wordpress-activitypub/includes/activity/class-base-object.php

<?php
/**
 * Inspired by the PHP ActivityPub Library by @Landrok
 *
 * @link https://github.com/landrok/activitypub
 */

namespace Activitypub\Activity;

use WP_Error;
use ReflectionClass;

use function Activitypub\camel_to_snake_case;
use function Activitypub\snake_to_camel_case;

/**
 * Base_Object is an implementation of one of the
 * Activity Streams Core Types.
 *
 * The Object is the primary base type for the Activity Streams
 * vocabulary.
 *
 * Note: Object is a reserved keyword in PHP. It has been suffixed with
 * 'Base_' for this reason.
 * 
 * @see https://www.w3.org/TR/activitystreams-core/#object
 */
class Base_Object {
	const CONTEXT_ACTIVITYSTREAMS = 'https://www.w3.org/ns/activitystreams';
	const CONTEXT_SECURITY = 'https://w3id.org/security/v1';

	/**
	 * The object's unique global identifier
	 *
	 * @see https://www.w3.org/TR/activitypub/#obj-id
	 *
	 * @var string
	 */
	protected $id;

	/**
	 * @var string
	 */
	protected $type = 'Object';

	/**
	 * A resource attached or related to an object that potentially
	 * requires special handling.
	 * The intent is to provide a model that is at least semantically
	 * similar to attachments in email.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attachment
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $attachment;

	/**
	 * One or more entities to which this object is attributed.
	 * The attributed entities might not be Actors. For instance, an
	 * object might be attributed to the completion of another activity.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-attributedto
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $attributed_to;

	/**
	 * One or more entities that represent the total population of
	 * entities for which the object can considered to be relevant.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-audience
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $audience;

	/**
	 * The content or textual representation of the Object encoded as a
	 * JSON string. By default, the value of content is HTML.
	 * The mediaType property can be used in the object to indicate a
	 * different content type.
	 *
	 * The content MAY be expressed using multiple language-tagged
	 * values.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-content
	 *
	 * @var string|null
	 */
	protected $content;

	/**
	 * The context within which the object exists or an activity was
	 * performed.
	 * The notion of "context" used is intentionally vague.
	 * The intended function is to serve as a means of grouping objects
	 * and activities that share a common originating context or
	 * purpose. An example could be all activities relating to a common
	 * project or event.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-context
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | null
	 */
	protected $context;

	/**
	 * The content MAY be expressed using multiple language-tagged
	 * values.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-content
	 *
	 * @var array|null
	 */
	protected $content_map;

	/**
	 * A simple, human-readable, plain-text name for the object.
	 * HTML markup MUST NOT be included.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-name
	 *
	 * @var string|null xsd:string
	 */
	protected $name;

	/**
	 * The name MAY be expressed using multiple language-tagged values.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-name
	 *
	 * @var array|null rdf:langString
	 */
	protected $name_map;

	/**
	 * The date and time describing the actual or expected ending time
	 * of the object.
	 * When used with an Activity object, for instance, the endTime
	 * property specifies the moment the activity concluded or
	 * is expected to conclude.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-endtime
	 *
	 * @var string|null
	 */
	protected $end_time;

	/**
	 * The entity (e.g. an application) that generated the object.
	 *
	 * @var string|null
	 */
	protected $generator;

	/**
	 * An entity that describes an icon for this object.
	 * The image should have an aspect ratio of one (horizontal)
	 * to one (vertical) and should be suitable for presentation
	 * at a small size.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-icon
	 *
	 * @var string
	 *    | Image
	 *    | Link
	 *    | array<Image>
	 *    | array<Link>
	 *    | null
	 */
	protected $icon;

	/**
	 * An entity that describes an image for this object.
	 * Unlike the icon property, there are no aspect ratio
	 * or display size limitations assumed.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-image-term
	 *
	 * @var string
	 *    | Image
	 *    | Link
	 *    | array<Image>
	 *    | array<Link>
	 *    | null
	 */
	protected $image;

	/**
	 * One or more entities for which this object is considered a
	 * response.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-inreplyto
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $in_reply_to;

	/**
	 * One or more physical or logical locations associated with the
	 * object.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-location
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $location;

	/**
	 * An entity that provides a preview of this object.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-preview
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | null
	 */
	protected $preview;

	/**
	 * The date and time at which the object was published
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-published
	 *
	 * @var string|null xsd:dateTime
	 */
	protected $published;

	/**
	 * The date and time describing the actual or expected starting time
	 * of the object.
	 * When used with an Activity object, for instance, the startTime
	 * property specifies the moment the activity began
	 * or is scheduled to begin.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-starttime
	 *
	 * @var string|null xsd:dateTime
	 */
	protected $start_time;

	/**
	 * A natural language summarization of the object encoded as HTML.
	 * Multiple language tagged summaries MAY be provided.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-summary
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | null
	 */
	protected $summary;

	/**
	 * The content MAY be expressed using multiple language-tagged
	 * values.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-summary
	 *
	 * @var array<string>|null
	 */
	protected $summary_map;

	/**
	 * One or more "tags" that have been associated with an objects.
	 * A tag can be any kind of Object.
	 * The key difference between attachment and tag is that the former
	 * implies association by inclusion, while the latter implies
	 * associated by reference.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-tag
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $tag;

	/**
	 * The date and time at which the object was updated
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-updated
	 *
	 * @var string|null xsd:dateTime
	 */
	protected $updated;

	/**
	 * One or more links to representations of the object.
	 *
	 * @var string
	 *    | array<string>
	 *    | Link
	 *    | array<Link>
	 *    | null
	 */
	protected $url;

	/**
	 * An entity considered to be part of the public primary audience
	 * of an Object
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-to
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $to;

	/**
	 * An Object that is part of the private primary audience of this
	 * Object.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-bto
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $bto;

	/**
	 * An Object that is part of the public secondary audience of this
	 * Object.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-cc
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $cc;

	/**
	 * One or more Objects that are part of the private secondary
	 * audience of this Object.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-bcc
	 *
	 * @var string
	 *    | ObjectType
	 *    | Link
	 *    | array<ObjectType>
	 *    | array<Link>
	 *    | null
	 */
	protected $bcc;

	/**
	 * The MIME media type of the value of the content property.
	 * If not specified, the content property is assumed to contain
	 * text/html content.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-mediatype
	 *
	 * @var string|null
	 */
	protected $media_type;

	/**
	 * When the object describes a time-bound resource, such as an audio
	 * or video, a meeting, etc, the duration property indicates the
	 * object's approximate duration.
	 * The value MUST be expressed as an xsd:duration as defined by
	 * xmlschema11-2, section 3.3.6 (e.g. a period of 5 seconds is
	 * represented as "PT5S").
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-duration
	 *
	 * @var string|null
	 */
	protected $duration;

	/**
	 * Intended to convey some sort of source from which the content
	 * markup was derived, as a form of provenance, or to support
	 * future editing by clients.
	 *
	 * @see https://www.w3.org/TR/activitypub/#source-property
	 *
	 * @var ObjectType
	 */
	protected $source;

	/**
	 * A Collection containing objects considered to be responses to
	 * this object.
	 *
	 * @see https://www.w3.org/TR/activitystreams-vocabulary/#dfn-replies
	 *
	 * @var string
	 *    | Collection
	 *    | Link
	 *    | null
	 */
	protected $replies;

	/**
	 * Magic function to implement getter and setter
	 *
	 * @param string $method The method name.
	 * @param string $params The method params.
	 *
	 * @return void
	 */
	public function __call( $method, $params ) {
		$var = \strtolower( \substr( $method, 4 ) );

		if ( \strncasecmp( $method, 'get', 3 ) === 0 ) {
			if ( ! $this->has( $var ) ) {
				return new WP_Error( 'invalid_key', __( 'Invalid key', 'activitypub' ), array( 'status' => 404 ) );
			}

			return $this->$var;
		}

		if ( \strncasecmp( $method, 'set', 3 ) === 0 ) {
			return $this->set( $var, $params[0] );
		}

		if ( \strncasecmp( $method, 'add', 3 ) === 0 ) {
			$this->add( $var, $params[0] );
		}
	}

	/**
	 * The ActivityPub object typicallly can define it's own JSON-LD context.
	 */
	public function __construct() {
		$this->context = $this->get_context();
	}

	/**
	 * Magic function, to transform the object to string.
	 *
	 * @return string The object id.
	 */
	public function __toString() {
		return $this->to_string();
	}

	/**
	 * Function to transform the object to string.
	 *
	 * @return string The object id.
	 */
	public function to_string() {
		return $this->get_id();
	}

	/**
	 * Generic getter.
	 *
	 * @param string $key The key to get.
	 *
	 * @return mixed The value.
	 */
	public function get( $key ) {
		if ( ! $this->has( $key ) ) {
			return new WP_Error( 'invalid_key', __( 'Invalid key', 'activitypub' ), array( 'status' => 404 ) );
		}

		return call_user_func( array( $this, 'get_' . $key ) );
	}

	/**
	 * Check if the object has a key
	 *
	 * @param string $key The key to check.
	 *
	 * @return boolean True if the object has the key.
	 */
	public function has( $key ) {		
		if ( $key === 'actor ') {
			$key = 'actor';
		}
		return property_exists( $this, $key );
	}

	/**
	 * Generic setter.
	 *
	 * @param string $key   The key to set.
	 * @param string $value The value to set.
	 *
	 * @return mixed The value.
	 */
	public function set( $key, $value ) {
		if ( ! $this->has( $key ) ) {
			if ( $key === 'actor' ) {
				$key = 'actor';
			}
			return new WP_Error( 'invalid_key', __( 'Invalid key', 'activitypub' ), array( 'status' => 404 ) );
		}


		$this->$key = $value;

		return $this;
	}

	/**
	 * Generic adder.
	 *
	 * @param string $key   The key to set.
	 * @param mixed  $value The value to add.
	 *
	 * @return mixed The value.
	 */
	public function add( $key, $value ) {
		if ( ! $this->has( $key ) ) {
			return new WP_Error( 'invalid_key', __( 'Invalid key', 'activitypub' ), array( 'status' => 404 ) );
		}

		if ( ! isset( $this->$key ) ) {
			$this->$key = array();
		}

		$attributes   = $this->$key;
		$attributes[] = $value;

		$this->$key = $attributes;

		return $this->$key;
	}

	/**
	 * Convert JSON input to an array.
	 *
	 * @return string The JSON string.
	 *
	 * @return \Activitypub\Activity\Base_Object An Object built from the JSON string.
	 */
	public static function init_from_json( $json ) {
		$array = \json_decode( $json, true );

		if ( ! is_array( $array ) ) {
			$array = array();
		}

		return self::init_from_array( $array );
	}

	/**
	 * Convert JSON input to an array.
	 *
	 * @return string The object array.
	 *
	 * @return \Activitypub\Activity\Base_Object An Object built from the JSON string.
	 */
	public static function init_from_array( $array ) {
		if ( ! is_array( $array ) ) {
			return new WP_Error( 'invalid_array', __( 'Invalid array', 'activitypub' ), array( 'status' => 404 ) );
		}

		$object = new static();

		foreach ( $array as $key => $value ) {
			$key = camel_to_snake_case( $key );
			call_user_func( array( $object, 'set_' . $key ), $value );
		}

		return $object;
	}

	/**
	 * Convert JSON input to an array and pre-fill the object.
	 *
	 * @param string $json The JSON string.
	 */
	public function from_json( $json ) {
		$array = \json_decode( $json, true );

		$this->from_array( $array );
	}

	/**
	 * Convert JSON input to an array and pre-fill the object.
	 *
	 * @param array $array The array.
	 */
	public function from_array( $array ) {
		foreach ( $array as $key => $value ) {
			if ( $value ) {
				$key = camel_to_snake_case( $key );
				call_user_func( array( $this, 'set_' . $key ), $value );
			}
		}
	}

	/**
	 * Convert Object to an array.
	 *
	 * It tries to get the object attributes if they exist
	 * and falls back to the getters. Empty values are ignored.
	 *
	 * @return array An array built from the Object.
	 */
	public function to_array() {
		$array = array();
		$vars  = get_object_vars( $this );

		foreach ( $vars as $key => $value ) {
			// ignotre all _prefixed keys.
			if ( '_' === substr( $key, 0, 1 ) ) {
				continue;
			}

			// if value is empty, try to get it from a getter.
			if ( ! $value ) {
				$value = call_user_func( array( $this, 'get_' . $key ) );
			}

			if ( is_object( $value ) ) {
				$value = $value->to_array();
			}

			// if value is still empty, ignore it for the array and continue.
			if ( isset( $value ) ) {
				$array[ snake_to_camel_case( $key ) ] = $value;
			}
		}

		// replace 'context' key with '@context' and move it to the top.
		if ( array_key_exists( 'context', $array ) ) {
			$context = $array['context'];
			unset( $array['context'] );
			$array = array_merge( array( '@context' => $context ), $array );
		}

		$class = new ReflectionClass( $this );
		$class = strtolower( $class->getShortName() );

		$array = \apply_filters( 'activitypub_activity_object_array', $array, $class, $this->id, $this );
		$array = \apply_filters( "activitypub_activity_{$class}_object_array", $array, $this->id, $this );

		return $array;
	}

	/**
	 * Convert Object to JSON.
	 *
	 * @return string The JSON string.
	 */
	public function to_json() {
		$array   = $this->to_array();
		$options = \JSON_HEX_TAG | \JSON_HEX_AMP | \JSON_HEX_QUOT;

		/*
		* Options to be passed to json_encode()
		*
		* @param int $options The current options flags
		*/
		$options = \apply_filters( 'activitypub_json_encode_options', $options );

		return \wp_json_encode( $array, $options );
	}

	/**
	 * Returns the keys of the object vars.
	 *
	 * @return array The keys of the object vars.
	 */
	public function get_object_var_keys() {
		return \array_keys( \get_object_vars( $this ) );
	}

	/**
	 * Get the context information for a property.
	 *
	 * @param string $property
	 *
	 * @return array|null
	 */
	private function get_property_context( string $property ) {
		$reflection_class = new \ReflectionClass( $this );

		if ( $reflection_class->hasProperty( $property ) ) {
			$reflection_property = $reflection_class->getProperty( $property );
			$doc_omment = $reflection_property->getDocComment();

			// Extract context information from the doc comment.
			preg_match( '/@context\s+([^\s]+)/', $doc_omment, $matches );

			if ( ! empty( $matches[1] ) ) {
				return $matches[1];
			} else {
				return self::CONTEXT_ACTIVITYSTREAMS;
			}
		}

		return null;
	}

	/**
	 * Compact the context via the JSON-LD syntax.
	 * 
	 * @param array $key_context A certain part of the whole context.
	 * @param array $array The full URIs of the contexts.
	 * @param array $abbreviation The short name of the context.
	 * 
	 * @return array $key_kontext The compacted context.
	 */
	private static function compact_context( $key_context, $namespace, $abbreviation ) {
		$abbreviation_added = false;
		foreach ( $key_context as $key => $value ) {
			// Check if the key starts with the namespace
			if ( strpos( $value, $namespace ) === 0 ) {
				// Replace the key
				$key_context[ $key ] = $abbreviation . ':' . substr( $value, strlen( $namespace ) );

				// Add abbreviation element for the namespace only once
				if ( ! $abbreviation_added ) {
					$key_context = array( $abbreviation => $namespace ) + $key_context;
					$abbreviation_added = true;
				}
			}
		}
		return $key_context;
	}

	/**
	 * Builds the context of the ActivityPub object via the PHP docs.
	 * 
	 * @return array $context A shortened and clean JSON-LD context for the ActivityPub object.
	 */
	public static function get_context() {
		$class = static::class;

		// Try to lookup the context from a transient.
		$transient = "activitypub_json_context_object_{$class}";
		$context = get_transient( $transient );
		if ( $context ) {
			return $context;
		}
		$reflection_class = new \ReflectionClass( static::class );
		$context = array(
			self::CONTEXT_ACTIVITYSTREAMS,
			self::CONTEXT_SECURITY,
		);

		$key_context = array();

		foreach ( $reflection_class->getProperties() as $property ) {
			$doc_omment = $property->getDocComment();

			// Extract context information from the doc comment.
			preg_match( '/@context\s+([^\s]+)/', $doc_omment, $matches );

			if ( ! empty( $matches[1] ) ) {
				$key_context[ snake_to_camel_case( $property->name ) ] = $matches[1];
			}
		}

		$namespace_abbreviations = array(
			'https://joinpeertube.org/ns#'        => 'pt',
			'https://joinmobilizon.org/ns#'       => 'mz',
			'https://schema.org/'                 => 'sc',
			'https://www.w3.org/2002/12/cal/ical#' => 'ical',
		);

		foreach ( $namespace_abbreviations as $namespace => $abbreviation ) {
			$key_context = self::compact_context( $key_context, $namespace, $abbreviation );
		}

		if ( ! empty( $key_context ) ) {
			$context[] = $key_context;
		}

		set_transient( $transient, $context );
		return $context;
	}
}