[Snippet] NavigateSiblings (requires MODx 0.9.2+)

<?php
/**
 * NavigateSiblings
 * 
 * Flexible prev/next/parent navigation for a document with siblings.  You can
 * use it to output templated links, or just set placeholders
 * 
 * @author Jason Coward, <[email protected]>.
 * @version 1.0
 * 
 * Example usage:
 * 
 * 
 * [!NavigateSiblings? &mode=`direct`!] -- returns the output directly in place
 * of the snippet; it is assumed you are using chunk templates for this mode.
 * This is also the default mode if not specified.
 * 
 * [!NavigateSiblings? &mode=`template`!] -- sets placeholders using template
 * mode by using the default template chunk names, prevSibling, nextSibling, and
 * navSiblingsParent, and producing output to placeholders of the same name as
 * the chunk: navSiblingsPrev, navSiblingsNext, and navSiblingsParent.
 * 
 * [!NavigateSiblings? &mode=`urlonly`!] -- no output is returned, and
 * no templates are processed; instead, the snippet only sets the values of
 * placeholders for each link URL: prevSiblingUrl, nextSiblingUrl, and
 * navSiblingParentUrl.
 */

/*
 * Define the mode of the snippet:
 * 
 * &mode=`template` -- will produce placeholders containing templates within
 * which the URL placeholders can be used (default mode).
 * 
 * &mode=`direct` -- will output the template chunks in the place where the
 * snippet is called within your content.
 *  
 * &mode=`urlonly` -- will only produce placeholders for the navigation URLs.
 * 
 */
if (!isset ($mode) || ($mode !== 'template') || $mode !== 'urlonly') {
    $mode= 'direct';
}

/*
 * Define a chunk representing the presentation of the previous sibling link.
 * &prevChunk=`myPrevSiblingChunkName`
 */ 
if (!isset ($prevChunk)) {
    $prevChunk= 'prevSibling';
}

/*
 * Define a chunk representing the presentation of the next sibling link.
 * &nextChunk=`myNextSiblingChunkName`
 */
if (!isset ($nextChunk)) {
    $nextChunk= 'nextSibling';
}

/*
 * Determine whether or not to show a link back to the parent.
 * &showParent=`0` -- will disable this, which is set to 1 by default.
 */
if (!isset ($showParent)) {
    $showParent= 1;
}

/*
 * Define a chunk representing the presentation of the parent link.
 * &parentChunk=`myNavParentChunkName`
 */
if (!isset ($parentChunk)) {
    $parentChunk= 'navSiblingsParent';
}

$output= '';
$prevOut= '';
$parentOut= '';
$nextOut= '';
$parentId= (string) $modx->documentObject['parent'];
if (!function_exists('filterNonSiblingsFromDocumentMap')) {
    function filterNonSiblingsFromDocumentMap($var) {
        global $modx;
        return (isset ($var[$modx->documentObject['parent']]));
    }
}
$siblings= array_filter($modx->documentMap, 'filterNonSiblingsFromDocumentMap');
$currentKey= false;
$prevSibling= false;
$nextSibling= false;
$firstSibling= current($siblings);
$currentSibling= $firstSibling;
while ($currentSibling !== false) {
    if (intval($currentSibling[$parentId]) === intval($modx->documentIdentifier)) {
        $currentKey= key($siblings);
        break;
    }
    $currentSibling= next($siblings);
}
$lastSibling= end($siblings);
if ($currentKey) {
    if (intval($firstSibling[$parentId]) !== intval($modx->documentIdentifier)) {
        $modx->setPlaceholder('prevSiblingUrl', $modx->makeUrl($siblings[$currentKey - 1][$parentId]));
        $prevOut= !empty ($prevChunk) ? $modx->getChunk($prevChunk) : '';
    }
    if ($showParent) {
        $modx->setPlaceholder('navSiblingParentUrl', $modx->makeUrl($parentId));
        $parentOut= !empty ($parentChunk) ? $modx->getChunk($parentChunk) : '';
    }
    if (intval($lastSibling[$parentId]) !== intval($modx->documentIdentifier)) {
        $modx->setPlaceholder('nextSiblingUrl', $modx->makeUrl($siblings[$currentKey + 1][$parentId]));
        $nextOut= !empty ($nextChunk) ? $modx->getChunk($nextChunk) : '';
    }
}
if ($mode == 'template') {
    if (!empty ($prevChunk)) {
        $this->setPlaceholder($prevChunk, $prevOut);
    }
    if (!empty ($nextChunk)) {
        $this->setPlaceholder($nextChunk, $nextOut);
    }
    if (!empty ($parentChunk)) {
        $this->setPlaceholder($parentChunk, $parentOut);
    }
} elseif ($mode == 'direct') {
    $output.= $prevOut . "\n";
    $output.= $parentOut . "\n";
    $output.= $nextOut . "\n";
}
return $output;
?>

<a href="[+prevSiblingUrl+]" title="Go to previous page">Prev</a>

<a href="[+nextSiblingUrl+]" title="Go to next page">Next</a>

<a href="[+navSiblingsParentUrl+]" title="Go to the parent page">Index</a>

<?php
if (!function_exists('filterNonSiblingsFromDocumentMap')) {
    function filterNonSiblingsFromDocumentMap($var) {
        global $modx;
        return (isset ($var[$modx->documentObject['parent']]));
    }
}


$siblings= array_filter($modx->documentMap, 'filterNonSiblingsFromDocumentMap');
?>

<?php
$siblings= array_filter($modx->documentMap, 
    create_function(  '$var',  'global $modx; return (isset ($var[$modx->documentObject["parent"]]));' )
);
?>

[[NavigateSibling? &mode=`template`]]

[+nextSibling:ifempty=`[+nextButton+]`+]

<!-- Empty previous value -->

[+nextSibling:ifempty=`[+nextButton+]`+]

[+nextSibling:ifempty=`{{nextButton}}`+]