add a checkin button to blog posts

<?php
/* sorry for this quick and dirty way */
add_filter('the_content', 'imath_test_checkin_for_post', 10, 1);

function imath_test_checkin_for_post( $content ) {
    if( is_single() ) {

        $post_address = get_post_meta( get_the_ID(), 'bpci_places_address', true );

        if( empty( $post_address ) )
            return $content;

        $lat = get_post_meta( get_the_ID(), 'bpci_places_lat', true );;
        $lng = get_post_meta( get_the_ID(), 'bpci_places_lng', true );;

        return $content . '<div style="clear:both" id="checkin-btn">
                            <a href="#checkin">Checkin</a>
                            <input type="hidden" id="lat" value="'.$lat.'">
                            <input type="hidden" id="lng" value="'.$lng.'">
                            <input type="hidden" id="address" value="'.$post_address.'">
                            <input type="hidden" id="ci_post_id" value="'.get_the_ID().'">
                           </div>';
    }
    else
        return $content;
}

add_action('wp_footer', 'imath_add_js_to_footer');

function imath_add_js_to_footer(){
    if( is_single() ) {
        ?>
        <script>
        jQuery(document).ready(function($){
            $("#checkin-btn a").click(function(){

                if( !$('#lat').val() || !$('#lng').val() || !$('#address').val() )
                    return false;

                $.post( ajaxurl, {
                    action: 'imath_regular_post_checkin',
                    'bpci-lat': $('#lat').val(),
                    'bpci-lng': $('#lng').val(),
                    'bpci-address': $('#address').val(),
                    'post_id': $('#ci_post_id').val()
                },
                function(response)
                {
                    if( response == "checkedin") {
                        $('#checkin-btn').html('checked in!');
                    }
                    else {
                        alert(response);
                    }
                });

                return false
            });
        });
        </script>
        <?php
    }
}

function imath_save_activity_checkin(){
    global $blog_id;

    //user stuff
    $user_id = bp_loggedin_user_id();
    $from_user_link   = bp_core_get_userlink( $user_id );

    //post stuff
    $post_id = intval( $_POST['post_id'] );
    $title = get_the_title( $post_id );
    $postlink = get_permalink( $post_id );

    $activity_link = '<a href="' . $postlink .'" title="' . $title . '">' . $title . '</a>';
    $activity_action  = sprintf( __( '%s checked-in %s'), $from_user_link, $activity_link );
    $primary_link     = bp_core_get_userlink( $user_id, false, true );
    $activity_content = false;

    $activity_id = bp_activity_add( array(
        'user_id'           => $user_id,
        'action'            => apply_filters( 'bp_activity_new_update_action', $activity_action ),
        'content'           => apply_filters( 'bp_activity_new_update_content', $activity_content ),
        'primary_link'      => apply_filters( 'bp_activity_new_update_primary_link', $primary_link ),
        'component'         => 'activity', /* replace with your custom component */
        'type'              => 'activity_update', /* replace with your custom type */
        'item_id'           => $blog_id,
        'secondary_item_id' => $post_id
    ) );

    // it's important to add this hook so that the geo data will be saved as activity meta...
    do_action( 'bp_activity_posted_update', $activity_content, $user_id, $activity_id );

    if( $activity_id )
        echo 'checkedin';

    else
        echo 'OOps caramba !';

    die();
}

add_action( 'wp_ajax_imath_regular_post_checkin', 'imath_save_activity_checkin' );
add_action( 'wp_ajax_nopriv_imath_regular_post_checkin', 'imath_save_activity_checkin' );
?>