Facade Pattern

0x00 Facade Pattern
Appearance Pattern.

Definition
** Provide a unified interface to a set of interface in a subsystem. Facade defines a higher-level interface that makes the subsystem easier to use. (要求一个子系统的外部与内部的通信必须通过一个统一的对象进行．)**

Roles
Facade - Facade role, knows all functions and responsibilities, delegate class.
Subsystem - Subsystem role, the subsystem doesn’t know the facade class exists.

Advantages
Reduces system interdependencies

Disadvantages
Doesn’t conform to the Open-Closed Principle.

Application Scenarios
Suitable for:

Providing an interface for the outside world to access a complex module or subsystem.
Subsystem is relatively independent.
Prevent risk diffusion from low-level personnel.

PHP Implementation1
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<?php

// Subsystem
class SubsystemOne {
public function dosthFir()
{
echo ‘subsystem class one.’;
}
}
class SubsystemTwo {
public function dosthSec()
{
echo ‘subsystem class two.’;
}
}
class SubsystemThr {
public function dosthThr()
{
echo ‘subsystem class three.’;
}
}

// Facade class
class Facade {
private $objOne;
private $objTwo;
private $objThree;
private $context;

public function __construct()
{
    $this->objOne = new SubsystemOne();
    $this->objTwo = new SubsystemTwo();
    $this->objThr = new SubsystemThr();
    $this->context = new Context();
}

public function jobFir()
{
    $this->objOne->dosthFir();
}
public function jobSec()
{
    $this->objTwo->dosthSec();
}
public function jobThr()
{
    $this->context->combineJob();
}

}

// Encapsulation class, don’t directly participate in subsystem business logic
class Context {
private $objOne;
private $objThr;

public function __construct()
{
    $this->objOne = new SubsystemOne();
    $this->objThr = new SubsystemThr();
}

public function combineJob()
{
    $this->objOne->doSthFir();
    $this->objThr->doSthThr();
}

}

0x01 Summary
The facade doesn’t participate in subsystem business logic. The Laravel framework uses quite a few Facades.