/*
 * 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.kafka.streams.kstream.internals;

import org.apache.kafka.streams.kstream.Aggregator;
import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.kstream.Initializer;
import org.apache.kafka.streams.kstream.Windows;
import org.apache.kafka.streams.kstream.Window;
import org.apache.kafka.streams.kstream.Windowed;
import org.apache.kafka.streams.processor.AbstractProcessor;
import org.apache.kafka.streams.processor.Processor;
import org.apache.kafka.streams.processor.ProcessorContext;
import org.apache.kafka.streams.state.WindowStore;
import org.apache.kafka.streams.state.WindowStoreIterator;

import java.util.Map;

public class KStreamWindowAggregate<K, V, T, W extends Window> implements KStreamAggProcessorSupplier<K, Windowed<K>, V, T> {

    private final String storeName;
    private final Windows<W> windows;
    private final Initializer<T> initializer;
    private final Aggregator<? super K, ? super V, T> aggregator;

    private boolean sendOldValues = false;

    public KStreamWindowAggregate(Windows<W> windows, String storeName, Initializer<T> initializer, Aggregator<? super K, ? super V, T> aggregator) {
        this.windows = windows;
        this.storeName = storeName;
        this.initializer = initializer;
        this.aggregator = aggregator;
    }

    @Override
    public Processor<K, V> get() {
        return new KStreamWindowAggregateProcessor();
    }

    @Override
    public void enableSendingOldValues() {
        sendOldValues = true;
    }

    private class KStreamWindowAggregateProcessor extends AbstractProcessor<K, V> {

        private WindowStore<K, T> windowStore;
        private TupleForwarder<Windowed<K>, T> tupleForwarder;

        @SuppressWarnings("unchecked")
        @Override
        public void init(ProcessorContext context) {
            super.init(context);

            windowStore = (WindowStore<K, T>) context.getStateStore(storeName);
            tupleForwarder = new TupleForwarder<>(windowStore, context, new ForwardingCacheFlushListener<Windowed<K>, V>(context, sendOldValues), sendOldValues);
        }

        @Override
        public void process(K key, V value) {
            // if the key is null, we do not need proceed aggregating the record
            // the record with the table
            if (key == null)
                return;

            // first get the matching windows
            long timestamp = context().timestamp();
            Map<Long, W> matchedWindows = windows.windowsFor(timestamp);

            long timeFrom = Long.MAX_VALUE;
            long timeTo = Long.MIN_VALUE;

            // use range query on window store for efficient reads
            for (long windowStartMs : matchedWindows.keySet()) {
                timeFrom = windowStartMs < timeFrom ? windowStartMs : timeFrom;
                timeTo = windowStartMs > timeTo ? windowStartMs : timeTo;
            }

            try (WindowStoreIterator<T> iter = windowStore.fetch(key, timeFrom, timeTo)) {

                // for each matching window, try to update the corresponding key
                while (iter.hasNext()) {
                    KeyValue<Long, T> entry = iter.next();
                    W window = matchedWindows.get(entry.key);

                    if (window != null) {

                        T oldAgg = entry.value;

                        if (oldAgg == null)
                            oldAgg = initializer.apply();

                        // try to add the new new value (there will never be old value)
                        T newAgg = aggregator.apply(key, value, oldAgg);

                        // update the store with the new value
                        windowStore.put(key, newAgg, window.start());
                        tupleForwarder.maybeForward(new Windowed<>(key, window), newAgg, oldAgg);
                        matchedWindows.remove(entry.key);
                    }
                }
            }

            // create the new window for the rest of unmatched window that do not exist yet
            for (Map.Entry<Long, W> entry : matchedWindows.entrySet()) {
                T oldAgg = initializer.apply();
                T newAgg = aggregator.apply(key, value, oldAgg);
                windowStore.put(key, newAgg, entry.getKey());
                tupleForwarder.maybeForward(new Windowed<>(key, entry.getValue()), newAgg, oldAgg);
            }
        }
    }

    @Override
    public KTableValueGetterSupplier<Windowed<K>, T> view() {

        return new KTableValueGetterSupplier<Windowed<K>, T>() {

            public KTableValueGetter<Windowed<K>, T> get() {
                return new KStreamWindowAggregateValueGetter();
            }

            @Override
            public String[] storeNames() {
                return new String[]{storeName};
            }
        };
    }

    private class KStreamWindowAggregateValueGetter implements KTableValueGetter<Windowed<K>, T> {

        private WindowStore<K, T> windowStore;

        @SuppressWarnings("unchecked")
        @Override
        public void init(ProcessorContext context) {
            windowStore = (WindowStore<K, T>) context.getStateStore(storeName);
        }

        @SuppressWarnings("unchecked")
        @Override
        public T get(Windowed<K> windowedKey) {
            K key = windowedKey.key();
            W window = (W) windowedKey.window();

            // this iterator should contain at most one element
            try (WindowStoreIterator<T> iter = windowStore.fetch(key, window.start(), window.start())) {
                return iter.hasNext() ? iter.next().value : null;
            }
        }
    }
}