Alter WordPress post title and body in view mode only - php

Question

I am looking for the way how to alter a WordPress post title and body when it is displayed to a normal user. But not in any other context, ie in admin module.
The task at hand is to fetch a query parameter, carry out some calls to external webservice and database operations and replace some text in both title and body. The <title> tag should also contain the changed title.
I do not look for a plugin solution, but rather were I should include a php file with all the code that does all the necessary processing.
My expectation was that I don't have to deeply meddle with the theme files. Of course, I could inject my code in the respective theme's page.php or content.php file. But I'd like to do it in less intrusive way, for example by including my functions_custom.php file in the top of functions.php, and this file would contain a collection of functions and add_filter() calls to hook those functions on certain events. Is that possible to achieve my goal that way?
This is my first attempt:
<?php
function alter_title( $title, $id = null ) {
return 'Altered title: ' . $title;
}
add_filter( 'the_title', 'alter_title', 10, 2 );
?>
This causes change in all the post titles in all contexts, including the post list in the Dashboard. But I need it to be altered only in view context (this also does not influence the text used in the <title> tag). Perhaps I can sniff this context somehow, and engage the alteration only when the view mode is detected?

Answer 1

While ago I needed to do similar thing and my fast and short workaround was to have an "API" (
Created a template for that specific post type and using PHP generated a post ID indicator:
$post = get_post(); echo "var post_id = '".$post->ID."';";
I created a custom API that "takes" $_POST request with "post_id" param and it would fetch adequate/custom (in your case a content that will be shown to the user) content from database for the post with the post_id from $_POST request.
Then for every post there would be an ajax request to that API which sends post_id and fetches all the needed info (in your case post title and body) and then using eg. jQuery
.append() would populate post title with response post title and body too, respectively.
Also, if you'd like to avoid a extra request than you should try to generate that 'user-visible' content with PHP. That would mean you need to collect the content before loading the page and echoit in the place of default content.
I suppose you should create a function in functions.php that takes an $post->ID and fetches title and body from the database. Then you should call that function on every loop and single post template, if you understand me.

Answer 2

is_admin() will return true if you are viewing an admin page.
So you could do this:
function alter_title( $title, $id = null ) {
if(is_admin()){
return $title;
}else{
return 'Altered title: ' . $title;
}
}
add_filter( 'the_title', 'alter_title', 10, 2 );