paypal.module

<?php

function paypal_help($path, $arg) {
   $output = '';
   switch ($path) {
      case "admin/help#paypal":
         $output = '<p>'.t("Converts shorthand into PayPal code").'</p>';
         break;
   }
   
   return $output;
}

/**
 * Possible permissions
 * @return array
 */
function paypal_perm() {
   return array("use PayPal filter");
}

/**
 * Our main controller
 */
function paypal_filter($op, $delta=0, $format=-1, $text='') {
   switch ($op) {
      case 'description':
         return t('Substitutes [paypal name="product" price="$10.00"] with PayPal code');
      case 'list':
         return array(0=>t('PayPal filter'));
      case 'no cache':
         // make sure we process on every page load
         return true;
      case 'prepare':                           
         return paypal_escape($text);
      case 'process':
         // Here is where we actually do our changes
         return paypal_process($text);
   }
}

/**
 * Escape our paypal tag
 */
function paypal_escape($text) {
   return $text;
}

/**
 * Do the work here
 */
function paypal_process($text) {
   $regex = '/\[paypal name="(.*?)" price="(.*?)"\]/';
   
   if (preg_match_all($regex, $text, $matches)) {
      $finds = $matches[0];
      $names = $matches[1];
      $prices = $matches[2];

      for ($i=0; $i<count($finds);$i++) {
         $find = $finds[$i];
         $name = $names[$i];
         $price = $prices[$i];
         
         $replacement = paypal_get_replacement($name, $price);

         $text = str_replace($find, $replacement, $text);
      }
   }

   return $text;
}

/**
 * Build the new PayPal code for a given name/price pairing
 */
function paypal_get_replacement($name, $price) {
   if (!strlen(trim($name))) {
      return "<p>Error: PayPal filter requires a name.</p>";
   }
   
   if (!strlen(trim($price))) {
      return "<p>Error: PayPal filter requires a price.</p>";
   }
   
   if (!is_numeric($price)) {
      return "<p>Error: Price must be numeric for $name.</p>";
   }
   
   return sprintf('<form action="https://www.paypal.com/cgi-bin/webscr" method="post">
<input type="hidden" name="cmd" value="_xclick">
<input type="hidden" name="business" value="<EMAIL_ADDRESS_HERE>">
<input type="hidden" name="item_name" value="%s">
<input type="hidden" name="amount" value="%d">
<input type="hidden" name="no_shipping" value="0">
<input type="hidden" name="no_note" value="1">
<input type="hidden" name="currency_code" value="USD">
<input type="hidden" name="lc" value="US">

<input type="hidden" name="bn" value="PP-BuyNowBF">
<input type="image" 
src="https://www.paypal.com/en_US/i/btn/btn_buynow_SM.gif" border="0" 
name="submit" alt="PayPal - The safer, easier way to pay online!"><br
/>
</form>', $name, $price);
}