<?php

namespace Illuminate\Support\Facades;

/**
 * @see \Illuminate\Validation\Factory
 */
class Validator extends Facade
{
  /**
   * Get the registered name of the component.
   *
   * @return string
   */
  protected static function getFacadeAccessor()
  {
    return 'validator';
  }
}

namespace Illuminate\Foundation;
...
class Application extends Container implements ApplicationContract, HttpKernelInterface
{
  ...
  public function registerCoreContainerAliases()
  {
    foreach ([
      ...
      'validator'=> [
        \Illuminate\Validation\Factory::class,
        \Illuminate\Contracts\Validation\Factory::class
      ],
    ])
    ...
  }
  ...
}

//\Illuminate\Contracts\Validation\Factory 源碼

protected function resolve(array $data, array $rules, array $messages, array $customAttributes)
{
  if (is_null($this->resolver)) {
    return new Validator(
      $this->translator,
      $data,
      $rules,
      $messages,
      $customAttributes
    );
  }

  return call_user_func(
    $this->resolver,
    $this->translator,
    $data,
    $rules,
    $messages,
    $customAttributes
  );
}

Validator::resolver(function($translator, $data, $rules, $messages, $customAttributes){
  return new ExtendValidator($translator, $data, $rules, $messages, $customAttributes);
});

//這是一個(gè)簡(jiǎn)單的參數(shù)比較的驗(yàn)證規(guī)則，Laravel5.8中提供，Laravel5.5中未提供
//驗(yàn)證規(guī)則如下: 'max_num'=>'gte:min',
Validator::extend('gte',function($attribute, $value, $parameters, $validator){
  if($value>=data_get($validator->getData(),$parameters[0]))
  {
    return true;
  }
  return false;
});

//\Illuminate\Contracts\Validation\Factory 源碼
public function extend($rule, $extension, $message = null)
{
  $this->extensions[$rule] = $extension;

  if ($message) {
    $this->fallbackMessages[Str::snake($rule)] = $message;
  }
}

//\Illuminate\Validation\Validator 源碼
protected function callExtension($rule, $parameters)
{
  $callback = $this->extensions[$rule];

  if (is_callable($callback)) {
    return call_user_func_array($callback, $parameters);
  } elseif (is_string($callback)) {
    return $this->callClassBasedExtension($callback, $parameters);
  }
}

protected function validateAttribute($attribute, $rule)
{
  ...
  $method = "validate{$rule}";
  if ($validatable && ! $this->$method($attribute, $value, $parameters, $this)) {
    $this->addFailure($attribute, $rule, $parameters);
  }
}

public function __call($method, $parameters)
{
  $rule = Str::snake(substr($method, 8));

  if (isset($this->extensions[$rule])) {
    return $this->callExtension($rule, $parameters);
  }

  throw new BadMethodCallException(sprintf(
    'Method %s::%s does not exist.', static::class, $method
  ));
}

<?php

namespace Illuminate\Contracts\Validation;

interface Rule
{
  /**
   * Determine if the validation rule passes.
   *
   * @param string $attribute
   * @param mixed $value
   * @return bool
   */
  public function passes($attribute, $value);

  /**
   * Get the validation error message.
   *
   * @return string
   */
  public function message();
}

protected function validateUsingCustomRule($attribute, $value, $rule)
{
  if(method_exists($rule, 'setValidator'))
  {
    $rule->setValidator($this);
  }
  return parent::validateUsingCustomRule($attribute,$value,$rule);
}

['min_num'=>'validateMinNum']

$rule = [
  'min'=>new ClosureValidationRule([$this,'checkv'])
];
$data = ['min'=>10];
$v = Validator::make($data,$rule);

$rule = [
  'min'=>'checkv'
];
Validator::extend('checkv',[$this,'checkv']);