Miniature JSON API for WordPress, returning posts of a specified post type in JSON format

wp-mini-json-api.php

<?php

class WPMiniJSONAPI {

    const API_ACTION_QUERY_VAR = "my-api";
    const API_PERMALINK_PART = "api";
    const API_EVENTS_PERMLINIK_PART = "events";
    const API_OUTPUT_FORMAT = "json";
    const API_EXPORT_EVENTS = "export-events";

    protected $version;

    public function __construct($version = 1) {

        $this->version = $version;

        add_action( 'init', array(&$this, 'setup_api_permalinks') );
        add_action( 'wp', array(&$this, 'handle_api_request') );
    }

    public function setup_api_permalinks() {

        global $wp;
        $wp->add_query_var(self::API_ACTION_QUERY_VAR);

        add_rewrite_rule(
            sprintf('%s/%s/%s.%s?', self::API_PERMALINK_PART, $this->version, self::API_EVENTS_PERMLINIK_PART, self::API_OUTPUT_FORMAT),
            sprintf('index.php?%s=%s&version=', self::API_ACTION_QUERY_VAR, self::API_EXPORT_EVENTS, $this->version),
            'top'
        );

        // Will rebuild rewrite rules on each page load - don't use in production
        // Instead, just load permalinks settings page once :)
        if (WP_DEBUG) {
            flush_rewrite_rules( $hard = true );
        }
    }

    public function handle_api_request() {

        global $wp_query;

        $api_action = get_query_var( self::API_ACTION_QUERY_VAR );

        if (empty($api_action))
            return;

        switch ($api_action) {
            case self::API_EXPORT_EVENTS:
    
                $post_type = 'event';
                
                // It would be wise to use the WP Obejct Cache / Transients API here,
                // so as not to query the database on each load. 
                // You could even use a really large expiration time and manually
                // clear the cache when the relevant data changes.
                
                $data = get_posts(array(
                    'post_type' => $post_type,
                    'number_posts' => -1,
                    'orderby' => 'date',
                    'order' => 'ASC',
                ));

                global $wpdb
                $mod_time = strtotime( $wpdb->query( $wpdb->prepare( "SELECT MAX(post_modified_gmt) FROM $wpdb->posts WHERE post_type %s", $post_type ) ) );
                if ($mod_time) {
                    header( 'Last-Modified: ' . gmdate( 'D, d M Y H:i:s', $mod_time ) . ' GMT' );
                }
                header('Content-Type: application/json; charset=utf8');

                echo json_encode($data);

                exit();
                break;
        }

    }
}

$api = new WPMiniJSONAPI();