gistfile.php

<?php

function whatismyip() {
    if (isset($_SERVER['HTTP_CLIENT_IP']))
        $ipaddress = $_SERVER['HTTP_CLIENT_IP'];
    else if(isset($_SERVER['HTTP_X_FORWARDED_FOR']))
        $ipaddress = $_SERVER['HTTP_X_FORWARDED_FOR'];
    else if(isset($_SERVER['HTTP_X_FORWARDED']))
        $ipaddress = $_SERVER['HTTP_X_FORWARDED'];
    else if(isset($_SERVER['HTTP_FORWARDED_FOR']))
        $ipaddress = $_SERVER['HTTP_FORWARDED_FOR'];
    else if(isset($_SERVER['HTTP_FORWARDED']))
        $ipaddress = $_SERVER['HTTP_FORWARDED'];
    else if(isset($_SERVER['REMOTE_ADDR']))
        $ipaddress = $_SERVER['REMOTE_ADDR'];
    else
        $ipaddress = null;
    return $ipaddress;
}

add_action('wp', function() {

    if( is_single() ) {

        global $post;

        $user_ip = whatismyip();
        $meta = get_post_meta( $post->ID, '_se_post_views', TRUE );
        $meta = '' !== $meta ? explode( ',', $meta ) : array();
        $meta = array_filter( array_unique( $meta ) );

        if( ! in_array( $user_ip, $meta ) ) {
            array_push( $meta, $user_ip );
            update_post_meta( $post->ID, '_se_post_views', implode(',', $meta) );
        }

    }

});

add_shortcode('se-post-views-count', function( $atts ) {
    
    $a = shortcode_atts( array(
        'post_id' => 0
    ), $atts );

    $post_id = esc_attr( "{$a['post_id']}" );

    if( 0 == $post_id && is_single() )
        $post_id = get_the_ID();

    if( ! get_post( $post_id ) || ( get_post( $post_id ) && 'post' !== get_post( $post_id )->post_type ) )
        return;

    $meta = get_post_meta( $post_id, '_se_post_views', TRUE );
    $meta = '' !== $meta ? explode( ',', $meta ) : array();
    return (int) count( $meta );


});


add_filter('the_content', function( $content ) {

    if( is_single() ) :;

        global $post;
        $meta = get_post_meta( $post->ID, '_se_post_views', TRUE );
        $meta = '' !== $meta ? explode( ',', $meta ) : array();
        $count = count( $meta );

        $message = "This post was viewed " . do_shortcode('[se-post-views-count]') . " time";
        $message .= (int) $count !== 1 ? 's' : '';

        $content .= $message;

    endif;

    return $content;


});