A simple Pico plugin adding a page's last modification time to its page data. Pico is a stupidly simple, blazing fast, flat file CMS. http://picocms.org/

PicoPageModPlugin.php

<?php

/**
 * Pico page modification time plugin
 *
 * Adds a page's last modification time to its page data.
 *
 * Example:
 *
 * ```twig
 * <p>Last modified: {{ current_page.modificationTime|date("Y-m-d H:i:s") }}</p>
 * ```
 *
 * @author  Daniel Rudolf
 * @link    http://picocms.org
 * @license http://opensource.org/licenses/MIT The MIT License
 * @version 0.0.1
 */
class PicoPageModPlugin extends AbstractPicoPlugin
{
    const API_VERSION = 2;
  
    public function onSinglePageLoaded(array &$pageData)
    {
        if ($pageData['id']) {
            $fileName = $this->getConfig('content_dir') . $pageData['id'] . $this->getConfig('content_ext');
            if (is_file($fileName) && !isset($pageData['modificationTime'])) {
                $pageData['modificationTime'] = filemtime($fileName);
            }
        }
    }
}

@PhrozenByte That's a great idea!

By the way, I read this: https://github.com/picocms/Pico/blob/master/plugins/DummyPlugin.php

I just don't have the best idea where to put the HTTP Caching script. I normally put it on index.php. Something like this:

$ret = $pico->run(); // exec pico and returns output

// Begin HTTP caching evaluation
$pageData = $pico->getCurrentPage();
$lastModified = $pageData['meta']['modificationTime'] ?? $pageData['modificationTime'] ?? null;

if (!is_null(lastModified) && isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && $lastModified <= strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']))
{
	header('HTTP/1.1 304 Not Modified');
	exit;
}

header('Pragma: public');
if (isset($pageData['meta']['CacheControl'])) {
   $maxAge = $pageData['meta']['CacheControl'] - $_SERVER['REQUEST_TIME'];
   header('Cache-Control: max-age='.$maxAge.', public');
   header('Expires: '.gmdate('D, d M Y H:i:s', $expiration).' GMT');
}
if ($last_modified) {
   header('Last-modified: '.gmdate('D, d M Y H:i:s', $last_modified).' GMT');
}

echo $ret; // print output

I wish I could done it better.

EDIT:
Was it onMetaParsed or onContentParsing? I assumed it's safe to execute exit; under a Pico plugin.