content: /*
   *  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.beam.learning.katas.util;
  
  import org.apache.beam.sdk.transforms.DoFn;
  import org.apache.beam.sdk.transforms.PTransform;
  import org.apache.beam.sdk.transforms.ParDo;
  import org.apache.beam.sdk.transforms.windowing.BoundedWindow;
  import org.apache.beam.sdk.transforms.windowing.GlobalWindow;
  import org.apache.beam.sdk.values.PCollection;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  public class Log {
  
    private static final Logger LOG = LoggerFactory.getLogger(Log.class);
  
    private Log() {}
  
    public static <T> PTransform<PCollection<T>, PCollection<T>> ofElements() {
      return new LoggingTransform<>();
    }
  
    public static <T> PTransform<PCollection<T>, PCollection<T>> ofElements(String prefix) {
      return new LoggingTransform<>(prefix);
    }
  
    private static class LoggingTransform<T> extends PTransform<PCollection<T>, PCollection<T>> {
  
      private String prefix;
  
      private LoggingTransform() {
        prefix = "";
      }
  
      private LoggingTransform(String prefix) {
        this.prefix = prefix;
      }
  
      @Override
      public PCollection<T> expand(PCollection<T> input) {
        return input.apply(
            ParDo.of(
                new DoFn<T, T>() {
  
                  @ProcessElement
                  public void processElement(
                      @Element T element, OutputReceiver<T> out, BoundedWindow window) {
  
                    String message = prefix + element.toString();
  
                    if (!(window instanceof GlobalWindow)) {
                      message = message + "  Window:" + window.toString();
                    }
  
                    LOG.info(message);
  
                    out.output(element);
                  }
                }));
      }
    }
  }
  