Manejo de errores de WordPress con WP_Error Clase II

<?php

/*

 Plugin Name: Contact Form Lite

 Plugin URI: https://code.tutsplus.com

 Description: Easy contact form plugin

 Author: Agbonghama Collins

 Author URI: http://tech4sky.com

 */

function contact_html_form() {

    global $name, $email, $phone_number, $subject, $message;

	echo '<form action="' . get_permalink() . '" method="post">

	<label for="name">Name <strong>*</strong></label>

	<input type="text" name="sender_name" value="' . ( isset( $_POST['sender_name'] ) ? $name : null ) . '" />

	<div>

	<label for="email">Email <strong>*</strong></label>

	<input type="text" name="sender_email" value="' . ( isset( $_POST['sender_email'] ) ? $email : null ) . '" />

	</div>

	<div>

	<label for="phonenumber">Phone Number <strong>*</strong></label>

	<input type="text" name="sender_phonenumber" value="' . ( isset( $_POST['sender_phonenumber'] ) ? $phone_number : null ) . '" />

	</div>

	<div>

	<label for="subject">Subject <strong>*</strong></label>

	<input type="text" name="email_subject" value="' . ( isset( $_POST['email_subject'] ) ? $subject : null ) . '" />

	</div>

	<div>

	<label for="message">Message <strong>*</strong></label>

	<textarea name="email_message">' . ( isset( $_POST['email_message'] ) ? $message : null ) . '</textarea>

	</div>

	<div>

	<input type="submit" name="send_message" value="Send" />

	</div>

	</form>';

}

function validate_form( $name, $email, $phone_number, $subject, $message ) {

    // Make the WP_Error object global    

	global $form_error;

	// instantiate the class

	$form_error = new WP_Error;

	// If any field is left empty, add the error message to the error object

	if ( empty( $name ) || empty( $email ) || empty( $phone_number ) || empty( $subject ) || empty( $message ) ) {

		$form_error->add( 'field', 'No field should be left empty' );

	}

	// if the name field isn't alphabetic, add the error message

	if ( ! ctype_alpha( $name ) ) {

		$form_error->add( 'invalid_name', 'Invalid name entered' );

	}

	// Check if the email is valid

	if ( ! is_email( $email ) ) {

		$form_error->add( 'invalid_email', 'Email is not valid' );

	}

	// if phone number isn't numeric, throw an error

	if ( ! is_numeric( $phone_number ) ) {

		$form_error->add( 'phone_number', 'Phone-number is not numbers' );

	}

	// if $form_error is WordPress Error, loop through the error object

	// and echo the error

	if ( is_wp_error( $form_error ) ) {

		foreach ( $form_error->get_error_messages() as $error ) {

			echo '<div>';

			echo '<strong>ERROR</strong>:';

			echo $error . '<br/>';

			echo '</div>';

		}

	}

}

function send_mail( $name, $email, $phone_number, $subject, $message ) {

    global $form_error;

	// Ensure WP_Error object ($form_error) contain no error

	if ( 1 > count( $form_error->get_error_messages() ) ) {

		// sanitize user form input

		$name 			= 	sanitize_text_field( $name );

		$email 			= 	sanitize_email( $email );

		$phone_number 	= 	esc_attr( $phone_number );

		$subject 		= 	sanitize_text_field( $subject );

		$message 		= 	esc_textarea( $message );

		// set the variable argument use by the wp_mail

		$message 	.= 	'\n Phone Number:' . $phone_number;

		$to 		= 	'admin@tech4sky.com';

		$headers 	= 	"From: $name <$email>" . "\r\n";

		// If email has been process for sending, display a success message	

		if ( wp_mail( $to, $subject, $message, $headers ) ) {

			echo "Thanks for contacting me.";

		}

	}

}

function contact_form_function() {

    global $name, $email, $phone_number, $subject, $message;

	if ( isset($_POST['send_message']) ) {

		// Get the form data

		$name 			= 	$_POST['sender_name'];

		$email 			= 	$_POST['sender_email'];

		$phone_number 	= 	$_POST['sender_phonenumber'];

		$subject 		= 	$_POST['email_subject'];

		$message 		= 	$_POST['email_message'];

		// validate the user form input

		validate_form( $name, $email, $phone_number, $subject, $message );

		// send the mail

		send_mail( $name, $email, $phone_number, $subject, $message );

	}

	// display the contact form

	contact_html_form();

}

// Register a new shortcode: [cf_contact_form]

add_shortcode('cf_contact_form', 'contact_form_shortcode');

// Shortcode callback function

function contact_form_shortcode() {

    ob_start();

    contact_form_function();

    return ob_get_clean();

}