done facade README and assets

Author: AdelDaniel

structural_design_pattern/facade/README.md

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+# Facade Structural Design Pattern
+> hides the complexities of the system by a class that provide a simple interface to a complex subsystem which contains lots of moving parts.
+
+<center><table>
+  <tr>
+    <td><img src="assets/Facade_Design_Pattern_Class_Diagram_UML_wikipedia_2.png"></td>
+    <td><img src="assets/Facade_Design_Pattern_Sequence_Diagram_UML_wikipeda.png"><td>
+    <td><img src="assets/Example_of_Facade_design_pattern_in_UML.png"></td>
+  </tr>
+</table></center>
+
+<center><img width=75% src="assets/facade-diagram.png"></center>
+
+
+
+## Sections
+- [Definitions](#Definitions)
+- [What Problem Facade Solve?](#What-Problem-Facade-Solve?)
+- [Examples](#Examples)
+    - [file converter example ](#file-converter-example)
+    - [Shape Marker](#Shape-Marker)  Tutorial point Example 
+- [Sources](#Sources)
+
+
+## **Definitions**
+   <dl>
+    <dt><b>tutorialspoint </b></dt>
+    <dd> 
+        <li>is a structural pattern.</li>
+        <li> this pattern adds an interface to existing system to hide its complexities.</li>
+        <li> and provides an interface to the client using which the client can access the system.</li>
+    </dd>
+    <dt><b>refactoring.guru </b></dt>
+    <dd>
+        <li>a structural pattern</li>
+        <li>provides a simplified interface to a library, a framework, or any other complex set of classes.</li>
+    </dd>
+    </dd>
+    <dt><b>Wikipedia </b></dt>
+    <dd>
+        <li>a structural pattern</li>
+        <li>provides a simplified interface to a library, a framework, or any other complex set of classes.</li>
+        </br>
+        <li>Facade describe how to solve recurring design problems</li>
+        <li>to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.</li>
+    </dd>
+</dl> 
+
+</br>
+
+## **What Problem Facade Solve?**
+
+- Imagine that you must make your code work with a broad set of objects that belong to a sophisticated library or framework.
+- Ordinarily, you’d need to initialize all of those objects, keep track of dependencies, execute methods in the correct order, and so on.
+
+> As a result, the business logic of your classes would become tightly coupled to the implementation details of 3rd-party classes, making it hard to comprehend and maintain.
+
+---
+
+### Solution 
+- A facade is a `class` that provides a simple interface to a complex subsystem which contains lots of moving parts.
+- A facade might provide limited functionality in comparison to working with the subsystem directly.
+- However, it includes only those features that clients really care about.
+
+- Having a facade is handy when you need to integrate your app with a sophisticated library that has dozens of features, but you just need a tiny bit of its functionality.
+
+
+
+## **Examples**
+
+### file converter example 
+ - Example in dart: <a href="file converter example ="_blank">file converter example  </a>
+ - Example Source: 
+    - <a href="https://refactoring.guru/design-patterns/bridge" target="_blank" >https://refactoring.guru/design-patterns/bridge</a>
+    - <a href="https://www.tutorialspoint.com/design_pattern/bridge_pattern.htm" target="_blank" >https://www.tutorialspoint.com/design_pattern/bridge_pattern.htm</a>
+
+### Shape Marker
+- source: <a href="https://www.tutorialspoint.com/design_pattern/facade_pattern.htm" target="_blank">tutorialspoint.com/design_pattern/facade_pattern</a>
+- Example in dart: <a href="shape_marker.dart" target="_blank">Shape Marker</a>
+
+
+
+## **Sources**
+
+- <a href="https://en.wikipedia.org/wiki/Facade_pattern" target="_blank"> wikipedia.org Facade_pattern</a>
+- <a href="https://refactoring.guru/design-patterns/facade" target="_blank"> refactoring.guru design-patterns facade</a>
+- <a href="https://www.tutorialspoint.com/design_pattern/facade_pattern.htm" target="_blank"> www.tutorialspoint.com facade_pattern </a>
+