/**
 * Copyright (c) 2002-2014 "Neo Technology,"
 * Network Engine for Objects in Lund AB [http://neotechnology.com]
 *
 * This file is part of Neo4j.
 *
 * Neo4j is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package com.ldbc.driver.csv.charseeker;

import java.io.Closeable;
import java.io.IOException;
import java.util.Iterator;

/**
 * Have multiple {@link CharReadable} instances look like one. The provided {@link CharReadable readables} should
 * be opened lazily, in {@link Iterator#next()}, and will be closed in here, if they implement {@link Closeable}.
 */
public class MultiReadable implements CharReadable, Closeable {
    private final RawIterator<CharReadable, IOException> actual;
    private CharReadable current = Readables.EMPTY;
    private int readFromCurrent;

    public MultiReadable(RawIterator<CharReadable, IOException> actual) {
        this.actual = actual;
    }

    @Override
    public int read(char[] buffer, int offset, int length) throws IOException {
        int read = 0;
        while (read < length) {
            int readThisTime = current.read(buffer, offset + read, length - read);
            if (readThisTime == -1) {
                if (actual.hasNext()) {
                    closeCurrent();
                    current = actual.next();

                    // Even if there's no line-ending at the end of this source we should introduce one
                    // otherwise the last line of this source and the first line of the next source will
                    // look like one long line.
                    if (readFromCurrent > 0) {
                        buffer[offset + read++] = '\n';
                        readFromCurrent = 0;
                    }
                } else {
                    break;
                }
            } else {
                read += readThisTime;
                readFromCurrent += readThisTime;
            }
        }
        return read == 0 ? -1 : read;
    }

    private void closeCurrent() throws IOException {
        current.close();
    }

    @Override
    public void close() throws IOException {
        closeCurrent();
    }
}