example to render today posts with prev day next day links if found . with url segments for category and day date

prev_next_day_posts.php

<?php

/* 
 * as per http://processwire.com/talk/topic/2928-pagination-by-date/
 * list posts by day, show prev next day if any posts found
 * 
 * - posts have a date field "publish_from" 
 * with no time selection but only days
 * this will save the timestamp of today 00:00 (starting) so we can simply 
 * use "publish_from=$prevday" in selectors
 * 
 * - posts have page fields "categories"
 * 
 * urls like:
 * /posts/[category]/[dd-mm-yyyy]/
 * 
 * enable url segments on posts template
 * 
 */



// check urls segments

if($input->urlSegment1){
    $cat = $sanitizer->pageName($input->urlSegment1);
} else {
    $cat = "training"; // default
}

if($input->urlSegment2) {
    $day = $sanitizer->pageName($input->urlSegment2);
} else {
    $day = date("d-m-Y", strtotime("today")); // default
}


// get the category page, if not found any show 404
$category_page = $pages->get("template=category, name=$cat");
if(!$category_page->id) {
    // throws 404 when category not found
    throw new Wire404Exception("Page Not Found");
}


// ok lets get some posts from today and render a list

$posts_day = $pages->find("categories=$category_page, template=posts, publish_from=$day");
if(count($posts_day)){
    foreach($posts_day as $post) {
        echo "<p>$post->title</p>";
        // whatever you wish to output
        // ..
    }
} else {
    echo "no posts found for today.";
}


/**
 * Now we construct the prev and next day links, if posts were found
 * ---------------------------------------------------------------------------
 */

// get timestamps for use in selectors

$prevday = strtotime( "$day -1 day" );
$nextday = strtotime( "$day +1 day" );


// ok lets search some posts but with $pages->count(selector)
// sicne we only want to know if any found this is much faster query

$posts_preday  = $pages->count("categories=$category_page, template=posts, publish_from=$prevday");
$posts_nextday = $pages->count("categories=$category_page, template=posts, publish_from=$nextday");


// convert back date to string for url segment

$prevday = date("d-m-Y",$prevday);
$nextday = date("d-m-Y",$nextday);


// print out prev and next url links

if($posts_preday) {
    echo "<a href='{$config->urls->root}posts/$category/$prevday/'>Prev Day</a> ";
}
if($posts_nextday) {
    echo "<a href='{$config->urls->root}posts/$category/$nextday/'>Next Day</a> ";
}