class SpanContext

final class SpanContext implements SpanContextInterface {
    private static ?SpanContextInterface $invalidContext = null;
    
    /**
     * @see https://www.w3.org/TR/trace-context/#trace-flags
     * @see https://www.w3.org/TR/trace-context/#sampled-flag
     */
    private readonly bool $isSampled;
    private bool $isValid = true;
    private function __construct(string $traceId, string $spanId, int $traceFlags, bool $isRemote, ?TraceStateInterface $traceState = null) {
        // TraceId must be exactly 16 bytes (32 chars) and at least one non-zero byte
        // SpanId must be exactly 8 bytes (16 chars) and at least one non-zero byte
        if (!SpanContextValidator::isValidTraceId($traceId) || !SpanContextValidator::isValidSpanId($spanId)) {
            $this->traceId = SpanContextValidator::INVALID_TRACE;
            $this->spanId = SpanContextValidator::INVALID_SPAN;
            $this->isValid = false;
        }
        $this->isSampled = ($traceFlags & TraceFlags::SAMPLED) === TraceFlags::SAMPLED;
    }
    public function getTraceId() : string {
        return $this->traceId;
    }
    public function getTraceIdBinary() : string {
        return hex2bin($this->traceId);
    }
    public function getSpanId() : string {
        return $this->spanId;
    }
    public function getSpanIdBinary() : string {
        return hex2bin($this->spanId);
    }
    public function getTraceState() : ?TraceStateInterface {
        return $this->traceState;
    }
    public function isSampled() : bool {
        return $this->isSampled;
    }
    public function isValid() : bool {
        return $this->isValid;
    }
    public function isRemote() : bool {
        return $this->isRemote;
    }
    public function getTraceFlags() : int {
        return $this->traceFlags;
    }
    
    /** @inheritDoc */
    public static function createFromRemoteParent(string $traceId, string $spanId, int $traceFlags = TraceFlags::DEFAULT, ?TraceStateInterface $traceState = null) : SpanContextInterface {
        return new self($traceId, $spanId, $traceFlags, true, $traceState);
    }
    
    /** @inheritDoc */
    public static function create(string $traceId, string $spanId, int $traceFlags = TraceFlags::DEFAULT, ?TraceStateInterface $traceState = null) : SpanContextInterface {
        return new self($traceId, $spanId, $traceFlags, false, $traceState);
    }
    
    /** @inheritDoc */
    public static function getInvalid() : SpanContextInterface {
        if (null === self::$invalidContext) {
            self::$invalidContext = self::create(SpanContextValidator::INVALID_TRACE, SpanContextValidator::INVALID_SPAN, 0);
        }
        return self::$invalidContext;
    }

}