/**
* Serialise an EasyRdf\Graph into a JSON-LD document.
*
* @param Graph $graph An EasyRdf\Graph object.
* @param string $format The name of the format to convert to.
* @param array $options
*
* @return string The RDF in the new desired format.
* @throws Exception
*/
public function serialise(Graph $graph, $format, array $options = array())
{
parent::checkSerialiseParams($format);
if ($format != 'jsonld') {
throw new Exception(__CLASS__ . ' does not support: ' . $format);
}
$ld_graph = new LD\Graph();
$nodes = array();
// cache for id-to-node association
foreach ($graph->toRdfPhp() as $resource => $properties) {
if (array_key_exists($resource, $nodes)) {
$node = $nodes[$resource];
} else {
$node = $ld_graph->createNode($resource);
$nodes[$resource] = $node;
}
foreach ($properties as $property => $values) {
foreach ($values as $value) {
if ($value['type'] == 'bnode' or $value['type'] == 'uri') {
if (array_key_exists($value['value'], $nodes)) {
$_value = $nodes[$value['value']];
} else {
$_value = $ld_graph->createNode($value['value']);
$nodes[$value['value']] = $_value;
}
} elseif ($value['type'] == 'literal') {
if (isset($value['lang'])) {
$_value = new LD\LanguageTaggedString($value['value'], $value['lang']);
} elseif (isset($value['datatype'])) {
$_value = new LD\TypedValue($value['value'], $value['datatype']);
} else {
$_value = $value['value'];
}
} else {
throw new Exception("Unable to serialise object to JSON-LD: " . $value['type']);
}
if ($property == "http://www.w3.org/1999/02/22-rdf-syntax-ns#type") {
$node->addType($_value);
} else {
$node->addPropertyValue($property, $_value);
}
}
}
}
// OPTIONS
$use_native_types = !(isset($options['expand_native_types']) and $options['expand_native_types'] == true);
$should_compact = (isset($options['compact']) and $options['compact'] == true);
$should_frame = isset($options['frame']);
// expanded form
$data = $ld_graph->toJsonLd($use_native_types);
if ($should_frame) {
$data = LD\JsonLD::frame($data, $options['frame'], $options);
}
if ($should_compact) {
// compact form
$compact_context = isset($options['context']) ? $options['context'] : null;
$compact_options = array('useNativeTypes' => $use_native_types, 'base' => $graph->getUri());
$data = LD\JsonLD::compact($data, $compact_context, $compact_options);
}
return LD\JsonLD::toString($data);
}
