A plugin for the flat file CMS Pico. Using this plugin, you can use the Tags and Filter headers in the page meta block in order to generate lists of pages matching specific tags. This creates the possibility to build index pages which show only posts of a certain type.

The Tags header accepts a comma-separated list of tags that apply to the current page.

The "Filter" header also accepts a comma-separated list of tags, but instead specifies which pages are included when filtering the pages array. The plugin makes a Twig filter available, "apply_tag_filter", which you can use on the pages array in your templates to be able to filter pages matching specific tags. On a page with no "Filter" header this is a no-op, but on a page that specifies the header "Filter: foo, bar", pages|apply_tag_filter will return only pages having at least one of those two tags.

If you were using an earlier version of the plugin, the current version will not work as before. Previously the pages array was directly modified to apply the page's filter. This approach was not compatible with other Pico plugins and themes which depend on the pages array to contain all pages.

Instead, this plugin now makes a Twig filter called apply_tag_filter available, which can be used in your templates to filter the pages array on demand: {% set filtered_pages = pages|apply_tag_filter %}. This also makes it possible to combine with other plugins that behave similarly: {% set results = pages|apply_tag_filter|apply_search|paginate %}

Copy the file PicoTags.php to the plugins subdirectory of your Pico installation directory. That's it!

To assign tags to a page, specify the Tags header inside the meta header block at the top of your file, e.g.:

---
Title: My first blog post
Date: 2015-09-16 13:37:00
Description: A thrilling, must-read blog post about pancakes.
Tags: blog, pancakes
Template: blog-post
---

Optionally, you can also use YAML sequences for Tags:

Tags:
  - blog
  - pancakes

To only show pages with certain tags on another page, use the Filter header, e.g.:

---
Title: Blog
Filter: blog
Template: blog-list
---

These are all my blog posts:

Actually looping through the filtered list of pages (in the above case, pages tagged blog) to display them would be done in the template file, e.g.:

{{ content }}
{% for page in pages|apply_tag_filter if page.title %}
    <article>
        <h2><a href="{{ page.url }}">{{ page.title }}</a></h2>
        <p>{{ page.description }}</p>
    </article>
{% endfor %}

You can list documents with the same tags as the current page by including something like this in your template:

<aside> 
{% for tag in meta.tags %}
    <h3>More pages tagged: <a href="{{ base_url }}/tags/?tag={{ tag }}">{{ tag }}</a></h3>
    <ul>
    {% for page in pages if page.title and page.meta.tags %}
        {% if tag in page.meta.tags and not (page.id ends with 'index') and page.id != current_page.id %}
        <li>
            <a href="{{ page.url }}">{{ page.title }}</a> - {{ page.description }}
        </li>
        {% endif %}
    {% endfor %}
    </ul>
{% endfor %}
</aside> 

The plugin also makes the function get_all_tags() available in your templates. This example uses it to create a dedicated tags page for either showing a list of available tags, or a list of documents with a specific tag:

---
Title: Tags
Template: tags
---

Content can go here

{% extends "index.twig" %}

{% set tag = url_param('tag', 'string') %}
{% set tags = get_all_tags() %}

{% block content %}
{{ parent() }}
{% if tag %}
    {# List of all pages with a specified tag #}
    <ul>
    {% for page in pages if page.title and tags and not (page.id ends with 'index') %}
        {% if page.meta.tags is iterable %}
            {% set pageTags = page.meta.tags %}
        {% else %}
            {% set pageTags = page.meta.tags|split(',') %}
        {% endif %}
        
        {% for pageTag in pageTags %}
            {% if pageTag|trim == tag %}
                <li>
                    <a href="{{ page.url }}">{{ page.title }}</a>
                </li>
            {% endif %}
        {% endfor %}
    {% endfor %}
    </ul>
{% else %}
    {# List of all tags used on the site #}
    <ul>
    {% for tag in tags|sort %}
        <li><a href="{{current_page.url}}/?tag={{ tag }}">{{ tag }}</li>
    {% endfor %}
    </ul>
{% endif %}
{% endblock content %}

This would make e.g. https://www.example.com/tags?tag=pancakes show a list of documents with the tag pancakes, whereas https://www.example.com/tags would show a list of all available tags.