<?php
/**
 * Copyright 2017 OpenCensus Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

namespace OpenCensus\Trace\Propagator;

use OpenCensus\Trace\SpanContext;

/**
 * This propagator contains the method for serializaing and deserializing
 * SpanContext over a binary format.
 *
 * See
 * <a href="https://github.com/census-instrumentation/opencensus-specs/blob/master/encodings/BinaryEncoding.md">specification</a>
 * for the encoding specification.
 */
class BinaryFormatter implements FormatterInterface
{
    const OPTION_ENABLED = 1;

    /**
     * Generate a SpanContext object from the Trace Context header
     *
     * @param string $header
     * @return SpanContext
     */
    public function deserialize($bin)
    {
        $data = @unpack('Cversion/Cfield0/H32traceId/Cfield1/H16spanId/Cfield2/Coptions', $bin);
        if ($data === false) {
            trigger_error('Invalid binary format for SpanContext', E_USER_WARNING);
            return new SpanContext();
        }
        $enabled = !!($data['options'] & self::OPTION_ENABLED);
        $spanId = $data['spanId'] == "0000000000000000"
            ? null
            : $data['spanId'];
        return new SpanContext($data['traceId'], $spanId, $enabled, true);
    }

    /**
     * Convert a SpanContext to header string
     *
     * @param SpanContext $context
     * @return string
     */
    public function serialize(SpanContext $context)
    {
        $spanHex = str_pad($context->spanId(), 16, "0", STR_PAD_LEFT);
        $traceOptions = $context->enabled() ? self::OPTION_ENABLED : 0;
        return pack("CCH*CH*CC", 0, 0, $context->traceId(), 1, $spanHex, 2, $traceOptions);
    }
}
