Ambrosite Next/Previous Post Link Plus w/ same_parent

<?php
/*
Plugin Name: Ambrosite Next/Previous Post Link Plus
Plugin URI: http://www.ambrosite.com/plugins
Description: Upgrades the next/previous post link template tags to reorder or loop adjacent post navigation links, return multiple links, truncate link titles, and display post thumbnails. IMPORTANT: If you are upgrading from plugin version 1.1, you will need to update your templates (refer to the <a href="http://www.ambrosite.com/plugins/next-previous-post-link-plus-for-wordpress">documentation</a> on configuring parameters).
Version: 2.4
Author: J. Michael Ambrosio
Author URI: http://www.ambrosite.com
License: GPL2
*/

/**
 * Retrieve adjacent post link.
 *
 * Can either be next or previous post link.
 *
 * Based on get_adjacent_post() from wp-includes/link-template.php
 *
 * @param array $r Arguments.
 * @param bool $previous Optional. Whether to retrieve previous post.
 * @return array of post objects.
 */
function get_adjacent_post_plus($r, $previous = true ) {
    global $post, $wpdb;

    extract( $r, EXTR_SKIP );

    if ( empty( $post ) )
        return null;

//  Sanitize $order_by, since we are going to use it in the SQL query. Default to 'post_date'.
    if ( in_array($order_by, array('post_date', 'post_title', 'post_excerpt', 'post_name', 'post_modified')) ) {
        $order_format = '%s';
    } elseif ( in_array($order_by, array('ID', 'post_author', 'post_parent', 'menu_order', 'comment_count')) ) {
        $order_format = '%d';
    } elseif ( $order_by == 'custom' && !empty($meta_key) ) { // Don't allow a custom sort if meta_key is empty.
        $order_format = '%s';
    } elseif ( $order_by == 'numeric' && !empty($meta_key) ) {
        $order_format = '%d';
    } else {
        $order_by = 'post_date';
        $order_format = '%s';
    }

//  Sanitize $order_2nd. Only columns containing unique values are allowed here. Default to 'post_date'.
    if ( in_array($order_2nd, array('post_date', 'post_title', 'post_modified')) ) {
        $order_format2 = '%s';
    } elseif ( in_array($order_2nd, array('ID')) ) {
        $order_format2 = '%d';
    } else {
        $order_2nd = 'post_date';
        $order_format2 = '%s';
    }

//  Sanitize num_results (non-integer or negative values trigger SQL errors)
    $num_results = intval($num_results) < 2 ? 1 : intval($num_results);

//  Queries involving custom fields require an extra table join
    if ( $order_by == 'custom' || $order_by == 'numeric' ) {
        $current_post = get_post_meta($post->ID, $meta_key, TRUE);
        $order_by = ($order_by === 'numeric') ? 'm.meta_value+0' : 'm.meta_value';
        $meta_join = $wpdb->prepare(" INNER JOIN $wpdb->postmeta AS m ON p.ID = m.post_id AND m.meta_key = %s", $meta_key );
    } elseif ( $in_same_meta ) {
        $current_post = $post->$order_by;
        $order_by = 'p.' . $order_by;
        $meta_join = $wpdb->prepare(" INNER JOIN $wpdb->postmeta AS m ON p.ID = m.post_id AND m.meta_key = %s", $in_same_meta );
    } else {
        $current_post = $post->$order_by;
        $order_by = 'p.' . $order_by;
        $meta_join = '';
    }

//  Get the current post value for the second sort column
    $current_post2 = $post->$order_2nd;
    $order_2nd = 'p.' . $order_2nd;

//  Get the list of post types. Default to current post type
    if ( empty($post_type) )
        $post_type = "'$post->post_type'";

//  Put this section in a do-while loop to enable the loop-to-first-post option
    do {
        $join = $meta_join;
        $excluded_categories = $ex_cats;
        $included_categories = $in_cats;
        $excluded_posts = $ex_posts;
        $included_posts = $in_posts;
        $in_same_term_sql = $in_same_author_sql = $parent_sql = $in_same_meta_sql = $ex_cats_sql = $in_cats_sql = $ex_posts_sql = $in_posts_sql = '';

//      Get the list of hierarchical taxonomies, including customs (don't assume taxonomy = 'category')
        $taxonomies = array_filter( get_post_taxonomies($post->ID), "is_taxonomy_hierarchical" );

        if ( ($in_same_cat || $in_same_tax || $in_same_format || !empty($excluded_categories) || !empty($included_categories)) && !empty($taxonomies) ) {
            $cat_array = $tax_array = $format_array = array();

            if ( $in_same_cat ) {
                $cat_array = wp_get_object_terms($post->ID, $taxonomies, array('fields' => 'ids'));
            }
            if ( $in_same_tax && !$in_same_cat ) {
                if ( $in_same_tax === true ) {
                    if ( $taxonomies != array('category') )
                        $taxonomies = array_diff($taxonomies, array('category'));
                } else
                    $taxonomies = (array) $in_same_tax;
                $tax_array = wp_get_object_terms($post->ID, $taxonomies, array('fields' => 'ids'));
            }
            if ( $in_same_format ) {
                $taxonomies[] = 'post_format';
                $format_array = wp_get_object_terms($post->ID, 'post_format', array('fields' => 'ids'));
            }

            $join .= " INNER JOIN $wpdb->term_relationships AS tr ON p.ID = tr.object_id INNER JOIN $wpdb->term_taxonomy tt ON tr.term_taxonomy_id = tt.term_taxonomy_id AND tt.taxonomy IN (\"" . implode('", "', $taxonomies) . "\")";

            $term_array = array_unique( array_merge( $cat_array, $tax_array, $format_array ) );
            if ( !empty($term_array) )
                $in_same_term_sql = "AND tt.term_id IN (" . implode(',', $term_array) . ")";

            if ( !empty($excluded_categories) ) {
//              Support for both (1 and 5 and 15) and (1, 5, 15) delimiter styles
                $delimiter = ( strpos($excluded_categories, ',') !== false ) ? ',' : 'and';
                $excluded_categories = array_map( 'intval', explode($delimiter, $excluded_categories) );
//              Three category exclusion methods are supported: 'strong', 'diff', and 'weak'.
//              Default is 'weak'. See the plugin documentation for more information.
                if ( $ex_cats_method === 'strong' ) {
                    $taxonomies = array_filter( get_post_taxonomies($post->ID), "is_taxonomy_hierarchical" );
                    if ( function_exists('get_post_format') )
                        $taxonomies[] = 'post_format';
                    $ex_cats_posts = get_objects_in_term( $excluded_categories, $taxonomies );
                    if ( !empty($ex_cats_posts) )
                        $ex_cats_sql = "AND p.ID NOT IN (" . implode($ex_cats_posts, ',') . ")";
                } else {
                    if ( !empty($term_array) && !in_array($ex_cats_method, array('diff', 'differential')) )
                        $excluded_categories = array_diff($excluded_categories, $term_array);
                    if ( !empty($excluded_categories) )
                        $ex_cats_sql = "AND tt.term_id NOT IN (" . implode($excluded_categories, ',') . ')';
                }
            }

            if ( !empty($included_categories) ) {
                $in_same_term_sql = ''; // in_cats overrides in_same_cat
                $delimiter = ( strpos($included_categories, ',') !== false ) ? ',' : 'and';
                $included_categories = array_map( 'intval', explode($delimiter, $included_categories) );
                $in_cats_sql = "AND tt.term_id IN (" . implode(',', $included_categories) . ")";
            }
        }

//      Optionally restrict next/previous links to same author
        if ( $in_same_author )
            $in_same_author_sql = $wpdb->prepare("AND p.post_author = %d", $post->post_author );

//      Optionally restrict parent of next/previous links
        if ( $same_parent )
            $parent_sql = $wpdb->prepare("AND p.post_parent = %d", $post->post_parent );

//      Optionally restrict next/previous links to same meta value
        if ( $in_same_meta && $r['order_by'] != 'custom' && $r['order_by'] != 'numeric' )
            $in_same_meta_sql = $wpdb->prepare("AND m.meta_value = %s", get_post_meta($post->ID, $in_same_meta, TRUE) );

//      Optionally exclude individual post IDs
        if ( !empty($excluded_posts) ) {
            $excluded_posts = array_map( 'intval', explode(',', $excluded_posts) );
            $ex_posts_sql = " AND p.ID NOT IN (" . implode(',', $excluded_posts) . ")";
        }

//      Optionally include individual post IDs
        if ( !empty($included_posts) ) {
            $included_posts = array_map( 'intval', explode(',', $included_posts) );
            $in_posts_sql = " AND p.ID IN (" . implode(',', $included_posts) . ")";
        }

        $adjacent = $previous ? 'previous' : 'next';
        $order = $previous ? 'DESC' : 'ASC';
        $op = $previous ? '<' : '>';

//      Optionally get the first/last post. Disable looping and return only one result.
        if ( $end_post ) {
            $order = $previous ? 'ASC' : 'DESC';
            $num_results = 1;
            $loop = false;
            if ( $end_post === 'fixed' ) // display the end post link even when it is the current post
                $op = $previous ? '<=' : '>=';
        }

//      If there is no next/previous post, loop back around to the first/last post.
        if ( $loop && isset($result) ) {
            $op = $previous ? '>=' : '<=';
            $loop = false; // prevent an infinite loop if no first/last post is found
        }

        $join  = apply_filters( "get_{$adjacent}_post_plus_join", $join, $r );

//      In case the value in the $order_by column is not unique, select posts based on the $order_2nd column as well.
//      This prevents posts from being skipped when they have, for example, the same menu_order.
        $where = apply_filters( "get_{$adjacent}_post_plus_where", $wpdb->prepare("WHERE ( $order_by $op $order_format OR $order_2nd $op $order_format2 AND $order_by = $order_format ) AND p.post_type IN ($post_type) AND p.post_status = 'publish' $in_same_term_sql $in_same_author_sql $parent_sql $in_same_meta_sql $ex_cats_sql $in_cats_sql $ex_posts_sql $in_posts_sql", $current_post, $current_post2, $current_post), $r );

        $sort  = apply_filters( "get_{$adjacent}_post_plus_sort", "ORDER BY $order_by $order, $order_2nd $order LIMIT $num_results", $r );

        $query = "SELECT DISTINCT p.* FROM $wpdb->posts AS p $join $where $sort";
        $query_key = 'adjacent_post_' . md5($query);
        $result = wp_cache_get($query_key);
        if ( false !== $result )
            return $result;

//      echo $query . '<br />';

//      Use get_results instead of get_row, in order to retrieve multiple adjacent posts (when $num_results > 1)
//      Add DISTINCT keyword to prevent posts in multiple categories from appearing more than once
        $result = $wpdb->get_results("SELECT DISTINCT p.* FROM $wpdb->posts AS p $join $where $sort");
        if ( null === $result )
            $result = '';

    } while ( !$result && $loop );

    wp_cache_set($query_key, $result);
    return $result;
}

/**
 * Display previous post link that is adjacent to the current post.
 *
 * Based on previous_post_link() from wp-includes/link-template.php
 *
 * @param array|string $args Optional. Override default arguments.
 * @return bool True if previous post link is found, otherwise false.
 */
function previous_post_link_plus($args = '') {
    return adjacent_post_link_plus($args, '&laquo; %link', true);
}

/**
 * Display next post link that is adjacent to the current post.
 *
 * Based on next_post_link() from wp-includes/link-template.php
 *
 * @param array|string $args Optional. Override default arguments.
 * @return bool True if next post link is found, otherwise false.
 */
function next_post_link_plus($args = '') {
    return adjacent_post_link_plus($args, '%link &raquo;', false);
}

/**
 * Display adjacent post link.
 *
 * Can be either next post link or previous.
 *
 * Based on adjacent_post_link() from wp-includes/link-template.php
 *
 * @param array|string $args Optional. Override default arguments.
 * @param bool $previous Optional, default is true. Whether display link to previous post.
 * @return bool True if next/previous post is found, otherwise false.
 */
function adjacent_post_link_plus($args = '', $format = '%link &raquo;', $previous = true) {
    $defaults = array(
        'order_by' => 'post_date', 'order_2nd' => 'post_date', 'meta_key' => '', 'post_type' => '',
        'loop' => false, 'end_post' => false, 'thumb' => false, 'max_length' => 0,
        'format' => '', 'link' => '%title', 'date_format' => '', 'tooltip' => '%title',
        'in_same_cat' => false, 'in_same_tax' => false, 'in_same_format' => false,
        'in_same_author' => false, 'same_parent' => false, 'in_same_meta' => false,
        'ex_cats' => '', 'ex_cats_method' => 'weak', 'in_cats' => '', 'ex_posts' => '', 'in_posts' => '',
        'before' => '', 'after' => '', 'num_results' => 1, 'return' => false, 'echo' => true
    );

//  If Post Types Order plugin is installed, default to sorting on menu_order
    if ( function_exists('CPTOrderPosts') )
        $defaults['order_by'] = 'menu_order';

    $r = wp_parse_args( $args, $defaults );
    if ( empty($r['format']) )
        $r['format'] = $format;
    if ( empty($r['date_format']) )
        $r['date_format'] = get_option('date_format');
    if ( !function_exists('get_post_format') )
        $r['in_same_format'] = false;

    if ( $previous && is_attachment() ) {
        $posts = array();
        $posts[] = & get_post($GLOBALS['post']->post_parent);
    } else
        $posts = get_adjacent_post_plus($r, $previous);

//  If there is no next/previous post, return false so themes may conditionally display inactive link text.
    if ( !$posts )
        return false;

//  If sorting by date, display posts in reverse chronological order. Otherwise display in alpha/numeric order.
    if ( ($previous && $r['order_by'] != 'post_date') || (!$previous && $r['order_by'] == 'post_date') )
        $posts = array_reverse( $posts, true );

//  Option to return something other than the formatted link
    if ( $r['return'] ) {
        if ( $r['num_results'] == 1 ) {
            reset($posts);
            $post = current($posts);
            if ( $r['return'] === 'id')
                return $post->ID;
            if ( $r['return'] === 'href')
                return get_permalink($post);
            if ( $r['return'] === 'object')
                return $post;
            if ( $r['return'] === 'title')
                return $post->post_title;
            if ( $r['return'] === 'date')
                return mysql2date($r['date_format'], $post->post_date);
        } elseif ( $r['return'] === 'object')
            return $posts;
    }

    $output = $r['before'];

//  When num_results > 1, multiple adjacent posts may be returned. Use foreach to display each adjacent post.
    foreach ( $posts as $post ) {
        $title = $post->post_title;
        if ( empty($post->post_title) )
            $title = $previous ? __('Previous Post') : __('Next Post');

        $title = apply_filters('the_title', $title, $post->ID);
        $date = mysql2date($r['date_format'], $post->post_date);
        $author = get_the_author_meta('display_name', $post->post_author);

//      Set anchor title attribute to long post title or custom tooltip text. Supports variable replacement in custom tooltip.
        if ( $r['tooltip'] ) {
            $tooltip = str_replace('%title', $title, $r['tooltip']);
            $tooltip = str_replace('%date', $date, $tooltip);
            $tooltip = str_replace('%author', $author, $tooltip);
            $tooltip = ' title="' . esc_attr($tooltip) . '"';
        } else
            $tooltip = '';

//      Truncate the link title to nearest whole word under the length specified.
        $max_length = intval($r['max_length']) < 1 ? 9999 : intval($r['max_length']);
        if ( strlen($title) > $max_length )
            $title = substr( $title, 0, strrpos(substr($title, 0, $max_length), ' ') ) . '...';

        $rel = $previous ? 'prev' : 'next';

        $anchor = '<a href="'.get_permalink($post).'" rel="'.$rel.'"'.$tooltip.'>';
        $link = str_replace('%title', $title, $r['link']);
        $link = str_replace('%date', $date, $link);
        $link = $anchor . $link . '</a>';

        $format = str_replace('%link', $link, $r['format']);
        $format = str_replace('%title', $title, $format);
        $format = str_replace('%date', $date, $format);
        $format = str_replace('%author', $author, $format);
        if ( ($r['order_by'] == 'custom' || $r['order_by'] == 'numeric') && !empty($r['meta_key']) ) {
            $meta = get_post_meta($post->ID, $r['meta_key'], true);
            $format = str_replace('%meta', $meta, $format);
        } elseif ( $r['in_same_meta'] ) {
            $meta = get_post_meta($post->ID, $r['in_same_meta'], true);
            $format = str_replace('%meta', $meta, $format);
        }

//      Get the category list, including custom taxonomies (only if the %category variable has been used).
        if ( (strpos($format, '%category') !== false) && version_compare(PHP_VERSION, '5.0.0', '>=') ) {
            $term_list = '';
            $taxonomies = array_filter( get_post_taxonomies($post->ID), "is_taxonomy_hierarchical" );
            if ( $r['in_same_format'] && get_post_format($post->ID) )
                $taxonomies[] = 'post_format';
            foreach ( $taxonomies as &$taxonomy ) {
//              No, this is not a mistake. Yes, we are testing the result of the assignment ( = ).
//              We are doing it this way to stop it from appending a comma when there is no next term.
                if ( $next_term = get_the_term_list($post->ID, $taxonomy, '', ', ', '') ) {
                    $term_list .= $next_term;
                    if ( current($taxonomies) ) $term_list .= ', ';
                }
            }
            $format = str_replace('%category', $term_list, $format);
        }

//      Optionally add the post thumbnail to the link. Wrap the link in a span to aid CSS styling.
        if ( $r['thumb'] && has_post_thumbnail($post->ID) ) {
            if ( $r['thumb'] === true ) // use 'post-thumbnail' as the default size
                $r['thumb'] = 'post-thumbnail';
            $thumbnail = '<a class="post-thumbnail" href="'.get_permalink($post).'" rel="'.$rel.'"'.$tooltip.'>' . get_the_post_thumbnail( $post->ID, $r['thumb'] ) . '</a>';
            $format = $thumbnail . '<span class="post-link">' . $format . '</span>';
        }

//      If more than one link is returned, wrap them in <li> tags
        if ( intval($r['num_results']) > 1 )
            $format = '<li>' . $format . '</li>';

        $output .= $format;
    }

    $output .= $r['after'];

    //  If echo is false, don't display anything. Return the link as a PHP string.
    if ( !$r['echo'] || $r['return'] === 'output' )
        return $output;

    $adjacent = $previous ? 'previous' : 'next';
    echo apply_filters( "{$adjacent}_post_link_plus", $output, $r );

    return true;
}
?>