Managing eMail Template Files

I want to maintain multiple email templates.

I created a db table 'email_templates' with fields as follow:

seq int <primary key, auto increment
message_id mediumtext
message_subject varchar(50)
message_text mediumtext
on_date datetime

I am using a rich text editor to edit the message_subject field.

I want to create a text file for each email template and include message_subject & message_text as two records within the .txt file.

I've written a simple after update event to be used on add & edit that would place the email template .txt file in the 'output' folder within the email_templates folder.

On my test system I fully specify the location of the file I wanted to create (this works).

My question is how do I structure the $filename correctly so that it works both on my local webserver (WAMP) and when I upload to my hosting service server.

I guess then the second question is how do I address the saved /email_templates/$filename to use it elsewhere.

Here is my event coding I am trying to test............................................................................................................

// Get fields from the table email_templates

$filename = $values["message_id"];
$subject = $values["message_subject"];
$msg_text = $values["message_text"];

print 'File Name: '.$filename.'
'.'Subject: '.$subject.'
'.'Text: '.$msg_text.'
';

// Construct Filename for eMail Template

$filename = "c:/wamp64/projects/rmac_email/output/email_templates/".$filename.".txt";

print 'Actual File Name: '.$filename.'
';

// Write output file with 2 records (Subject & Text)

$template_file = fopen($filename, "w") or die("Unable to open '$filename'!");
fwrite($template_file, $subject.PHP_EOL);
fwrite($template_file, $msg_text.PHP_EOL);
fclose($template_file);

Thank you//