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1   package com.github.searls.jasmine.io;
2   
3   import org.apache.commons.lang3.StringEscapeUtils;
4   import org.apache.commons.lang3.StringUtils;
5   
6   import java.io.File;
7   import java.io.IOException;
8   
9   public class RelativizesFilePaths {
10  
11    public String relativize(File from, File to) throws IOException {
12      String fromPath = from.getCanonicalPath();
13      String toPath = to.getCanonicalPath();
14  
15      String root = StringUtils.getCommonPrefix(new String[]{fromPath, toPath});
16      StringBuffer result = new StringBuffer();
17      if (this.fromPathIsNotADirectAncestor(fromPath, root)) {
18        for (@SuppressWarnings("unused") String dir : this.divergentDirectories(root, fromPath)) {
19          result.append("..").append(File.separator);
20        }
21      }
22      result.append(this.pathAfterRoot(toPath, root));
23  
24      return this.convertSlashes(this.trimLeadingSlashIfNecessary(result));
25    }
26  
27    private String convertSlashes(String path) {
28      return path.replace(File.separatorChar, '/');
29    }
30  
31    private boolean fromPathIsNotADirectAncestor(String fromPath, String root) {
32      return !StringUtils.equals(root, fromPath);
33    }
34  
35    private String[] divergentDirectories(String root, String fullPath) {
36      return this.pathAfterRoot(fullPath, root).split(StringEscapeUtils.escapeJava(File.separator));
37    }
38  
39    private String pathAfterRoot(String path, String root) {
40      return StringUtils.substringAfterLast(path, root);
41    }
42  
43    private String trimLeadingSlashIfNecessary(StringBuffer result) {
44      return StringUtils.removeStart(result.toString(), File.separator);
45    }
46  
47  }