/*
 * Copyright 2004-2009 the original author or authors.
 *
 * 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.apache.lucene.store.jdbc.index;

import java.io.IOException;
import java.sql.Blob;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

import org.apache.lucene.store.IndexInput;
import org.apache.lucene.store.jdbc.JdbcDirectory;
import org.apache.lucene.store.jdbc.JdbcFileEntrySettings;
import org.apache.lucene.store.jdbc.JdbcStoreException;
import org.apache.lucene.store.jdbc.support.JdbcTemplate;

/**
 * An <code>IndexInput</code> implementation that will read all the relevant data from the
 * database when created, and will cache it untill it is closed.
 * <p/>
 * Used for small file entries in the database like the segments file.
 *
 * @author kimchy
 */
public class FetchOnOpenJdbcIndexInput extends IndexInput implements JdbcIndexConfigurable {

    //There is no synchronizaiton since Lucene RAMDirecoty performs no synchronizations.
    // Need to get to the bottom of it.

    private int length;

    private int position = 0;

    private byte[] data;

    public void configure(final String name, final JdbcDirectory jdbcDirectory, JdbcFileEntrySettings settings) throws IOException {
        jdbcDirectory.getJdbcTemplate().executeSelect(jdbcDirectory.getTable().sqlSelectSizeValueByName(),
                new JdbcTemplate.ExecuteSelectCallback() {
                    public void fillPrepareStatement(PreparedStatement ps) throws Exception {
                        ps.setFetchSize(1);
                        ps.setString(1, name);
                    }

                    public Object execute(ResultSet rs) throws Exception {
                        if (!rs.next()) {
                            throw new JdbcStoreException("No entry for [" + name + "] table " + jdbcDirectory.getTable());
                        }
                        length = rs.getInt(3);

                        Blob blob = rs.getBlob(2);
                        data = blob.getBytes(1, length);
                        if (data.length != length) {
                            throw new IOException("read past EOF");
                        }
                        return null;
                    }
                });
    }

    public byte readByte() throws IOException {
        return data[position++];
    }

    public void readBytes(byte[] b, int offset, int len) throws IOException {
        System.arraycopy(data, position, b, offset, len);
        position += len;
    }

    public void close() throws IOException {

    }

    public long getFilePointer() {
        return position;
    }

    public void seek(long pos) throws IOException {
        position = (int) pos;
    }

    public long length() {
        return this.length;
    }
}