Extending Timber - wordpress

Question

I'm using Timber for the first time, and I find that it is hard to convert my pure PHP thinking to this templating model.
What I'm confused about at the moment is using a date which is an input field, not the post date.
So I've got a repeater field from ACF. It has three sub-fields: release_date, document_file, and document_title. My release date format is YYYY-MM-DD.
As you might have guessed, this repeater field is output as a list of PDFs.
So far so good, but then I want some advanced functionality - namely, to have the PDFs display by release_date by default. I also want to be able to filter by the year, i.e. - if you click "2015", it would only show the documents from that year.
I know exactly how I would do this in straight WordPress, but I'm pretty confused making it on Timber. I've been trying to do it using a custom filter, but I have felt what I actually want is a custom class?
In addition, when I installed Timber it didn't come with the starter theme, so I did a search and downloaded one from GitHub. I've got a feeling this is a legacy version though, because the file structure and syntax doesn't seem to match the documentation.
Downloaded from here: https://github.com/timber/starter-theme
But for example this code in the starter theme functions.php:
function add_to_twig( $twig ) {
/* this is where you can add your own functions to twig */
$twig->addExtension( new Twig_Extension_StringLoader() );
$twig->addFilter('split_date', new Twig_SimpleFilter('split_date', array($this, 'split_date')));
return $twig;
}
Doesn't quite match the syntax in https://github.com/timber/timber/wiki/Extending-Timber under "Adding to Twig".

Answer 1

Here are a few helper functions to make it easy for me to extend timber.
function add_context_var( $key, $var ) {
add_filter( 'timber_context', function ( $context ) use ( $key, $var ) {
$context[ $key ] = $var;
return $context;
} );
}
function add_context_func( $key, $callback ) {
add_filter( 'timber/twig', function ( $twig ) use ( $key, $callback ) {
$twig->addFunction( new \Twig_SimpleFunction( $key, $callback ) );
return $twig;
} );
}
function add_to_context( $key, $val ) {
if ( is_callable( $val ) ) {
add_context_func( $key, $val );
} else {
add_context_var( $key, $val );
}
}
function add_to_context_filter( $key, $callback ) {
add_filter( 'get_twig', function ( $twig ) use ( $key, $callback ) {
$twig->addExtension( new Twig_Extension_StringLoader() );
$twig->addFilter( new Twig_SimpleFilter( $key, $callback ) );
return $twig;
} );
}
//php file
add_to_context("blue", "this key is blue")
add_to_context("red", function($extra = ""){
return "this key is red and it has $extra";
})
add_to_context_filter( "relative_link", function ( $content ) {
return str_replace( "http://", "//", $content );;
} );
//twig file
color: {{ blue }}
color: {{ red("a function parameter") }}
github: {{ "http://github.com/"|relative_link }}
//output html
color: this key is blue
color: this key is red and it has function parameter
github: //github.com/