const NAME = 'smarter-navigation';

const SEP = '__SEP__';

static $data = false;

static function init() {

add_action( 'template_redirect', array( __CLASS__, 'manage_cookie' ) );

add_action( 'posts_clauses', array( __CLASS__, 'posts_clauses' ), 10, 2 );

}

static function manage_cookie() {

// Default conditions

$clear_condition = false;

$read_condition = is_singular();

$set_condition = !is_404();

if ( apply_filters( 'smarter_nav_clear', $clear_condition ) )

self::clear_cookie();

elseif ( apply_filters( 'smarter_nav_read', $read_condition ) )

self::read_cookie();

elseif ( apply_filters( 'smarter_nav_set', $set_condition ) )

self::set_cookie();

}

private static function read_cookie() {

if ( empty( $_COOKIE[self::NAME] ) )

return;

$data = $_COOKIE[self::NAME];

// No referrer

if ( !isset( $data['query'] ) )

return;

$data['query'] = json_decode( stripslashes( $data['query'] ), true );

// JSON is invalid

if ( is_null( $data['query'] ) )

return;

self::$data = $data;

self::$cache['same'] = self::get_posts( array(

'_sn_post' => get_queried_object(),

'_sn_op' => '=',

'order' => 'ASC',

'fields' => 'ids',

'nopaging' => true

) );

// The current post doesn't belong to the group

if ( !in_array( get_queried_object_id(), self::$cache['same'] ) )

self::$data = false;

}

public static function set_cookie( $data = '' ) {

$data = wp_parse_args( $data, array(

'query' => json_encode( $GLOBALS['wp_query']->query ),

'url' => ( is_ssl() ? 'https://' : 'http://' ) . $_SERVER['HTTP_HOST'] . $_SERVER['REQUEST_URI'],

'title' => trim( wp_title( self::SEP, false, 'left' ) ),

) );

foreach ( $data as $key => $value )

setcookie( self::get_name( $key ), $value, 0, '/' );

}

public static function clear_cookie() {

if ( empty( $_COOKIE[self::NAME] ) )

return;

foreach ( array_keys( $_COOKIE[self::NAME] ) as $key )

setcookie( self::get_name( $key ), false, 0, '/' );

}

private static function get_name( $key ) {

return self::NAME . '[' . $key . ']';

}

static function adjacent_post( $format, $title_format, $previous, $fallback, $in_same_term, $excluded_terms, $taxonomy ) {

$id = self::get_adjacent_id( $previous );

if ( !$id )

return false;

if ( -1 == $id ) {

if ( !$fallback )

return false;

if ( $previous )

return previous_post_link( $format, $title_format, $in_same_term, $excluded_terms, $taxonomy );

else

return next_post_link( $format, $title_format, $in_same_term, $excluded_terms, $taxonomy );

}

echo self::parse_format( $format, $title_format, get_permalink( $id ), get_the_title( $id ) );

}

private static $cache;

/**

* @return -1 if there's no data, 0 if no post found, post id otherwise

*/

static function get_adjacent_id( $previous = false ) {

if ( !self::$data )

return -1;

$previous = (bool) $previous;

if ( !isset( self::$cache[$previous] ) ) {

self::$cache[$previous] = self::find_adjacent_post( $previous );

}

return self::$cache[$previous];

}

private static function find_adjacent_post( $previous ) {

$poz = array_search( get_queried_object_id(), self::$cache['same'] );

$poz += $previous ? 1 : -1;

if ( isset( self::$cache['same'][ $poz ] ) )

return self::$cache['same'][ $poz ];

// find first post in the adjacent interval

$next_posts = self::get_posts( array(

'_sn_post' => get_queried_object(),

'_sn_op' => $previous ? '<' : '>',

'order' => $previous ? 'DESC' : 'ASC',

'posts_per_page' => 2,

'paged' => 1

) );

if ( empty( $next_posts ) )

return 0;

$post = reset( $next_posts );

if ( count( $next_posts ) == 1 )

return $post->ID;

// there's more than one post in the adjacent interval, so need to get the first/last one

$final_posts = self::get_posts( array(

'_sn_post' => $post,

'_sn_op' => '=',

'order' => 'ASC',

'nopaging' => true,

) );

if ( $previous )

return reset( $final_posts )->ID;

return end( $final_posts )->ID;

}

private static function get_posts( $args = array() ) {

$args = array_merge( self::$data['query'], $args, array(

'ignore_sticky_posts' => true

) );

$q = new WP_Query( $args );

return $q->posts;

}

static function posts_clauses( $bits, $wp_query ) {

global $wpdb;

$op = $wp_query->get( '_sn_op' );

$post = $wp_query->get( '_sn_post' );

if ( !$op )

return $bits;

$orderby = preg_split( '|\s+|', $bits['orderby'] );

$orderby = reset( $orderby );

$field = explode( '.', $orderby );

$field = end( $field );

if ( isset( $post->$field ) ) {

$bits['where'] .= $wpdb->prepare( " AND $orderby $op %s ", $post->$field );

} else {

$bits['where'] = ' AND 1 = 0';

}

return $bits;

}

static function referrer_link( $format = '%link', $title_format = '%title', $sep = '&raquo;', $sepdirection = 'left' ) {

$url = self::get_referrer_url();

if ( empty( $url ) )

return;

$title = self::get_title( $sep, $sepdirection );

if ( empty( $title ) )

return;

echo self::parse_format( $format, $title_format, $url, $title );

}

static function get_referrer_url() {

if ( !isset( self::$data['url'] ) || !isset( self::$data['query'] ) )

return '';

return self::$data['url'];

}

static function get_title( $sep, $sepdir ) {

$sep = trim( $sep );

if ( ! $title = @self::$data['title'] )

$title = 'Referrer';

$parts = array_slice( explode( self::SEP, $title ), 1 );

if ( 'right' == $sepdir )

$parts = array_reverse( $parts );

return implode( " $sep ", $parts );

}

private static function parse_format( $link_format, $title_format, $url, $title ) {

$title = str_replace( '%title', $title, $title_format );

$link = sprintf( "<a href='%s'>%s</a>", $url, $title );

return str_replace( '%link', $link, $link_format );

}