package org.eclipse.aether.spi.connector.transport;

/*
 * 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.
 */

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.ByteBuffer;
import java.util.Objects;
import java.util.concurrent.atomic.AtomicBoolean;

import org.eclipse.aether.transfer.TransferCancelledException;

/**
 * A skeleton implementation for custom transporters.
 */
public abstract class AbstractTransporter
    implements Transporter
{

    private final AtomicBoolean closed;

    /**
     * Enables subclassing.
     */
    protected AbstractTransporter()
    {
        closed = new AtomicBoolean();
    }

    public void peek( PeekTask task )
        throws Exception
    {
        Objects.requireNonNull( task, "task cannot be null" );

        failIfClosed( task );
        implPeek( task );
    }

    /**
     * Implements {@link #peek(PeekTask)}, gets only called if the transporter has not been closed.
     *
     * @param task The existence check to perform, must not be {@code null}.
     * @throws Exception If the existence of the specified resource could not be confirmed.
     */
    protected abstract void implPeek( PeekTask task )
        throws Exception;

    public void get( GetTask task )
        throws Exception
    {
        Objects.requireNonNull( task, "task cannot be null" );

        failIfClosed( task );
        implGet( task );
    }

    /**
     * Implements {@link #get(GetTask)}, gets only called if the transporter has not been closed.
     *
     * @param task The download to perform, must not be {@code null}.
     * @throws Exception If the transfer failed.
     */
    protected abstract void implGet( GetTask task )
        throws Exception;

    /**
     * Performs stream-based I/O for the specified download task and notifies the configured transport listener.
     * Subclasses might want to invoke this utility method from within their {@link #implGet(GetTask)} to avoid
     * boilerplate I/O code.
     *
     * @param task The download to perform, must not be {@code null}.
     * @param is The input stream to download the data from, must not be {@code null}.
     * @param close {@code true} if the supplied input stream should be automatically closed, {@code false} to leave the
     *            stream open.
     * @param length The size in bytes of the downloaded resource or {@code -1} if unknown, not to be confused with the
     *            length of the supplied input stream which might be smaller if the download is resumed.
     * @param resume {@code true} if the download resumes from {@link GetTask#getResumeOffset()}, {@code false} if the
     *            download starts at the first byte of the resource.
     * @throws IOException If the transfer encountered an I/O error.
     * @throws TransferCancelledException If the transfer was cancelled.
     */
    protected void utilGet( GetTask task, InputStream is, boolean close, long length, boolean resume )
        throws IOException, TransferCancelledException
    {
        try ( OutputStream os = task.newOutputStream( resume ) )
        {
            task.getListener().transportStarted( resume ? task.getResumeOffset() : 0L, length );
            copy( os, is, task.getListener() );
        }
        finally
        {
            if ( close )
            {
                is.close();
            }
        }
    }

    public void put( PutTask task )
        throws Exception
    {
        Objects.requireNonNull( task, "task cannot be null" );

        failIfClosed( task );
        implPut( task );
    }

    /**
     * Implements {@link #put(PutTask)}, gets only called if the transporter has not been closed.
     *
     * @param task The upload to perform, must not be {@code null}.
     * @throws Exception If the transfer failed.
     */
    protected abstract void implPut( PutTask task )
        throws Exception;

    /**
     * Performs stream-based I/O for the specified upload task and notifies the configured transport listener.
     * Subclasses might want to invoke this utility method from within their {@link #implPut(PutTask)} to avoid
     * boilerplate I/O code.
     *
     * @param task The upload to perform, must not be {@code null}.
     * @param os The output stream to upload the data to, must not be {@code null}.
     * @param close {@code true} if the supplied output stream should be automatically closed, {@code false} to leave
     *            the stream open.
     * @throws IOException If the transfer encountered an I/O error.
     * @throws TransferCancelledException If the transfer was cancelled.
     */
    protected void utilPut( PutTask task, OutputStream os, boolean close )
        throws IOException, TransferCancelledException
    {
        try ( InputStream is = task.newInputStream() )
        {
            task.getListener().transportStarted( 0, task.getDataLength() );
            copy( os, is, task.getListener() );
        }
        finally
        {
            if ( close )
            {
                os.close();
            }
            else
            {
                os.flush();
            }
        }
    }

    public void close()
    {
        if ( closed.compareAndSet( false, true ) )
        {
            implClose();
        }
    }

    /**
     * Implements {@link #close()}, gets only called if the transporter has not already been closed.
     */
    protected abstract void implClose();

    private void failIfClosed( TransportTask task )
    {
        if ( closed.get() )
        {
            throw new IllegalStateException( "transporter closed, cannot execute task " + task );
        }
    }

    private static void copy( OutputStream os, InputStream is, TransportListener listener )
        throws IOException, TransferCancelledException
    {
        byte[] buffer = new byte[ 1024 * 32 ];
        for ( int read = is.read( buffer ); read >= 0; read = is.read( buffer ) )
        {
            os.write( buffer, 0, read );
            listener.transportProgressed( ByteBuffer.wrap( buffer, 0, read ) );
        }
    }

}