Simple function to convert a text into formatted HTML in PHP. The function implements some text cleanups (double space removal) and accepts some HTML in the text, like links (a href), lists (ul, ol), blockquotes and tables. This makes it perfect for use inside custom-made blogging engines and CMSs. There's also an implementation of case-insensitive search/replace for php < 5.

<?php

function stri_replace( $find, $replace, $string ) {
// Case-insensitive str_replace()

  $parts = explode( strtolower($find), strtolower($string) );

  $pos = 0;

  foreach( $parts as $key=>$part ){
    $parts[ $key ] = substr($string, $pos, strlen($part));
    $pos += strlen($part) + strlen($find);
  }

  return( join( $replace, $parts ) );
}


function txt2html($txt) {
// Transforms txt in html

  //Kills double spaces and spaces inside tags.
  while( !( strpos($txt,'  ') === FALSE ) ) $txt = str_replace('  ',' ',$txt);
  $txt = str_replace(' >','>',$txt);
  $txt = str_replace('< ','<',$txt);

  //Transforms accents in html entities.
  $txt = htmlentities($txt);

  //We need some HTML entities back!
  $txt = str_replace('&quot;','"',$txt);
  $txt = str_replace('&lt;','<',$txt);
  $txt = str_replace('&gt;','>',$txt);
  $txt = str_replace('&amp;','&',$txt);

  //Ajdusts links - anything starting with HTTP opens in a new window
  $txt = stri_replace("<a href=\"http://","<a target=\"_blank\" href=\"http://",$txt);
  $txt = stri_replace("<a href=http://","<a target=\"_blank\" href=http://",$txt);

  //Basic formatting
  $eol = ( strpos($txt,"\r") === FALSE ) ? "\n" : "\r\n";
  $html = '<p>'.str_replace("$eol$eol","</p><p>",$txt).'</p>';
  $html = str_replace("$eol","<br />\n",$html);
  $html = str_replace("</p>","</p>\n\n",$html);
  $html = str_replace("<p></p>","<p>&nbsp;</p>",$html);

  //Wipes <br> after block tags (for when the user includes some html in the text).
  $wipebr = Array("table","tr","td","blockquote","ul","ol","li");

  for($x = 0; $x < count($wipebr); $x++) {

    $tag = $wipebr[$x];
    $html = stri_replace("<$tag><br />","<$tag>",$html);
    $html = stri_replace("</$tag><br />","</$tag>",$html);

  }

  return $html;
}

?>