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// Copyright 2016 Google Inc. All rights reserved.
//
// 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 com.google.cloud.trace;

import com.google.cloud.trace.core.EndSpanOptions;
import com.google.cloud.trace.core.IdFactory;
import com.google.cloud.trace.core.Labels;
import com.google.cloud.trace.core.SpanContext;
import com.google.cloud.trace.core.SpanContextFactory;
import com.google.cloud.trace.core.SpanContextHandle;
import com.google.cloud.trace.core.SpanId;
import com.google.cloud.trace.core.StackTrace;
import com.google.cloud.trace.core.StartSpanOptions;
import com.google.cloud.trace.core.TraceContext;
import com.google.cloud.trace.core.TraceId;
import com.google.cloud.trace.core.TraceOptions;
import com.google.cloud.trace.core.TraceOptionsFactory;
import com.google.cloud.trace.service.TraceService;
import java.util.ServiceLoader;

/**
 * A class that provides trace services. This class uses a ServiceLoader to locate instances of
 * {@link TraceService}.
 */
public class Trace {
  private static final Object monitor = new Object();

  private static TraceService service = new NoTraceService();
  private static boolean initialized = false;

  static {
    for (TraceService service : ServiceLoader.load(TraceService.class)) {
      init(service);
    }
  }

  public static void init(TraceService traceService) {
    synchronized (monitor) {
      if (initialized) {
        throw new IllegalArgumentException("Trace service is already initialized.");
      }
      service = traceService;
      initialized = true;
    }
  }

  private static class NoTraceService implements TraceService {
    private final SpanContext spanContext = new SpanContext(
        TraceId.invalid(), SpanId.invalid(), new TraceOptions());
    private final TraceContext traceContext = new TraceContext(new NoSpanContextHandle(spanContext));
    private final Tracer tracer = new NoTracer(traceContext);
    private final SpanContextHandler spanContextHandler = new NoSpanContextHandler(spanContext);
    private final SpanContextFactory spanContextFactory = new SpanContextFactory(
        new TraceDisabledOptionsFactory(), new InvalidTraceIdFactory(),
        new InvalidSpanIdFactory());

    @Override
    public Tracer getTracer() {
      return tracer;
    }

    @Override
    public SpanContextHandler getSpanContextHandler() {
      return spanContextHandler;
    }

    @Override
    public SpanContextFactory getSpanContextFactory() {
      return spanContextFactory;
    }
  }

  public static Tracer getTracer() {
    return service.getTracer();
  }

  public static SpanContextHandler getSpanContextHandler() {
    return service.getSpanContextHandler();
  }

  public static SpanContextFactory getSpanContextFactory() {
    return service.getSpanContextFactory();
  }

  private static class NoTracer implements Tracer {
    private final TraceContext context;
    private NoTracer(TraceContext context) {
      this.context = context;
    }
    @Override
    public TraceContext startSpan(String name) {
      return context;
    }
    @Override
    public TraceContext startSpan(String name, StartSpanOptions options) {
      return context;
    }
    @Override
    public void endSpan(TraceContext traceContext) {}
    @Override
    public void endSpan(TraceContext traceContext, EndSpanOptions options) {}
    @Override
    public void annotateSpan(TraceContext traceContext, Labels labels) {}
    @Override
    public void setStackTrace(TraceContext traceContext, StackTrace stackTrace) {}
  }

  private static class NoSpanContextHandler implements SpanContextHandler {
    private final SpanContext context;
    private NoSpanContextHandler(SpanContext context) {
      this.context = context;
    }
    @Override
    public SpanContext current() {
      return context;
    }
    @Override
    public SpanContextHandle attach(SpanContext context) {
      return new NoSpanContextHandle(context);
    }
  }

  private static class NoSpanContextHandle implements SpanContextHandle {
    private final SpanContext context;

    private NoSpanContextHandle(SpanContext context) {
      this.context = context;
    }

    @Override
    public SpanContext getCurrentSpanContext() {
      return context;
    }

    @Override
    public void detach() {}
  }

  private static class InvalidTraceIdFactory implements IdFactory {
    @Override
    public TraceId nextId() {
      return TraceId.invalid();
    }
  }

  private static class InvalidSpanIdFactory implements IdFactory {
    @Override
    public SpanId nextId() {
      return SpanId.invalid();
    }
  }

  private static class TraceDisabledOptionsFactory implements TraceOptionsFactory {
    private static final TraceOptions options = TraceOptions.forTraceDisabled();

    @Override
    public TraceOptions create() {
      return options;
    }

    @Override
    public TraceOptions create(TraceOptions parent) {
      return options;
    }
  }
}