Laravel Form Request Array Validation Custom Rules

I want to create a Form Request validation and don't know how-to.

I have a form:

<form>
  <input type="text" name="fullname[0]">
  <input type="text" name="document_num[0]">

  <input type="text" name="fullname[1]">
  <input type="text" name="document_num[1]">

  <input type="text" name="fullname[2]">
  <input type="text" name="document_num[2]">

   .....

  <input type="text" name="fullname[n]">
  <input type="text" name="document_num[n]">

  <input type="submit">
</form>

table 'users':

  id | fullname | document_num
  1  | John     | 111
  2  | Jane     | 112
 ..  | ...      | ...

when user clicks submit a request is sent to controller method where it’s first being validated by Form Request (or it can be a regular Validator). So I want to write a rule which checks:

for (i=0; i<numberOfUsersToAdd; i++)

    if  (‘document_num[$i]’ exists in ‘users’ in field ‘document_num’ ) {

       $user = Users::find(id of user in DB having this ‘document_num[$i]’) ; 

       check if (fullname[$i] == $user->fullname) {

                return true} // input-ed users name match his/her name in DB.

        else {return false}  // input-ed users name doesn't match his/her name in DB.

        } 

    else return true; // document_num[$i] doesn't exists in the database which's ok

if in words: check if any input-ed document_num[$i] exists in the table users, if yes, get the user having this document_nubmer from DB and compare his/her fullname value to fullname[$i] from input.

How to do it?:)

Appreciate any help!:)

Ok. Logic of this validation in YourFormRequest is next:

Let mark all fields as required and document_num field additionaly as integer. You can add other additional constraints - it dont matter.
In rules method of YourFormRequest check in loop "is user exists for given document_num?".
If it not exists then ok - validation of this field is success.
If it exists then check "is user fullname equals for given fullname. If equals then ok - validation of this field is success. Otherwise if it fails then attach to this field your custom rule that always fails.

Let see this approach on a working example.

YourFormRequest.php

public function rules()
{
    $rules = [
        'fullname.*' => 'required',
        'document_num.*' => 'required|integer',
    ];

    $documentNums = request()->get('document_num');
    $fullnames = request()->get('fullname');

    for ($i = 0; $i < count($documentNums); $i++) {
        $user = User::where('document_num', $documentNums[$i])->first();
        if ($user && ($user->fullname != $fullnames[$i]) {
            $rules['document_num.' . $i] = "document_num_fail:$i"; //some rule that always fails. As argument we pass a row number of field that fails
        }
    }
    return $rules;
}

CustomValidator.php (place it for example in App\Services folder)

namespace App\Services;

class CustomValidator {

    public function documentNumFailValidate($attribute, $value, $parameters, $validator) {
        return false;
    }

    public function documentNumFailReplacer($message, $attribute, $rule, $parameters) {
        return str_replace([':index'], $parameters[0], $message);
    }
}

Here you can see two functions. First - to validate rule (we always pass false cause we need it). Second - it just a replacer for error message. You want to know on what field line was this error (for example on third line and fields: fullname[2] and document_num[2] respectively). As i wrote above in comment for attaching fail rule we give the number of row that fails to the validation method (documentNumFailReplacer method will replace placeholder :index in error message with the given value)

Next step - register this methods in AppServiceProvider.php

public function boot()
{
    Validator::extend('document_num_fail',  'App\Services\CustomValidator@documentNumFailValidate');
    Validator::replacer('document_num_fail', 'App\Services\CustomValidator@documentNumFailReplacer');
}

And final step - define your custom messages in validation.php

'custom' => [
        'document_num.*' => [
            'document_num_fail' => 'Input-ed user name doesn`t match his/her name in DB for specified :attribute (field position/number: :index)',
        ]
    ],

'attributes' => [
    'document_num.*' => 'document number',
],