/**
 * 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.camel.component.file.strategy;

import java.io.File;
import java.io.IOException;

import org.apache.camel.Exchange;
import org.apache.camel.component.file.GenericFile;
import org.apache.camel.component.file.GenericFileEndpoint;
import org.apache.camel.component.file.GenericFileOperations;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

/**
 * Acquires exclusive read lock to the given file by checking whether the file is being
 * changed by scanning the file at different intervals (to detec changes).
 */
public class FileChangedExclusiveReadLockStrategy extends MarkerFileExclusiveReadLockStrategy {
    private static final transient Log LOG = LogFactory.getLog(FileChangedExclusiveReadLockStrategy.class);
    private long timeout;

    @Override
    public void prepareOnStartup(GenericFileOperations<File> operations, GenericFileEndpoint<File> endpoint) {
        // noop
    }

    public boolean acquireExclusiveReadLock(GenericFileOperations<File> operations, GenericFile<File> file, Exchange exchange) throws Exception {
        File target = new File(file.getAbsoluteFilePath());
        boolean exclusive = false;

        if (LOG.isTraceEnabled()) {
            LOG.trace("Waiting for exclusive read lock to file: " + file);
        }

        try {
            long lastModified = Long.MIN_VALUE;
            long length = Long.MIN_VALUE;

            long start = System.currentTimeMillis();

            while (!exclusive) {
                // timeout check
                if (timeout > 0) {
                    long delta = System.currentTimeMillis() - start;
                    if (delta > timeout) {
                        LOG.warn("Cannot acquire read lock within " + timeout + " millis. Will skip the file: " + file);
                        // we could not get the lock within the timeout period, so return false
                        return false;
                    }
                }

                long newLastModified = target.lastModified();
                long newLength = target.length();

                if (LOG.isTraceEnabled()) {
                    LOG.trace("Previous last modified: " + lastModified + ", new last modified: " + newLastModified);
                    LOG.trace("Previous length: " + length + ", new length: " + newLength);
                }

                if (newLastModified == lastModified && newLength == length) {
                    // let super handle the last part of acquiring the lock now the file is not
                    // currently being in progress of being copied as file length and modified
                    // are stable
                    exclusive = super.acquireExclusiveReadLock(operations, file, exchange);
                } else {
                    // set new base file change information
                    lastModified = newLastModified;
                    length = newLength;

                    boolean interrupted = sleep();
                    if (interrupted) {
                        // we were interrupted while sleeping, we are likely being shutdown so return false
                        return false;
                    }
                }
            }
        } catch (IOException e) {
            // must handle IOException as some apps on Windows etc. will still somehow hold a lock to a file
            // such as AntiVirus or MS Office that has special locks for it's supported files
            if (timeout == 0) {
                // if not using timeout, then we cant retry, so rethrow
                throw e;
            }
            if (LOG.isDebugEnabled()) {
                LOG.debug("Cannot acquire read lock. Will try again.", e);
            }
            boolean interrupted = sleep();
            if (interrupted) {
                // we were interrupted while sleeping, we are likely being shutdown so return false
                return false;
            }
        }

        return exclusive;
    }

    private boolean sleep() {
        if (LOG.isTraceEnabled()) {
            LOG.trace("Exclusive read lock not granted. Sleeping for 1000 millis.");
        }
        try {
            Thread.sleep(1000);
            return false;
        } catch (InterruptedException e) {
            if (LOG.isDebugEnabled()) {
                LOG.debug("Sleep interrupted while waiting for exclusive read lock, so breaking out");
            }
            return true;
        }
    }

    public long getTimeout() {
        return timeout;
    }

    public void setTimeout(long timeout) {
        this.timeout = timeout;
    }

}
