MailChimp WordPress Plugin with React: The Form and Form Submission | http://www.ibenic.com/mailchimp-wordpress-plugin-with-react-form-subscription

form.php

<?php

/**
 * Functions for handling everything about the forms
 */

/**
 * Add Form error
 * @param  numeric $form_id POST ID of the form
 * @param  string $message Message
 * @return void          
 */
function mwp_add_form_error( $form_id, $message ) {
	$mwp = mwp();
	$mwp->errors->add( 'form-' . $form_id, $message );
}

/**
 * Get Form errors
 * @param  numeric $form_id 
 * @return array          
 */
function mwp_get_form_errors( $form_id ) {
	$mwp = mwp();
	return $mwp->errors->get_error_messages( 'form-' . $form_id );
}

form2.php

<?php

/**
 * Renders the form
 * @param  int $id POST ID of our CPT mwp_form
 * @return void     
 */
function mwp_render_form( $id ) {
	$form = new MWP_Form( $id );
	$form->render();
}

/**
 * Returns the list ID that is assigned to the form
 * @param  number $form_id ID of the form
 * @return number          List ID
 */
function mwp_get_form_list_id( $form_id ) {
	return get_post_meta( $form_id, 'mwp_mailchimp_list_id', true );
}

form3.php

<?php

/**
 * Subscribe User on Form Submit
 * Redirecting on a successful subscribe
 *
 * @hooked init
 * @return void
 */
function mwp_subscribe_user_on_form_submit() {

	if( isset( $_POST['mwp_subscribe_form_submit'] ) && $_POST['mwp_subscribe_form_submit'] != '' ) {
		$name = '';
		$email = '';
		$form_id = '';
     
		if( isset( $_POST['mwp_name'] ) ) {
			$name = $_POST['mwp_name'];
		}

		if( isset( $_POST['mwp_email'] ) ) {
			$email = $_POST['mwp_email'];
		}

		if( isset( $_POST['mwp_subscribe_form_submit'] ) ) {
			$form_id = $_POST['mwp_subscribe_form_submit'];
		}
 
		$result = mwp_subscribe_user( $form_id, $name, $email );
 
		if( $result['success'] == 1 && isset( $result['redirect'] ) ) {

			 
			$redirect = $result['redirect'];
			if( filter_var($redirect, FILTER_VALIDATE_URL) !== false && strpos( $redirect, 'http' ) !== false ) {
				wp_redirect( $redirect, 301 );
				exit;
			}
			

		}
	
	} 
}

form4.php

<?php

/**
 * Subscribes a user to the Form (List)
 * @param  numeric $form_id
 * @param  string $name    
 * @param  string $email   
 * @return array          Contains success, redirect url and error messages
 */
function mwp_subscribe_user( $form_id, $name, $email ) {

  // Setting the default $result array
  $result = array( 'success' => 1, 'redirect' => '', 'errors' => 0 );

  // If empty name, add error
  if( $name == '' ) {

    mwp_add_form_error( $form_id, __( 'Enter a name', 'mwp' ) );

  }
  
  // If empty email, add error
  if( $email == '' ) {

    mwp_add_form_error( $form_id, __( 'Enter an email', 'mwp' ) );

  } else {
    
    // If email is valid
    if ( !filter_var( $email, FILTER_VALIDATE_EMAIL ) === false ) {
      // Get the List ID
      $list_id = mwp_get_form_list_id( $form_id );
      
      if( $list_id != '' ) {
        // Subscribe User
        $subscribe = mwp_subscribe_user_to_list( $list_id, $name, $email );
        
        // If subscribed, get the redirect url
        if( $subscribe == true ) {

          $result['redirect'] = get_post_meta( $form_id, 'mwp_mailchimp_list_redirect', true );

        } else {
          // If not subscribed, get the error
          mwp_add_form_error( $form_id, $subscribe['title'] );

        }

      } else {
        // If no list ID, add a generic error message
        mwp_add_form_error( $form_id, __( 'We can\' subscribe you right now. Please contact the administrator.', 'socialnano' ) );

      }

    } else {
      // If email is not valid, add error
      mwp_add_form_error( $form_id, __( 'Enter a valid email', 'socialnano' ) );

    }
  }

  $form_errors = mwp_get_form_errors( $form_id );
  // If there are errors, it was not successful
  if( count( $form_errors ) > 0 ) {

    $result['success'] = 0;
    $result['errors']  = $form_errors;

  }

  return $result;

}

hooks.php

<?php

// wp-mailchimp-plugin.php

/**
 * Various hooks where we hook our functions
 */
public function hooks() {
    add_action( 'admin_menu', 'mwp_settings' );
    add_action( 'init', 'mwp_cpt_form', 0 );
    add_action( 'init', 'mwp_subscribe_user_on_form_submit' );

}

includes.php

<?php

// wp-mailchimp-plugin

/**
 * Includes that are essential for this plugin
 */
public function includes(){

    /** Core **/

    require_once MWP_PATH . 'inc/settings.php';
    require_once MWP_PATH . 'inc/cpt-form.php';
    require_once MWP_PATH . 'inc/class-mwp-form.php';

    /** Functions **/
    require_once MWP_PATH . 'inc/functions-mailchimp.php';
    require_once MWP_PATH . 'inc/functions-form.php';
  
    // ...
  
}

mailchimp.php

<?php

// inc/functions-mailchimp.php

/**
 * Subscribe the user to a list
 * When this function is called, we have already checked everything
 * @param  number $list_id 
 * @param  string $name    
 * @param  string $email   
 * @return mixed  True if it's a new one or a subscribed one, if not the result array          
 */
function mwp_subscribe_user_to_list( $list_id, $name, $email ) {
	$api_key = get_option( 'mwp_mailchimp_api_key', false );

	if( $api_key ) {
		$MailChimp = new MailChimp( $api_key );
		$result = $MailChimp->post("lists/" . $list_id . "/members", array(
                'email_address' => $email,
                'status'        => 'pending', // We want them to confirm
                'merge_fields' => array( 'FNAME' => $name )
        ));

        // New subscriber
		if( isset( $result['id'] ) && isset( $result['email_address'] ) ) {
			return true;
		}

		if( isset( $result[ 'title' ] ) && $result[ 'title' ] == 'Member Exists' ) {
			return true;
		}

		return $result;
	}

	return false;
}

metabox.php

<?php

//inc/admin/metabox-form.php

/**
 * Renders the meta box.
 */
public function render_metabox( $post ) {
    // Add nonce for security and authentication.
    wp_nonce_field( 'form_nonce_save', 'form_nonce' );
    $redirect_url  = get_post_meta( $post->ID, 'mwp_mailchimp_list_redirect', true );
    $list_id_saved = get_post_meta( $post->ID, 'mwp_mailchimp_list_id', true );
    // ...
    
}

metabox2.php

<?php

// inc/admin/metabox-form.php

/**
 * Renders the meta box.
 */
public function render_metabox( $post ) {
     // ...  
    ?>
     
    <!-- ... --->
        <tr>
            <th>
                <?php _e( 'Redirect URL', 'mwp'); ?>
            </th>
            <td>
                <input type="url" name="mwp_mailchimp_list_redirect" placeholder="<?php _e( 'Enter an URL (http://...)', 'mwp' ); ?>" value="<?php echo $redirect_url; ?>"
            </td>
        </tr>

    <!-- ... --->
    <?php
}

metabox3.php

<?php

// inc/admin/metabox-form.php

/**
 * Handles saving the meta box.
 *
 * @param int     $post_id Post ID.
 * @param WP_Post $post    Post object.
 * @return null
 */
public function save_metabox( $post_id, $post ) {

    // ...

    if( isset( $_POST[ 'mwp_mailchimp_list_redirect' ] ) ) {
        update_post_meta( $post_id, 'mwp_mailchimp_list_redirect', esc_url_raw( $_POST[ 'mwp_mailchimp_list_redirect' ], array( 'http', 'https') ) );
    }

}

mwp_form.php

<?php

// inc/class-mwp-form.php

/**
 * Class used to render the form
 */
class MWP_Form {

	/**
	 * Form ID 
	 * @var integer
	 */
	public $form_id = 0;

	public function __construct( $id = 0 ) {
		$this->form_id = $id;
	}
  
}

mwp_form2.php

<?php

// inc/class-mwp-form.php

/**
 * Class used to render the form
 */
class MWP_Form {
  
  // ...
  
	/**
	 * Rendering the form
	 * @return void
	 */
	public function render() {
		
		if( $this->form_id == 0 ) {
			return;
		}

		?>
		<div class="mwp-subscribe-form" data-id="<?php echo $this->form_id; ?>">
			<form action="" method="POST">
				<?php $this->render_errors(); ?>
				<input type="text" name="mwp_name" placeholder="<?php _e( 'Your Name', 'mwp' ); ?>"/>
				<input type="email" name="mwp_email" placeholder="<?php _e( 'Your Email', 'mwp'); ?>"/>
				<button class="button" type="submit" name="mwp_subscribe_form_submit" value="<?php echo $this->form_id; ?>" ><?php _e( 'Subscribe', 'mwp' ); ?></button>
			</form>
		</div>
		<?php
	}
}

mwp_form3.php

<?php

// inc/class-mwp-form.php

/**
 * Class used to render the form
 */
class MWP_Form {

	// ...
  
	/**
	 * Renders errors if any
	 * @return void
	 */
	public function render_errors() {

		$errors = mwp_get_form_errors( $this->form_id );

		if( is_array( $errors ) && count( $errors ) > 0 ) {
			echo '<ul class="errors">';
			foreach ($errors as $error) {
				echo '<li>' . $error . '</li>';
			}
			echo '</ul>';
		}
	}

	// ...
}

plugin.php

<?php

// wp-mailchimp-plugin.php

/**
 * Create objects, call functions to start various features
 */
public function create() {

    // Create only in admin
    if( is_admin() ) {
        new MWP_Form_Metabox();
    }

    $this->errors = new WP_Error();

}

render.php

<?php

mwp_render_form( 304 );