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 );
  
?>

current-user-likes.php

<?php
  
  function frontEndUserLikes() {
    $theme_object = wp_get_theme();
    $themename = esc_attr( $theme_object->Name ); // the theme name
    if ( is_user_logged_in() ) { // user is logged in
      global $current_user;
      $like_list = '';
      $user_id = $current_user->ID; // current user
      $user_likes = get_user_meta( $user_id, "_liked_posts");
      $the_likes = ( $user_likes && count( $user_likes ) > 0 ) ? $the_likes = $user_likes[0] : $the_likes = '' ;
      if ( !is_array( $the_likes ) )
        $the_likes = array();
      $count = count($the_likes);
      if ( $count > 0 ) {
        $limited_likes = array_slice( $the_likes, 0, 5 ); // this will limit the number of posts returned to 5
        $like_list .= "<aside>\n";
        $like_list .= "<h3>" . __( 'You Like:', $themename ) . "</h3>\n";
        $like_list .= "<ul>\n";
        foreach ( $limited_likes as $the_like ) {
          $like_list .= "<li><a href='" . esc_url( get_permalink( $the_like ) ) . "' title='" . esc_attr( get_the_title( $the_like ) ) . "'>" . get_the_title( $the_like ) . "</a></li>\n";
        }
        $like_list .= "</ul>\n";
        $like_list .= "</aside>\n";
      }
      echo $like_list;
    }
  }

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

<?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 );
  }

likes-today.php

<?php

  function jm_most_popular_today() {
    global $post;
    $today = date('j');
    $year = date('Y');
    $args = array(
      'year' => $year,
      'day' => $today,
      'post_type' => array( 'post', 'enter-your-comma-separated-post-types-here' ),
      'meta_key' => '_post_like_count',
      'orderby' => 'meta_value_num',
      'order' => 'DESC',
      'posts_per_page' => 5
    );
    $pop_posts = new WP_Query( $args );
    if ( $pop_posts->have_posts() ) {
      echo "<aside>\n";
      echo "<h3>Today's Most Popular Posts</h3>\n";
      echo "<ul>\n";
      while ( $pop_posts->have_posts() ) {
        $pop_posts->the_post();
        echo "<li><a href='" . get_permalink($post->ID) . "'>" . get_the_title() . "</a></li>\n";
      }
      echo "</ul>\n";
      echo "</aside>\n";
    }
    wp_reset_postdata();
  }

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
  }

shortcode.php

<?php

  function jm_like_shortcode() {
    return getPostLikeLink( get_the_ID() );
  }
  add_shortcode('jmliker', 'jm_like_shortcode');

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;