/*
    * 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.maven.plugins.shade.mojo;
  
  import java.io.File;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  /**
   *
   */
  public final class RelativizePath {
      private RelativizePath() {
          //
      }
  
      /**
       * relativize a pathname.
       * @param thing Absolute File of something. (e.g., a parent pom)
       * @param relativeTo base to relativize it do. (e.g., a pom into which a relative pathname to the 'thing' is to be
       *        installed).
       * @return
       */
      static String convertToRelativePath(File thing, File relativeTo) {
          StringBuilder relativePath;
  
          if (thing.getParentFile().equals(relativeTo.getParentFile())) {
              return thing.getName(); // a very simple relative path.
          }
  
          List<String> thingDirectories = RelativizePath.parentDirs(thing);
          List<String> relativeToDirectories = RelativizePath.parentDirs(relativeTo);
  
          // Get the shortest of the two paths
          int length = Math.min(thingDirectories.size(), relativeToDirectories.size());
  
          int lastCommonRoot = -1; // index of the lowest directory down from the root that the two have in common.
          int index;
  
          // Find common root
          for (index = 0; index < length; index++) {
              if (thingDirectories.get(index).equals(relativeToDirectories.get(index))) {
                  lastCommonRoot = index;
              } else {
                  break;
              }
          }
          if (lastCommonRoot != -1) { // possible on Windows or other multi-root cases.
              // Build up the relative path
              relativePath = new StringBuilder();
              // add ..'s to get from the base up to the common point
              for (index = lastCommonRoot + 1; index < relativeToDirectories.size(); index++) {
                  relativePath.append("../");
              }
  
              // now add down from the common point to the actual 'thing' item.
              for (index = lastCommonRoot + 1; index < thingDirectories.size(); index++) {
                  relativePath.append(thingDirectories.get(index)).append('/');
              }
              relativePath.append(thing.getName());
              return relativePath.toString();
          }
          return null;
      }
  
      static List<String> parentDirs(File of) {
          List<String> results = new ArrayList<>();
          for (File p = of.getParentFile(); p != null; p = p.getParentFile()) {
              if (!"".equals(p.getName())) {
                  results.add(p.getName());
              }
          }
  
          Collections.reverse(results);
          return results;
      }
  }