Laravel Rule for valid Discourse usernames

DiscourseUsernameRule.php

<?php

namespace App\Rules;

use Illuminate\Contracts\Validation\Rule;

/**
 * PHP implementation of
 * https://github.com/discourse/discourse/blob/888e68a1637ca784a7bf51a6bbb524dcf7413b13/app/models/username_validator.rb
 * @package App\Rules
 */
class DiscourseUsernameRule implements Rule
{
    private $value;

    // usernames must consist of a-z A-Z 0-9 _ - .
    private const ASCII_INVALID_CHARACTERS = "/[^\w.-]/";
    // usernames can start with a-z A-Z 0-0 _
    private const VALID_LEADING_CHARACTERS = "/^[a-zA-Z0-9_]/";
    // usernames must end with a-z A-Z 0-9
    private const VALID_TRAILING_CHARACTERS = "/[a-zA-Z0-9]$/";
    // underscores, dashes and dots can't be repeated consecutively
    private const REPEATING_CONFUSING_CHARACTERS = "/[-_.]{2,}/";

    private const CONFUSING_EXTENSIONS = "/\.(js|json|css|htm|html|xml|jpg|jpeg|png|gif|bmp|ico|tif|tiff|woff)$/i";

    /**
     * Create a new rule instance.
     *
     * @return void
     */
    public function __construct()
    {
        //
    }

    private function minimumLength()
    {
        return strlen($this->value) > 3;
    }

    private function maximumLength()
    {
        return strlen($this->value) <= 20;
    }

    private function charactersValid()
    {
        return !preg_match(self::ASCII_INVALID_CHARACTERS, $this->value);
    }

    private function firstCharacterValid()
    {
        return preg_match(self::VALID_LEADING_CHARACTERS, $this->value);
    }

    private function lastCharacterValid()
    {
        return preg_match(self::VALID_TRAILING_CHARACTERS, $this->value);
    }

    private function noDoubleSpecial()
    {
        return !preg_match(self::REPEATING_CONFUSING_CHARACTERS, $this->value);
    }

    private function noConfusingExtension()
    {
        return !preg_match(self::CONFUSING_EXTENSIONS, $this->value);
    }

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

        return $this->minimumLength() &&
            $this->maximumLength() &&
            $this->charactersValid() &&
            $this->firstCharacterValid() &&
            $this->lastCharacterValid() &&
            $this->noDoubleSpecial() &&
            $this->noConfusingExtension();
    }

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

DiscourseUsernameRule_Test.php

<?php


namespace Tests\Rules;


use App\Rules\DiscourseUsernameRule;
use Tests\TestCase;

class DiscourseUsernameRule_Test extends TestCase
{
    private $rule;

    protected function setUp(): void
    {
        parent::setUp();

        $this->rule = new DiscourseUsernameRule();
    }

    public function testBlankUsernameIsInvalid()
    {
        $this->assertFalse($this->rule->passes("username", ""));
    }

    public function testUsernameTooShort()
    {
        $this->assertFalse($this->rule->passes("username", "abc"));
    }

    public function testUsernameWithMinLength()
    {
        $this->assertTrue($this->rule->passes("username", "abcd"));
    }

    public function testUsernameTooLong()
    {
        $this->assertFalse($this->rule->passes("username", "abcdefgjijklmnopqrstu"));
    }

    public function testUsernameWithMaxLength()
    {
        $this->assertTrue($this->rule->passes("username", "abcdefgjijklmnopqrst"));
    }

    public function testValidCharacters()
    {
        $this->assertTrue($this->rule->passes("username", "ab-cd.123_ABC-xYz"));
    }

    public function testInvalidCharacters()
    {
        $this->assertFalse($this->rule->passes("username", "abc|"));
        $this->assertFalse($this->rule->passes("username", "a#bc"));
        $this->assertFalse($this->rule->passes("username", "abc xyz"));
    }

    public function testStartingWithAlphanumericOrUnderscore()
    {
        $this->assertTrue($this->rule->passes("username", "abcd"));
        $this->assertTrue($this->rule->passes("username", "1abc"));
        $this->assertTrue($this->rule->passes("username", "_abc"));
    }

    public function testStartingWithDotOrDash()
    {
        $this->assertFalse($this->rule->passes("username", ".abc"));
        $this->assertFalse($this->rule->passes("username", "-abc"));
    }

    public function testEndingWithAlphanumeric()
    {
        $this->assertTrue($this->rule->passes("username", "abcd"));
        $this->assertTrue($this->rule->passes("username", "abc9"));
    }

    public function testEndingWithInvalidCharacter()
    {
        $this->assertFalse($this->rule->passes("username", "abc_"));
        $this->assertFalse($this->rule->passes("username", "abc."));
        $this->assertFalse($this->rule->passes("username", "abc-"));
    }

    public function testConsecutiveSpecialCharacters()
    {
        $this->assertFalse($this->rule->passes("username", "a__bc"));
        $this->assertFalse($this->rule->passes("username", "a..bc"));
        $this->assertFalse($this->rule->passes("username", "a--bc"));
    }

    public function testFileExtensionEnding()
    {
        $this->assertFalse($this->rule->passes("username", "abc.json"));
        $this->assertFalse($this->rule->passes("username", "abc.png"));
    }

    public function testUnicodeCharacters()
    {
        $this->assertFalse($this->rule->passes("username", "abcö"));
        $this->assertFalse($this->rule->passes("username", "abc象"));
    }
}