How to create a Post Like System for WordPress.

README.md

Post Like System for WordPress

Full tutorial: http://hofmannsven.com/2013/laboratory/wordpress-post-like-system/

anon.php

<?php

  $meta_IPS = get_post_meta($post_id, "_user_IP"); // get previously voted IP address
  $ip = $_SERVER["REMOTE_ADDR"]; // Retrieve current user IP
  $liked_IPS = ""; // set up array variable

  if ( count( $meta_IPS ) != 0 ) { // meta exists, set up values
    $liked_IPS = $meta_IPS[0];
  }

  if ( !is_array( $liked_IPS ) ) // make array just in case
    $liked_IPS = array();

  if ( in_array( $ip, $liked_IPS ) ) { // True is IP in array
    return true;
  }
  return false;

check.php

<?php
  
  if ( is_user_logged_in() ) { (...) }

content-single.php

<?php
  
  echo getPostLikeLink( $post->ID );
  
?>

default.php

<?php

  else { // normal like button
    $output .= '<span class="unliker"></span><span class="like"><i class="fa fa-heart"></i></span>';
    $output .= ' <span class="count">'.$likes.'</span></a></span>&nbsp; ';
  }
  return $output;

frontend.php

function getPostLikeLink( $post_id ) {
	$like_count = get_post_meta( $post_id, "_post_like_count", true ); // get post likes
	$count = ( empty( $like_count ) || $like_count == "0" ) ? 'Like' : esc_attr( $like_count );
	if ( AlreadyLiked( $post_id ) ) {
		$class = esc_attr( ' liked' );
		$title = esc_attr( 'Unlike' );
		$heart = '<i class="fa fa-heart"></i>';
	} else {
		$class = esc_attr( '' );
		$title = esc_attr( 'Like' );
		$heart = '<i class="fa fa-heart-o"></i>';
	}
	$output = '<a href="#" class="jm-post-like'.$class.'" data-post_id="'.$post_id.'" title="'.$title.'">'.$heart.'&nbsp;'.$count.'</a>';
	return $output;
}

get-likes.php

<?php
  
  global $current_user;
  $user_likes = get_user_meta( $user->ID, "_liked_posts");

hooks.php

<?php
  
  add_action( 'wp_ajax_nopriv_jm-post-like', 'jm_post_like' );
  add_action( 'wp_ajax_jm-post-like', 'jm_post_like' );

like.php

<?php

  $like_count = get_post_meta( $post_id, "_post_like_count", true ); // get post likes
  
  if ( ( !$like_count ) || ( $like_count && $like_count == "0" ) ) { // no votes, set up empty variable
    $likes = 'Like';
  } elseif ( $like_count && $like_count != "0" ) { // there are votes!
    $likes = esc_attr( $like_count );
  }

meta.php

<?php

  if ( isset( $_POST['jm_post_like'] ) ) {
    $post_id = $_POST['post_id']; // post id
    $post_like_count = get_post_meta( $post_id, "_post_like_count", true ); // post like count

    if ( is_user_logged_in() ) { // user is logged in
      global $current_user;
        $user_id = $current_user->ID; // current user
        $meta_POSTS = get_user_meta( $user_id, "_liked_posts" ); // post ids from user meta
        $meta_USERS = get_post_meta( $post_id, "_user_liked" ); // user ids from post meta
        $liked_POSTS = ""; // setup array variable
        $liked_USERS = ""; // setup array variable

        if ( count( $meta_POSTS ) != 0 ) { // meta exists, set up values
          $liked_POSTS = $meta_POSTS[0];
        }

        if ( !is_array( $liked_POSTS ) ) // make array just in case
          $liked_POSTS = array();
  
        if ( count( $meta_USERS ) != 0 ) { // meta exists, set up values
          $liked_USERS = $meta_USERS[0];
        }		

        if ( !is_array( $liked_USERS ) ) // make array just in case
          $liked_USERS = array();

          $liked_POSTS['post-'.$post_id] = $post_id; // Add post id to user meta array
          $liked_USERS['user-'.$user_id] = $user_id; // add user id to post meta array
          $user_likes = count( $liked_POSTS ); // count user likes
    }
  }

most-liked-posts.php

<?php

  query_posts('meta_key=_post_like_count&orderby=meta_value_num&order=DESC&posts_per_page=5');
  
?>

no-user-likes.php

<?php

  else {
    echo '<p>You don\'t like anything yet.</p>';
  }

nonce.php

<?php

  $nonce = $_POST['nonce']; 
  if ( ! wp_verify_nonce( $nonce, 'ajax-nonce' ) ) 
    die ( 'Nope!' );

set.php

<?php

  if ( !AlreadyLiked( $post_id ) ) { // like the post
    update_post_meta( $post_id, "_user_liked", $liked_USERS ); // Add user ID to post meta
    update_post_meta( $post_id, "_post_like_count", ++$post_like_count ); // +1 count post meta
    update_user_meta( $user_id, "_liked_posts", $liked_POSTS ); // Add post ID to user meta
    update_user_meta( $user_id, "_user_like_count", $user_likes ); // +1 count user meta
    echo $post_like_count; // update count on front end
  }

unlike.php

<?php

  $output = '<span class="jm-post-like">';
  $output .= '<a href="#" data-post_id="'.$post_id.'">';

  if ( AlreadyLiked( $post_id ) ) { // already liked, set up unlike addon
    $output .= '<span class="unliker"><i class="fa fa-times-circle"></i></span><span class="like prevliked"><i class="fa fa-heart"></i></span>';
    $output .= ' <span class="count alreadyliked">'.$likes.'</span></a></span>&nbsp; ';
  }

unset.php

<?php

  else { // unlike the post
    $pid_key = array_search( $post_id, $liked_POSTS ); // find the key
    $uid_key = array_search( $user_id, $liked_USERS ); // find the key
    unset( $liked_POSTS[$pid_key] ); // remove from array
    unset( $liked_USERS[$uid_key] ); // remove from array
    $user_likes = count( $liked_POSTS ); // recount user likes
    update_post_meta( $post_id, "_user_liked", $liked_USERS ); // Remove user ID from post meta
    update_post_meta($post_id, "_post_like_count", --$post_like_count ); // -1 count post meta
    update_user_meta( $user_id, "_liked_posts", $liked_POSTS ); // Remove post ID from user meta  
    update_user_meta( $user_id, "_user_like_count", $user_likes ); // -1 count user meta
    echo "already".$post_like_count; // update count on front end
  }

user-likes.php

<?php

  if ( !empty( $user_likes ) && count( $user_likes ) > 0 ) {
    $the_likes = $user_likes[0];
  } else {
    $the_likes = '';
  }

  if ( !is_array( $the_likes ) )
    $the_likes = array();
    $count = count($the_likes); $i=0;
  
  if ( $count > 0 ) {
    $like_list = '';
    echo '<p>';
    foreach ( $the_likes as $the_like ) {
      $i++;
      $like_list .= '<a href="' . esc_url( get_permalink( $the_like ) ) . '" title="' . esc_attr( get_the_title( $the_like ) ) . '">' . get_the_title( $the_like ) . '</a>';
      if ($count != $i) $like_list .= ' &middot; ';
        else $like_list .= '</p>';
      }
    echo $like_list;
  }

user.php

<?php

  global $current_user;
    $user_id = $current_user->ID; // current user
    $meta_USERS = get_post_meta( $post_id, "_user_liked" ); // user ids from post meta
    $liked_USERS = ""; // set up array variable

    if ( count( $meta_USERS ) != 0 ) { // meta exists, set up values
      $liked_USERS = $meta_USERS[0];
    }

    if( !is_array( $liked_USERS ) ) // make array just in case
      $liked_USERS = array();

    if ( in_array( $user_id, $liked_USERS ) ) { // True if User ID in array
      return true;
    }
    return false;

How to Implement this code with a wordpress theme ?

You can find the full documentation here:
https://github.com/JonMasterson/WordPress-Post-Like-System

Is there any possibility to keep a remove button from in the list of liked posts (current-user-likes.php) In this is there any option to keep remove button for each liked post to remove individually.

Removing liked posts from page template not working. But added same code how it was for posts page.

<?php
/*
* Template Name: Liked Posts
*/
get_header();
$current_user = get_current_user_id();
?>
	<table class="form-table">
		<tr>
			<th><label for="user_likes"><?php _e( 'You Like:', 'YourThemeTextDomain' ); ?></label></th>
			<td>
			<?php
			$types = get_post_types( array( 'public' => true ) );
			$args = array(
			  'numberposts' => -1,
			  'post_type' => $types,
			  'meta_query' => array (
				array (
				  'key' => '_user_liked',
				  'value' => $current_user,
				  'compare' => 'LIKE'
				)
			  ) );		
			$sep = '';
			$like_query = new WP_Query( $args );
			if ( $like_query->have_posts() ) : ?>
			<p>
			<?php 
            
 while ( $like_query->have_posts() ) : $like_query->the_post(); 
 echo $sep; 
 $post_id = get_the_ID();
 $nonce = wp_create_nonce( 'simple-likes-nonce' );
 $is_comment = '0';
?>
 <a href="<?php the_permalink(); ?>" title="<?php the_title_attribute(); ?>">
 <?php the_title(); ?></a> 
 <?php echo  $post_id; ?>
 <a href="<?php echo admin_url( 'admin-ajax.php?action=process_simple_like' . '&post_id=' . $post_id . '&nonce=' . $nonce . '&is_comment=' . $is_comment . '&disabled=true') ?>">Remove</a>
 <?php echo do_shortcode('[jmliker]'); ?>
			<?php
			$sep = ' &middot; ';
			endwhile; 
			?>
			</p>
			<?php else : ?>
			<p><?php _e( 'You do not like anything yet.', 'YourThemeTextDomain' ); ?></p>
			<?php 
			endif; 
			wp_reset_postdata(); 
			?>
			</td>
		</tr>
	</table>
<?php get_footer(); ?>

Getting following error while integrating.

Fatal error: Uncaught Error: Call to undefined function AlreadyLiked() in