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Where all the magic happens
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/*
 * Copyright 2013 eXo Platform SAS
 *
 * Licensed 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 juzu.impl.fs;

import juzu.impl.fs.spi.ReadFileSystem;
import juzu.impl.common.Content;
import juzu.impl.common.Tools;

import java.io.IOException;
import java.io.InputStream;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.ArrayList;

/** @author Julien Viet */
public abstract class FileSystemScanner implements Filter
 {

  public static 
 FileSystemScanner
 createTimestamped(ReadFileSystem
 fs) {
    return new Timestamped
(fs);
  }

  public static 
 FileSystemScanner
 createHashing(ReadFileSystem
 fs) {
    return new Hash
(fs);
  }

  public static class Timestamped
 extends FileSystemScanner
 {
    public Timestamped(ReadFileSystem
 fs) {
      super(fs);
    }

    @Override
    protected long stampOf(P file) throws IOException {
      return fs.getLastModified(file);
    }

    @Override
    protected boolean isModified(long snapshot, long current) {
      return snapshot < current;
    }
  }

  public static class Hash
 extends FileSystemScanner
 {
    public Hash(ReadFileSystem
 fs) {
      super(fs);
    }

    @Override
    protected long stampOf(P file) throws IOException {
      try {
        juzu.impl.common.Timestamped content = fs.getContent(file);
        MessageDigest digest = MessageDigest.getInstance("MD5");
        InputStream in = content.getObject().getInputStream();
        byte[] bytes = Tools.bytes(in);
        byte[] md5 = digest.digest(bytes);
        long value = 0;
        for (byte b : md5) {
          value = value * 256 + Tools.unsignedByteToInt(b);
        }
        return value;
      }
      catch (NoSuchAlgorithmException e) {
        throw new AssertionError(e);
      }
    }

    @Override
    protected boolean isModified(long snapshot, long current) {
      return snapshot != current;
    }
  }

  /** . */
  protected final ReadFileSystem
 fs;

  /** . */
  final ArrayList stack = new ArrayList();

  private FileSystemScanner(ReadFileSystem
 fs) {
    this.fs = fs;
  }

  public ReadFileSystem
 getFileSystem() {
    return fs;
  }

  public Snapshot
 take() {
    return new Snapshot(this);
  }

  public boolean acceptDir(P dir, String name) throws IOException {
    return !name.startsWith(".");
  }

  public boolean acceptFile(P file, String name) throws IOException {
    return !name.startsWith(".");
  }

  protected abstract long stampOf(P file) throws IOException;

  protected abstract boolean isModified(long snapshot, long current);

}