RelativizesFilePaths.java

package com.github.searls.jasmine.io;

import org.apache.commons.lang3.StringEscapeUtils;
import org.apache.commons.lang3.StringUtils;

import java.io.File;
import java.io.IOException;

public class RelativizesFilePaths {

  public String relativize(File from, File to) throws IOException {
    String fromPath = from.getCanonicalPath();
    String toPath = to.getCanonicalPath();

    String root = StringUtils.getCommonPrefix(new String[]{fromPath, toPath});
    StringBuffer result = new StringBuffer();
    if (this.fromPathIsNotADirectAncestor(fromPath, root)) {
      for (@SuppressWarnings("unused") String dir : this.divergentDirectories(root, fromPath)) {
        result.append("..").append(File.separator);
      }
    }
    result.append(this.pathAfterRoot(toPath, root));

    return this.convertSlashes(this.trimLeadingSlashIfNecessary(result));
  }

  private String convertSlashes(String path) {
    return path.replace(File.separatorChar, '/');
  }

  private boolean fromPathIsNotADirectAncestor(String fromPath, String root) {
    return !StringUtils.equals(root, fromPath);
  }

  private String[] divergentDirectories(String root, String fullPath) {
    return this.pathAfterRoot(fullPath, root).split(StringEscapeUtils.escapeJava(File.separator));
  }

  private String pathAfterRoot(String path, String root) {
    return StringUtils.substringAfterLast(path, root);
  }

  private String trimLeadingSlashIfNecessary(StringBuffer result) {
    return StringUtils.removeStart(result.toString(), File.separator);
  }

}