Abstract class for dealing with common tasks over WordPress post objects

wp_post_objects.php

<?php

/**
 * Basically, a posts objects iterator
 * @author Felipe Lavín Z. <felipe@yukei.net>
 **/
abstract class av_post_objects{
	public $id;
	public $meta;
	public $type;	
	public $i = 0;
	public $params;
	public $query;
	function __construct($args=null){
		$s = wp_parse_args($args, array(
			'loop_wrap' => 'div',
			'loop_class' => '',
			'loop_id' => '',
			'loop_elements' => 'div',
			'elements_class' => '',
			'is_hatom' => false, // if set to true, add hatom classes
			'postmeta' => false, // name of a post_meta key that would be used in each post
			'echo' => true
		));
		$s = array_merge($s, $this->defaults);
		$this->params = (object)$s;
		$this->id = get_class($this);
	}
	/**
	 * Register post type
	 **/
	abstract function register_type();
	/**
	 * Get post objects
	 * @param array $args Array or query string of arguments
	 * @return object WP_Query object
	 **/
	function get($args=null){
		$s = wp_parse_args( (array)$args, (array)$this->params );
		// set this to a class variable, so we can have access to the WP_Query properties
		$this->query = new WP_Query( $s );
		return $this->query;
	}
	/**
	 * The "view" method should be implemented by each extending class
	 * Format item output for each of the query results
	 * @param $post A $post object
	 * @args $args
	 * @return string Item output
	 **/
	abstract function view($post=null, $args=null);
	/**
	 * Loop should handle all objects retrieving and looping
	 * and let the view method handle the display of each item
	 * Class constructors can define the wrapping and other presentational
	 * attributes that should be applied on the loop
	 **/
	function loop($objects=null, $view=null){
		global $post;
		$the_post = $post;
		if ( !$objects ) $objects = $this->get();
		$out = '';
		if ( $objects->have_posts() ) {
			apply_filters('pre_'. $this->id .'_loop', &$out, $objects);
			$out .= '<'. $this->params->loop_wrap . $this->get_wrap_classes($this->params->loop_class) . (( $this->params->loop_id ) ?' id="'. esc_attr($this->params->loop_id) .'"' : '' ) .'>';			
			// here there should be a variable-name action, passing $objects as argument
			// do_action ...
			apply_filters('start_'. $this->id .'_loop', &$out, $objects);
			while ( $objects->have_posts() ) {				
				$objects->the_post(); $this->meta = null;
				$this->meta = $this->get_meta($post);
				// here there should be a variable-name action, passing the post as argument
				// do_action...
				//  perhaps this should be captured in an output buffer, just to make sure
				// that the view action it's not echoing, instead of returning
				$out .= '<'. $this->params->loop_elements . $this->get_item_classes($this->params->item_class) .' id="'. esc_attr($post->post_name) .'">';
					$out .= !is_null($view) && is_callable($view) ? call_user_func($view) : $this->view();
				$out .= '</'. $this->params->loop_elements .'>';
				$this->i++;
			}
			apply_filters('end_'. $this->id .'_loop', &$out, $objects);
			$out .= '</'. $this->params->loop_wrap .'>';
			apply_filters('post_'. $this->id .'_loop', &$out, $objects);
			wp_reset_query();
			$post = $the_post;
			// here there shoud be a variable-name action, so we can do stuff such as removing query filters 
		} else {
			$out .= '<p>'. __('No posts have been found') .'</p>';
		}
		if ( $this->params->echo ) echo $out;
		else return $out;
	}
	public function get_meta($post=null){
		if ( is_null($post) ) global $post;
		if ( $this->params->postmeta ) {
			if ( is_string($this->params->postmeta) ) {
				$meta = get_post_meta($post->ID, $this->params->postmeta, true);
				$this->meta = $post->meta = $meta ? $meta : null;
			} elseif ( is_array($this->params->postmeta) ) {
				$this->meta = $post->meta = $this->get_meta_arr();
			}
		}
	}
	/**
	 * Fetch various meta fields and set them to $this->meta so we can access
	 * them in the posts loop
	 * @param array $metas List of meta keys to fetch
	 * @return array Associative array with meta keys as keys and values as values
	 **/
	public function get_meta_arr( $metas = null ){
		global $wpdb, $post; $out = new stdClass;
		if ( is_null($metas) ) $metas = $this->params->postmeta;
		// If metas is an associative array, we'll use our custom names as keys
		if ( $this->is_associative($metas) ) {
			$assoc = true;
			$names2keys = array_flip($metas);
		}
		// Prepare meta keys for query
		array_walk($metas, array($this, 'prepare_meta_keys'));
		(array)$meta_values = $wpdb->get_results("SELECT meta_key, meta_value FROM $wpdb->postmeta WHERE post_id = $post->ID AND meta_key IN(". implode(',', (array)$metas) .")");
		if ( $assoc ) {
			$out = $this->map_meta_keys($meta_values, $names2keys);
		} else {
			foreach ( $meta_values as $m ) {
				$out->{$m->meta_key} = maybe_unserialize($m->meta_value);
			}
		}
		return $out;
	}
	/**
	 * Map meta_keys and meta_values to our custom meta names
	 * @param array $values DDBB Query results
	 * @param array $names2keys Associative array with meta keys as keys and our custom names as values
	 * @return array Associative array with custom keys
	 **/
	private function map_meta_keys($values, $names2keys){
		$out = new stdClass;
		foreach ( $values as $v ) {
			$out->$names2keys[$v->meta_key] = maybe_unserialize($v->meta_value);
		}
		return $out;
	}
	/**
	 * Add slashes to array keys so they won't be mistaken for columns
	 * @param arr $key The array that's checked
	 * @return void Return by reference
	 * */
	private function prepare_meta_keys(&$key){
		$key = "'$key'";
	}
	/**
	 * Check if it's an associative array
	 * @param array $arr The array that will be tested
	 * @return boolean True if assocative, false if numeric
	 * */
	private function is_associative($arr){
		return !ctype_digit( implode('', array_keys($arr)) );
	}
	public function get_item_classes($custom=null){
		$out = ' class="'. $this->params->post_type .'-entry';
		$out .= ( $this->i%2 ) ? ' odd' : ' even';
		if ( $this->i === 0 ) $out .= ' first';
		if ( $this->i === ( $this->query->found_posts - 1 ) ) $out .= ' last';
		if ( $custom ) $out .= ' '. esc_attr($custom);
		if ( $this->params->hatom ) $out .= ' hentry';
		$out .= '"';
		return $out;
	}
	public function get_wrap_classes($custom=null){
		$out = ' class="'. $this->params->post_type .'-loop';
		if ( $custom ) $out .= ' '. esc_attr($custom);
		if ( $this->params->hatom ) $out .= ' hfeed';
		$out .= '"';
		return $out;
	}
}

?>