/*
 * 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.tika.fork;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
import java.util.Set;

import org.apache.tika.exception.TikaException;
import org.apache.tika.metadata.Metadata;
import org.apache.tika.mime.MediaType;
import org.apache.tika.parser.AbstractParser;
import org.apache.tika.parser.AutoDetectParser;
import org.apache.tika.parser.ParseContext;
import org.apache.tika.parser.Parser;
import org.apache.tika.sax.TeeContentHandler;
import org.xml.sax.ContentHandler;
import org.xml.sax.SAXException;

public class ForkParser extends AbstractParser {

    /** Serial version UID */
    private static final long serialVersionUID = -4962742892274663950L;

    private final ClassLoader loader;

    private final Parser parser;

    /** Java command line */
    private List<String> java = Arrays.asList("java", "-Xmx32m");

    /** Process pool size */
    private int poolSize = 5;

    private int currentlyInUse = 0;

    private final Queue<ForkClient> pool =
        new LinkedList<ForkClient>();

    /**
     * @param loader The ClassLoader to use 
     * @param parser the parser to delegate to. This one cannot be another ForkParser
     */
    public ForkParser(ClassLoader loader, Parser parser) {
        if (parser instanceof ForkParser) {
            throw new IllegalArgumentException("The underlying parser of a ForkParser should not be a ForkParser, but a specific implementation.");
        }
        this.loader = loader;
        this.parser = parser;
    }

    public ForkParser(ClassLoader loader) {
        this(loader, new AutoDetectParser());
    }

    public ForkParser() {
        this(ForkParser.class.getClassLoader());
    }

    /**
     * Returns the size of the process pool.
     *
     * @return process pool size
     */
    public synchronized int getPoolSize() {
        return poolSize;
    }

    /**
     * Sets the size of the process pool.
     *
     * @param poolSize process pool size
     */
    public synchronized void setPoolSize(int poolSize) {
        this.poolSize = poolSize;
    }

    /**
     * Returns the command used to start the forked server process.
     *
     * @return java command line
     * @deprecated since 1.8
     * @see ForkParser#getJavaCommandAsList()
     */
    @Deprecated
    public String getJavaCommand() {
        StringBuilder sb = new StringBuilder();
        for (String part : getJavaCommandAsList()) {
            sb.append(part).append(' ');
        }
        sb.deleteCharAt(sb.length() - 1);
        return sb.toString();
    }

    /**
     * Returns the command used to start the forked server process.
     * <p/>
     * Returned list is unmodifiable.
     * @return java command line args
     */
    public List<String> getJavaCommandAsList() {
        return Collections.unmodifiableList(java);
    }

    /**
     * Sets the command used to start the forked server process.
     * The arguments "-jar" and "/path/to/bootstrap.jar" are
     * appended to the given command when starting the process.
     * The default setting is {"java", "-Xmx32m"}.
     * <p/>
     * Creates a defensive copy.
     * @param java java command line
     */
    public void setJavaCommand(List<String> java) {
        this.java = new ArrayList<String>(java);
    }

    /**
     * Sets the command used to start the forked server process.
     * The given command line is split on whitespace and the arguments
2    * "-jar" and "/path/to/bootstrap.jar" are appended to it when starting
2    * the process. The default setting is "java -Xmx32m".
     *
     * @param java java command line
     * @deprecated since 1.8
     * @see ForkParser#setJavaCommand(List)
     */
    @Deprecated
    public void setJavaCommand(String java) {
        setJavaCommand(Arrays.asList(java.split(" ")));
    }

    public Set<MediaType> getSupportedTypes(ParseContext context) {
        return parser.getSupportedTypes(context);
    }

    public void parse(
            InputStream stream, ContentHandler handler,
            Metadata metadata, ParseContext context)
            throws IOException, SAXException, TikaException {
        if (stream == null) {
            throw new NullPointerException("null stream");
        }

        Throwable t;

        boolean alive = false;
        ForkClient client = acquireClient();
        try {
            ContentHandler tee = new TeeContentHandler(
                    handler, new MetadataContentHandler(metadata));
            t = client.call("parse", stream, tee, metadata, context);
            alive = true;
        } catch (TikaException te) {
            // Problem occurred on our side
            alive = true;
            throw te;
        } catch (IOException e) {
            // Problem occurred on the other side
            throw new TikaException(
                    "Failed to communicate with a forked parser process."
                    + " The process has most likely crashed due to some error"
                    + " like running out of memory. A new process will be"
                    + " started for the next parsing request.", e);
        } finally {
            releaseClient(client, alive);
        }

        if (t instanceof IOException) {
            throw (IOException) t;
        } else if (t instanceof SAXException) {
            throw (SAXException) t;
        } else if (t instanceof TikaException) {
            throw (TikaException) t;
        } else if (t != null) {
            throw new TikaException(
                    "Unexpected error in forked server process", t);
        }
    }

    public synchronized void close() {
        for (ForkClient client : pool) {
            client.close();
        }
        pool.clear();
        poolSize = 0;
    }

    private synchronized ForkClient acquireClient()
            throws IOException, TikaException {
        while (true) {
            ForkClient client = pool.poll();

            // Create a new process if there's room in the pool
            if (client == null && currentlyInUse < poolSize) {
                client = new ForkClient(loader, parser, java);
            }

            // Ping the process, and get rid of it if it's inactive
            if (client != null && !client.ping()) {
                client.close();
                client = null;
            }

            if (client != null) {
                currentlyInUse++;
                return client;
            } else if (currentlyInUse >= poolSize) {
                try {
                    wait();
                } catch (InterruptedException e) {
                    throw new TikaException(
                            "Interrupted while waiting for a fork parser", e);
                }
            }
        }
    }

    private synchronized void releaseClient(ForkClient client, boolean alive) {
        currentlyInUse--;
        if (currentlyInUse + pool.size() < poolSize && alive) {
            pool.offer(client);
            notifyAll();
        } else {
            client.close();
        }
    }

}
