Require users to agree to updated terms

<?php // Add below this line to functions.php

add_filter( 'wpmem_member_links', 'update_terms_agreement' );
function update_terms_agreement( $links ) {
    
    // Settings.
    $process_name = 'update_terms'; 
    $button_text  = 'Agree to Terms';
    $success_msg  = 'Thank you for updating your information.';
    $error_msg    = 'Sorry, the updated terms must be agreed to before continuing to use the site. If you do not agree to the new terms,
        please <a href="#">log out</a>.';
    
    $meta_key     = 'tos';
    $meta_value   = 'agree';
    
    global $wp, $wpmem; 
    
    /*
     * Handle form processing here so we can return a success
     * message on the links page or an error message on the 
     * form page depending on result.
     */
    $update_success  = false;
    $form_validation = false;
    // Check if custom form was submitted, and if so, process update.
    if ( isset( $_POST[ $process_name . '_save' ] ) && 1 == $_POST[ $process_name . '_save' ] ) {
        
        // You'll need the current user ID.
        $user_id = get_current_user_id();
        
        // ToS agreement is required. If not checked, the user will not be able to continue.
        if ( isset( $_POST[ $meta_key ] ) ) {
            $form_validation = ( $meta_value == $_POST[ $meta_key ] ) ? true : false;
        }
         
        if ( $form_validation ) {
            // Use update_user_meta( $user_id, $meta_key, $meta_value ) to save user meta
            update_user_meta( $user_id, $meta_key, $_POST[ $meta_key ] );
            
            // Set $update_success to true for displaying success message.
            $update_success = true;
        } else {
            // We are in an error state.
            $update_success = 'error';
        }
    }    
    
    // If the page is the custom process page, build and display the form.
    if ( ( isset( $_REQUEST['a' ] ) && $process_name == $_REQUEST['a'] ) || 'error' == $update_success ) {
        // If form submission was not successful, add the error message.
        $error_msg  = '<div class="wpmem_msg" align="center"><p>' . $error_msg . '</p></div>';
        $form_before = ( 'error' == $update_success ) ? $error_msg : '';
        // Build the form.
        $form_before.= '<div id="wpmem_reg">';
        $form_before.= '<form name="form" method="post" action="' . $wpmem->user_pages['profile'] . '" id="" class="form">';
        
        /*
         * Custom HTML for the form here.
         *
         * Custom HTML is built into the variable $form_custom.  To build onto the $form custom variable,
         * each additional line should be $form_custom.= '<p>your additional html</p>'; (note the "."
         * between the variable name and the = in each additional line.  This basically means "add this
         * to the what is already in the variable."
         */
        $form_custom = '<p><strong>Our Terms of Service have changed.</strong><br />Please agree to the new terms to continue using the site.</p>';
        $form_custom.= '<p><input type="checkbox" name="tos" value="agree" /> I agree</p>'.
        /*
         * End custom HTML.
         */
        
        // Add a hidden input for us to check if the form is submitted so we can save the selection.
        $form_after = '<input type="hidden" name="' . $process_name . '_save" value="1" />';
        // Add a form submit button.
        $form_after.= '<br /><input type="submit" name="submit" value="' . $button_text . '" class="buttons" />';
        // Close the form tag.
        $form_after.= '</form></div>';
        
        // Assemble components.
        $links = $form_before . $form_custom . $form_after;
        
    } else {
        
        // If update was successful, add the success message.
        if ( $update_success ) {
            $links = '<div class="wpmem_msg" align="center"><p>' . $success_msg . '</p></div>' . $links;
        }
        
    }
    
    return $links;
}