PHP Looping Template Engine - From Scratch

Question

For a group project I am trying to create a template engine for PHP for the people less experienced with the language can use tags like {name} in their HTML and the PHP will

Answer 1

A simple approach is to convert the template into PHP and run it.

$template = preg_replace('~\{(\w+)\}~', 'showVariable(\'$1\'); ?>', $template);
$template = preg_replace('~\{LOOP:(\w+)\}~', 'data[\'$1\'] as $ELEMENT): $this->wrap($ELEMENT); ?>', $template);
$template = preg_replace('~\{ENDLOOP:(\w+)\}~', 'unwrap(); endforeach; ?>', $template);

For example, this converts the template tags to embedded PHP tags.

You'll see that I made references to $this->showVariable(), $this->data, $this->wrap() and $this->unwrap(). That's what I'm going to implement.

The showVariable function shows the variable's content. wrap and unwrap is called on each iteration to provide closure.

Here is my implementation:

class TemplateEngine {
    function showVariable($name) {
        if (isset($this->data[$name])) {
            echo $this->data[$name];
        } else {
            echo '{' . $name . '}';
        }
    }
    function wrap($element) {
        $this->stack[] = $this->data;
        foreach ($element as $k => $v) {
            $this->data[$k] = $v;
        }
    }
    function unwrap() {
        $this->data = array_pop($this->stack);
    }
    function run() {
        ob_start ();
        eval (func_get_arg(0));
        return ob_get_clean();
    }
    function process($template, $data) {
        $this->data = $data;
        $this->stack = array();
        $template = str_replace('<', '', $template);
        $template = preg_replace('~\{(\w+)\}~', 'showVariable(\'$1\'); ?>', $template);
        $template = preg_replace('~\{LOOP:(\w+)\}~', 'data[\'$1\'] as $ELEMENT): $this->wrap($ELEMENT); ?>', $template);
        $template = preg_replace('~\{ENDLOOP:(\w+)\}~', 'unwrap(); endforeach; ?>', $template);
        $template = '?>' . $template;
        return $this->run($template);
    }
}

In wrap() and unwrap() function, I use a stack to keep track of current state of variables. Precisely, wrap($ELEMENT) saves the current data to the stack, and then add the variables inside $ELEMENT into current data, and unwrap() restores the data from the stack back.

For extra security, I added this extra bit to replace < with PHP echos:

$template = str_replace('<', '', $template);

Basically to prevent any kind of injecting PHP codes directly, either , <%, or