/* =========================================================================================
 * Copyright © 2013-2017 the kamon project <http://kamon.io/>
 *
 * 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.
 * =========================================================================================
 */


package kamon.trace

import java.util.concurrent.ThreadLocalRandom

import com.typesafe.config.Config
import io.opentracing.propagation.{Format, TextMap}
import io.opentracing.propagation.Format.Builtin.{BINARY, HTTP_HEADERS, TEXT_MAP}
import io.opentracing.util.ThreadLocalActiveSpanSource
import kamon.ReporterRegistryImpl
import kamon.metric.MetricLookup
import kamon.util.Clock
import org.slf4j.LoggerFactory


class Tracer(metrics: MetricLookup, reporterRegistry: ReporterRegistryImpl, initialConfig: Config)
    extends ThreadLocalActiveSpanSource with io.opentracing.Tracer {

  private val logger = LoggerFactory.getLogger(classOf[Tracer])
  private val tracerMetrics = new TracerMetrics(metrics)

  @volatile private var configuredSampler: Sampler = Sampler.never
  @volatile private var textMapSpanContextCodec = SpanContextCodec.TextMap
  @volatile private var httpHeaderSpanContextCodec = SpanContextCodec.ZipkinB3

  reconfigure(initialConfig)

  override def buildSpan(operationName: String): io.opentracing.Tracer.SpanBuilder =
    new SpanBuilder(operationName)

  override def extract[C](format: Format[C], carrier: C): io.opentracing.SpanContext = format match {
    case HTTP_HEADERS => httpHeaderSpanContextCodec.extract(carrier.asInstanceOf[TextMap], configuredSampler)
    case TEXT_MAP     => textMapSpanContextCodec.extract(carrier.asInstanceOf[TextMap], configuredSampler)
    case BINARY       => null // TODO: Implement Binary Encoding
    case _            => null
  }

  override def inject[C](spanContext: io.opentracing.SpanContext, format: Format[C], carrier: C): Unit = format match {
    case HTTP_HEADERS => httpHeaderSpanContextCodec.inject(spanContext.asInstanceOf[SpanContext], carrier.asInstanceOf[TextMap])
    case TEXT_MAP     => textMapSpanContextCodec.inject(spanContext.asInstanceOf[SpanContext], carrier.asInstanceOf[TextMap])
    case BINARY       =>
    case _            =>
  }

  def sampler: Sampler =
    configuredSampler

  def setTextMapSpanContextCodec(codec: SpanContextCodec[TextMap]): Unit =
    this.textMapSpanContextCodec = codec

  def setHttpHeaderSpanContextCodec(codec: SpanContextCodec[TextMap]): Unit =
    this.httpHeaderSpanContextCodec = codec

  private class SpanBuilder(operationName: String) extends io.opentracing.Tracer.SpanBuilder {
    private var parentContext: SpanContext = _
    private var startTimestamp = 0L
    private var initialTags = Map.empty[String, String]
    private var useActiveSpanAsParent = true

    override def asChildOf(parent: io.opentracing.SpanContext): io.opentracing.Tracer.SpanBuilder = parent match {
      case spanContext: kamon.trace.SpanContext =>
        this.parentContext = spanContext
        this
      case _ => logger.error("Can't extract the parent ID from a non-Kamon SpanContext"); this
    }

    override def asChildOf(parent: io.opentracing.BaseSpan[_]): io.opentracing.Tracer.SpanBuilder =
      asChildOf(parent.context())

    override def addReference(referenceType: String, referencedContext: io.opentracing.SpanContext): io.opentracing.Tracer.SpanBuilder = {
      if(referenceType != null && referenceType.equals(io.opentracing.References.CHILD_OF)) {
        asChildOf(referencedContext)
      } else this
    }

    override def withTag(key: String, value: String): io.opentracing.Tracer.SpanBuilder = {
      this.initialTags = this.initialTags + (key -> value)
      this
    }

    override def withTag(key: String, value: Boolean): io.opentracing.Tracer.SpanBuilder = {
      this.initialTags = this.initialTags + (key -> value.toString)
      this
    }

    override def withTag(key: String, value: Number): io.opentracing.Tracer.SpanBuilder = {
      this.initialTags = this.initialTags + (key -> value.toString)
      this
    }

    override def withStartTimestamp(microseconds: Long): io.opentracing.Tracer.SpanBuilder = {
      this.startTimestamp = microseconds
      this
    }

    override def ignoreActiveSpan(): io.opentracing.Tracer.SpanBuilder = {
      this.useActiveSpanAsParent = false
      this
    }

    override def start(): io.opentracing.Span =
      startManual()

    override def startActive(): io.opentracing.ActiveSpan =
      makeActive(startManual())

    override def startManual(): Span = {
      val startTimestampMicros = if(startTimestamp != 0L) startTimestamp else Clock.microTimestamp()

      if(parentContext == null && useActiveSpanAsParent) {
        val possibleParent = activeSpan()
        if(possibleParent != null)
          parentContext = possibleParent.context().asInstanceOf[SpanContext]
      }

      val spanContext =
        if(parentContext != null)
          new SpanContext(parentContext.traceID, createID(), parentContext.spanID, parentContext.sampled, initialTags)
        else {
          val traceID = createID()
          new SpanContext(traceID, traceID, 0L, configuredSampler.decide(traceID), initialTags)
        }

      tracerMetrics.createdSpans.increment()
      new Span(spanContext, operationName, initialTags, startTimestampMicros, reporterRegistry)
    }

    private def createID(): Long =
      ThreadLocalRandom.current().nextLong()
  }


  private[kamon] def reconfigure(config: Config): Unit = synchronized {
    val traceConfig = config.getConfig("kamon.trace")

    configuredSampler = traceConfig.getString("sampler") match {
      case "always" => Sampler.always
      case "never"  => Sampler.never
      case "random" => Sampler.random(traceConfig.getDouble("sampler-random.chance"))
      case other    => sys.error(s"Unexpected sampler name $other.")
    }
  }

  private final class TracerMetrics(metricLookup: MetricLookup) {
    val createdSpans = metricLookup.counter("tracer.spans-created")
  }
}