/*
 * Copyright 2014 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.service.impl;

import static org.onlab.util.Tools.namedThreads;
import static org.slf4j.LoggerFactory.getLogger;
import static org.onosproject.store.service.impl.ClusterMessagingProtocol.DB_SERIALIZER;

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.zip.DeflaterOutputStream;
import java.util.zip.InflaterInputStream;

import net.kuujo.copycat.Command;
import net.kuujo.copycat.Query;
import net.kuujo.copycat.StateMachine;

import org.onosproject.store.cluster.messaging.MessageSubject;
import org.onosproject.store.service.BatchReadRequest;
import org.onosproject.store.service.BatchWriteRequest;
import org.onosproject.store.service.ReadRequest;
import org.onosproject.store.service.ReadResult;
import org.onosproject.store.service.ReadStatus;
import org.onosproject.store.service.VersionedValue;
import org.onosproject.store.service.WriteRequest;
import org.onosproject.store.service.WriteResult;
import org.onosproject.store.service.WriteStatus;
import org.slf4j.Logger;

import com.google.common.base.MoreObjects;
import com.google.common.collect.ImmutableMap;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.common.collect.Maps;
import com.google.common.collect.Sets;

/**
 * StateMachine whose transitions are coordinated/replicated
 * by Raft consensus.
 * Each Raft cluster member has a instance of this state machine that is
 * independently updated in lock step once there is consensus
 * on the next transition.
 */
public class DatabaseStateMachine implements StateMachine {

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

    private final ExecutorService updatesExecutor =
            Executors.newSingleThreadExecutor(namedThreads("database-statemachine-updates"));

    // message subject for database update notifications.
    public static final MessageSubject DATABASE_UPDATE_EVENTS =
            new MessageSubject("database-update-events");

    private final Set<DatabaseUpdateEventListener> listeners = Sets.newIdentityHashSet();

    // durable internal state of the database.
    private State state = new State();

    // TODO make this configurable
    private boolean compressSnapshot = true;

    @Command
    public boolean createTable(String tableName) {
        TableMetadata metadata = new TableMetadata(tableName);
        return createTable(metadata);
    }

    @Command
    public boolean createTable(String tableName, Integer ttlMillis) {
        TableMetadata metadata = new TableMetadata(tableName, ttlMillis);
        return createTable(metadata);
    }

    private boolean createTable(TableMetadata metadata) {
        Map<String, VersionedValue> existingTable = state.getTable(metadata.tableName());
        if (existingTable != null) {
            return false;
        }
        state.createTable(metadata);

        updatesExecutor.submit(new Runnable() {
            @Override
            public void run() {
                for (DatabaseUpdateEventListener listener : listeners) {
                    listener.tableCreated(metadata);
                }
            }
        });

        return true;
    }

    @Command
    public boolean dropTable(String tableName) {
        if (state.removeTable(tableName)) {

            updatesExecutor.submit(new Runnable() {
                @Override
                public void run() {
                    for (DatabaseUpdateEventListener listener : listeners) {
                        listener.tableDeleted(tableName);
                    }
                }
            });

            return true;
        }
        return false;
    }

    @Command
    public boolean dropAllTables() {
        Set<String> tableNames = state.getTableNames();
        state.removeAllTables();

        updatesExecutor.submit(new Runnable() {
            @Override
            public void run() {
                for (DatabaseUpdateEventListener listener : listeners) {
                    for (String tableName : tableNames) {
                        listener.tableDeleted(tableName);
                    }
                }
            }
        });

        return true;
    }

    @Query
    public Set<String> listTables() {
        return ImmutableSet.copyOf(state.getTableNames());
    }

    @Query
    public List<ReadResult> read(BatchReadRequest batchRequest) {
        List<ReadResult> results = new ArrayList<>(batchRequest.batchSize());
        for (ReadRequest request : batchRequest.getAsList()) {
            Map<String, VersionedValue> table = state.getTable(request.tableName());
            if (table == null) {
                results.add(new ReadResult(ReadStatus.NO_SUCH_TABLE, request.tableName(), request.key(), null));
                continue;
            }
            VersionedValue value = VersionedValue.copy(table.get(request.key()));
            results.add(new ReadResult(ReadStatus.OK, request.tableName(), request.key(), value));
        }
        return results;
    }

    @Query
    public Map<String, VersionedValue> getAll(String tableName) {
        return ImmutableMap.copyOf(state.getTable(tableName));
    }


    WriteStatus checkIfApplicable(WriteRequest request, VersionedValue value) {

        switch (request.type()) {
        case PUT:
            return WriteStatus.OK;

        case PUT_IF_ABSENT:
            if (value == null) {
                return WriteStatus.OK;
            }
            return WriteStatus.PRECONDITION_VIOLATION;

        case PUT_IF_VALUE:
        case REMOVE_IF_VALUE:
            if (value != null && Arrays.equals(value.value(), request.oldValue())) {
                return WriteStatus.OK;
            }
            return WriteStatus.PRECONDITION_VIOLATION;

        case PUT_IF_VERSION:
        case REMOVE_IF_VERSION:
            if (value != null && request.previousVersion() == value.version()) {
                return WriteStatus.OK;
            }
            return WriteStatus.PRECONDITION_VIOLATION;

        case REMOVE:
            return WriteStatus.OK;

        default:
            break;
        }
        log.error("Should never reach here {}", request);
        return WriteStatus.ABORTED;
    }

    @Command
    public List<WriteResult> write(BatchWriteRequest batchRequest) {

        // applicability check
        boolean abort = false;
        List<WriteResult> results = new ArrayList<>(batchRequest.batchSize());

        for (WriteRequest request : batchRequest.getAsList()) {
            Map<String, VersionedValue> table = state.getTable(request.tableName());
            if (table == null) {
                results.add(new WriteResult(WriteStatus.NO_SUCH_TABLE, null));
                abort = true;
                continue;
            }
            final VersionedValue value = table.get(request.key());
            WriteStatus result = checkIfApplicable(request, value);
            results.add(new WriteResult(result, value));
            if (result != WriteStatus.OK) {
                abort = true;
            }
        }

        if (abort) {
            for (int i = 0; i < results.size(); ++i) {
                if (results.get(i).status() == WriteStatus.OK) {
                    results.set(i, new WriteResult(WriteStatus.ABORTED, null));
                }
            }
            return results;
        }

        List<TableModificationEvent> tableModificationEvents = Lists.newLinkedList();

        // apply changes
        for (WriteRequest request : batchRequest.getAsList()) {
            Map<String, VersionedValue> table = state.getTable(request.tableName());

            TableModificationEvent tableModificationEvent = null;
            // FIXME: If this method could be called by multiple thread,
            // synchronization scope is wrong.
            // Whole function including applicability check needs to be protected.
            // Confirm copycat's thread safety requirement for StateMachine
            // TODO: If we need isolation, we need to block reads also
            synchronized (table) {
                switch (request.type()) {
                case PUT:
                case PUT_IF_ABSENT:
                case PUT_IF_VALUE:
                case PUT_IF_VERSION:
                    VersionedValue newValue = new VersionedValue(request.newValue(), state.nextVersion());
                    VersionedValue previousValue = table.put(request.key(), newValue);
                    WriteResult putResult = new WriteResult(WriteStatus.OK, previousValue);
                    results.add(putResult);
                    tableModificationEvent = (previousValue == null) ?
                            TableModificationEvent.rowAdded(request.tableName(), request.key(), newValue) :
                            TableModificationEvent.rowUpdated(request.tableName(), request.key(), newValue);
                    break;

                case REMOVE:
                case REMOVE_IF_VALUE:
                case REMOVE_IF_VERSION:
                    VersionedValue removedValue = table.remove(request.key());
                    WriteResult removeResult = new WriteResult(WriteStatus.OK, removedValue);
                    results.add(removeResult);
                    if (removedValue != null) {
                        tableModificationEvent =
                                TableModificationEvent.rowDeleted(request.tableName(), request.key(), removedValue);
                    }
                    break;

                default:
                    log.error("Invalid WriteRequest type {}", request.type());
                    break;
                }
            }

            if (tableModificationEvent != null) {
                tableModificationEvents.add(tableModificationEvent);
            }
        }

        // notify listeners of table mod events.

        updatesExecutor.submit(new Runnable() {
            @Override
            public void run() {
                for (DatabaseUpdateEventListener listener : listeners) {
                    for (TableModificationEvent tableModificationEvent : tableModificationEvents) {
                        log.trace("Publishing table modification event: {}", tableModificationEvent);
                        listener.tableModified(tableModificationEvent);
                    }
                }
            }
        });

        return results;
    }

    public static class State {

        private final Map<String, TableMetadata> tableMetadata = Maps.newHashMap();
        private final Map<String, Map<String, VersionedValue>> tableData = Maps.newHashMap();
        private long versionCounter = 1;

        Map<String, VersionedValue> getTable(String tableName) {
            return tableData.get(tableName);
        }

        void createTable(TableMetadata metadata) {
            tableMetadata.put(metadata.tableName, metadata);
            tableData.put(metadata.tableName, Maps.newHashMap());
        }

        TableMetadata getTableMetadata(String tableName) {
            return tableMetadata.get(tableName);
        }

        long nextVersion() {
            return versionCounter++;
        }

        Set<String> getTableNames() {
            return ImmutableSet.copyOf(tableMetadata.keySet());
        }


        boolean removeTable(String tableName) {
            if (!tableMetadata.containsKey(tableName)) {
                return false;
            }
            tableMetadata.remove(tableName);
            tableData.remove(tableName);
            return true;
        }

        void removeAllTables() {
            tableMetadata.clear();
            tableData.clear();
        }
    }

    public static class TableMetadata {
        private final String tableName;
        private final boolean expireOldEntries;
        private final int ttlMillis;

        public TableMetadata(String tableName) {
            this.tableName = tableName;
            this.expireOldEntries = false;
            this.ttlMillis = Integer.MAX_VALUE;

        }

        public TableMetadata(String tableName, int ttlMillis) {
            this.tableName = tableName;
            this.expireOldEntries = true;
            this.ttlMillis = ttlMillis;
        }

        public String tableName() {
            return tableName;
        }

        public boolean expireOldEntries() {
            return expireOldEntries;
        }

        public int ttlMillis() {
            return ttlMillis;
        }

        @Override
        public String toString() {
            return MoreObjects.toStringHelper(getClass())
                    .add("tableName", tableName)
                    .add("expireOldEntries", expireOldEntries)
                    .add("ttlMillis", ttlMillis)
                    .toString();
        }
    }

    @Override
    public byte[] takeSnapshot() {
        try {
            if (compressSnapshot) {
                byte[] input = DB_SERIALIZER.encode(state);
                ByteArrayOutputStream comp = new ByteArrayOutputStream(input.length);
                DeflaterOutputStream compressor = new DeflaterOutputStream(comp);
                compressor.write(input, 0, input.length);
                compressor.close();
                return comp.toByteArray();
            } else {
                return DB_SERIALIZER.encode(state);
            }
        } catch (Exception e) {
            log.error("Failed to take snapshot", e);
            throw new SnapshotException(e);
        }
    }

    @Override
    public void installSnapshot(byte[] data) {
        try {
            if (compressSnapshot) {
                ByteArrayInputStream in = new ByteArrayInputStream(data);
                InflaterInputStream decompressor = new InflaterInputStream(in);
                this.state = DB_SERIALIZER.decode(decompressor);
            } else {
                this.state = DB_SERIALIZER.decode(data);
            }

            updatesExecutor.submit(new Runnable() {
                @Override
                public void run() {
                    for (DatabaseUpdateEventListener listener : listeners) {
                        listener.snapshotInstalled(state);
                    }
                }
            });

        } catch (Exception e) {
            log.error("Failed to install from snapshot", e);
            throw new SnapshotException(e);
        }
    }

    /**
     * Adds specified DatabaseUpdateEventListener.
     * @param listener listener to add
     */
    public void addEventListener(DatabaseUpdateEventListener listener) {
        listeners.add(listener);
    }

    /**
     * Removes specified DatabaseUpdateEventListener.
     * @param listener listener to remove
     */
    public void removeEventListener(DatabaseUpdateEventListener listener) {
        listeners.remove(listener);
    }
}