Add wash certificate generation feature and refine booking logic

Introduces a form for generating wash certificates associated with bookings, along with validations and access restrictions. Refactors booking management to integrate a new `bookings_new_o` class, enhancing structure and adding functionalities like caching and detailed error handling.

services/nginx/app/classes/form.php

@@ -12,11 +12,13 @@ use Exception;
 use forms\book_interior_wash_f;
 use forms\book_wash_f;
 use forms\form_helper_c;
+use forms\generate_booking_wash_certificate_f;
 use traits\form_t;
 
 /** Require the forms */
 require_once WD . '/modules/forms/book_wash_f.php';
 require_once WD . '/modules/forms/book_interior_wash_f.php';
+require_once WD . '/modules/forms/generate_booking_wash_certificate_f.php';
 
 class form
 {
@@ -30,11 +32,17 @@ class form
      * @var book_interior_wash_f $book_interior_wash The BOOK_INTERIOR_WASH form
      */
     public book_interior_wash_f $book_interior_wash;
+    /**
+     * The GENERATE_BOOKING_CERTIFICATE form
+     * @var generate_booking_wash_certificate_f $generate_booking_wash_certificate The GENERATE_BOOKING_CERTIFICATE form
+     */
+    public generate_booking_wash_certificate_f $generate_booking_wash_certificate;
 
     public function __construct()
     {
         $this->book_wash = new book_wash_f();
         $this->book_interior_wash = new book_interior_wash_f();
+        $this->generate_booking_wash_certificate = new generate_booking_wash_certificate_f();
     }
 
     /**

services/nginx/app/modules/email/templates/email_template_wash_certificate.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace email\templates;
+
+use email\helpers\email_template;
+
+class email_template_wash_certificate
+{
+    use email_template;
+
+    protected int $booking_id;
+    protected string $company_name;
+
+    public function __construct(
+        int    $booking_id,
+        string $company_name,
+    )
+    {
+        $this->booking_id = $booking_id;
+        $this->company_name = $company_name;
+    }
+
+    public function generate_text(): string
+    {
+        return "";
+    }
+
+    public function generate_html(): string
+    {
+        ob_start();
+        # Start of the html
+        ?>
+
+        <!-- Email template -->
+        <p>Kære <?= $this->company_name ?>,</p>
+        <br>
+        <p>Din ordre er udført.</p>
+        <p>Vi har vedhæftet dit vaskecertifikat til denne email.</p>
+        <br>
+        <p>Tak fordi du valgte Truck Wash – vi sætter stor pris på dit samarbejde.</p>
+        <p>Har du behov for yderligere assistance, er vi kun en e-mail eller et opkald væk.</p>
+        <p>De bedste hilsner - Kind regards</p>
+        <p>Truck Wash</p>
+        <!-- End of the email template -->
+
+        <?php
+        # End of the html
+        return ob_get_clean();
+    }
+}

services/nginx/app/modules/forms/book_wash_f.php

@@ -3,6 +3,7 @@
 namespace forms;
 
 use classes\email;
+use objects\bookings_new_o;
 use objects\departments_o;
 use objects\users_o;
 use traits\form_t;
@@ -53,9 +54,28 @@ class book_wash_f extends form_helper_c
         $user = (new users_o())->getUserByCustomerNumber(self::getSanitizedData('customer_number'));
         // Get the department name from the department id
         $department = (new departments_o())->selectId(self::getSanitizedData('department_id'));
+        // Get the bookings_new object
+        $bookings_new = new bookings_new_o();
+        // Create a new booking
+        $bookings_new->add(
+            self::getCustomerNumber(),
+            self::getFormIdentifier(),
+            self::getSanitizedData('contact_email'),
+            self::getSanitizedData('reference'),
+            strtoupper(self::getSanitizedData('registration_number_tractor')),
+            strtoupper(self::getSanitizedData('registration_number_trailer')),
+            self::getSanitizedData('wants_wash_certificate') ? self::getSanitizedData('wants_wash_certificate_email') : '',
+            self::getSanitizedData('date'),
+            $department->id,
+            (bool)self::getSanitizedData('wants_pickup'),
+            self::getSanitizedData('notes'),
+            'pending',
+            '',
+            'pending'
+        );
         // Send the booking confirmation email
         $email->sendBookingConfirmationEmail(
-            123,
+            $bookings_new->id,
             $user->getCustomerName($user->customer_number->value()),
             self::getCustomerNumber(),
             self::getSanitizedData('contact_email'),

services/nginx/app/modules/forms/form_helper_c.php

@@ -2,6 +2,8 @@
 
 namespace forms;
 
-abstract class form_helper_c
+require_once __DIR__ . '/form_restrictions_helper_c.php';
+
+abstract class form_helper_c extends form_restrictions_helper_c
 {
 }

services/nginx/app/modules/forms/form_restrictions_helper_c.php

@@ -0,0 +1,62 @@
+<?php
+
+namespace forms;
+
+use classes\authentication;
+use Exception;
+use objects\users_o;
+
+abstract class form_restrictions_helper_c
+{
+    protected users_o $users_o;
+
+    /**
+     * @throws Exception
+     */
+    public function __construct()
+    {
+        // Initialize the users_o object
+        $tmp_users_o = (new authentication())->get_user();
+        if (!!$tmp_users_o) {
+            $this->users_o = $tmp_users_o;
+        }
+    }
+
+    /**
+     * Restrict access, if the user does not have access to the department
+     * @throws Exception If the user does not have access to the department
+     */
+    public function restrictAccessDepartment($department_id): void
+    {
+        self::requirePermission(
+            'department_access_' . $department_id,
+            'User does not have access to the department',
+        );
+    }
+
+    /**
+     * Require permission to continue
+     * @param string $permission The permission to check
+     * @param string $message The error message to throw, if the user does not have permission
+     * @throws Exception If the user does not have permission
+     */
+    public function requirePermission(string $permission, string $message): void
+    {
+        self::requireAuth();
+        // Check if the user has permission
+        if (!$this->users_o->hasPermission($permission)) {
+            throw new Exception($message);
+        }
+    }
+
+    /**
+     * @throws Exception
+     */
+    protected function requireAuth(): void
+    {
+        // Check if the user is authenticated
+        if (!isset($this->users_o)) {
+            throw new Exception('User not authenticated');
+        }
+    }
+}

services/nginx/app/modules/forms/generate_booking_wash_certificate_f.php

@@ -0,0 +1,124 @@
+<?php
+
+namespace forms;
+
+use objects\bookings_new_o;
+use traits\form_t;
+
+class generate_booking_wash_certificate_f extends form_helper_c
+{
+    use form_t;
+
+    /**
+     * @inheritDoc
+     */
+    public function sanitize(): void
+    {
+        foreach ( $this->form_unsanitized_data as $key => $value ) {
+            // Sanitize the input TODO: Implement the sanitization logic
+            $this->form_unsanitized_data[$key] = $value;
+        }
+        // Set the sanitized data
+        $this->form_sanitized_data = $this->form_unsanitized_data;
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function validateInput(): void
+    {
+
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function beforeSave(): void
+    {
+        // Get the booking from the booking id
+        $bookings_new = new bookings_new_o();
+        $bookings_new->select(self::getSanitizedData('booking_id'));
+        // Check if the user has access to the booking
+        self::restrictAccessDepartment($bookings_new->department->value());
+        // Check if the user has access to issue wash certificates
+        self::requirePermission(
+            'issue_wash_certificates',
+            'User does not have access to issue wash certificates',
+        );
+        // Set the department id to the department id of the user
+        self::setDepartmentId($bookings_new->department->value());
+        // Set the customer number to the customer number of the user
+        self::setCustomerNumber($bookings_new->customer_number->value());
+        // Check if the booking is cancelled
+        switch ($bookings_new->status->value()) {
+            case 'cancelled':
+                throw new \Exception('Booking is cancelled');
+                break;
+            case 'completed':
+                throw new \Exception('Booking is completed');
+                break;
+            case 'pending':
+                break;
+            default:
+                throw new \Exception('Booking status is unknown, expected cancelled, completed or pending');
+                break;
+        }
+        // Generate the wash certificate
+        $bookings_new->generateWashCertificate(
+            self::getSanitizedData('safety_seal'),
+            self::getSanitizedData('operator'),
+        );
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function afterSubmit(): void
+    {
+        // TODO: Implement afterSubmit() method.
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function setup(): void
+    {
+        self::setFormIdentifier('GENERATE_BOOKING_WASH_CERTIFICATE');
+        self::setFormName('Opret vaskecertifikat');
+        self::setFormDescription('Du kan oprette et vaskecertifikat til en vask, der allerede er booket. Du skal blot indtaste de nødvendige oplysninger nedenfor.');
+        self::setSubmitButtonText('Opret vaskecertifikat');
+        // Set the form fields
+        self::defineInputFieldsAdvanced([
+            'booking_id' => [
+                'description' => 'Booking ID er det unikke ID for den booking, du vil oprette et vaskecertifikat til.',
+                'required' => true,
+                'placeholder' => 'Indtast booking ID',
+                'label' => 'Booking ID',
+                'help' => 'Dette er det unikke ID for den booking, du vil oprette et vaskecertifikat til.',
+                'error' => 'Du skal indtaste et gyldigt booking ID.',
+                'validation_method' => 'validateBookingId',
+            ],
+            'safety_seal' => [
+                'description' => 'En sikkerhedssikring er en form for beskyttelse, der sikrer, at køretøjet ikke er blevet åbnet eller ændret efter vasken.',
+                'required' => false,
+                'placeholder' => 'Indtast sikkerhedssikring',
+                'label' => 'Sikkerhedssikring',
+                'help' => 'Dette er en sikkerhedssikring, der bruges til at sikre køretøjet.',
+                'error' => 'Du skal indtaste en gyldig sikkerhedssikring.',
+                'validation_method' => 'validateInt',
+                'default' => '',
+            ],
+            'operator' => [
+                'description' => 'En operatør er en person, der arbejder med køretøjet.',
+                'required' => false,
+                'placeholder' => 'Indtast operatør',
+                'label' => 'Operatør',
+                'help' => 'Dette er en operatør, der arbejder med køretøjet.',
+                'error' => 'Du skal indtaste en gyldig operatør.',
+                'validation_method' => 'validateString',
+                'default' => '',
+            ],
+        ]);
+
+    }
+}

services/nginx/app/objects/bookings_new_o.php

@@ -0,0 +1,212 @@
+<?php
+
+namespace objects;
+
+use classes\db;
+use classes\email;
+use classes\object_property;
+use classes\pdf_generator;
+use Exception;
+use traits\db_object_t;
+
+class bookings_new_o extends db
+{
+    use db_object_t;
+
+    public object_property $customer_number;
+    public object_property $wash_type;
+    public object_property $contact_email;
+    public object_property $reference_number;
+    public object_property $regNrTraekker;
+    public object_property $regNrTrailer;
+    public object_property $washCertificateEmail;
+    public object_property $date;
+    public object_property $department;
+    public object_property $pickup_bool;
+    public object_property $notes;
+    public object_property $washCertificateStatus;
+    public object_property $washCertificateUrl;
+    public object_property $status;
+
+    private static function isCancelled(int $id): bool
+    {
+        global $db;
+        // Check if the booking has been cancelled
+        $sql = "SELECT status FROM bookings WHERE id = $id";
+        $result = $db->query($sql);
+        $row = $db->fetch_assoc($result);
+        return $row['status'] === 'cancelled';
+    }
+
+    public function structure(): void
+    {
+        $this->setTable('bookings_new');
+    }
+
+    public function objectChanged(): void
+    {
+        // Clear the cache
+        redis->clear_department_booking_count($this->department->value());
+    }
+
+    public function delete(int $id): void
+    {
+        $this->id = $id;
+        $this->getObjectProperties();
+        // Set the status to cancelled
+        $this->status->set('cancelled');
+        // Remove the cache
+        redis->clear_department_booking_count($this->department->value());
+    }
+
+    public function getObjectProperties(): void
+    {
+        $this->customer_number = new object_property($this->table, $this->id, 'customer_number', 'int', true);
+        $this->wash_type = new object_property($this->table, $this->id, 'wash_type', 'string', true);
+        $this->contact_email = new object_property($this->table, $this->id, 'contact_email', 'string', true);
+        $this->reference_number = new object_property($this->table, $this->id, 'reference_number', 'string', true);
+        $this->regNrTraekker = new object_property($this->table, $this->id, 'regNrTraekker', 'string', true);
+        $this->regNrTrailer = new object_property($this->table, $this->id, 'regNrTrailer', 'string', true);
+        $this->washCertificateEmail = new object_property($this->table, $this->id, 'washCertificateEmail', 'string', true);
+        $this->date = new object_property($this->table, $this->id, 'date', 'string', true);
+        $this->department = new object_property($this->table, $this->id, 'department', 'int', true);
+        $this->pickup_bool = new object_property($this->table, $this->id, 'pickup_bool', 'int', true);
+        $this->notes = new object_property($this->table, $this->id, 'notes', 'string', true);
+        $this->washCertificateStatus = new object_property($this->table, $this->id, 'washCertificateStatus', 'string', true);
+        $this->washCertificateUrl = new object_property($this->table, $this->id, 'washCertificateUrl', 'string', true);
+        $this->status = new object_property($this->table, $this->id, 'status', 'string', true);
+    }
+
+    public function parseBookings(array $listObjectsWithPaginationIfSet): array
+    {
+        // Parse the customer numbers
+        $bookings = $this->parseCustomerNumbers($listObjectsWithPaginationIfSet);
+        return $bookings;
+    }
+
+    public function parseCustomerNumbers(array $listObjectsWithPaginationIfSet): array
+    {
+        // Parse the customer numbers
+        foreach ( $listObjectsWithPaginationIfSet as $key => $value ) {
+            $listObjectsWithPaginationIfSet[$key]['customer_name'] = (new users_o())->getCustomerName($value['customer_number']);
+        }
+        return $listObjectsWithPaginationIfSet;
+
+    }
+
+    /**
+     * @param int $customer_number
+     * @param string $wash_type
+     * @param string $contact_email
+     * @param string $reference_number
+     * @param string $regNrTraekker
+     * @param string $regNrTrailer
+     * @param string $washCertificateEmail
+     * @param string $date
+     * @param string $department
+     * @param int $pickup_bool
+     * @param string $notes
+     * @param string $washCertificateStatus
+     * @param string $washCertificateUrl
+     * @param string $status
+     * @return void
+     */
+    public function add(int $customer_number, string $wash_type, string $contact_email, string $reference_number, string $regNrTraekker, string $regNrTrailer, string $washCertificateEmail, string $date, string $department, int $pickup_bool, string $notes, string $washCertificateStatus, string $washCertificateUrl, string $status): void
+    {
+        global $db;
+        // Avoid SQL injection
+        $wash_type = $db->escape_string($wash_type);
+        $contact_email = $db->escape_string($contact_email);
+        $reference_number = $db->escape_string($reference_number);
+        $regNrTraekker = $db->escape_string($regNrTraekker);
+        $regNrTrailer = $db->escape_string($regNrTrailer);
+        $washCertificateEmail = $db->escape_string($washCertificateEmail);
+        $date = $db->escape_string($date);
+        $department = $db->escape_string($department);
+        $notes = $db->escape_string($notes);
+        $washCertificateStatus = $db->escape_string($washCertificateStatus);
+        $washCertificateUrl = $db->escape_string($washCertificateUrl);
+        $status = $db->escape_string($status);
+        // Create a new record in the database ( Replace the code, if an entry already exists )
+        $sql = "INSERT INTO $this->table (customer_number, wash_type, contact_email, reference_number, regNrTraekker, regNrTrailer, washCertificateEmail, date, department, pickup_bool, notes, washCertificateStatus, washCertificateUrl, status) VALUES ($customer_number, '$wash_type', '$contact_email', '$reference_number', '$regNrTraekker', '$regNrTrailer', '$washCertificateEmail', '$date', '$department', $pickup_bool, '$notes', '$washCertificateStatus', '$washCertificateUrl', '$status')";
+        $db->query($sql);
+        // Clear the cache
+        redis->clear_department_booking_count($department);
+
+        // Get the id of the new record
+        $this->id = $db->insert_id();
+    }
+
+    /**
+     * Generate a wash certificate for the booking
+     * @param string|null $safety_seal
+     * @param string|null $operator
+     * @return void
+     * @throws Exception If the booking is cancelled
+     * @throws Exception If the booking is completed
+     * @throws Exception If the booking status is unknown
+     */
+    public function generateWashCertificate(string|null $safety_seal, string|null $operator): void
+    {
+        self::requireSelected();
+        // Prepare the date and time
+        $date = date('d-m-Y', strtotime($this->date->value()));
+        $time = date('H:i', strtotime($this->date->value()));
+        // Get the customer name
+        $customer_name = (new users_o())->getCustomerName($this->customer_number->value());
+        $pdf_generator = new pdf_generator();
+        $pdf_generator->add_html($pdf_generator->templates->getTemplate('wash_certificate')
+            ->setCompany([
+                'name' => 'Truck Wash',
+                'address' => 'Letland Allé 2',
+                'zip' => 2630,
+                'city' => 'Taastrup',
+                'phone_prefix' => 45,
+                'phone' => 43717886,
+                'email' => 'cph@truckwash.dk',
+                'website' => 'www.truckwash.dk',
+                'images' => [
+                    'logo' => '/truckwash-banner-png.png',
+                    'banner' => '/truckwash-banner-png.png',
+                    'signature' => '/truckwash-underskrift.png',
+                ],
+            ])
+            ->addData([
+                'seal_number' => $safety_seal,
+                'reg_1' => $this->regNrTraekker->value(),
+                'reg_2' => $this->regNrTrailer->value(),
+                'date' => $date,
+                'time' => $time,
+                'carried_out_by' => $operator,
+                'department_id' => $this->department->value(),
+                'customer_name' => $customer_name,
+                'type' => $this->wash_type->value(),
+            ])
+            ->getHtml()
+        );
+        $pdf_path = $pdf_generator->generate_pdf();
+        // Set the wash certificate url
+        $this->washCertificateUrl->set($pdf_path);
+        // Set the wash certificate status
+        $this->washCertificateStatus->set('completed');
+        // Set the status to completed
+        $this->status->set('completed');
+    }
+
+    public function sendWashCertificateEmail(string $email): void
+    {
+        // Send the wash certificate email
+        $email = new email();
+        $email->sendWashCertificateEmail(
+            $this->id,
+            (new users_o())->getCustomerName($this->customer_number->value()),
+            $this->customer_number->value(),
+            $email,
+            $this->reference_number->value(),
+            strtoupper($this->regNrTraekker->value()),
+            strtoupper($this->regNrTrailer->value()),
+            $this->washCertificateUrl->value()
+        );
+    }
+
+}

services/nginx/app/objects/bookings_o.php

@@ -8,6 +8,7 @@ use classes\response;
 use classes\slack;
 use classes\wash_certificate_store;
 use classes\wordpress_bookings_remote;
+use Exception;
 use traits\db_object_t;
 
 class bookings_o extends db
@@ -31,7 +32,7 @@ class bookings_o extends db
 
     public function structure(): void
     {
-        $this->setTable('bookings');
+        $this->setTable('bookings_new');
     }
 
     public function objectChanged(): void
@@ -118,6 +119,11 @@ class bookings_o extends db
 
     public function syncBookings(): array
     {
+        return [
+            "bookings" => 0,
+            "cancelled" => 0,
+            "parsed" => 0,
+        ];
         global /** @var response $response */
         $db, $response;
         $wordpress_bookings_remote = new wordpress_bookings_remote();
@@ -213,7 +219,7 @@ class bookings_o extends db
                     $washCertificateUrl,
                     $status
                 ));
-            } catch (\Exception $e) {
+            } catch (Exception $e) {
                 // Log the error
                 $logs = new logs_o();
                 $logs->add('slack', 0, 3, 0, 'SEND_DEPARTMENT_BOOKING_NOTIFICATION', $e->getMessage());
@@ -306,7 +312,7 @@ class bookings_o extends db
             $slack = new slack();
             try {
                 $slack->send_department_booking_notification($department, 'There are ' . $count . ' unfulfilled bookings');
-            } catch (\Exception $e) {
+            } catch (Exception $e) {
                 // Log the error
                 $logs = new logs_o();
                 $logs->add('slack', 0, 3, 0, 'SEND_DEPARTMENT_UNFULFILLED_BOOKINGS_NOTIFICATION', $e->getMessage());
@@ -339,4 +345,29 @@ class bookings_o extends db
         $db->query($sql);
     }
 
+    /**
+     * @throws Exception If the object is not selected
+     */
+    public function asArray(): array
+    {
+        self::requireSelected();
+        return [
+            'id' => (int)$this->id,
+            'customer_number' => (int)$this->customer_number->value(),
+            'wash_type' => $this->wash_type->value(),
+            'contact_email' => $this->contact_email->value(),
+            'reference_number' => $this->reference_number->value(),
+            'regNrTraekker' => $this->regNrTraekker->value(),
+            'regNrTrailer' => $this->regNrTrailer->value(),
+            'washCertificateEmail' => $this->washCertificateEmail->value(),
+            'date' => $this->date->value(),
+            'department' => (int)$this->department->value(),
+            'pickup_bool' => $this->pickup_bool->value() ? true : false,
+            'notes' => $this->notes->value(),
+            'washCertificateStatus' => $this->washCertificateStatus->value(),
+            'washCertificateUrl' => $this->washCertificateUrl->value(),
+            'status' => $this->status->value()
+        ];
+    }
+
 }

services/nginx/app/routes/bookingsRoute.php

@@ -35,6 +35,25 @@ class bookingsRoute
                     $response->add_meta('wash_certificate_token', $EMAIL_WASH_CERTIFICATE_TOKEN);
                 }
                 $bookings_o = new bookings_o();
+                // Check if the user has specified a booking id
+                if (self::isParametersSet(['id'])) {
+                    // Check if the booking id is a number
+                    if (!is_numeric(self::getParameter('id'))) {
+                        $response->error('Booking ID must be a number', 400);
+                    }
+                    // Check if the booking exists
+                    if (!$bookings_o->select((int)self::getParameter('id'))->exists()) {
+                        $response->error('Booking not found', 404);
+                    }
+                    // Check if the user has access to the booking
+                    if (!$user->hasAccessToBooking((int)self::getParameter('id'))) {
+                        $response->error('You are not allowed to access this booking', 403);
+                    }
+                    // Return the booking
+                    $response->success(
+                        $bookings_o->asArray()
+                    );
+                }
                 // Return the list of bookings
                 $response->success(
                     $bookings_o->parseBookings($bookings_o->listObjectsWithPaginationIfSet(

services/nginx/app/traits/form_t.php

@@ -110,6 +110,7 @@ trait form_t
      */
     public function __construct()
     {
+        parent::__construct();
         self::setup();
     }
 
@@ -188,8 +189,19 @@ trait form_t
                     $callable = is_callable($validation_method) ? $validation_method : [$this, $validation_method];
                     $is_valid = call_user_func($callable, $DATA[self::getFormFieldPrefix() . $field]);
                     if (!$is_valid) {
-                        // If the value is empty, and the field isn't required, we don't need to add it to the errors
-                        if (empty($DATA[self::getFormFieldPrefix() . $field]) && self::isFieldRequired($field)) {
+                        // Check if the value is empty, and the field isn't required
+                        // If the field is required, we don't need to add it to the errors
+                        // If the field is not required, we need to add it to the errors
+
+                        if (self::isFieldRequired($field)) {
+                            // If the value is not valid, add it to the errors
+                            $errors[self::getFormFieldPrefix() . $field] = [
+                                'error' => 'The field is invalid, please check the format',
+                                'field' => self::getFormFieldPrefix() . $field,
+                            ];
+                        } else if (!self::isFieldRequired($field) && empty($DATA[self::getFormFieldPrefix() . $field])) {
+                            // If the value is empty, and the field isn't required, we don't need to add it to the errors
+                        } else {
                             // If the value is not valid, add it to the errors
                             $errors[self::getFormFieldPrefix() . $field] = [
                                 'error' => 'The field is invalid, please check the format',
@@ -554,6 +566,17 @@ trait form_t
         return preg_match('/^[+-]?[0-9]{1,10}$/', $int) === 1;
     }
 
+    /**
+     * Validation method for booking ids
+     * @param int $int The integer to validate
+     * @return bool True if the integer is valid, false otherwise
+     */
+    public function validateBookingId(int $int): bool
+    {
+        // Check if the booking id is valid (A positive integer)
+        return preg_match('/^[1-9][0-9]*$/', $int) === 1;
+    }
+
     /**
      * Validation method for strings
      * @param string $string The string to validate