PathSpec.java

/*
   Copyright (c) 2012 LinkedIn Corp.

   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.
*/

/**
 * $Id: $
 */

package com.linkedin.data.schema;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

/**
 * A PathSpec represents a path within a complex data object.  PathSpecs may be obtained from
 * generated RecordTemplate subclasses using the .fields() method.  Because the primary use cases
 * for PathSpecs are to generate uniform references in hierarchical data maps
 * (used in the data-transform) component, the path segments are all represented as String,
 * including the representation for wildcards and integer array indices.
 *
 * @author Josh Walker
 * @version $Revision: $
 */

public class PathSpec
{
  //use this specific instance to differentiate a true wildcard from a "*" key
  public static final String WILDCARD = new String("*");

  /**
   * Construct a new {@link PathSpec} from a list of parent segments and a current
   * segment.
   *
   * @param parentPath provides the parent path.
   * @param segment provides the current path segment.
   */
  public PathSpec(List<String> parentPath, String segment)
  {
    _path = new ArrayList<String>(parentPath.size()+1);
    _path.addAll(parentPath);
    _path.add(segment);
  }

  /**
   * Construct a new {@link PathSpec} from just one segment.
   *
   * @param segment provides the only segment of the path.
   */
  public PathSpec(String segment)
  {
    _path = new ArrayList<String>(1);
    _path.add(segment);
  }

  /**
   * Construct a new {@link PathSpec} from a list of segments.
   *
   * @param segments provides the list of path segments.
   */
  public PathSpec(String... segments)
  {
    _path = new ArrayList<String>(Arrays.asList(segments));
  }

  /**
   * Construct a new empty {@link PathSpec} that has no segments.
   */
  public PathSpec()
  {
    _path = Collections.emptyList();
  }

  /**
   * Return an empty {@link PathSpec} that has no segments.
   *
   * @return an empty {@link PathSpec} that has no segments.
   */
  public static PathSpec emptyPath()
  {
    return EMPTY_PATH_SPEC;
  }

  public List<String> getPathComponents()
  {
    return Collections.unmodifiableList(_path);
  }

  @Override
  public String toString()
  {
    StringBuilder rep = new StringBuilder();
    for (String s: getPathComponents())
    {
      rep.append(SEPARATOR);
      rep.append(s);
    }

    return rep.toString();
  }

  @Override
  public boolean equals(Object obj)
  {
    if (obj instanceof PathSpec)
    {
      PathSpec other = (PathSpec)obj;
      if (other._path.size() != _path.size())
      {
        return false;
      }
      for (int ii=0; ii<_path.size(); ++ii)
      {
        //Identity comparisons
        if ((_path.get(ii) == WILDCARD) != (other._path.get(ii) == WILDCARD))
        {
          return false;
        }
        if (! _path.get(ii).equals(other._path.get(ii)))
        {
          return false;
        }
      }
      return true;
    }
    return false;
  }

  @Override
  public int hashCode()
  {
    return _path.hashCode();
  }

  private final List<String> _path;
  private static final PathSpec EMPTY_PATH_SPEC = new PathSpec();
  private static final char SEPARATOR = '/';
}