/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 org.apache.htrace.core;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;

/**
 * Base interface for gathering and reporting statistics about a block of
 * execution.
 * <p/>
 * Spans should form a directed acyclic graph structure.  It should be possible
 * to keep following the parents of a span until you arrive at a span with no
 * parents.<p/>
 */
@JsonSerialize(using = Span.SpanSerializer.class)
public interface Span {
  /**
   * The block has completed, stop the clock
   */
  void stop();

  /**
   * Get the start time, in milliseconds
   */
  long getStartTimeMillis();

  /**
   * Get the stop time, in milliseconds
   */
  long getStopTimeMillis();

  /**
   * Return the total amount of time elapsed since start was called, if running,
   * or difference between stop and start
   */
  long getAccumulatedMillis();

  /**
   * Has the span been started and not yet stopped?
   */
  boolean isRunning();

  /**
   * Return a textual description of this span.<p/>
   *
   * Will never be null.
   */
  String getDescription();

  /**
   * A pseudo-unique (random) number assigned to this span instance.<p/>
   *
   * The spanId is immutable and cannot be changed.  It is safe to access this
   * from multiple threads.
   */
  SpanId getSpanId();

  /**
   * Create a child span of this span with the given description
   * @deprecated Since 4.0.0. Use {@link MilliSpan.Builder}
   */
  @Deprecated
  Span child(String description);

  @Override
  String toString();

  /**
   * Returns the parent IDs of the span.<p/>
   *
   * The array will be empty if there are no parents.
   */
  SpanId[] getParents();

  /**
   * Set the parents of this span.<p/>
   *
   * Any existing parents will be cleared by this call.
   */
  void setParents(SpanId[] parents);

  /**
   * Add a data annotation associated with this span
   */
  void addKVAnnotation(String key, String value);

  /**
   * Add a timeline annotation associated with this span
   */
  void addTimelineAnnotation(String msg);

  /**
   * Get data associated with this span (read only)<p/>
   *
   * Will never be null.
   */
  Map<String, String> getKVAnnotations();

  /**
   * Get any timeline annotations (read only)<p/>
   *
   * Will never be null.
   */
  List<TimelineAnnotation> getTimelineAnnotations();

  /**
   * Return a unique id for the process from which this Span originated.<p/>
   *
   * Will never be null.
   */
  String getTracerId();

  /**
   * Set the process id of a span.
   */
  void setTracerId(String s);

  /**
   * Serialize to Json
   */
  String toJson();

  public static class SpanSerializer extends JsonSerializer<Span> {
    @Override
    public void serialize(Span span, JsonGenerator jgen, SerializerProvider provider)
        throws IOException {
      jgen.writeStartObject();
      if (span.getSpanId().isValid()) {
        jgen.writeStringField("a", span.getSpanId().toString());
      }
      if (span.getStartTimeMillis() != 0) {
        jgen.writeNumberField("b", span.getStartTimeMillis());
      }
      if (span.getStopTimeMillis() != 0) {
        jgen.writeNumberField("e", span.getStopTimeMillis());
      }
      if (!span.getDescription().isEmpty()) {
        jgen.writeStringField("d", span.getDescription());
      }
      String tracerId = span.getTracerId();
      if (!tracerId.isEmpty()) {
        jgen.writeStringField("r", tracerId);
      }
      jgen.writeArrayFieldStart("p");
      for (SpanId parent : span.getParents()) {
        jgen.writeString(parent.toString());
      }
      jgen.writeEndArray();
      Map<String, String> traceInfoMap = span.getKVAnnotations();
      if (!traceInfoMap.isEmpty()) {
        jgen.writeObjectFieldStart("n");
        String[] keys = traceInfoMap.keySet().
            toArray(new String[traceInfoMap.size()]);
        Arrays.sort(keys);
        for (String key : keys) {
          jgen.writeStringField(key, traceInfoMap.get(key));
        }
        jgen.writeEndObject();
      }
      List<TimelineAnnotation> timelineAnnotations =
          span.getTimelineAnnotations();
      if (!timelineAnnotations.isEmpty()) {
        jgen.writeArrayFieldStart("t");
        for (TimelineAnnotation tl : timelineAnnotations) {
          jgen.writeStartObject();
          jgen.writeNumberField("t", tl.getTime());
          jgen.writeStringField("m", tl.getMessage());
          jgen.writeEndObject();
        }
        jgen.writeEndArray();
      }
      jgen.writeEndObject();
    }
  }
}