import org.apache.flink.api.common.functions.MapFunction;
import org.apache.flink.api.common.functions.ReduceFunction;
import org.apache.flink.api.java.tuple.Tuple2;
import org.apache.flink.core.fs.FileSystem;
import org.apache.flink.streaming.api.datastream.DataStream;
import org.apache.flink.streaming.api.environment.StreamExecutionEnvironment;

public class UserTransactionSum {
    public static void main(String[] args) throws Exception {
        StreamExecutionEnvironment env = StreamExecutionEnvironment.getExecutionEnvironment();

        
        DataStream<String> input = env.readTextFile("/opt/flink/input.txt");

        
        DataStream<Tuple2<String, Integer>> transactions = input.map(new MapFunction<String, Tuple2<String, Integer>>() {
            @Override
            public Tuple2<String, Integer> map(String line) {
                String[] parts = line.split(",");
                String user = parts[0];
                Integer amount = Integer.parseInt(parts[1]);
                return new Tuple2<>(user, amount);
            }
        });

        
        DataStream<Tuple2<String, Integer>> result = transactions
                .keyBy(value -> value.f0)
                .reduce(new ReduceFunction<Tuple2<String, Integer>>() {
                    @Override
                    public Tuple2<String, Integer> reduce(Tuple2<String, Integer> value1, Tuple2<String, Integer> value2) {
                        return new Tuple2<>(value1.f0, value1.f1 + value2.f1);
                    }
                });

        
        result.writeAsCsv("/opt/flink/output", FileSystem.WriteMode.OVERWRITE);

        
        env.execute("User Transaction Sum");
    }
}