DataStream API (Traditional)

/**
 * Main entry point for streaming programs
 */
class StreamExecutionEnvironment {
    /**
     * Get execution environment with default configuration
     * @return Execution environment
     */
    public static StreamExecutionEnvironment getExecutionEnvironment();
    
    /**
     * Create local execution environment
     * @return Local execution environment
     */
    public static StreamExecutionEnvironment createLocalEnvironment();
    
    /**
     * Add source function to create data stream
     * @param function Source function
     * @param <T> Element type
     * @return DataStream with elements from source
     */
    public <T> DataStream<T> addSource(SourceFunction<T> function);
    
    /**
     * Create data stream from collection
     * @param data Collection of elements
     * @param <T> Element type
     * @return DataStream with elements
     */
    public <T> DataStream<T> fromCollection(Collection<T> data);
    
    /**
     * Create data stream from elements
     * @param data Varargs elements
     * @param <T> Element type
     * @return DataStream with elements
     */
    public <T> DataStream<T> fromElements(@SuppressWarnings("unchecked") T... data);
    
    /**
     * Execute the streaming program
     * @return Job execution result
     * @throws Exception
     */
    public JobExecutionResult execute() throws Exception;
    
    /**
     * Execute with job name
     * @param jobName Job name
     * @return Job execution result
     * @throws Exception
     */
    public JobExecutionResult execute(String jobName) throws Exception;
    
    /**
     * Set parallelism for operations
     * @param parallelism Parallelism level
     */
    public void setParallelism(int parallelism);
    
    /**
     * Enable checkpointing
     * @param interval Checkpoint interval in milliseconds
     */
    public void enableCheckpointing(long interval);
}

/**
 * Core stream abstraction for traditional API
 * @param <T> Element type
 */
class DataStream<T> {
    /**
     * Apply map transformation
     * @param mapper Map function
     * @param <R> Result type
     * @return Transformed stream
     */
    public <R> DataStream<R> map(MapFunction<T, R> mapper);
    
    /**
     * Apply flatMap transformation
     * @param flatMapper FlatMap function
     * @param <R> Result type
     * @return Transformed stream
     */
    public <R> DataStream<R> flatMap(FlatMapFunction<T, R> flatMapper);
    
    /**
     * Filter elements
     * @param filter Filter function
     * @return Filtered stream
     */
    public DataStream<T> filter(FilterFunction<T> filter);
    
    /**
     * Partition stream by key
     * @param keySelector Key selector function
     * @param <K> Key type
     * @return Keyed stream
     */
    public <K> KeyedStream<T, K> keyBy(KeySelector<T, K> keySelector);
    
    /**
     * Connect with another stream
     * @param dataStream Other stream
     * @param <T2> Other stream type
     * @return Connected streams
     */
    public <T2> ConnectedStreams<T, T2> connect(DataStream<T2> dataStream);
    
    /**
     * Union with other streams
     * @param streams Other streams
     * @return Union of streams
     */
    public DataStream<T> union(DataStream<T>... streams);
    
    /**
     * Apply process function
     * @param processFunction Process function
     * @param <R> Result type
     * @return Processed stream
     */
    public <R> DataStream<R> process(ProcessFunction<T, R> processFunction);
    
    /**
     * Add sink
     * @param sinkFunction Sink function
     * @return Data stream sink
     */
    public DataStreamSink<T> addSink(SinkFunction<T> sinkFunction);
    
    /**
     * Print elements to output
     * @return Data stream sink
     */
    public DataStreamSink<T> print();
}

/**
 * Keyed stream for stateful operations
 * @param <T> Element type
 * @param <K> Key type
 */
class KeyedStream<T, K> {
    /**
     * Reduce elements by key
     * @param reducer Reduce function
     * @return Stream with reduced elements
     */
    public DataStream<T> reduce(ReduceFunction<T> reducer);
    
    /**
     * Apply process function with key context
     * @param keyedProcessFunction Keyed process function
     * @param <R> Result type
     * @return Processed stream
     */
    public <R> DataStream<R> process(KeyedProcessFunction<K, T, R> keyedProcessFunction);
    
    /**
     * Create windowed stream
     * @param assigner Window assigner
     * @param <W> Window type
     * @return Windowed stream
     */
    public <W extends Window> WindowedStream<T, K, W> window(WindowAssigner<? super T, W> assigner);
    
    /**
     * Create time windowed stream
     * @param assigner Time window assigner
     * @return Time windowed stream
     */
    public WindowedStream<T, K, TimeWindow> timeWindow(Time size);
    
    /**
     * Create sliding time windowed stream
     * @param size Window size
     * @param slide Slide interval
     * @return Time windowed stream
     */
    public WindowedStream<T, K, TimeWindow> timeWindow(Time size, Time slide);
}

/**
 * Windowed stream operations
 * @param <T> Element type
 * @param <K> Key type
 * @param <W> Window type
 */
class WindowedStream<T, K, W extends Window> {
    /**
     * Reduce elements within windows
     * @param function Reduce function
     * @return Stream with window results
     */
    public DataStream<T> reduce(ReduceFunction<T> function);
    
    /**
     * Aggregate elements within windows
     * @param function Aggregate function
     * @param <ACC> Accumulator type
     * @param <R> Result type
     * @return Stream with aggregated results
     */
    public <ACC, R> DataStream<R> aggregate(AggregateFunction<T, ACC, R> function);
    
    /**
     * Apply window function
     * @param function Window function
     * @param <R> Result type
     * @return Stream with window results
     */
    public <R> DataStream<R> apply(WindowFunction<T, R, K, W> function);
    
    /**
     * Apply process window function
     * @param function Process window function
     * @param <R> Result type
     * @return Stream with processed results
     */
    public <R> DataStream<R> process(ProcessWindowFunction<T, R, K, W> function);
    
    /**
     * Set window trigger
     * @param trigger Window trigger
     * @return Windowed stream with trigger
     */
    public WindowedStream<T, K, W> trigger(Trigger<? super T, ? super W> trigger);
    
    /**
     * Set window evictor
     * @param evictor Window evictor
     * @return Windowed stream with evictor
     */
    public WindowedStream<T, K, W> evictor(Evictor<? super T, ? super W> evictor);
}

/**
 * Process function for single input streams
 * @param <I> Input type
 * @param <O> Output type
 */
abstract class ProcessFunction<I, O> {
    /**
     * Process element
     * @param value Input element
     * @param ctx Process context
     * @param out Output collector
     * @throws Exception
     */
    public abstract void processElement(I value, Context ctx, Collector<O> out) throws Exception;
    
    /**
     * Process timer
     * @param timestamp Timer timestamp
     * @param ctx OnTimer context
     * @param out Output collector
     * @throws Exception
     */
    public void onTimer(long timestamp, OnTimerContext ctx, Collector<O> out) throws Exception {}
    
    /**
     * Process context
     */
    public abstract class Context {
        /**
         * Get current element timestamp
         * @return Element timestamp
         */
        public abstract Long timestamp();
        
        /**
         * Register processing time timer
         * @param timestamp Timer timestamp
         */
        public abstract void timerService().registerProcessingTimeTimer(long timestamp);
        
        /**
         * Output to side output
         * @param outputTag Output tag
         * @param value Value to output
         * @param <X> Value type
         */
        public abstract <X> void output(OutputTag<X> outputTag, X value);
    }
}

/**
 * Keyed process function
 * @param <K> Key type
 * @param <I> Input type
 * @param <O> Output type
 */
abstract class KeyedProcessFunction<K, I, O> {
    /**
     * Process element with key context
     * @param value Input element
     * @param ctx Keyed context
     * @param out Output collector
     * @throws Exception
     */
    public abstract void processElement(I value, Context ctx, Collector<O> out) throws Exception;
    
    /**
     * Process timer with key context
     * @param timestamp Timer timestamp
     * @param ctx OnTimer context
     * @param out Output collector
     * @throws Exception
     */
    public void onTimer(long timestamp, OnTimerContext ctx, Collector<O> out) throws Exception {}
    
    /**
     * Keyed process context
     */
    public abstract class Context {
        /**
         * Get current key
         * @return Current key
         */
        public abstract K getCurrentKey();
        
        /**
         * Get timer service
         * @return Timer service
         */
        public abstract TimerService timerService();
    }
}

/**
 * Source function interface for creating data streams
 * @param <T> Element type
 */
interface SourceFunction<T> {
    /**
     * Run source function
     * @param ctx Source context
     * @throws Exception
     */
    void run(SourceContext<T> ctx) throws Exception;
    
    /**
     * Cancel source function
     */
    void cancel();
    
    /**
     * Source context for emitting elements
     * @param <T> Element type
     */
    interface SourceContext<T> {
        /**
         * Collect element
         * @param element Element to collect
         */
        void collect(T element);
        
        /**
         * Collect element with timestamp
         * @param element Element to collect
         * @param timestamp Element timestamp
         */
        void collectWithTimestamp(T element, long timestamp);
        
        /**
         * Emit watermark
         * @param mark Watermark
         */
        void emitWatermark(Watermark mark);
        
        /**
         * Mark source as temporarily idle
         */
        void markAsTemporarilyIdle();
        
        /**
         * Get checkpoint lock
         * @return Checkpoint lock
         */
        Object getCheckpointLock();
        
        /**
         * Close the source context
         */
        void close();
    }
}

/**
 * Sink function interface for consuming data streams
 * @param <IN> Input element type
 */
interface SinkFunction<IN> {
    /**
     * Invoke sink function with element
     * @param value Input element
     * @param context Sink context
     * @throws Exception
     */
    void invoke(IN value, Context context) throws Exception;
    
    /**
     * Sink context
     */
    interface Context {
        /**
         * Get current processing time
         * @return Current processing time
         */
        long currentProcessingTime();
        
        /**
         * Get current watermark
         * @return Current watermark
         */
        long currentWatermark();
        
        /**
         * Get element timestamp
         * @return Element timestamp
         */
        Long timestamp();
    }
}

/**
 * Data stream sink
 * @param <T> Element type
 */
class DataStreamSink<T> {
    /**
     * Set sink parallelism
     * @param parallelism Parallelism level
     * @return Data stream sink
     */
    public DataStreamSink<T> setParallelism(int parallelism);
    
    /**
     * Disable chaining for this sink
     * @return Data stream sink
     */
    public DataStreamSink<T> disableChaining();
    
    /**
     * Set slot sharing group
     * @param slotSharingGroup Slot sharing group
     * @return Data stream sink
     */
    public DataStreamSink<T> slotSharingGroup(String slotSharingGroup);
    
    /**
     * Set sink name
     * @param name Sink name
     * @return Data stream sink
     */
    public DataStreamSink<T> name(String name);
}

/**
 * Job execution result
 */
class JobExecutionResult {
    /**
     * Get job execution time
     * @return Execution time in milliseconds
     */
    public long getNetRuntime();
    
    /**
     * Get accumulator result
     * @param accumulatorName Accumulator name
     * @param <T> Result type
     * @return Accumulator result
     */
    public <T> T getAccumulatorResult(String accumulatorName);
    
    /**
     * Get all accumulator results
     * @return Map of accumulator results
     */
    public Map<String, Object> getAllAccumulatorResults();
}

/**
 * Timer service for managing timers
 */
interface TimerService {
    /**
     * Get current processing time
     * @return Current processing time
     */
    long currentProcessingTime();
    
    /**
     * Get current watermark
     * @return Current watermark
     */
    long currentWatermark();
    
    /**
     * Register processing time timer
     * @param timestamp Timer timestamp
     */
    void registerProcessingTimeTimer(long timestamp);
    
    /**
     * Register event time timer
     * @param timestamp Timer timestamp
     */
    void registerEventTimeTimer(long timestamp);
    
    /**
     * Delete processing time timer
     * @param timestamp Timer timestamp
     */
    void deleteProcessingTimeTimer(long timestamp);
    
    /**
     * Delete event time timer
     * @param timestamp Timer timestamp
     */
    void deleteEventTimeTimer(long timestamp);
}

/**
 * Connected streams for processing two input streams
 * @param <IN1> First input type
 * @param <IN2> Second input type
 */
class ConnectedStreams<IN1, IN2> {
    /**
     * Apply co-map function
     * @param coMapper Co-map function
     * @param <R> Result type
     * @return Data stream
     */
    public <R> DataStream<R> map(CoMapFunction<IN1, IN2, R> coMapper);
    
    /**
     * Apply co-flat-map function
     * @param coFlatMapper Co-flat-map function
     * @param <R> Result type
     * @return Data stream
     */
    public <R> DataStream<R> flatMap(CoFlatMapFunction<IN1, IN2, R> coFlatMapper);
    
    /**
     * Apply co-process function
     * @param coProcessFunction Co-process function
     * @param <R> Result type
     * @return Data stream
     */
    public <R> DataStream<R> process(CoProcessFunction<IN1, IN2, R> coProcessFunction);
}

/**
 * Co-map function for connected streams
 * @param <IN1> First input type
 * @param <IN2> Second input type
 * @param <OUT> Output type
 */
interface CoMapFunction<IN1, IN2, OUT> extends Function {
    /**
     * Map function for first input
     * @param value Value from first input
     * @return Mapped value
     * @throws Exception
     */
    OUT map1(IN1 value) throws Exception;
    
    /**
     * Map function for second input
     * @param value Value from second input
     * @return Mapped value
     * @throws Exception
     */
    OUT map2(IN2 value) throws Exception;
}

/**
 * Co-flat-map function for connected streams
 * @param <IN1> First input type
 * @param <IN2> Second input type
 * @param <OUT> Output type
 */
interface CoFlatMapFunction<IN1, IN2, OUT> extends Function {
    /**
     * Flat-map function for first input
     * @param value Value from first input
     * @param out Output collector
     * @throws Exception
     */
    void flatMap1(IN1 value, Collector<OUT> out) throws Exception;
    
    /**
     * Flat-map function for second input
     * @param value Value from second input
     * @param out Output collector
     * @throws Exception
     */
    void flatMap2(IN2 value, Collector<OUT> out) throws Exception;
}

/**
 * Co-process function for connected streams
 * @param <IN1> First input type
 * @param <IN2> Second input type
 * @param <OUT> Output type
 */
abstract class CoProcessFunction<IN1, IN2, OUT> {
    /**
     * Process element from first input
     * @param value Element from first input
     * @param ctx Process context
     * @param out Output collector
     * @throws Exception
     */
    public abstract void processElement1(IN1 value, Context ctx, Collector<OUT> out) throws Exception;
    
    /**
     * Process element from second input
     * @param value Element from second input
     * @param ctx Process context
     * @param out Output collector
     * @throws Exception
     */
    public abstract void processElement2(IN2 value, Context ctx, Collector<OUT> out) throws Exception;
    
    /**
     * Process timer
     * @param timestamp Timer timestamp
     * @param ctx OnTimer context
     * @param out Output collector
     * @throws Exception
     */
    public void onTimer(long timestamp, OnTimerContext ctx, Collector<OUT> out) throws Exception {}
    
    /**
     * Process context
     */
    public abstract class Context {
        /**
         * Get timer service
         * @return Timer service
         */
        public abstract TimerService timerService();
        
        /**
         * Get current timestamp
         * @return Current timestamp
         */
        public abstract Long timestamp();
        
        /**
         * Output to side output
         * @param outputTag Output tag
         * @param value Value to output
         * @param <X> Value type
         */
        public abstract <X> void output(OutputTag<X> outputTag, X value);
    }
    
    /**
     * OnTimer context
     */
    public abstract class OnTimerContext extends Context {
        /**
         * Get timer timestamp
         * @return Timer timestamp
         */
        public abstract Long timestamp();
        
        /**
         * Get timer domain
         * @return Timer domain
         */
        public abstract TimeDomain timeDomain();
    }
}

/**
 * Time domain enumeration
 */
enum TimeDomain {
    /** Event time domain */
    EVENT_TIME,
    /** Processing time domain */
    PROCESSING_TIME
}

/**
 * Function interface for asynchronous operations
 * @param <IN> Input type
 * @param <OUT> Output type
 */
interface AsyncFunction<IN, OUT> extends Function {
    /**
     * Trigger async operation for input element
     * @param input Input element
     * @param resultFuture Future to complete with results
     * @throws Exception
     */
    void asyncInvoke(IN input, ResultFuture<OUT> resultFuture) throws Exception;
    
    /**
     * Handle timeout for async operation (optional)
     * @param input Input element that timed out
     * @param resultFuture Future to complete with results
     * @throws Exception
     */
    default void timeout(IN input, ResultFuture<OUT> resultFuture) throws Exception {
        resultFuture.completeExceptionally(
            new TimeoutException("Async operation timed out"));
    }
}

/**
 * Rich async function with runtime context access
 * @param <IN> Input type
 * @param <OUT> Output type
 */
abstract class RichAsyncFunction<IN, OUT> extends AbstractRichFunction implements AsyncFunction<IN, OUT> {}

/**
 * Utility class for applying async operations to data streams
 */
class AsyncDataStream {
    /**
     * Apply async function to stream with unordered output
     * @param input Input stream
     * @param function Async function
     * @param timeout Operation timeout
     * @param timeUnit Timeout time unit
     * @param capacity Maximum number of concurrent async operations
     * @param <IN> Input type
     * @param <OUT> Output type
     * @return Stream with async results
     */
    public static <IN, OUT> DataStream<OUT> unorderedWait(
        DataStream<IN> input,
        AsyncFunction<IN, OUT> function,
        long timeout,
        TimeUnit timeUnit,
        int capacity);
    
    /**
     * Apply async function to stream with unordered output (default capacity)
     * @param input Input stream
     * @param function Async function
     * @param timeout Operation timeout
     * @param timeUnit Timeout time unit
     * @param <IN> Input type
     * @param <OUT> Output type
     * @return Stream with async results
     */
    public static <IN, OUT> DataStream<OUT> unorderedWait(
        DataStream<IN> input,
        AsyncFunction<IN, OUT> function,
        long timeout,
        TimeUnit timeUnit);
    
    /**
     * Apply async function to stream with ordered output
     * @param input Input stream
     * @param function Async function
     * @param timeout Operation timeout
     * @param timeUnit Timeout time unit
     * @param capacity Maximum number of concurrent async operations
     * @param <IN> Input type
     * @param <OUT> Output type
     * @return Stream with async results (order preserved)
     */
    public static <IN, OUT> DataStream<OUT> orderedWait(
        DataStream<IN> input,
        AsyncFunction<IN, OUT> function,
        long timeout,
        TimeUnit timeUnit,
        int capacity);
    
    /**
     * Apply async function to stream with ordered output (default capacity)
     * @param input Input stream
     * @param function Async function
     * @param timeout Operation timeout
     * @param timeUnit Timeout time unit
     * @param <IN> Input type
     * @param <OUT> Output type
     * @return Stream with async results (order preserved)
     */
    public static <IN, OUT> DataStream<OUT> orderedWait(
        DataStream<IN> input,
        AsyncFunction<IN, OUT> function,
        long timeout,
        TimeUnit timeUnit);
}

/**
 * Future for collecting async operation results
 * @param <OUT> Result type
 */
interface ResultFuture<OUT> {
    /**
     * Complete future with single result
     * @param result Result value
     */
    void complete(Collection<OUT> result);
    
    /**
     * Complete future with single result
     * @param result Result value
     */
    default void complete(OUT result) {
        complete(Collections.singletonList(result));
    }
    
    /**
     * Complete future exceptionally
     * @param error Exception
     */
    void completeExceptionally(Throwable error);
}