/**
 * WPSE Category Specific Widget
 *
 * This widget will change post according to the current category being viewed.
 *
 * @package   WPSE Category Specific Widget
 * @author    Pieter Goosen
 * @license   GPL-2.0+
 * @requires  PHP 5.4+
 * @requires  Categories Images Plugin https://wordpress.org/plugins/categories-images/
 * @ref       http://wordpress.stackexchange.com/q/158337/31545
 *
 */

class WPSE_Category_Specific_Widget extends WP_Widget {

    /**
     * wpse-category-specific-widget
     *
     * Unique identifier for your widget.
     *
     *
     * The variable name is used as the text domain when internationalizing strings
     * of text. Its value should match the Text Domain file header in the main
     * widget file.
     *
     * @since    1.0.0
     *
     * @var      string
     */
    protected $widget_slug = 'wpse-category-specific-widget';

    /*--------------------------------------------------*/
    /* Constructor
    /*--------------------------------------------------*/

    /**
     * Specifies the class name and description, instantiates the widget,
     * loads localization files, and includes necessary stylesheets and JavaScript.
     */
    public function __construct() {

        parent::__construct(
            $this->get_widget_slug(),
            __( 'WPSE Category Specific Widget', $this->get_widget_slug() ),
            array(
                'classname'  => $this->get_widget_slug().'-class',
                'description' => __( 'This widget will change post according to the current category being viewed.', $this->get_widget_slug() )
            )
        );


        // Refreshing the widget's cached output with each new post
        add_action( 'save_post',    array( $this, 'flush_widget_cache' ) );
        add_action( 'deleted_post', array( $this, 'flush_widget_cache' ) );
        add_action( 'switch_theme', array( $this, 'flush_widget_cache' ) );

    } // end constructor


    /**
     * Return the widget slug.
     *
     * @since    1.0.0
     *
     */
    public function get_widget_slug() {
        return $this->widget_slug;
    }

    /*--------------------------------------------------*/
    /* Widget API Functions
    /*--------------------------------------------------*/

    /**
     * Outputs the content of the widget.
     *
     * @param array args  The array of form elements
     * @param array instance The current instance of the widget
     */
    public function widget( $args, $instance ) {


        // Check if there is a cached output
        $cache = wp_cache_get( $this->get_widget_slug(), 'widget' );

        if ( !is_array( $cache ) )
            $cache = array();

        if ( ! isset ( $args['widget_id'] ) )
            $args['widget_id'] = $this->id;

        if ( isset ( $cache[ $args['widget_id'] ] ) )
            return print $cache[ $args['widget_id'] ];

        // go on with your widget logic, put everything into a string and …


        extract( $args, EXTR_SKIP );

        $widget_string = $before_widget;


        ob_start();

            if( is_category() || is_tax() ) {

                // Get the image from the category or taxonomy term
                if (function_exists('z_taxonomy_image_url')) {

                    echo '<p><img src="' . z_taxonomy_image_url() . '"/></p>';

                }

                // Create the custom query
                $queried_object = get_queried_object( 'term' );
                $taxonomy = $queried_object->taxonomy;
                $term = $queried_object->term_id;

                $args = [
                    'posts_per_page'    => 1,
                    'order'             => 'DESC',
                    'orderby'           => 'rand',
                    'tax_query'         => [
                        [
                        'taxonomy'      => $taxonomy,
                        'field'         => 'term_id',
                        'terms'         => $term
                        ]
                    ]
                ];

            }elseif( !is_404() ) {

                $args = [
                    'post_type'         => 'any',
                    'posts_per_page'    => 1,
                    'orderby'           => 'rand'
                ];
            }


            $q = new WP_Query( $args );

            if($q->have_posts()) {
                while($q->have_posts()) {
                    $q->the_post(); ?>

                        <p><?php the_title(); //  Display post title ?></p>

                        <?php if ( has_post_thumbnail() ) { // check if the post has a Post Thumbnail assigned to it.
                            the_post_thumbnail();
                        } ?>

                        <p><?php the_excerpt(); // Show an excerpt of the post ?></p>

                <?php }
            }
            wp_reset_postdata();

        $widget_string .= ob_get_clean();
        $widget_string .= $after_widget;


        $cache[ $args['widget_id'] ] = $widget_string;

        wp_cache_set( $this->get_widget_slug(), $cache, 'widget' );

        print $widget_string;

    } // end widget


    public function flush_widget_cache()
    {
        wp_cache_delete( $this->get_widget_slug(), 'widget' );
    }
    /**
     * Processes the widget's options to be saved.
     *
     * @param array new_instance The new instance of values to be generated via the update.
     * @param array old_instance The previous instance of values before the update.
     */
    public function update( $new_instance, $old_instance ) {

        $instance = $old_instance;

        // TODO: Here is where you update your widget's old values with the new, incoming values

        return $instance;

    } // end widget

    /**
     * Generates the administration form for the widget.
     *
     * @param array instance The array of keys and values for the widget.
     */
    public function form( $instance ) {

        // TODO: Define default values for your variables
        $instance = wp_parse_args(
            (array) $instance
        );


    } // end form


} // end class

add_action( 'widgets_init', function(){
     register_widget( 'WPSE_Category_Specific_Widget' );
});