | 
-| | Facade | 
+|:heavy_check_mark:| [Facade](/StructuralPatterns/Facade) | 
 | | Flyweight |
 | | Proxy |
 
diff --git a/StructuralPatterns/Facade/README.md b/StructuralPatterns/Facade/README.md
@@ -0,0 +1,39 @@
+﻿# Facade
+
+Provide a **unifed interface to a set of interfaces in a subsystem**. Facade defines a higher-level interface that makes the subsystem easier to use.
+
+## Problem
+
+* To make a complex subsystem easier to use, a simpler interface should be provided for a set of interfaces in the subsystems.
+* The dependencies on a subsystem should be minimized.
+
+## Solution
+
+Define a `Facade` object that
+* implements a simple interface which delegates the requests to the interfaces in the subsystem
+* may perform additional functionality before/after forwarding a request.
+
+## Benefits
+
+* A facade not only simplifies an interface, it decouples a client from a subsystem of components.
+* Facades help layer a system.
+
+## Drawbacks
+
+* Duplicated methods
+* Lower visibility of subsystem functionality.
+* It leads to a larger API to maintain.
+
+## Common Structure
+
+![Common structure of facade pattern](https://upload.wikimedia.org/wikipedia/commons/9/96/W3sDesign_Facade_Design_Pattern_UML.jpg)
+
+* Facade
+  * knows which subsystem classes are responsible for a request.
+  * delegates client requests to appropriate subsystem objects.
+* Subsystem classes
+  * implement subsystem functionality.
+  * handle work assigned by the Facade object
+  * have no knowledge of the facade and keep no reference to it.
+
+_[Source: http://www.dofactory.com/net/facade-design-pattern]_
