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The Apache Cassandra Project develops a highly scalable second-generation distributed database, bringing together Dynamo's fully distributed design and Bigtable's ColumnFamily-based data model.
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/*
 * 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.cassandra.schema;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.util.UUID;

import javax.annotation.Nullable;

import org.apache.commons.lang3.ArrayUtils;

import org.apache.cassandra.utils.ByteBufferUtil;
import org.apache.cassandra.utils.Pair;

import static org.apache.cassandra.utils.TimeUUID.Generator.nextTimeUUID;

import static java.nio.charset.StandardCharsets.UTF_8;

/**
 * The unique identifier of a table.
 * 
 * This is essentially a UUID, but we wrap it as it's used quite a bit in the code and having a nicely named class make
 * the code more readable.
 */
public class TableId
{
    // TODO: should this be a TimeUUID?
    private final UUID id;

    private TableId(UUID id)
    {
        this.id = id;
    }

    public static TableId fromUUID(UUID id)
    {
        return new TableId(id);
    }

    // TODO: should we be using UUID.randomUUID()?
    public static TableId generate()
    {
        return new TableId(nextTimeUUID().asUUID());
    }

    public static TableId fromString(String idString)
    {
        return new TableId(UUID.fromString(idString));
    }

    @Nullable
    public static Pair tableNameAndIdFromFilename(String filename)
    {
        int dash = filename.lastIndexOf('-');
        if (dash <= 0 || dash != filename.length() - 32 - 1)
            return null;

        TableId id = fromHexString(filename.substring(dash + 1));
        String tableName = filename.substring(0, dash);

        return Pair.create(tableName, id);
    }

    private static TableId fromHexString(String nonDashUUID)
    {
        ByteBuffer bytes = ByteBufferUtil.hexToBytes(nonDashUUID);
        long msb = bytes.getLong(0);
        long lsb = bytes.getLong(8);
        return fromUUID(new UUID(msb, lsb));
    }

    /**
     * Creates the UUID of a system table.
     *
     * This is deterministically based on the table name as system tables are hardcoded and initialized independently
     * on each node (they don't go through a CREATE), but we still want them to have the same ID everywhere.
     *
     * We shouldn't use this for any other table.
     */
    public static TableId forSystemTable(String keyspace, String table)
    {
        assert SchemaConstants.isSystemKeyspace(keyspace) : String.format("Table %s.%s is not a system table; only keyspaces allowed are %s", keyspace, table, SchemaConstants.getSystemKeyspaces());
        return unsafeDeterministic(keyspace, table);
    }

    public static TableId unsafeDeterministic(String keyspace, String table)
    {
        return new TableId(UUID.nameUUIDFromBytes(ArrayUtils.addAll(keyspace.getBytes(UTF_8), table.getBytes(UTF_8))));
    }

    public String toHexString()
    {
        return ByteBufferUtil.bytesToHex(ByteBufferUtil.bytes(id));
    }

    public UUID asUUID()
    {
        return id;
    }

    @Override
    public final int hashCode()
    {
        return id.hashCode();
    }

    @Override
    public final boolean equals(Object o)
    {
        return this == o || (o instanceof TableId && this.id.equals(((TableId) o).id));
    }

    @Override
    public String toString()
    {
        return id.toString();
    }

    public void serialize(DataOutput out) throws IOException
    {
        out.writeLong(id.getMostSignificantBits());
        out.writeLong(id.getLeastSignificantBits());
    }

    public int serializedSize()
    {
        return 16;
    }

    public static TableId deserialize(DataInput in) throws IOException
    {
        return new TableId(new UUID(in.readLong(), in.readLong()));
    }
}