Best practice for including plugin output in a template without using shortcode?

Question

I need your recommendation for the best practice here:

• A custom post type I have created needs a list of attachments at the end of the post content.
• I have created a series of functions that handle displaying the list of appropriate attachments for a post.
• I don't want to use shortcode to insert this attachment list, since every post of this post type should have the list
• I'm looking for a portable, reusable approach

My initial approach was to encapsulate the attachment functions into a standalone plugin. But how to integrate the plugin output into the page if I don't use shortcode?

My solution was to create my own pseudo-template-tag ("the_attachments()") which is defined in the plugin. Then my custom-post-type.php template page uses this pseudo-template-tag right after the_content() and we get our nice list.

But is this really the best approach? Now we have a template that's dependent on an external plugin. If the plugin isn't there, the template "breaks". It's tough to "require" a plugin, from a template perspective because is_plugin_active() is only available at the admin level, and that's probably for a reason (because it's a stupid idea to make a template dependent on a plugin!)

So I'm left with either: A) decouple the plugin output from the template, similar to the way a widget works (if so, how do I pass the $post information to that widget?), or B) embed the "plugin" code within the template functions (but is this then truly portable?)

Answer 1

<?php
// A)
// inside your template
if ( function_exists( 'the_attachment_stuff()' ) )
{
    // do stuff
}
// better/faster
if ( class_exists( 'attachment_plugin_class' ) )
{
    // do stuff
}

// B) 
// inside your template
do_action( 'the_attachment_suff');
// means setting this inside your plugin
// this avoids throwing errors or aborting if the hook isn't in your template
add_action( 'the_attachment_stuff', 'your_callback_fn' );

// C)
function add_attachment_stuff()
{
    if ( ! is_admin() )
        return;

    // the following is guess and theory...
    $content  = get_the_content();
    $content .= the_attachment_stuff(); // in case the attachment_stuff returns instead of echos the result/output.
}
// @link http://codex.wordpress.org/Plugin_API/Action_Reference
// only add on publish, on 'post_save' we would add it multiple times
add_action( 'publish_post', 'add_attachment_stuff', 100 );
add_action( 'publish_phone', 'add_attachment_stuff', 100 );

Answer 2

You can output your plugins function to the_content by adding with a filter.

function ta_post_attachment() {
    if ( is_singular( 'your_custom_post_type' ) {
        // do stuff
        }
}

add_filter( 'the_content', 'ta_post_attachment' );