RelativizesFilePathsTest.java

package com.github.searls.jasmine.io;

import static org.hamcrest.Matchers.*;
import static org.junit.Assert.*;

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

import org.junit.Test;

public class RelativizesFilePathsTest {

	private RelativizesFilePaths subject = new RelativizesFilePaths();
	
	private File from;
	private File to;
	
	@Test
	public void resolvesWithinDir() throws IOException {
		from = new File("/panda/");
		to = new File("/panda/pants.txt");
		
		String result = subject.relativize(from,to);
		
		assertThat(result,is("pants.txt"));
	}
	
	@Test
	public void resolvesSubDir() throws IOException {
		from = new File("/panda/");
		to = new File("/panda/target/jasmine/");
		
		String result = subject.relativize(from,to);
		
		assertThat(result,is("target/jasmine"));
	}
	
	
	@Test
	public void resolvesDeepChild() throws IOException {
		from = new File("/Volumes/blah/Users/justin/code/workspaces/jasmine_maven/jasmine-maven-plugin/src/test/resources/examples/jasmine-webapp-coffee/target/jasmine");
		to = new File("/Volumes/blah/Users/justin/code/workspaces/jasmine_maven/jasmine-maven-plugin/src/test/resources/examples/jasmine-webapp-coffee/src/test/javascript/fun-spec.js");
		
		String result = subject.relativize(from,to);
		
		assertThat(result,is("../../src/test/javascript/fun-spec.js"));		
	}
	
}

RelativizesPaths.java

package com.github.searls.jasmine.io;

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

import org.apache.commons.lang.StringUtils;

import static org.apache.commons.lang.StringUtils.*;

@SuppressWarnings("unused")
public class RelativizesFilePaths {

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

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

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

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

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

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

}