auto-paragraphs.php

<?php 
/**
 * Replaces double line-breaks with paragraph elements.
 *
 * A group of regex replaces used to identify text formatted with newlines and
 * replace double line-breaks with HTML paragraph tags. The remaining
 * line-breaks after conversion become <<br />> tags, unless $br is set to '0'
 * or 'false'.
 *
 * @param string $para The text which has to be formatted.
 * @param bool $br Optional. If set, this will convert all remaining line-breaks after paragraphing. Default true.
 * @return string Text which has been converted into correct paragraph tags.
 */
function autop($para, $br = true) {
  $pre_tags = array();
	if ( trim($para) === '' )
		return '';
	$para = $para . "\n"; // just to make things a little easier, pad the end
	if ( strpos($para, '<pre') !== false ) {
		$para_parts = explode( '</pre>', $para );
		$last_para = array_pop($para_parts);
		$para = '';
		$i = 0;
		foreach ( $para_parts as $para_part ) {
			$start = strpos($para_part, '<pre');
			// Malformed html?
			if ( $start === false ) {
				$para .= $para_part;
				continue;
			}
			$name = "<pre wp-pre-tag-$i></pre>";
			$pre_tags[$name] = substr( $para_part, $start ) . '</pre>';
			$para .= substr( $para_part, 0, $start ) . $name;
			$i++;
		}
		$para .= $last_para;
	}
	$para = preg_replace('|<br />\s*<br />|', "\n\n", $para);
	// Space things out a little
	$allblocks = '(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|select|option|form|map|area|blockquote|address|math|style|p|h[1-6]|hr|fieldset|noscript|samp|legend|section|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary)';
	$para = preg_replace('!(<' . $allblocks . '[^>]*>)!', "\n$1", $para);
	$para = preg_replace('!(</' . $allblocks . '>)!', "$1\n\n", $para);
	$para = str_replace(array("\r\n", "\r"), "\n", $para); // cross-platform newlines
	if ( strpos($para, '<object') !== false ) {
		$para = preg_replace('|\s*<param([^>]*)>\s*|', "<param$1>", $para); // no para inside object/embed
		$para = preg_replace('|\s*</embed>\s*|', '</embed>', $para);
	}
	$para = preg_replace("/\n\n+/", "\n\n", $para); // take care of duplicates
	// make paragraphs, including one at the end
	$paras = preg_split('/\n\s*\n/', $para, -1, PREG_SPLIT_NO_EMPTY);
	$para = '';
	foreach ( $paras as $tinkle )
		$para .= '<p>' . trim($tinkle, "\n") . "</p>\n";
	$para = preg_replace('|<p>\s*</p>|', '', $para); // under certain strange conditions it could create a P of entirely whitespace
	$para = preg_replace('!<p>([^<]+)</(div|address|form)>!', "<p>$1</p></$2>", $para);
	$para = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)\s*</p>!', "$1", $para); // don't para all over a tag
	$para = preg_replace("|<p>(<li.+?)</p>|", "$1", $para); // problem with nested lists
	$para = preg_replace('|<p><blockquote([^>]*)>|i', "<blockquote$1><p>", $para);
	$para = str_replace('</blockquote></p>', '</p></blockquote>', $para);
	$para = preg_replace('!<p>\s*(</?' . $allblocks . '[^>]*>)!', "$1", $para);
	$para = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*</p>!', "$1", $para);
	if ( $br ) {
		$para = preg_replace_callback('/<(script|style).*?<\/\\1>/s', create_function('$matches', 'return str_replace("\n", "<PreserveNewline />", $matches[0]);'), $para);
		$para = preg_replace('|(?<!<br />)\s*\n|', "<br />\n", $para); // optionally make line breaks
		$para = str_replace('<PreserveNewline />', "\n", $para);
	}
	$para = preg_replace('!(</?' . $allblocks . '[^>]*>)\s*<br />!', "$1", $para);
	$para = preg_replace('!<br />(\s*</?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)!', '$1', $para);
	$para = preg_replace( "|\n</p>$|", '</p>', $para );
	if ( !empty($pre_tags) )
		$para = str_replace(array_keys($pre_tags), array_values($pre_tags), $para);
	return $para;
}