/*
 * 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.solr.util;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FilenameFilter;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collection;
import java.util.HashSet;
import java.util.List;
import java.util.Set;


/**
 * 
 * @since solr 1.3
 */
public class VersionedFile 
{
  /* Open the latest version of a file... fileName if that exists, or
   * the last fileName.* after being sorted lexicographically.
   * Older versions of the file are deleted (and queued for deletion if
   * that fails).
   */
  public static InputStream getLatestFile(String dirName, String fileName) throws FileNotFoundException 
  {
    Collection<File> oldFiles=null;
    final String prefix = fileName+'.';
    File f = new File(dirName, fileName);
    InputStream is = null;

    // there can be a race between checking for a file and opening it...
    // the user may have just put a new version in and deleted an old version.
    // try multiple times in a row.
    for (int retry=0; retry<10 && is==null; retry++) {
      try {
        if (!f.exists()) {
          File dir = new File(dirName);
          String[] names = dir.list(new FilenameFilter() {
            @Override
            public boolean accept(File dir, String name) {
              return name.startsWith(prefix);
            }
          });
          Arrays.sort(names);
          f = new File(dir, names[names.length-1]);
          oldFiles = new ArrayList<>();
          for (int i=0; i<names.length-1; i++) {
            oldFiles.add(new File(dir, names[i]));
          }
        }

        is = new FileInputStream(f);
      } catch (Exception e) {
        // swallow exception for now
      }
    }

    // allow exception to be thrown from the final try.
    if (is == null) {
      is = new FileInputStream(f);
    }

    // delete old files only after we have successfully opened the newest
    if (oldFiles != null) {
      delete(oldFiles);
    }

    return is;
  }

  private static final Set<File> deleteList = new HashSet<>();
  private static synchronized void delete(Collection<File> files) {
    synchronized (deleteList) {
      deleteList.addAll(files);
      List<File> deleted = new ArrayList<>();
      for (File df : deleteList) {
        try {
          try {
            Files.deleteIfExists(df.toPath());
          } catch (IOException cause) {
            // TODO: should this class care if a file couldn't be deleted?
            // this just emulates previous behavior, where only SecurityException would be handled.
          }
          // deleteList.remove(df);
          deleted.add(df);
        } catch (SecurityException e) {
          if (!df.exists()) {
            deleted.add(df);
          }
        }
      }
      deleteList.removeAll(deleted);
    }
  }
}