php shortcode function to add other sum other shortcode values - php

Question

im doing some web designing with wordpress at the moment.
I have created a page with a web form where a client can input some information (name, email, invoice number, price, gst, etc).
I used a plugin called contact form 7 to provide the web form, when the user inputs all of their information, the plugin then emails an html formatted invoice to my email address, with the fields occupied by shortcodes which take on the value from the web form.
For example, in the name field of my invoice table, i enter [first-name] and the name the user inputs gets emailed to me in the invoice.
I need to find a way to sum the value of two of the other fields, one of the fields on my invoice form is called total, which should be equal to [gst]+[price] that the user inputs on the web form.
Ive tried to look for a php shortcode function that can take its arguments as the values of other shortcodes, but havent had any luck. I have never really used php before either so wouldnt know how to write one.
I managed to find this, which doesnt seem to work, as when the email comes through all i see is [sumsc][gst] [price][/sumsc]
add_shortcode('sumsc','sumsc_func');
function sumsc_func( $atts, $content = null ) {
$sum=0;
$content=str_replace(array(" ","] [","]["),array(" ","][","]|["),$content);
$codes=explode("|",$content);
foreach($codes as $code){
$sum+=do_shortcode($code);
}
return " <div>".$sum."
</div>";
}
Any help would be greatly appreciated, I also need to the functionality to be able to multiply a shortcode value by a certain number. For example the price needs to be divided by 0.6 to give the quantity which appears on the invoice. Thanks!

Answer 1

Create a hidden field in the form say with a unique id say it fields_sum.
Use jquery on that page and catch form submission event. Get values of those fields, sum it and set the result to fields_sum field. And then use field shortcode where you want.
jQuery script would be something like (Algorithm)
$(document).ready(function(){
$("your_form_id").submit(function(e){
// get value of field one
// get value of field two
// sum them
// set sum to the hidden field
});
});
I hope this works and enough to get a solution like this.