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/**
 * Copyright (c) 2014 SQUARESPACE, Inc.
 *
 * 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 com.squarespace.less;

import java.nio.file.Files;
import java.nio.file.Path;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

import com.squarespace.less.model.Import;


/**
 * Forces all imports to be children of a given filesystem root.
 *
 * No {@link Import} instruction will be allowed to read files outside this root.
 * It also restricts the file extensions of imports to those matching the "\.(less|css)$"
 * pattern.
 */
public class JailedFilesystemLessLoader extends FilesystemLessLoader {

  /**
   * Pattern to ensure import paths end in a legal extension.
   */
  private static final Pattern ACCEPT_IMPORT = Pattern.compile(".*\\.(less|css)$");

  /**
   * Parent path. All imported paths must be children of this path.
   */
  private final Path jailRoot;

  public JailedFilesystemLessLoader(Path jailRoot) {
    this.jailRoot = jailRoot.toAbsolutePath().normalize();
  }

  @Override
  public boolean exists(Path path) {
    Matcher matcher = ACCEPT_IMPORT.matcher(path.getFileName().toString());
    if (!matcher.matches()) {
      return false;
    }
    Path tempPath = jailRoot.resolve(path).toAbsolutePath().normalize();
    if (!tempPath.startsWith(jailRoot)) {
      return false;
    }
    return Files.exists(tempPath);
  }

}