Simple template var replacement, but with a twist

Question

So I'm setting up a system that has a lot of emails, and variable replacement within it, so I'm writing a class to manage some variable replacement for templates stored in the database.

Here's a brief example:

// template is stored in db, so that's how this would get loaded in 
$template = "Hello, %customer_name%, thank you for contacting %website_name%"; 
// The array of replacements is built manually and passed to the class 
// with actual values being called from db 
$replacements = array('%customer_name%'=>'Bob', '%website_name%'=>'Acme'); 
$rendered = str_replace(array_keys($replacements), $replacements, $template); 

Now, that works well and good for single var replacements, basic stuff. However, there are some places where there should be a for loop, and I'm lost how to implement it.

The idea is there'd be a template like this:

"hello, %customer_name%, thank you for requesting information on {products}"

Where, {products} would be an array passed to the template, which the is looped over for products requested, with a format like:

Our product %product_name% has a cost of %product_price%. Learn more at %product_url%.

So an example rendered version of this would be:

"hello, bob, thank you for requesting information on:

Our product WidgetA has a cost of $1. Learn more at example/A

Our product WidgetB has a cost of $2. Learn more at example/B

Our product WidgetC has a cost of $3. Learn more at example/C.

What's the best way to accomplish this?

Answer 1

$products = array('...');
function parse_products($matches)
{
    global $products;
    $str = '';
    foreach($products as $product) {
       $str .= str_replace('%product_name%', $product, $matches[1]); // $matches[1] is whatever is between {products} and {/products}
    }
    return $str;
}

$str = preg_replace_callback('#\{products}(.*)\{/products}#s', 'parse_products', $str);

The idea is to find string between {products} and {products}, pass it to some function, do whatever you need to do with it, iterating over $products array. Whatever the function returns replaces whole "{products}[anything here]{/products}".

The input string would look like that:

Requested products: {products}%product_name%{/products}

Answer 2

Well, I really dont see the point in a template engine that uses repalcements/regex

PHP Is already a template engine, when you write <?php echo $var?> its just like doing <{$var}> or {$var}

Think of it this way, PHP Already translates <?php echo '<b>hello</b>'?> into <b>hello</b> by its engine, so why make it do everything 2 times over.

The way i would implement a template engine is like so

Firstly create a template class

class Template
{
   var $vars = array();

   function __set($key,$val)
   {
      $this->vars[$key] = $val;
   }

   function __get($key)
   {
     return isset($this->vars[$key]) ? $this->vars[$key] : false;
   }

   function output($tpl = false)
   {
      if($tpl === false)
      {
         die('No template file selected in Template::output(...)');
      }

      if(!file_exists(($dir = 'templates/' . $tpl . '.php')))
      {
         die(sprintf('Tpl file does not exists (%s)',$dir));
      }

      new TemplateLoader($dir,$this->vars);
      return true;
   }
}

This is what you use in your login such as index.php, you will set data just like an stdClass just google it if your unsure. and when you run the output command it sends the data and tpl to the next class below.

---

And then create a standalone class to compile the tpl file within.

class TemplateLoader
{
    private $vars = array();
    private $_vars = array(); //hold vars set within the tpl file
    function __construct($file,$variables)
    {
        $this->vars = $variables;
        //Start the capture;
        ob_start();
           include $file;
           $contents = ob_get_contents();
        ob_end_clean(); //Clean it

       //Return here if you wish
       echo $contents;
    }

    function __get($key)
    {
        return isset($this->vars[$key]) ? $this->vars[$key] : (isset($this->_vars[$key]) ? $this->_vars[$key] : false) : false;
    }

    function __set($key,$val)
    {
       $this->_vars[$key] = $val;
       return true;
    }

   function bold($key)
   {
      return '<strong>' . $this->$key . '</string>';
   }
}

The reason we keep this seperate is so it has its own space to run in, you just load your tpl file as an include in your constructor so it only can be loaded once, then when the file is included it has access to all the data and methods within TemplateLoader.

---

Index.php

<?php
   require_once 'includes/Template.php';
   require_once 'includes/TemplateLoader.php';


   $Template = new Template();

   $Template->foo = 'somestring';
   $Template->bar = array('some' => 'array');

   $Template->zed = new stdClass(); // Showing Objects

   $Template->output('index'); // loads templates/index.php
?>

Now here we dont really want to mix html with this page because by seperating the php and the view / templates you making sure all your php has completed because when you send html or use html it stops certain aspects of your script from running.

---

templates/index.php

header

    <h1><?php $this->foo;?></h1>
    <ul>
        <?php foreach($this->bar as $this->_foo):?>
            <li><?php echo $this->_foo; ?></li>
        <?php endforeach; ?>
    </ul>
     <p>Testing Objects</p>
     <?php $this->sidebar = $this->foo->show_sidebar ? $this->foo->show_sidebar : false;?>
     <?php if($this->sidebar):?>
        Showing my sidebar.
     <?php endif;?>
footer

Now here we can see that were mixing html with php but this is ok because in ehre you should only use basic stuff such as Foreach,For etc. and Variables.

---

NOTE: IN the TemplateLoader Class you can add a function like..

function bold($key)
{
   return '<strong>' . $this->$key . '</string>';
}

This will allow you to increase your actions in your templates so bold,italic,atuoloop,css_secure,stripslashs..

You still have all the normal tools such as stripslashes/htmlentites etc.

Heres a small example of the bold.

$this->bold('foo'); //Returns <strong>somestring</string>

---

You can add lots of tools into the TempalteLoader class such as inc() to load other tpl files, you can develop a helper system so you can go $this->helpers->jquery->googleSource

If you have any more questions feel free to ask me.

----------

An example of storing in your database.

<?php
if(false != ($data = mysql_query('SELECT * FROM tpl_catch where item_name = \'index\' AND item_save_time > '.time() - 3600 .' LIMIT 1 ORDER BY item_save_time DESC')))
{
    if(myslq_num_rows($data) > 0)
    {
       $row = mysql_fetch_assc($data);
       die($row[0]['item_content']);
    }else
    {
       //Compile it with the sample code in first section (index.php)
       //Followed by inserting it into the database
       then print out the content.
    }
}
?>

If you wish to store your tpl files including PHP then that's not a problem, within Template where you passing in the tpl file name just search db instead of the filesystem