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// The following code will not do anything and just serves as a demonstration.
$response = new WP_REST_Response( 'This is some data' );

// To get the response data we can use this method. It should equal 'This is some data'.
$our_data = $response->get_data();

// To access the HTTP status code we can use this method. The most common status code is probably 200, which means OK!
$our_status = $response->get_status();

// To access the HTTP response headers we can use this method.
$our_headers = $response->get_headers();

// Register our mock batch endpoint.
function prefix_register_broken_route() {
    register_rest_route( 'my-namespace/v1', '/broken', array(
        // Supported methods for this endpoint. WP_REST_Server::READABLE translates to GET.
        'methods' => WP_REST_Server::READABLE,
        // Register the callback for the endpoint.
        'callback' => 'prefix_get_an_error',
    ) );
}

add_action( 'rest_api_init', 'prefix_register_broken_route' );

/**
 * Our registered endpoint callback. Notice how we are passing in $request as an argument.
 * By default, the WP_REST_Server will pass in the matched request object to our callback.
 *
 * @param WP_REST_Request $request The current matched request object.
 */
function prefix_get_an_error( $request ) {
    return new WP_Error( 'oops', esc_html__( 'This endpoint is currently broken, try another endpoint, I promise the API is cool! EEEK!!!!', 'my-textdomain' ), array( 'status' => 400 ) );
}

// Register our mock endpoints.
function prefix_register_my_routes() {
    register_rest_route( 'my-namespace/v1', '/posts/(?P<id>[\d]+)', array(
        // Supported methods for this endpoint. WP_REST_Server::READABLE translates to GET.
        'methods' => WP_REST_Server::READABLE,
        // Register the callback for the endpoint.
        'callback' => 'prefix_get_rest_post',
    ) );
    register_rest_route( 'my-namespace/v1', '/comments', array(
        // Supported methods for this endpoint. WP_REST_Server::READABLE translates to GET.
        'methods' => WP_REST_Server::READABLE,
        // Register the callback for the endpoint.
        'callback' => 'prefix_get_rest_comments',
        // Register the post argument to limit results to a specific post parent.
        'args' => array(
            'post' => array(
                'description' => esc_html__( 'The post ID that the comment is assigned to.', 'my-textdomain' ),
                'type'        => 'integer',
                'required'    => true,
            ),
        ),
    ) );
    register_rest_route( 'my-namespace/v1', '/comments/(?P<id>[\d]+)', array(
        // Supported methods for this endpoint. WP_REST_Server::READABLE translates to GET.
        'methods' => WP_REST_Server::READABLE,
        // Register the callback for the endpoint.
        'callback' => 'prefix_get_rest_comment',
    ) );
}

add_action( 'rest_api_init', 'prefix_register_my_routes' );

// Grab a post.
function prefix_get_rest_post( $request ) {
    $id = (int) $request['id'];
    $post = get_post( $id );

    $response = rest_ensure_response( array( $post ) );

    $response->add_links( prefix_prepare_post_links( $post ) );

    return $response;
}

// Prepare post links.
function prefix_prepare_post_links( $post ) {
    $links = array();

    $replies_url = rest_url( 'my-namespace/v1/comments' );
    $replies_url = add_query_arg( 'post', $post->ID, $replies_url );
    $links['replies'] = array(
		'href'         => $replies_url,
		'embeddable'   => true,
    );

    return $links;
}

// Grab a comments.
function prefix_get_rest_comments( $request ) {
    if ( ! isset( $request['post'] ) ) {
        return new WP_Error( 'rest_bad_request', esc_html__( 'You must specify the post parameter for this request.', 'my-text-domain' ), array( 'status' => 400 ) );
    }

    $data = array();

    $comments = get_comments( array( 'post__in' => $request['post'] ) );

    if ( empty( $comments ) ) {
        return array();
    }

    foreach( $comments as $comment ) {
        $response = rest_ensure_response( $comment );
        $response->add_links( prefix_prepare_comment_links( $comment ) );
        $data[] = prefix_prepare_for_collection( $response );
    }

    $response = rest_ensure_response( $data );
    return $response;
}

// Grab a comment.
function prefix_get_rest_comment( $request ) {
    $id = (int) $request['id'];
    $post = get_comment( $id );

    $response = rest_ensure_response( $comment );

    $response->add_links( prefix_prepare_comment_links( $comment ) );

    return $response;
}

// Prepare comment links.
function prefix_prepare_comment_links( $comment ) {
    $links = array();
    if ( 0 !== (int) $comment->comment_post_ID ) {
        $post = get_post( $comment->comment_post_ID );
        if ( ! empty( $post->ID ) ) {
        $links['up'] = array(
                'href'       => rest_url( 'my-namespace/v1/posts/' . $comment->comment_post_ID ),
                'embeddable' => true,
                'post_type'  => $post->post_type,
            );
        }
    }
    return $links;
}

/**
 * Prepare a response for inserting into a collection of responses.
 *
 * This is lifted from WP_REST_Controller class in the WP REST API v2 plugin.
 *
 * @param WP_REST_Response $response Response object.
 * @return array Response data, ready for insertion into collection data.
 */
function prefix_prepare_for_collection( $response ) {
	if ( ! ( $response instanceof WP_REST_Response ) ) {
		return $response;
	}

	$data = (array) $response->get_data();
	$server = rest_get_server();

	if ( method_exists( $server, 'get_compact_response_links' ) ) {
		$links = call_user_func( array( $server, 'get_compact_response_links' ), $response );
	} else {
		$links = call_user_func( array( $server, 'get_response_links' ), $response );
	}

	if ( ! empty( $links ) ) {
		$data['_links'] = $links;
	}

	return $data;
}