How to replace custom html tag with html code in php

This is my scenario: In a custom CMS developed in PHP, I need to parse HTML string searching some custom tags to replace them with some HTML code. Here is an example for clarifying:

<h2>Some Title</h2>
<p>Some text</p>
[[prod_id=123]] [[prod_id=165]] // custom tag
<p>More text</p>

I need to find the custom tags and replace them with the template of the item, as a result:

<h2>Some Title</h2>
<p>Some text</p>
<!--Start Product123-->
<p>Title Product 123</p>
<!--End Product123-->
<!--Start Product165-->
<p>Title Product 165</p>
<!--End Product165-->
<p>More text</p>

This would be very helpful, but I need to do something else, I need to detect blocks of tags and add some code before – after the tags, but only once per block of tags. In this example, the final code needed would be something like:

<h2>Some Title</h2>
<p>Some text</p>
<div><!-- Here the start of the block -->
<!--Start Product123-->
<p>Title Product 123</p>
<!--End Product123-->
<!--Start Product165-->
<p>Title Product 165</p>
<!--End Product165-->
</div><!-- Here the end of the block -->
<p>More text</p>

The perfect solution for me would be a function with the original HTML code as argument, and returning the final html code. Any help is appreciated.

Answer

I will advise you to not use Regex along with HTML, this can result in a lot of problems. Instead do something like where you store the text/content of articles and then only process that.

But for the sake of completeness, you can use something like this:

$html = preg_replace_callback("/[[prod_id=(d+)]]/",
    function($matches)
    {
        $prod_id = $matches[1];

        return '<p>Title Product ' . $prod_id . '</p>';
    },
    $html); // where $html is the html you want to process

If you don’t “have” the HTML, then you can use ob_start() and ob_get_clean().

ob_start();
?>

<h2>Some Title</h2>
<p>Some text</p>
[[prod_id=123]] [[prod_id=165]] // custom tag
<p>More text</p>

<?php
$html = ob_get_clean();

// do the regex_replace_callback here

I haven’t tested this, just did it on top of my head. So there might be some typos!