/*
 * 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.sdk.extensions.jackson;

import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.IOException;
import org.apache.beam.sdk.transforms.MapElements;
import org.apache.beam.sdk.transforms.PTransform;
import org.apache.beam.sdk.transforms.SimpleFunction;
import org.apache.beam.sdk.values.PCollection;
import org.apache.beam.vendor.guava.v20_0.com.google.common.base.Optional;

/**
 * {@link PTransform} for parsing JSON {@link String Strings}. Parse {@link PCollection} of {@link
 * String Strings} in JSON format into a {@link PCollection} of objects represented by those JSON
 * {@link String Strings} using Jackson.
 */
public class ParseJsons<OutputT> extends PTransform<PCollection<String>, PCollection<OutputT>> {
  private static final ObjectMapper DEFAULT_MAPPER = new ObjectMapper();

  private final Class<? extends OutputT> outputClass;
  private ObjectMapper customMapper;

  /**
   * Creates a {@link ParseJsons} {@link PTransform} that will parse JSON {@link String Strings}
   * into a {@code PCollection<OutputT>} using a Jackson {@link ObjectMapper}.
   */
  public static <OutputT> ParseJsons<OutputT> of(Class<? extends OutputT> outputClass) {
    return new ParseJsons<>(outputClass);
  }

  private ParseJsons(Class<? extends OutputT> outputClass) {
    this.outputClass = outputClass;
  }

  /** Use custom Jackson {@link ObjectMapper} instead of the default one. */
  public ParseJsons<OutputT> withMapper(ObjectMapper mapper) {
    ParseJsons<OutputT> newTransform = new ParseJsons<>(outputClass);
    newTransform.customMapper = mapper;
    return newTransform;
  }

  @Override
  public PCollection<OutputT> expand(PCollection<String> input) {
    return input.apply(
        MapElements.via(
            new SimpleFunction<String, OutputT>() {
              @Override
              public OutputT apply(String input) {
                try {
                  ObjectMapper mapper = Optional.fromNullable(customMapper).or(DEFAULT_MAPPER);
                  return mapper.readValue(input, outputClass);
                } catch (IOException e) {
                  throw new RuntimeException(
                      "Failed to parse a " + outputClass.getName() + " from JSON value: " + input,
                      e);
                }
              }
            }));
  }
}