Current File : //www/varak.net/wiki.varak.net/vendor/wikimedia/purtle/src/JsonLdRdfWriter.php
<?php
namespace Wikimedia\Purtle;
use LogicException;
/**
* RdfWriter implementation for generating JSON-LD output.
*
* @license GPL-2.0-or-later
* @author C. Scott Ananian
*/
class JsonLdRdfWriter extends RdfWriterBase {
/**
* The JSON-LD "@context", which maps terms to IRIs. This is shared with all sub-writers, and a
* single context is emitted when the writer is finalized.
*
* @see https://www.w3.org/TR/json-ld/#the-context
*
* @var string[]
*/
protected $context = [];
/**
* A set of predicates which rely on the default typing rules for
* JSON-LD; that is, values for the predicate have been emitted which
* would be broken if an explicit "@type" was added to the context
* for the predicate.
*
* @var boolean[]
*/
protected $defaulted = [];
/**
* The JSON-LD "@graph", which lists all the nodes described by this JSON-LD object.
* We apply an optimization eliminating the "@graph" entry if it consists
* of a single node; in that case we will set $this->graph to null in
* #finishJson() to ensure that the deferred callback in #finishDocument()
* doesn't later emit "@graph".
*
* @see https://www.w3.org/TR/json-ld/#named-graphs
*
* @var array[]|null
*/
private $graph = [];
/**
* A collection of predicates about a specific subject. The
* subject is identified by the "@id" key in this array; the other
* keys identify JSON-LD properties.
*
* @see https://www.w3.org/TR/json-ld/#dfn-edge
*
* @var array
*/
private $predicates = [];
/**
* A sequence of zero or more IRIs, nodes, or values, which are the
* destination targets of the current predicates.
*
* @see https://www.w3.org/TR/json-ld/#dfn-list
*
* @var array
*/
private $values = [];
/**
* True iff we have written the opening of the "@graph" field.
*
* @var bool
*/
private $wroteGraph = false;
/**
* JSON-LD objects describing a single node can omit the "@graph" field;
* this variable remains false only so long as we can guarantee that
* only a single node has been described.
*
* @var bool
*/
private $disableGraphOpt = false;
/**
* The IRI for the RDF `type` property.
*/
const RDF_TYPE_IRI = 'http://www.w3.org/1999/02/22-rdf-syntax-ns#type';
/**
* The type internally used for "default type", which is a string or
* otherwise default-coerced type.
*/
const DEFAULT_TYPE = '@purtle@default@';
/**
* @param string $role
* @param BNodeLabeler|null $labeler
*/
public function __construct( $role = parent::DOCUMENT_ROLE, BNodeLabeler $labeler = null ) {
parent::__construct( $role, $labeler );
// The following named methods are protected, not private, so we
// can invoke them directly w/o function wrappers.
$this->transitionTable[self::STATE_START][self::STATE_DOCUMENT] =
[ $this, 'beginJson' ];
$this->transitionTable[self::STATE_DOCUMENT][self::STATE_FINISH] =
[ $this, 'finishJson' ];
$this->transitionTable[self::STATE_OBJECT][self::STATE_PREDICATE] =
[ $this, 'finishPredicate' ];
$this->transitionTable[self::STATE_OBJECT][self::STATE_SUBJECT] =
[ $this, 'finishSubject' ];
$this->transitionTable[self::STATE_OBJECT][self::STATE_DOCUMENT] =
[ $this, 'finishDocument' ];
}
/**
* Emit $val as JSON, with $indent extra indentations on each line.
* @param array $val
* @param int $indent
* @return string the JSON string for $val
*/
public function encode( $val, $indent ) {
$str = json_encode( $val, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES );
// Strip outermost open/close braces/brackets
$str = preg_replace( '/^[[{]\n?|\n?[}\]]$/', '', $str );
if ( $indent > 0 ) {
// add extra indentation
$str = preg_replace( '/^/m', str_repeat( ' ', $indent ), $str );
}
return $str;
}
/**
* Return a "compact IRI" corresponding to the given base/local pair.
* This adds entries to the "@context" key when needed to allow use
* of a given prefix.
* @see https://www.w3.org/TR/json-ld/#dfn-compact-iri
*
* @param string $base A QName prefix if $local is given, or an IRI if $local is null.
* @param string|null $local A QName suffix, or null if $base is an IRI.
*
* @return string A compact IRI.
*/
private function compactify( $base, $local = null ) {
$this->expandShorthand( $base, $local );
if ( $local === null ) {
return $base;
} else {
if ( $base !== '_' && isset( $this->prefixes[ $base ] ) ) {
if ( $base === '' ) {
// Empty prefix not supported; use full IRI
return $this->prefixes[ $base ] . $local;
}
if ( !isset( $this->context[ $base ] ) ) {
$this->context[ $base ] = $this->prefixes[ $base ];
}
if ( $this->context[ $base ] !== $this->prefixes[ $base ] ) {
// Context name conflict; use full IRI
return $this->prefixes[ $base ] . $local;
}
}
return $base . ':' . $local;
}
}
/**
* Return an absolute IRI from the given base/local pair.
* @see https://www.w3.org/TR/json-ld/#dfn-absolute-iri
*
* @param string $base A QName prefix if $local is given, or an IRI if $local is null.
* @param string|null $local A QName suffix, or null if $base is an IRI.
*
* @return string|null An absolute IRI, or null if it cannot be constructed.
*/
private function toIRI( $base, $local ) {
$this->expandShorthand( $base, $local );
$this->expandQName( $base, $local );
if ( $local !== null ) {
throw new LogicException( 'Unknown prefix: ' . $base );
}
return $base;
}
/**
* Return a appropriate term for the current predicate value.
*/
private function getCurrentTerm() {
list( $base, $local ) = $this->currentPredicate;
$predIRI = $this->toIRI( $base, $local );
if ( $predIRI === self::RDF_TYPE_IRI ) {
return $predIRI;
}
$this->expandShorthand( $base, $local );
if ( $local === null ) {
return $base;
} elseif ( $base !== '_' && !isset( $this->prefixes[ $local ] ) ) {
// Prefixes get priority over field names in @context
$pred = $this->compactify( $base, $local );
if ( !isset( $this->context[ $local ] ) ) {
$this->context[ $local ] = [ '@id' => $pred ];
}
if ( $this->context[ $local ][ '@id' ] === $pred ) {
return $local;
}
return $pred;
}
return $this->compactify( $base, $local );
}
/**
* Write document header.
*/
protected function beginJson() {
if ( $this->role === self::DOCUMENT_ROLE ) {
$this->write( "{\n" );
$this->write( function () {
// If this buffer is drained early, disable @graph optimization
$this->disableGraphOpt = true;
return '';
} );
}
}
/**
* Write document footer.
*/
protected function finishJson() {
// If we haven't drained yet, and @graph has only 1 element, then we
// can optimize our output and hoist the single node to top level.
if ( $this->role === self::DOCUMENT_ROLE ) {
if ( ( !$this->disableGraphOpt ) && count( $this->graph ) === 1 ) {
$this->write( $this->encode( $this->graph[0], 0 ) );
$this->graph = null; // We're done with @graph.
} else {
$this->disableGraphOpt = true;
$this->write( "\n ]" );
}
}
if ( count( $this->context ) ) {
// Write @context field.
$this->write( ",\n" );
$this->write( $this->encode( [
'@context' => $this->context
], 0 ) );
}
$this->write( "\n}" );
}
protected function finishDocument() {
$this->finishSubject();
$this->write( function () {
// if this is drained before finishJson(), then disable
// the graph optimization and dump what we've got so far.
$str = '';
if ( $this->graph !== null && count( $this->graph ) > 0 ) {
$this->disableGraphOpt = true;
if ( $this->role === self::DOCUMENT_ROLE && !$this->wroteGraph ) {
$str .= " \"@graph\": [\n";
$this->wroteGraph = true;
} else {
$str .= ",\n";
}
$str .= $this->encode( $this->graph, 1 );
$this->graph = [];
return $str;
}
// Delay; maybe we'll be able to optimize this later.
return $str;
} );
}
/**
* @param string $base
* @param string|null $local
*/
protected function writeSubject( $base, $local = null ) {
$this->predicates = [
'@id' => $this->compactify( $base, $local )
];
}
protected function finishSubject() {
$this->finishPredicate();
$this->graph[] = $this->predicates;
}
/**
* @param string $base
* @param string|null $local
*/
protected function writePredicate( $base, $local = null ) {
// no op
}
/**
* @param string $base
* @param string|null $local
*/
protected function writeResource( $base, $local = null ) {
$pred = $this->getCurrentTerm();
$value = $this->compactify( $base, $local );
$this->addTypedValue( '@id', $value, [
'@id' => $value
], ( $pred === self::RDF_TYPE_IRI ) );
}
/**
* @param string $text
* @param string|null $language
*/
protected function writeText( $text, $language = null ) {
if ( !$this->isValidLanguageCode( $language ) ) {
$this->addTypedValue( self::DEFAULT_TYPE, $text );
} else {
$expanded = [
'@language' => $language,
'@value' => $text
];
$this->addTypedValue( self::DEFAULT_TYPE, $expanded, $expanded );
}
}
/**
* @param string $literal
* @param string|null $typeBase
* @param string|null $typeLocal
*/
public function writeValue( $literal, $typeBase, $typeLocal = null ) {
if ( $typeBase === null && $typeLocal === null ) {
$this->addTypedValue( self::DEFAULT_TYPE, $literal );
return;
}
switch ( $this->toIRI( $typeBase, $typeLocal ) ) {
case 'http://www.w3.org/2001/XMLSchema#string':
$this->addTypedValue( self::DEFAULT_TYPE, strval( $literal ) );
return;
case 'http://www.w3.org/2001/XMLSchema#integer':
$this->addTypedValue( self::DEFAULT_TYPE, intval( $literal ) );
return;
case 'http://www.w3.org/2001/XMLSchema#boolean':
$this->addTypedValue( self::DEFAULT_TYPE, ( $literal === 'true' ) );
return;
case 'http://www.w3.org/2001/XMLSchema#double':
$v = doubleval( $literal );
// Only "numbers with fractions" are xsd:double. We need
// to verify that the JSON string will contain a decimal
// point, otherwise the value would be interpreted as an
// xsd:integer.
// TODO: consider instead using JSON_PRESERVE_ZERO_FRACTION
// in $this->encode() once our required PHP >= 5.6.6.
// OTOH, the spec language is ambiguous about whether "5."
// would be considered an integer or a double.
if ( strpos( json_encode( $v ), '.' ) !== false ) {
$this->addTypedValue( self::DEFAULT_TYPE, $v );
return;
}
}
$type = $this->compactify( $typeBase, $typeLocal );
$literal = strval( $literal );
$this->addTypedValue( $type, $literal, [
'@type' => $type,
'@value' => $literal
] );
}
/**
* Add a typed value for the given predicate. If possible, adds a
* default type to the context to avoid having to repeat type information
* in each value for this predicate. If there is already a default
* type which conflicts with this one, or if $forceExpand is true,
* then use the "expanded" value which will explicitly override any
* default type.
*
* @param string $type The compactified JSON-LD @type for this value, or
* self::DEFAULT_TYPE to indicate the default JSON-LD type coercion rules
* should be used.
* @param string|int|float|bool $simpleVal The "simple" representation
* for this value, used if the type can be hoisted into the context.
* @param array|null $expandedVal The "expanded" representation for this
* value, used if the context @type conflicts with this value; or null
* to use "@value" for the expanded representation.
* @param bool $forceExpand If true, don't try to add this type to the
* context. Defaults to false.
*/
protected function addTypedValue( $type, $simpleVal, $expandedVal=null, $forceExpand=false ) {
if ( !$forceExpand ) {
$pred = $this->getCurrentTerm();
if ( $type === self::DEFAULT_TYPE ) {
if ( !isset( $this->context[ $pred ][ '@type' ] ) ) {
$this->defaulted[ $pred ] = true;
}
if ( isset( $this->defaulted[ $pred ] ) ) {
$this->values[] = $simpleVal;
return;
}
} elseif ( !isset( $this->defaulted[ $pred ] ) ) {
if ( !isset( $this->context[ $pred ] ) ) {
$this->context[ $pred ] = [];
}
if ( !isset( $this->context[ $pred ][ '@type' ] ) ) {
$this->context[ $pred ][ '@type' ] = $type;
}
if ( $this->context[ $pred ][ '@type' ] === $type ) {
$this->values[] = $simpleVal;
return;
}
}
}
if ( $expandedVal === null ) {
$this->values[] = [ '@value' => $simpleVal ];
} else {
$this->values[] = $expandedVal;
}
}
protected function finishPredicate() {
$name = $this->getCurrentTerm();
if ( $name === self::RDF_TYPE_IRI ) {
$name = '@type';
$this->values = array_map( function ( array $val ) {
return $val[ '@id' ];
}, $this->values );
}
if ( isset( $this->predicates[$name] ) ) {
$was = $this->predicates[$name];
// Wrap $was into a numeric indexed array if it isn't already.
// Note that $was could have non-numeric indices, eg
// [ "@id" => "foo" ], in which was it still needs to be wrapped.
if ( !( is_array( $was ) && isset( $was[0] ) ) ) {
$was = [ $was ];
}
$this->values = array_merge( $was, $this->values );
}
$cnt = count( $this->values );
if ( $cnt === 0 ) {
throw new LogicException( 'finishPredicate can\'t be called without at least one value' );
} elseif ( $cnt === 1 ) {
$this->predicates[$name] = $this->values[0];
} else {
$this->predicates[$name] = $this->values;
}
$this->values = [];
}
/**
* @param string $role
* @param BNodeLabeler $labeler
*
* @return RdfWriterBase
*/
protected function newSubWriter( $role, BNodeLabeler $labeler ) {
$writer = new self( $role, $labeler );
// Have subwriter share context with this parent.
$writer->context = &$this->context;
$writer->defaulted = &$this->defaulted;
// We can't use the @graph optimization.
$this->disableGraphOpt = true;
return $writer;
}
/**
* @return string a MIME type
*/
public function getMimeType() {
return 'application/ld+json; charset=UTF-8';
}
}
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