<?php
//IoC容器类，参考《Laravel框架关键技术解析》第六章，可以直接运行测试。
class Container
{
	//存储注册的回调函数，为键值对关联数组，
	//键为$abstract，值为对应注册的回调函数数组array("concrete"=>回调函数，"shared"=>boolean)
	protected $bindings = [];
	
	//注册函数，最开始需要调用本函数绑定接口和对应回调函数到$bindings
	public function bind($abstract, $concrete = null, $shared = false)
	{
		if (!$concrete instanceof Closure) {
			$concrete = $this->getClosure($abstract, $concrete);
		}
		$this->bindings[$abstract] = compact('concrete','shared');
	}

	//默认生成实例的回调函数
	protected function getClosure($abstract, $concrete)
	{
		return function($c) use ($abstract, $concrete)
		{
			$method = ($abstract == $concrete) ? 'build' : 'make';
			return $c->$method($concrete);
		};
	}

	//生成实例化的对象，被用户直接调用的方法。首先解决接口和要实例化类之间的依赖关系
	public function make($abstract)
	{
		$concrete = $this->getConcrete($abstract);
		$object;
		if ($this->isBuildable($concrete, $abstract)) {
			$object = $this->build($concrete);
		} else {
			$object = $this->make($concrete);
		}
		return $object;
	}

	//判断是否$concrete可以直接使用build实例化
	protected function isBuildable($concrete, $abstract)
	{
		return $concrete === $abstract || $concrete instanceof Closure;
	}

	//获取在$bindings中的回调函数，如果不存在说明之前并未注册，则直接返回，尝试使用反射实例化
	protected function getConcrete($abstract)
	{
		if (!isset($this->bindings[$abstract])) {
			return $abstract;
		}
		return $this->bindings[$abstract]['concrete'];
	}

	//实例化对象，如果是回调函数，直接调用其进行实例化
	//如果不是则尝试通过反射实例化
	public function build($concrete) 
	{
		if ($concrete instanceof Closure) {
			return $concrete($this);
		}
		//生成反射类
		$reflector = new ReflectionClass($concrete);
		//判断是否可以实例化
		if (!$reflector->isInstantiable()) {
			echo $message = "Target ($concrete) is not instantiable";
			return NULL;
		}
		//获取构造函数
		$constructor = $reflector->getConstructor();
		if (is_null($constructor)) {
			return new $concrete;
		}
		//获取构造函数需要的参数
		$dependencies = $constructor->getParameters();
		//生成参数，同样是调用了make来生成
		$instances =$this->getDependencies($dependencies);
		//生成实例化对象，并返回
		return $reflector->newInstanceArgs($instances);
	} 

	//根据array(ReflectionParameter)来获取构造函数需要的参数数组
	protected function getDependencies($parameters)
	{
		$dependencies = [];
		foreach ($parameters as $parameter) 
		{
			//获取参数的类名，除了自定义类对象，均会返回NULL
			$dependency = $parameter->getClass();
			if (is_null($dependency)){
				$dependencies[] = NULL;
			} else {
				//自动生成对象参数
				$dependencies[] = $this->resolveClass($parameter);
			}
		}
		return (array) $dependencies;
	}
	
	protected function resolveClass(ReflectionParameter $parameter)
	{
		//调用make生成对象
		return $this->make($parameter->getClass()->name);
	}
	
}

//IoC容器使用方法
//定义一个接口
interface Visit
{
	public function go();
}
//实现了接口的两个类
class Train implements Visit
{
	public function go(){
		echo "go to by Train!\n";
	}
}

class Bus implements Visit
{
	public function go(){
		echo "go to by Bus!\n";
	}
}

//需要使用IoC容器的类
class Traveller
{
	protected $trafficTool;
	public function __construct(Visit $trafficTool)
	{
		$this->trafficTool = $trafficTool;
	}
	public function visit()
	{
		$this->trafficTool->go();
	}
	
}

//创建一个IoC容器
$container= new Container();
//注册一个"Visit"为Train类的接口
$container->bind("Visit", "Train");
//注册一个"traveller"为Traveller类的接口
$container->bind("traveller","Traveller");
//实例化一个"traveller"的对象，实际是实例化Traveller对象，而Traveller需要"Visit"的对象参数，
//则传进去之前注册的Train
$tra = $container->make("traveller");
//输出：go to by Train!
$tra->visit();

//注册一个"Visit"为BUS类的接口
$container->bind("Visit", "Bus");
//此时需要的参数"Visit"已经被替换为Bus
$tra = $container->make("traveller");
//输出：go to by Bus!
$tra->visit();