Dynamic post / custom post type filter using taxonomies, categories and tags.

dynamic-post-filter.php

<?php 

$post_type = 'posts';
$post_count = 6;

/**
* @var [$current_post_type_taxonomies] Get all the taxonomies registered in wordpress
* @var [$actual_taxonomies] Remove post_format from the taxonomies
* @var [$tax_terms_array] Create an empty array for the taxonomy terms, this later is used to populate the tax_query in the loop
*/
$current_post_type_taxonomies = get_object_taxonomies( $post_type, 'names'  );
$actual_taxonomies = ( in_array('post_format', $current_post_type_taxonomies) ) ? array_diff( $current_post_type_taxonomies, array('post_format') ) : $current_post_type_taxonomies;
$tax_terms_array = array(); // taxonomy arguments are set within the loop
if ( !empty($actual_taxonomies) ) :
    $filters_wrapper = array('<div class="filters"><br id="filters"><form action="#filters" method="GET"><h3 class="button arrow purple200">You may want to use these filters</h3>', '</form></div>');
    echo $filters_wrapper[0];

    /**
        * Automatgically create the filters
        */
    foreach ( $actual_taxonomies as $atax ) :
        // Create the Placeholder text for chosen dropdown menus.
        $placeholder = str_replace('_', ' ', $atax);
        // Simple way to make a string plural
        $last_letter = substr($atax, -1);
        if ( $last_letter != 's' ) :
            // If it ends in a "Y" replace that with "IES" other wise add an "S"
            $placeholder = ( $last_letter == 'y' ) ? substr($placeholder, 0, -1) . 'ies' : $placeholder . 's';
        endif;
        // Select menu wrapper 
        // Using jQuery chosen plugin, so requires a data-attr and empty option to display the placeholder.
        $select_tag = array('<div class="filter"><select name="' . $atax . '" id="' . $atax . '" data-placeholder="All ' . $placeholder . '">', '</select></div>');
        
            /**
                * Use get_terms to grab all the taxonomies including the default tag and category.
                * These then create the options for the dropdown menu
                */
            $taxonomies = get_terms( array(
                'taxonomy' => $atax,
                'orderby' => 'name',
                'order'   => 'ASC',
                'hide_empty' => false
            ) );
            
            echo $select_tag[0];
            echo '<option value=""></option>'; // Empty option for placeholder
            foreach ( $taxonomies as $tax ) :

                $taxonomy_slug = $tax->slug;
                $taxonomy_name = $tax->name;
                $selected = ( isset($_GET[$atax]) && !empty( $_GET[$atax] ) && $_GET[$atax] == $taxonomy_slug) ? 'selected' : '';

                echo '<option value="' . $taxonomy_slug . '" ' . $selected . '>' . $taxonomy_name . '</option>';
            
            endforeach; // foreach (  as  ) :
            echo $select_tag[1];
        

            /**
                * Check the query string for our custom taxonomies.
                * Skip the default category and post_tags...
                * If the taxonomy has a term in the query string create the terms array
                */
            if ($atax == 'category' || $atax == 'post_tag') continue;
            if ( isset($_GET[$atax]) && !empty( $_GET[$atax] ) ) :
                $tax_terms_array[] = array(
                                'taxonomy' => $atax,
                                'field'    => 'slug',
                                'terms'    => array( $_GET[$atax] ),
                            );
            endif;
    endforeach; // foreach ( $actual_taxonomies as $atax ) :
    
        echo '<button type="submit" class="submit button"><img src="' . get_template_directory_uri() . '/assets/img/arrow/right.svg"></button>';
    echo $filters_wrapper[1];


endif; // if ( !empty($remove_post_format) ) :


    /**
     * Start the post loop
     *
     * @return  [type]  [return description]
     */

    // Set the args for the post loop and begin the query.
    $paged_key = ( is_front_page() ) ? 'page' : 'paged';// Front page uses "page" not "paged"

    $paged = ( get_query_var( $paged_key ) ) ? get_query_var( $paged_key ) : 1;
    $default_args = array(
        'post_type' => $post_type,
        'posts_per_page' => $post_count,
        'paged' => $paged
    );
    /**
     * Build the arguments for the post loop
     * 
     * @var [$tax_relation] merge the relationship into the taxonomy array
     * @var [$tax_args, $cat_args, $tag_args, $args] create all the arguments for each of the taxonomies.
     */
    $tax_relation = array_merge($tax_terms_array, array('relation' => 'AND'));
    $tax_args = ( !empty( $tax_terms_array ) ) ? array( 'tax_query' => $tax_relation ) : array();
    $cat_args = ( isset($_GET['category']) && !empty( $_GET['category'] ) ) ? array('category_name' => $_GET['category'] ) : array('');
    $tag_args = ( isset($_GET['post_tag']) && !empty( $_GET['post_tag'] ) ) ? array('tag' => $_GET['post_tag'] ) : array('');
    $args = array_merge($default_args, $cat_args, $tag_args, $tax_args);

    // get the posts and loop the shit out of it.
    $temp = $wp_query; 
    $wp_query = null; 
    $wp_query = new WP_Query( array_filter($args) ); # array_filter out the empty arrays if they exist.
    // Start the loop
    if ( $wp_query->have_posts() ) :

        echo '<div class="post-wrapper">';
        // Time for the Post loop
        while ($wp_query->have_posts()) : $wp_query->the_post();
            echo '<div class="post clearfix">'
                .   get_the_post_thumbnail( $post->ID, 'column_image_full', array( 'class' => 'alignleft' ) )
                .   '<article>'
                .       '<h3>' . get_the_title() . '</h3>'
                .       '<div class="all-terms">' . wpdocs_custom_taxonomies_terms_links() . '</div>'
                .       wpautop(excerpt(25))
                .       '<a href="' . get_the_permalink() . '" class="post-link"><span class="logo-button">More details</span></a>'
                .   '</article>'
                . '</div>';
            
        endwhile; // foreach ($post_loop as $pl ) :

        // Using https://wordpress.org/plugins/wp-paginate/
        // But could be standard pagination here
        if(function_exists('wp_paginate')):
            wp_paginate(); 
        endif;
        
        
        $wp_query = null; 
        $wp_query = $temp;  // Reset
        echo '</div>';
    else :
        echo '<h2>Sorry no posts could be found, please try a different search!</h2>';
    endif; // if ( $wp_query->have_posts() ) :