<?php

class WP_Post_IDs_Iterator implements Iterator {
    private $limit = 100;
    private $post_ids;
    private $ids_left;
    private $results = array();

    public function __construct( $post_ids, $limit = null ) {
        $this->db       = $GLOBALS['wpdb'];
        $this->post_ids = $post_ids;
        $this->ids_left = $post_ids;
        if ( ! is_null( $limit ) ) {
            $this->limit = $limit;
        }
    }

    public function current() {
        return $this->results[ $this->index_in_results ];
    }

    public function key() {
        return $this->global_index;
    }

    public function next() {
        ++$this->index_in_results;
        ++$this->global_index;
    }

    public function rewind() {
        $this->results          = array();
        $this->global_index     = 0;
        $this->index_in_results = 0;
        $this->ids_left         = $this->post_ids;
    }

    public function valid() {
        if ( isset( $this->results[ $this->index_in_results ] ) ) {
            return true;
        }
        if ( empty( $this->ids_left ) ) {
            return false;
        }
        $has_posts = $this->load_next_posts_from_db();
        if ( ! $has_posts ) {
            return false;
        }
        $this->index_in_results = 0;
        return true;
    }

    private function load_next_posts_from_db() {
        $next_batch_post_ids = array_splice( $this->ids_left, 0, $this->limit );
        $in_post_ids_sql     = _wp_export_build_IN_condition( 'ID', $next_batch_post_ids );
        $this->results       = $this->db->get_results( "SELECT * FROM {$this->db->posts} WHERE {$in_post_ids_sql}" );
        if ( ! $this->results ) {
            if ( $this->db->last_error ) {
                throw new WP_Iterator_Exception( "Database error: {$this->db->last_error}" );
            } else {
                return false;
            }
        }
        return true;
    }
}