/*
 * Copyright 2015 Open Networking Laboratory
 *
 * Licensed 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.onosproject.store.consistent.impl;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.Maps;

import org.onlab.util.HexString;
import org.onlab.util.SharedExecutors;
import org.onlab.util.Tools;
import org.onosproject.core.ApplicationId;
import org.onosproject.store.service.AsyncConsistentMap;
import org.onosproject.store.service.ConsistentMapException;
import org.onosproject.store.service.MapEvent;
import org.onosproject.store.service.MapEventListener;
import org.onosproject.store.service.Serializer;
import org.onosproject.store.service.Versioned;
import org.slf4j.Logger;

import java.util.Collection;
import java.util.Collections;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.CompletableFuture;
import java.util.concurrent.CopyOnWriteArraySet;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.BiFunction;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;

import static com.google.common.base.Preconditions.checkNotNull;
import static org.onosproject.store.consistent.impl.StateMachineUpdate.Target.MAP_UPDATE;
import static org.onosproject.store.consistent.impl.StateMachineUpdate.Target.TX_COMMIT;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * AsyncConsistentMap implementation that is backed by a Raft consensus
 * based database.
 *
 * @param <K> type of key.
 * @param <V> type of value.
 */
public class DefaultAsyncConsistentMap<K, V>  implements AsyncConsistentMap<K, V> {

    private final String name;
    private final ApplicationId applicationId;
    private final Database database;
    private final Serializer serializer;
    private final boolean readOnly;
    private final boolean purgeOnUninstall;

    private static final String PRIMITIVE_NAME = "consistentMap";
    private static final String SIZE = "size";
    private static final String IS_EMPTY = "isEmpty";
    private static final String CONTAINS_KEY = "containsKey";
    private static final String CONTAINS_VALUE = "containsValue";
    private static final String GET = "get";
    private static final String COMPUTE_IF = "computeIf";
    private static final String PUT = "put";
    private static final String PUT_AND_GET = "putAndGet";
    private static final String PUT_IF_ABSENT = "putIfAbsent";
    private static final String REMOVE = "remove";
    private static final String CLEAR = "clear";
    private static final String KEY_SET = "keySet";
    private static final String VALUES = "values";
    private static final String ENTRY_SET = "entrySet";
    private static final String REPLACE = "replace";
    private static final String COMPUTE_IF_ABSENT = "computeIfAbsent";

    private final Set<MapEventListener<K, V>> listeners = new CopyOnWriteArraySet<>();

    private final Logger log = getLogger(getClass());
    private final MeteringAgent monitor;

    private static final String ERROR_NULL_KEY = "Key cannot be null";
    private static final String ERROR_NULL_VALUE = "Null values are not allowed";

    // String representation of serialized byte[] -> original key Object
    private final LoadingCache<String, K> keyCache = CacheBuilder.newBuilder()
            .softValues()
            .build(new CacheLoader<String, K>() {

                @Override
                public K load(String key) {
                    return serializer.decode(HexString.fromHexString(key));
                }
            });

    protected String sK(K key) {
        String s = HexString.toHexString(serializer.encode(key));
        keyCache.put(s, key);
        return s;
    }

    protected K dK(String key) {
        return keyCache.getUnchecked(key);
    }

    public DefaultAsyncConsistentMap(String name,
                                     ApplicationId applicationId,
                                     Database database,
                                     Serializer serializer,
                                     boolean readOnly,
                                     boolean purgeOnUninstall,
                                     boolean meteringEnabled) {
        this.name = checkNotNull(name, "map name cannot be null");
        this.applicationId = applicationId;
        this.database = checkNotNull(database, "database cannot be null");
        this.serializer = checkNotNull(serializer, "serializer cannot be null");
        this.readOnly = readOnly;
        this.purgeOnUninstall = purgeOnUninstall;
        this.database.registerConsumer(update -> {
            SharedExecutors.getSingleThreadExecutor().execute(() -> {
                if (listeners.isEmpty()) {
                    return;
                }
                try {
                    if (update.target() == MAP_UPDATE) {
                        Result<UpdateResult<String, byte[]>> result = update.output();
                        if (result.success() && result.value().mapName().equals(name)) {
                            MapEvent<K, V> mapEvent = result.value()
                                                            .<K, V>map(this::dK,
                                                                       v -> serializer.decode(Tools.copyOf(v)))
                                                            .toMapEvent();
                            notifyListeners(mapEvent);
                        }
                    } else if (update.target() == TX_COMMIT) {
                        CommitResponse response = update.output();
                        if (response.success()) {
                            response.updates().forEach(u -> {
                                if (u.mapName().equals(name)) {
                                    MapEvent<K, V> mapEvent =
                                            u.<K, V>map(this::dK,
                                                        v -> serializer.decode(Tools.copyOf(v)))
                                             .toMapEvent();
                                    notifyListeners(mapEvent);
                                }
                            });
                        }
                    }
                } catch (Exception e) {
                    log.warn("Error notifying listeners", e);
                }
            });
        });
        this.monitor = new MeteringAgent(PRIMITIVE_NAME, name, meteringEnabled);
    }

    /**
     * Returns this map name.
     * @return map name
     */
    public String name() {
        return name;
    }

    /**
     * Returns the serializer for map entries.
     * @return map entry serializer
     */
    public Serializer serializer() {
        return serializer;
    }

    /**
     * Returns the applicationId owning this map.
     * @return application Id
     */
    public ApplicationId applicationId() {
        return applicationId;
    }

    /**
     * Returns whether the map entries should be purged when the application
     * owning it is uninstalled.
     * @return true is map needs to cleared on app uninstall; false otherwise
     */
    public boolean purgeOnUninstall() {
        return purgeOnUninstall;
    }

    @Override
    public CompletableFuture<Integer> size() {
        final MeteringAgent.Context timer = monitor.startTimer(SIZE);
        return database.mapSize(name)
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Boolean> isEmpty() {
        final MeteringAgent.Context timer = monitor.startTimer(IS_EMPTY);
        return database.mapIsEmpty(name)
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Boolean> containsKey(K key) {
        checkNotNull(key, ERROR_NULL_KEY);
        final MeteringAgent.Context timer = monitor.startTimer(CONTAINS_KEY);
        return database.mapContainsKey(name, sK(key))
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Boolean> containsValue(V value) {
        checkNotNull(value, ERROR_NULL_VALUE);
        final MeteringAgent.Context timer = monitor.startTimer(CONTAINS_VALUE);
        return database.mapContainsValue(name, serializer.encode(value))
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Versioned<V>> get(K key) {
        checkNotNull(key, ERROR_NULL_KEY);
        final MeteringAgent.Context timer = monitor.startTimer(GET);
        return database.mapGet(name, sK(key))
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(v -> v != null ? v.map(serializer::decode) : null);
    }

    @Override
    public CompletableFuture<Versioned<V>> computeIfAbsent(K key,
                                                           Function<? super K, ? extends V> mappingFunction) {
        checkNotNull(key, ERROR_NULL_KEY);
        checkNotNull(mappingFunction, "Mapping function cannot be null");
        final MeteringAgent.Context timer = monitor.startTimer(COMPUTE_IF_ABSENT);
        return updateAndGet(key, Match.ifNull(), Match.any(), mappingFunction.apply(key))
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(v -> v.newValue());
    }

    @Override
    public CompletableFuture<Versioned<V>> computeIfPresent(K key,
                            BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        return computeIf(key, Objects::nonNull, remappingFunction);
    }

    @Override
    public CompletableFuture<Versioned<V>> compute(K key,
                                                   BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        return computeIf(key, v -> true, remappingFunction);
    }

    @Override
    public CompletableFuture<Versioned<V>> computeIf(K key,
                                                     Predicate<? super V> condition,
                                                     BiFunction<? super K, ? super V, ? extends V> remappingFunction) {
        checkNotNull(key, ERROR_NULL_KEY);
        checkNotNull(condition, "predicate function cannot be null");
        checkNotNull(remappingFunction, "Remapping function cannot be null");
        final MeteringAgent.Context timer = monitor.startTimer(COMPUTE_IF);
        return get(key).thenCompose(r1 -> {
            V existingValue = r1 == null ? null : r1.value();
            // if the condition evaluates to false, return existing value.
            if (!condition.test(existingValue)) {
                return CompletableFuture.completedFuture(r1);
            }

            AtomicReference<V> computedValue = new AtomicReference<>();
            // if remappingFunction throws an exception, return the exception.
            try {
                computedValue.set(remappingFunction.apply(key, existingValue));
            } catch (Exception e) {
                return Tools.exceptionalFuture(e);
            }
            if (computedValue.get() == null && r1 == null) {
                return CompletableFuture.completedFuture(null);
            }
            Match<V> valueMatcher = r1 == null ? Match.ifNull() : Match.any();
            Match<Long> versionMatcher = r1 == null ? Match.any() : Match.ifValue(r1.version());
            return updateAndGet(key, valueMatcher, versionMatcher, computedValue.get())
                    .whenComplete((r, e) -> timer.stop(e))
                    .thenApply(v -> {
                        if (v.updated()) {
                            return v.newValue();
                        } else {
                            throw new ConsistentMapException.ConcurrentModification();
                        }
                    });
        });
    }

    @Override
    public CompletableFuture<Versioned<V>> put(K key, V value) {
        checkNotNull(key, ERROR_NULL_KEY);
        checkNotNull(value, ERROR_NULL_VALUE);
        final MeteringAgent.Context timer = monitor.startTimer(PUT);
        return updateAndGet(key, Match.any(), Match.any(), value).thenApply(v -> v.oldValue())
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Versioned<V>> putAndGet(K key, V value) {
        checkNotNull(key, ERROR_NULL_KEY);
        checkNotNull(value, ERROR_NULL_VALUE);
        final MeteringAgent.Context timer = monitor.startTimer(PUT_AND_GET);
        return updateAndGet(key, Match.any(), Match.any(), value).thenApply(v -> v.newValue())
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Versioned<V>> remove(K key) {
        checkNotNull(key, ERROR_NULL_KEY);
        final MeteringAgent.Context timer = monitor.startTimer(REMOVE);
        return updateAndGet(key, Match.any(), Match.any(), null).thenApply(v -> v.oldValue())
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Void> clear() {
        checkIfUnmodifiable();
        final MeteringAgent.Context timer = monitor.startTimer(CLEAR);
        return database.mapClear(name).thenApply(this::unwrapResult)
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Set<K>> keySet() {
        final MeteringAgent.Context timer = monitor.startTimer(KEY_SET);
        return database.mapKeySet(name)
                .thenApply(s -> newMappingKeySet(s))
                .whenComplete((r, e) -> timer.stop(e));
    }

    @Override
    public CompletableFuture<Collection<Versioned<V>>> values() {
        final MeteringAgent.Context timer = monitor.startTimer(VALUES);
        return database.mapValues(name)
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(c -> c
                        .stream()
                        .map(v -> v.<V>map(serializer::decode))
                        .collect(Collectors.toList()));
    }

    @Override
    public CompletableFuture<Set<Entry<K, Versioned<V>>>> entrySet() {
        final MeteringAgent.Context timer = monitor.startTimer(ENTRY_SET);
        return database.mapEntrySet(name)
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(s -> newMappingEntrySet(s));
    }

    @Override
    public CompletableFuture<Versioned<V>> putIfAbsent(K key, V value) {
        checkNotNull(key, ERROR_NULL_KEY);
        checkNotNull(value, ERROR_NULL_VALUE);
        final MeteringAgent.Context timer = monitor.startTimer(PUT_IF_ABSENT);
        return updateAndGet(key, Match.ifNull(), Match.any(), value)
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(v -> v.oldValue());
    }

    @Override
    public CompletableFuture<Boolean> remove(K key, V value) {
        checkNotNull(key, ERROR_NULL_KEY);
        checkNotNull(value, ERROR_NULL_VALUE);
        final MeteringAgent.Context timer = monitor.startTimer(REMOVE);
        return updateAndGet(key, Match.ifValue(value), Match.any(), null)
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(v -> v.updated());
    }

    @Override
    public CompletableFuture<Boolean> remove(K key, long version) {
        checkNotNull(key, ERROR_NULL_KEY);
        final MeteringAgent.Context timer = monitor.startTimer(REMOVE);
        return updateAndGet(key, Match.any(), Match.ifValue(version), null)
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(v -> v.updated());
    }

    @Override
    public CompletableFuture<Boolean> replace(K key, V oldValue, V newValue) {
        checkNotNull(key, ERROR_NULL_KEY);
        checkNotNull(oldValue, ERROR_NULL_VALUE);
        checkNotNull(newValue, ERROR_NULL_VALUE);
        final MeteringAgent.Context timer = monitor.startTimer(REPLACE);
        return updateAndGet(key, Match.ifValue(oldValue), Match.any(), newValue)
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(v -> v.updated());
    }

    @Override
    public CompletableFuture<Boolean> replace(K key, long oldVersion, V newValue) {
        final MeteringAgent.Context timer = monitor.startTimer(REPLACE);
        return updateAndGet(key, Match.any(), Match.ifValue(oldVersion), newValue)
                .whenComplete((r, e) -> timer.stop(e))
                .thenApply(v -> v.updated());
    }

    /**
     * Pre-update hook for performing required checks/actions before going forward with an update operation.
     * @param key map key.
     */
    protected void beforeUpdate(K key) {
        checkIfUnmodifiable();
    }

    private Set<K> newMappingKeySet(Set<String> s) {
        return new MappingSet<>(s, Collections::unmodifiableSet,
                                this::sK, this::dK);
    }

    private Set<Entry<K, Versioned<V>>> newMappingEntrySet(Set<Entry<String, Versioned<byte[]>>> s) {
        return new MappingSet<>(s, Collections::unmodifiableSet,
                                this::reverseMapRawEntry, this::mapRawEntry);
    }

    private Map.Entry<K, Versioned<V>> mapRawEntry(Map.Entry<String, Versioned<byte[]>> e) {
        return Maps.immutableEntry(dK(e.getKey()), e.getValue().<V>map(serializer::decode));
    }

    private Map.Entry<String, Versioned<byte[]>> reverseMapRawEntry(Map.Entry<K, Versioned<V>> e) {
        return Maps.immutableEntry(sK(e.getKey()), e.getValue().map(serializer::encode));
    }

    private CompletableFuture<UpdateResult<K, V>> updateAndGet(K key,
                                                               Match<V> oldValueMatch,
                                                               Match<Long> oldVersionMatch,
                                                               V value) {
        beforeUpdate(key);
        return database.mapUpdate(name,
                sK(key),
                oldValueMatch.map(serializer::encode),
                oldVersionMatch,
                value == null ? null : serializer.encode(value))
                .thenApply(this::unwrapResult)
                .thenApply(r -> r.<K, V>map(this::dK, serializer::decode));
    }

    private <T> T unwrapResult(Result<T> result) {
        if (result.status() == Result.Status.LOCKED) {
            throw new ConsistentMapException.ConcurrentModification();
        } else if (result.success()) {
            return result.value();
        } else {
            throw new IllegalStateException("Must not be here");
        }
    }

    private void checkIfUnmodifiable() {
        if (readOnly) {
            throw new UnsupportedOperationException();
        }
    }

    @Override
    public void addListener(MapEventListener<K, V> listener) {
        listeners.add(listener);
    }

    @Override
    public void removeListener(MapEventListener<K, V> listener) {
        listeners.remove(listener);
    }

    protected void notifyListeners(MapEvent<K, V> event) {
        if (event == null) {
            return;
        }
        listeners.forEach(listener -> {
            try {
                listener.event(event);
            } catch (Exception e) {
                log.warn("Failure notifying listener about {}", event, e);
            }
        });
    }

}