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import org.apache.avro.io.BinaryDecoder;
import org.apache.avro.io.DatumReader;
import org.apache.avro.io.DecoderFactory;
import org.apache.avro.reflect.ReflectDatumReader;
import org.apache.avro.specific.SpecificDatumReader;
import org.apache.flink.api.common.typeinfo.TypeInformation;
import org.apache.flink.api.java.typeutils.TypeExtractor;

public class AvroDeserializationSchema<T> implements DeserializationSchema<T> {
	
	private final Class<T> avroType;

	private transient DatumReader<T> reader;
	private transient BinaryDecoder decoder;
	
	public AvroDeserializationSchema(Class<T> avroType) {
		this.avroType = avroType;
	}

	@Override
	public T deserialize(byte[] message) {
		ensureInitialized();
		
		try {
			decoder = DecoderFactory.get().binaryDecoder(message, decoder);
			return reader.read(null, decoder);
		}
		catch (Exception e) {
			throw new RuntimeException(e);
		}
	}

	@Override
	public boolean isEndOfStream(T nextElement) {
		return false;
	}

	@Override
	public TypeInformation<T> getProducedType() {
		return TypeExtractor.getForClass(avroType);
	}
	
	private void ensureInitialized() {
		if (reader == null) {
			if (org.apache.avro.specific.SpecificRecordBase.class.isAssignableFrom(avroType)) {
				reader = new SpecificDatumReader<T>(avroType);
			} else {
				reader = new ReflectDatumReader<T>(avroType);
			}
		}
	}
}