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package com.launchdarkly.client;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;

import java.io.IOException;

abstract class JsonHelpers {
  private static final Gson gson = new Gson();
  
  /**
   * Returns a shared instance of Gson with default configuration. This should not be used for serializing
   * event data, since it does not have any of the configurable behavior related to private attributes.
   */
  static Gson gsonInstance() {
    return gson;
  }
  
  /**
   * Creates a Gson instance that will correctly serialize users for the given configuration (private attributes, etc.).
   */
  static Gson gsonInstanceForEventsSerialization(EventsConfiguration config) {
    return new GsonBuilder()
        .registerTypeAdapter(LDUser.class, new LDUser.UserAdapterWithPrivateAttributeBehavior(config))
        .create();    
  }
  
  /**
   * Implement this interface on any internal class that needs to do some kind of post-processing after
   * being unmarshaled from JSON. You must also add the annotation {@code JsonAdapter(JsonHelpers.PostProcessingDeserializableTypeAdapterFactory)}
   * to the class for this to work.
   */
  static interface PostProcessingDeserializable {
    void afterDeserialized();
  }
  
  static class PostProcessingDeserializableTypeAdapterFactory implements TypeAdapterFactory {
    @Override
    public  TypeAdapter create(Gson gson, TypeToken type) {
      return new PostProcessingDeserializableTypeAdapter<>(gson.getDelegateAdapter(this, type));
    }
  }
  
  private static class PostProcessingDeserializableTypeAdapter extends TypeAdapter {
    private final TypeAdapter baseAdapter;
    
    PostProcessingDeserializableTypeAdapter(TypeAdapter baseAdapter) {
      this.baseAdapter = baseAdapter;
    }
    
    @Override
    public void write(JsonWriter out, T value) throws IOException {
      baseAdapter.write(out, value);
    }

    @Override
    public T read(JsonReader in) throws IOException {
      T instance = baseAdapter.read(in);
      if (instance instanceof PostProcessingDeserializable) {
        ((PostProcessingDeserializable)instance).afterDeserialized();
      }
      return instance;
    }
  }
}