规格模式（Specification）

> 构建一个清晰的业务规则规范，其中每条规则都能被针对性地检查。

## 目的

构建一个清晰的业务规则规范，其中每条规则都能被针对性地检查。每个规范类中都有一个称为 isSatisfiedBy 的方法，方法判断给定的规则是否满足规范从而返回 true 或 false。

## 例子

* [RulerZ](https://github.com/K-Phoen/rulerz)

## UML

![file](/media/202203/2022-03-29_2011170.10845092269626777.png)

## 示例代码

### PHP

```php
class Item
{
    /**
     * @var float
     */
    private $price;

public function __construct(float $price)
    {
        $this->price = $price;
    }

public function getPrice(): float
    {
        return $this->price;
    }
}

interface SpecificationInterface
{
    public function isSatisfiedBy(Item $item): bool;
}

class OrSpecification implements SpecificationInterface
{
    /**
     * @var SpecificationInterface[]
     */
    private $specifications;

/**
     * @param SpecificationInterface[] ...$specifications
     */
    public function __construct(SpecificationInterface ...$specifications)
    {
        $this->specifications = $specifications;
    }

/**
     * 如果有一条规则符合条件，返回 true，否则返回 false
     */
    public function isSatisfiedBy(Item $item): bool
    {
        foreach ($this->specifications as $specification) {
            if ($specification->isSatisfiedBy($item)) {
                return true;
            }
        }
        return false;
    }
}
class PriceSpecification implements SpecificationInterface
{
    /**
     * @var float|null
     */
    private $maxPrice;

/**
     * @var float|null
     */
    private $minPrice;

/**
     * @param float $minPrice
     * @param float $maxPrice
     */
    public function __construct($minPrice, $maxPrice)
    {
        $this->minPrice = $minPrice;
        $this->maxPrice = $maxPrice;
    }

public function isSatisfiedBy(Item $item): bool
    {
        if ($this->maxPrice !== null && $item->getPrice() > $this->maxPrice) {
            return false;
        }

if ($this->minPrice !== null && $item->getPrice() < $this->minPrice) {
            return false;
        }

return true;
    }
}

class AndSpecification implements SpecificationInterface
{
    /**
     * @var SpecificationInterface[]
     */
    private $specifications;

/**
     * @param SpecificationInterface[] ...$specifications
     */
    public function __construct(SpecificationInterface ...$specifications)
    {
        $this->specifications = $specifications;
    }

/**
     * 如果有一条规则不符合条件，返回 false，否则返回 true
     */
    public function isSatisfiedBy(Item $item): bool
    {
        foreach ($this->specifications as $specification) {
            if (!$specification->isSatisfiedBy($item)) {
                return false;
            }
        }

return true;
    }
}

class NotSpecification implements SpecificationInterface
{
    /**
     * @var SpecificationInterface
     */
    private $specification;

public function __construct(SpecificationInterface $specification)
    {
        $this->specification = $specification;
    }

public function isSatisfiedBy(Item $item): bool
    {
        return !$this->specification->isSatisfiedBy($item);
    }
}

class SpecificationTest extends TestCase
{
    public function testCanOr()
    {
        $spec1 = new PriceSpecification(50, 99);
        $spec2 = new PriceSpecification(101, 200);

$orSpec = new OrSpecification($spec1, $spec2);

$this->assertFalse($orSpec->isSatisfiedBy(new Item(100)));
        $this->assertTrue($orSpec->isSatisfiedBy(new Item(51)));
        $this->assertTrue($orSpec->isSatisfiedBy(new Item(150)));
    }

public function testCanAnd()
    {
        $spec1 = new PriceSpecification(50, 100);
        $spec2 = new PriceSpecification(80, 200);

$andSpec = new AndSpecification($spec1, $spec2);

$this->assertFalse($andSpec->isSatisfiedBy(new Item(150)));
        $this->assertFalse($andSpec->isSatisfiedBy(new Item(1)));
        $this->assertFalse($andSpec->isSatisfiedBy(new Item(51)));
        $this->assertTrue($andSpec->isSatisfiedBy(new Item(100)));
    }

public function testCanNot()
    {
        $spec1 = new PriceSpecification(50, 100);
        $notSpec = new NotSpecification($spec1);

$this->assertTrue($notSpec->isSatisfiedBy(new Item(150)));
        $this->assertFalse($notSpec->isSatisfiedBy(new Item(50)));
    }
}
```