/*
 * 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.state.internals;

import org.apache.kafka.streams.KeyValue;
import org.apache.kafka.streams.errors.InvalidStateStoreException;
import org.apache.kafka.streams.state.KeyValueIterator;
import org.apache.kafka.streams.state.QueryableStoreType;
import org.apache.kafka.streams.state.ReadOnlyKeyValueStore;

import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;

/**
 * A wrapper over the underlying {@link ReadOnlyKeyValueStore}s found in a {@link
 * org.apache.kafka.streams.processor.internals.ProcessorTopology}
 *
 * @param <K> key type
 * @param <V> value type
 */
public class CompositeReadOnlyKeyValueStore<K, V> implements ReadOnlyKeyValueStore<K, V> {

    private final StateStoreProvider storeProvider;
    private final QueryableStoreType<ReadOnlyKeyValueStore<K, V>> storeType;
    private final String storeName;

    public CompositeReadOnlyKeyValueStore(final StateStoreProvider storeProvider,
                                          final QueryableStoreType<ReadOnlyKeyValueStore<K, V>> storeType,
                                          final String storeName) {
        this.storeProvider = storeProvider;
        this.storeType = storeType;
        this.storeName = storeName;
    }

    @Override
    public V get(final K key) {
        final List<ReadOnlyKeyValueStore<K, V>> stores = storeProvider.stores(storeName, storeType);
        for (ReadOnlyKeyValueStore<K, V> store : stores) {
            try {
                final V result = store.get(key);
                if (result != null) {
                    return result;
                }
            } catch (InvalidStateStoreException e) {
                throw new InvalidStateStoreException("State store is not available anymore and may have been migrated to another instance; please re-discover its location from the state metadata.");
            }

        }
        return null;
    }

    @Override
    public KeyValueIterator<K, V> range(final K from, final K to) {
        final NextIteratorFunction<K, V> nextIteratorFunction = new NextIteratorFunction<K, V>() {
            @Override
            public KeyValueIterator<K, V> apply(final ReadOnlyKeyValueStore<K, V> store) {
                try {
                    return store.range(from, to);
                } catch (InvalidStateStoreException e) {
                    throw new InvalidStateStoreException("State store is not available anymore and may have been migrated to another instance; please re-discover its location from the state metadata.");
                }
            }
        };
        final List<ReadOnlyKeyValueStore<K, V>> stores = storeProvider.stores(storeName, storeType);
        return new DelegatingPeekingKeyValueIterator<>(storeName, new CompositeKeyValueIterator(stores.iterator(), nextIteratorFunction));
    }

    @Override
    public KeyValueIterator<K, V> all() {
        final NextIteratorFunction<K, V> nextIteratorFunction = new NextIteratorFunction<K, V>() {
            @Override
            public KeyValueIterator<K, V> apply(final ReadOnlyKeyValueStore<K, V> store) {
                try {
                    return store.all();
                } catch (InvalidStateStoreException e) {
                    throw new InvalidStateStoreException("State store is not available anymore and may have been migrated to another instance; please re-discover its location from the state metadata.");
                }
            }
        };
        final List<ReadOnlyKeyValueStore<K, V>> stores = storeProvider.stores(storeName, storeType);
        return new DelegatingPeekingKeyValueIterator<>(storeName, new CompositeKeyValueIterator(stores.iterator(), nextIteratorFunction));
    }

    @Override
    public long approximateNumEntries() {
        final List<ReadOnlyKeyValueStore<K, V>> stores = storeProvider.stores(storeName, storeType);
        long total = 0;
        for (ReadOnlyKeyValueStore<K, V> store : stores) {
            total += store.approximateNumEntries();
        }
        return total < 0 ? Long.MAX_VALUE : total;
    }

    interface NextIteratorFunction<K, V> {

        KeyValueIterator<K, V> apply(final ReadOnlyKeyValueStore<K, V> store);
    }


    private class CompositeKeyValueIterator implements KeyValueIterator<K, V> {

        private final Iterator<ReadOnlyKeyValueStore<K, V>> storeIterator;
        private final NextIteratorFunction<K, V> nextIteratorFunction;

        private KeyValueIterator<K, V> current;

        CompositeKeyValueIterator(final Iterator<ReadOnlyKeyValueStore<K, V>> underlying,
                                  final NextIteratorFunction<K, V> nextIteratorFunction) {
            this.storeIterator = underlying;
            this.nextIteratorFunction = nextIteratorFunction;
        }

        @Override
        public void close() {
            if (current != null) {
                current.close();
                current = null;
            }
        }

        @Override
        public K peekNextKey() {
            throw new UnsupportedOperationException("peekNextKey not supported");
        }

        @Override
        public boolean hasNext() {
            while ((current == null || !current.hasNext())
                    && storeIterator.hasNext()) {
                close();
                current = nextIteratorFunction.apply(storeIterator.next());
            }
            return current != null && current.hasNext();
        }


        @Override
        public KeyValue<K, V> next() {
            if (!hasNext()) {
                throw new NoSuchElementException();
            }
            return current.next();
        }

        @Override
        public void remove() {
            throw new UnsupportedOperationException("Remove not supported");
        }
    }
}