/**
 * Tries to force the minicalendar widget to show the month of the next upcoming event by default, rather
 * than simply showing the current month (which might be empty).
 */
class Tribe_Advance_Minical
{
    protected $target_date = false;

    /**
     * Sets up auto advance for minicalendar widgets. If an optional target date is provided that will be used to
     * set the month.
     *
     * @param bool $target_date
     */
    public function __construct($target_date = false) {
        if (is_string($target_date)) $this->set_target_date($target_date);
        add_filter('widget_display_callback', array($this, 'advance_minical'), 20, 2);
    }

    /**
     * Basic check to help filter out spurious date formats.
     *
     * @param $date
     */
    protected function set_target_date($date) {
        if (1 === preg_match('#^\d{4}-\d{2}(-\d{2})?$#', $date))
            $this->target_date = $date;
    }

    public function advance_minical($instance, $widget) {
        if ('tribe-mini-calendar' !== $widget->id_base || isset($instance['eventDate'])) return $instance;
        add_action('tribe_events_before_view', array($this, 'modify_list_query'), 5);
        $instance['eventDate'] = $this->determine_date();
        return $instance;
    }

    public function modify_list_query($template) {
        if (false === strpos($template, 'mini-calendar/list.php')) return;
        add_action('parse_query', array($this, 'amend_list_query'));
    }

    public function amend_list_query($query) {
        remove_action('parse_query', array($this, 'amend_list_query')); // Run this once only
        $the_query = $query->query_vars;

        $the_query['start_date'] = $this->determine_date() . '-01';
        $last_day = TribeDateUtils::getLastDayOfMonth(strtotime($the_query['start_date']));
        $the_query['end_date'] = substr_replace($the_query['start_date'], $last_day, -2);
        $the_query['end_date'] = TribeDateUtils::endOfDay($the_query['end_date']);

        $query->query_vars = $the_query;
    }

    protected function determine_date() {
        return (false !== $this->target_date) ? $this->target_date : $this->next_upcoming_date();
    }

    protected function next_upcoming_date() {
        $next_event = tribe_get_events(array(
            'eventDisplay' => 'upcoming',
            'posts_per_page' => 1
        ));

        if (empty($next_event) || ! isset($next_event[0]->EventStartDate)) return date('Y-m');
        return substr($next_event[0]->EventStartDate, 0, 7);
    }
}

/**
 * If we don't pass a parameter it will try to advance the calendar to the same month as the next upcoming event.
 * However, we can also pass in a specific month:
 *
 *     new Tribe_Advance_Minical('2014-12'); // Set it to December 2014
 */
new Tribe_Advance_Minical();