Simple Likes

like-actions.js

jQuery( document ).ready( function ( $ ) {
	$( document ).on( 'click', '.simple-like-btn', function( e ) {
		e.preventDefault();
		var like = {
			'action' : $( this ).data( 'action' ),
			'pid'    : $( this ).data( 'pid' )
		}
		var likebtn = this;
		$.post( ajax_object.ajax_url, like ).done( function( response ) {
			response = JSON.parse( response );
			if ( response.status == 'success' ) {
				if ( response.action == 'like' ) {
					$( '.eig-like-gravatars' ).fadeIn('slow').append( response.gravatar );
					$( likebtn ).data( 'action', 'eig-unlike' );
					$( likebtn ).html( 'Liked' );
					$( likebtn ).removeClass( 'like' );
					$( likebtn ).addClass( 'liked' );
				} else {
					$( '.eig-like-gravatars .eig-like-user-' + response.uid ).fadeOut();
					$( likebtn ).data( 'action', 'eig-like' );
					$( likebtn ).html( 'Like' );
					$( likebtn ).removeClass( 'liked' );
					$( likebtn ).addClass( 'like' );
				}
			}
		} );
	} );
} );

simple-likes.php

<?php
/*
Plugin Name: Simple Likes
Description: This plugin adds simple like functionality per post.
Version: 1.0
Author: Luke Cavanagh
Author URI: http://www.lcavanagh.bluehoststaff.com/
License: GPLv2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
*/

function simple_like_css() {
?>
<style type="text/css">
.simple-like-btn {
  background: transparent;
  border: 1px #cccccc solid;
  border-radius: 3px;
  box-shadow: none;
  text-align: left;
  text-decoration: none;
  color: #666666 !important;
  padding: 3px;
  padding-top: 5px;
  padding-right: 10px;
  margin: 0;
  line-hsimpleht: 1.5;
  hsimpleht: auto;
  font-size: 12px;
  background-color: #f8f8f8;
  box-shadow: 0 1px 0 rgba(0, 0, 0, 0.08);
  -webkit-box-shadow: 0 1px 0 0 rgba(0, 0, 0, 0.08);
  -webkit-font-smoothing: auto !important;
  -moz-osx-font-smoothing: auto;
}

.simple-like-btn:hover {
  border-color: #999999;
  color: #777777;
  background-color: #f8f8f8;
}

.simple-like-gravatars {
  padding-right: 5px;
  padding-left: 5px;
}
.simple-like-gravatars img{
  margin: 3px;
}
</script>
<?php
}
add_action( 'wp_head', 'simple_like_css' );

function simple_ajax_like() {
	if ( isset( $_POST['pid'] ) && is_numeric( $_POST['pid'] ) ) {
		$pid = (int)$_POST['pid'];
		$likes = get_post_meta( $pid, 'likes', true );
		if ( is_array( $likes ) ) {
			$likes[] = get_current_user_id();
		} else {
			$likes = array( get_current_user_id() );
		}
		$likes = array_unique( $likes );
		if ( update_post_meta( $pid, 'likes', $likes ) ) {
			echo json_encode( array( 'status' => 'success', 'action' => 'like', 'gravatar' => get_avatar( get_current_user_id(), 30, '', false, array( 'class' => 'simple-like-user-' . get_current_user_id() ) ) ) );
		} else {
			echo json_encode( array( 'status' => 'error' ) );
		}
	}
	die;
}
add_action( 'wp_ajax_simple-like', 'simple_ajax_like' );

function simple_ajax_unlike() {
	if ( isset( $_POST['pid'] ) && is_numeric( $_POST['pid'] ) ) {
		$pid = (int)$_POST['pid'];
		$likes = get_post_meta( $pid, 'likes', true );
		if ( is_array( $likes ) && false !== ( $key = array_search( get_current_user_id(), $likes ) ) ) {
			unset( $likes[ $key ] );
		}
		$likes = array_unique( $likes );
		if ( update_post_meta( $pid, 'likes', $likes ) ) {
			echo json_encode( array( 'status' => 'success', 'action' => 'unlike', 'uid' => get_current_user_id() ) );
		} else {
			echo json_encode( array( 'status' => 'error' ) );
		}
	}
	die;
}
add_action( 'wp_ajax_simple-unlike', 'simple_ajax_unlike' );

function simple_add_button( $content ) {
	global $post;
	$post_id = $post->ID;
	$likes = get_post_meta( $post_id, 'likes', true );
	if ( ! is_array( $likes ) || ! in_array( get_current_user_id(), $likes ) ) {
		$output = '<a data-action="simple-like" data-pid="' . $post_id . '" class="simple-like-btn like genericon genericon-star" title="Like" href="#">Like</a>';
	} else {
		$output = '<a data-action="simple-unlike" data-pid="' . $post_id . '" class="simple-like-btn liked genericon genericon-star" title="Like" href="#">Liked</a>';
	}
	$output .= '<span class="simple-like-gravatars">';
	if ( is_array( $likes ) ) {
		foreach ( $likes as $user ) {
			$output .=  get_avatar( $user, 30, '', false, array( 'class' => 'simple-like-user-' . $user ) );
		}
	}
	$output .= '</span>';
	return $content . $output;
}
add_filter( 'the_content', 'simple_add_button', 40, 1 );

function simple_head_js() {
	wp_enqueue_script( 'simple-like-actions', plugin_dir_url( __FILE__ ) . 'js/like-actions.js', 'jquery' );
	wp_localize_script( 'simple-like-actions', 'ajax_object', array( 'ajax_url' => admin_url( 'admin-ajax.php' ) ) );
}
add_action( 'wp_enqueue_scripts', 'simple_head_js', 80 );