Flickr-to-WordPress: a class defining a REST API endpoint to determine the local WordPress equivalent of an imported Flickr photo

class-api-routes.php

<?php

/**
 * Class JCHPhotos_Plugin_API_Routes
 *
 * Handles API endpoints for looking up Flickr-to-WordPres translation stuff.
 */

class JCHPhotos_Plugin_API_Routes {

	protected $flickr_username = 'yourflickrusernamehere';

	public function __construct() {
		add_action( 'rest_api_init', array( $this, 'jchphotos_register_rest_routes' ) );
	}

	/**
	 * Register some REST API routes
	 */
	public function jchphotos_register_rest_routes() {

		// Looks like: /wp-json/myphotos/v1/find-by-flickr-url/?flickr-url=https://www.flickr.com/...
		register_rest_route(
			'myphotos/v1',
			'/find-by-flickr-url/',
			array(
				'methods'  => 'GET',
				'callback' => array( $this, 'jchphotos_find_by_flickr_url' ),
				'args'     => array(
					'flickr-url' => array(
						'required'          => true,
						'validate_callback' => array( $this, 'validate_flickr_url' ),
					),
					'width'      => array(
						'sanitize_callback' => static function( $param ) {
							return (int) $param;
						},
					),
					'height'     => array(
						'sanitize_callback' => static function( $param ) {
							return (int) $param;
						},
					),
				),
			)
		);
	}

	/**
	 * Get the local photo post and attachment information, given a Flickr URL and optional width/height.
	 * @param $data
	 */
	public function jchphotos_find_by_flickr_url( $data ) {

		// This is validated by the REST API route, so doing just basic sanitizing here.
		$flickr_url = esc_url_raw( $data['flickr-url'], array( 'https', 'http' ) );

		// Query WordPress for a matching photo post.
		// TODO we may need to loosen up the comparison here
		$matching_photos = get_posts(
			array(
				'post_type'      => 'post',
				'post_status'    => 'publish',
				'posts_per_page' => 1,
				'meta_query'     => array(
					array(
						'key'     => '_flickr_photopage',
						'value'   => $flickr_url,
						'compare' => '=',
					),
				),
			)
		);

		$response = array();

		// If we got some kind of valid result back, use it.
		if ( ! is_wp_error( $matching_photos ) ) {

			// If the result wasn't empty,
			if ( 0 < count( $matching_photos ) ) {

				// Use the first result, since we only asked for one.
				$matching_photo = $matching_photos[0];

				// Prep an API response
				$response = array(
					'result'    => 'found',
					'post_id'   => $matching_photo->ID,
					'permalink' => get_permalink( $matching_photo ),
				);
			} else {
				$response['result'] = 'notfound';
			}

			// If we have a featured image / thumbnail, use it.
			$thumbnail_id = get_post_thumbnail_id( $matching_photo );
			if ( $thumbnail_id ) {
				$response['thumbnail_id'] = (int) $thumbnail_id;

				// If we received a target width and height, then try to get the right intermediate image size.
				if ( $data['width'] && $data['height'] ) {

					$width_for_passing  = (int) $data['width'];
					$height_for_passing = (int) $data['height'];

					// wp_get_attachment_image_src does a thing where if you pass it a width and height,
					// and they aren't in the right proportions of the image itself, it'll return the full
					// size version. By only sending the max, it should come back with the appropriate next size up.
					( max( $width_for_passing, $height_for_passing ) === $height_for_passing ) ? $width_for_passing = 0 : $height_for_passing = 0;

					$thumbnail_url_result = wp_get_attachment_image_src( $thumbnail_id, array( $width_for_passing, $height_for_passing ) );
				} else {
					// Otherwise, use the full size image (often scaled from original)
					$thumbnail_url_result = wp_get_attachment_image_src( $thumbnail_id, 'full' );
				}

				$response['thumbnail_url'] = esc_url( $thumbnail_url_result[0] );

				// Despite the documentation, the returned width/height are only the appropriate display dimensions given
				// the input/desired size, not the actual size of the image URL being returned. This is fine.
				$response['thumbnail_width']  = (int) $thumbnail_url_result[1];
				$response['thumbnail_height'] = (int) $thumbnail_url_result[2];
			}
		} else {
			$response['result'] = 'error';
		}

		wp_send_json( $response );

	}

	/**
	 * Check that the passed Flickr URL is valid.
	 * @param string $flickr_url
	 * @return bool
	 */
	public function validate_flickr_url( $flickr_url = null ) {

		return ( 1 === preg_match( '^https?://(www.)?flickr.com/photos/' . $this->flickr_username . '/\d+/?.*$^', $flickr_url ) );

	}
}

new JCHPhotos_Plugin_API_Routes();