Adding CssTransformer - a metaphor to transform input to output css w…

…ith the help of a Transform

a) CssTransformer parses the input css and generates CssToken's. BackgroundImage is one such token
b) These tokens are then sent to a Transform implementation.
c) Adding several unit tests to verify css parsing

Yet to add concrete implementations of Transform

pom.xml

@@ -53,6 +53,11 @@
 		    <version>1.8.2</version>
 		    <scope>provided</scope>
 		</dependency>
+		<dependency>
+		    <groupId>commons-io</groupId>
+		    <artifactId>commons-io</artifactId>
+		    <version>2.0.1</version>
+		</dependency>
 		<dependency>
 			<groupId>junit</groupId>
 			<artifactId>junit</artifactId>

src/main/java/net/nczonline/web/cssembed/BackgroundImage.java

@@ -0,0 +1,40 @@
+package net.nczonline.web.cssembed;
+
+public class BackgroundImage implements CssToken {
+	private final String url;
+
+	BackgroundImage(String url) {
+		this.url = url;
+	}
+	public String getUrl() {
+		return url;
+	}
+
+	@Override
+	public int hashCode() {
+		final int prime = 31;
+		int result = 1;
+		result = prime * result + ((url == null) ? 0 : url.hashCode());
+		return result;
+	}
+	@Override
+	public boolean equals(Object obj) {
+		if (this == obj)
+			return true;
+		if (obj == null)
+			return false;
+		if (getClass() != obj.getClass())
+			return false;
+		BackgroundImage other = (BackgroundImage) obj;
+		if (url == null) {
+			if (other.url != null)
+				return false;
+		} else if (!url.equals(other.url))
+			return false;
+		return true;
+	}
+
+	public String toCss() {
+		return " background-image:url(\"" + url + "\"); ";
+	}
+}

src/main/java/net/nczonline/web/cssembed/CssToken.java

@@ -0,0 +1,5 @@
+package net.nczonline.web.cssembed;
+
+public interface CssToken {
+	public String toCss();
+}

src/main/java/net/nczonline/web/cssembed/CssTransformer.java

@@ -0,0 +1,83 @@
+package net.nczonline.web.cssembed;
+
+import java.io.IOException;
+import java.io.Reader;
+import java.io.Writer;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.apache.commons.io.IOUtils;
+
+public class CssTransformer {
+
+	private static final String URL_PATTERN_REGEX = "([\\\\/\\.a-zA-Z0-9%\\?\\-_:=&]+)";
+	private static final String WHITE_SPACE = "\\s*";
+	private static final String OPTIONAL_QUOTE = "(['\"]{0,1})";
+	private static final String MATCH_OPENING_QUOTE = "\\1";
+	private static final String CASE_INSENSITIVE = "(?i)";
+	private static final String OPTIONAL_SEMI_COLON = "[;]{0,1}";
+
+	static final int URL_GROUP = 2;
+	static final Pattern BACKGROUND_IMAGE = getBackgroundImagePattern();
+
+
+	static final Pattern getBackgroundImagePattern() {
+		StringBuilder regex = new StringBuilder();
+		regex
+			.append(CASE_INSENSITIVE)
+			.append(rightWhiteSpace("background-image"))
+			.append(rightWhiteSpace(":"))
+			.append(rightWhiteSpace("url"))
+			.append(rightWhiteSpace("\\("))
+				.append(OPTIONAL_QUOTE)
+				.append(URL_PATTERN_REGEX)
+				.append(MATCH_OPENING_QUOTE)
+			.append(leftWhiteSpace("\\)"))
+			.append(leftWhiteSpace(OPTIONAL_SEMI_COLON));
+
+		return Pattern.compile(regex.toString());
+	}
+
+	private static String leftWhiteSpace(String literal) {
+		return WHITE_SPACE + literal;
+	}
+
+	private static String rightWhiteSpace(String literal) {
+		return literal + WHITE_SPACE;
+	}
+
+	/**
+	 * Reads a CSS file from input, transforms it according to transformation, and then writes the transformed css to output
+	 * 
+	 * This method parses the input files into 'Tokens'. For each token, the appropriate transform() method 
+	 * is called on the transformation. The output of the transformation is written to the output <em>instead of</em> the token
+	 * 
+	 * 
+	 * @param input the source css file
+	 * @param t the transformation to apply on the CSS
+	 * @param output the output css file
+	 * @throws IOException If the input can't be read, or the output can't be written for some reason
+	 */
+	public void transform(Reader input, Transform t, Writer output) throws IOException {
+		String source = IOUtils.toString(input);
+
+		source = t.preTransform(source);
+
+		/*
+		 * At present, we only generate background image tokens
+		 */
+		Matcher m = BACKGROUND_IMAGE.matcher(source);
+		StringBuffer sb = new StringBuffer();
+		while(m.find()) {
+
+			String url = m.group(URL_GROUP);
+			BackgroundImage image = new BackgroundImage(url);
+			String replacement = t.transform(image);
+			m.appendReplacement(sb, replacement);
+		}
+		m.appendTail(sb);
+
+		String finalOutput = t.postTransform(sb.toString());
+		IOUtils.write(finalOutput, output);
+	}
+}

src/main/java/net/nczonline/web/cssembed/DefaultTransform.java

@@ -0,0 +1,23 @@
+package net.nczonline.web.cssembed;
+
+public class DefaultTransform implements Transform {
+
+	public String preTransform(String source) {
+		return source;
+	}
+
+	public String transform(CssToken token) {
+		if(token instanceof BackgroundImage) {
+			transform((BackgroundImage)token);
+		}
+		throw new IllegalArgumentException("Unknown token type - " + token.getClass());
+	}
+
+	protected String transform(BackgroundImage image) {
+		return image.toCss();
+	}
+
+	public String postTransform(String source) {
+		return source;
+	}
+}

src/main/java/net/nczonline/web/cssembed/Transform.java

@@ -0,0 +1,11 @@
+package net.nczonline.web.cssembed;
+
+public interface Transform {
+
+	String preTransform(String source);
+
+	String transform(CssToken token);	
+
+	String postTransform(String source);
+
+}

src/test/java/net/nczonline/web/cssembed/BackgroundImageRegexTest.java

@@ -0,0 +1,78 @@
+package net.nczonline.web.cssembed;
+
+import java.util.regex.Matcher;
+
+import org.junit.Test;
+import static junit.framework.Assert.*;
+
+public class BackgroundImageRegexTest {
+
+	@Test
+	public void testRegex() {
+		RegexTest[] positive_matches = {
+				new RegexTest("No quotes", "background-image:url(image.png)", "image.png"),
+				new RegexTest("Single quotes", "background-image:url('image.png')", "image.png"),
+				new RegexTest("Double quotes", "background-image:url(\"image.png\")", "image.png"),
+
+				new RegexTest("With semi-colon at end", "background-image:url(\"image.png\") ;", "image.png"),
+
+				new RegexTest("With spaces", "background-image: url( \"image.png\" )", "image.png"),
+				new RegexTest("With tabs", "background-image\t:\turl(\"image.png\")", "image.png"),
+				new RegexTest("Multiple lines", "background-image:\nurl(\n\t'image.png')", "image.png"),
+
+				new RegexTest("Mixed case", "Background-Image:Url('image.png')", "image.png"),
+				new RegexTest("Case preserved in url", "Background-Image:Url('ImagE.png')", "ImagE.png"),
+
+				new RegexTest("Forward slashes", "background-image:url(/path/to/image.png)", "/path/to/image.png"),
+				new RegexTest("Back slashes", "background-image:url(\\path\\to\\image.png)", "\\path\\to\\image.png"),
+
+				new RegexTest("Absolute URL", "background-image:url(http://some.server.com/path/to/image.png)", 
+						"http://some.server.com/path/to/image.png"),
+
+				new RegexTest("URL with port number", "background-image:url(http://some.server.com:8080/path/to/image.png)", 
+						"http://some.server.com:8080/path/to/image.png"),
+
+				new RegexTest("URL with query parameters", "background-image:url(http://some.server.com/path/to/image.png?key=value&key2=value2)", 
+						"http://some.server.com/path/to/image.png?key=value&key2=value2"),
+
+				new RegexTest("Absolute URL in double quotes", "background-image:url(\"http://some.server.com/path/to/image.png?key=value&key2=value2\")", 
+						"http://some.server.com/path/to/image.png?key=value&key2=value2"),
+
+				new RegexTest("Absolute URL in single quotes", "background-image:url('http://some.server.com/path/to/image.png?key=value&key2=value2')", 
+						"http://some.server.com/path/to/image.png?key=value&key2=value2"),
+
+				new RegexTest("Absolute URL with % encoding", "background-image:url('http://some.server.com/image.png?key=value%20with%20space')", 
+						"http://some.server.com/image.png?key=value%20with%20space"),
+
+		};
+
+		String negative_matches[][] = {
+				{"Mismatched quotes", "background-image:url(\"image.png')"},
+				{"Path with spaces", "background-image:url(\"my images/image.png')"},
+		};
+
+		for(RegexTest test : positive_matches) {
+			Matcher matcher = CssTransformer.BACKGROUND_IMAGE.matcher(test.css);
+			assertTrue(test.description, matcher.matches());
+			assertEquals(test.description + " - URL does not match", test.expectedUrl, matcher.group(CssTransformer.URL_GROUP));
+		}
+
+		for(int i=0; i<negative_matches.length; i++) {
+			String message = negative_matches[i][0];
+			String css = negative_matches[i][1];
+			assertFalse(message, CssTransformer.BACKGROUND_IMAGE.matcher(css).matches());
+		}
+	}
+
+	static class RegexTest {
+		String description;
+		String css;
+		String expectedUrl;
+
+		RegexTest(String description, String css, String expectedUrl) {
+			this.description = description;
+			this.css = css;
+			this.expectedUrl = expectedUrl;
+		}
+	}
+}

src/test/java/net/nczonline/web/cssembed/CssTransformerTest.java

@@ -0,0 +1,66 @@
+package net.nczonline.web.cssembed;
+
+import static junit.framework.Assert.*;
+
+import java.io.IOException;
+import java.io.StringReader;
+import java.io.StringWriter;
+
+import org.junit.Test;
+
+public class CssTransformerTest {
+
+	private CssTransformer transformer = new CssTransformer();
+
+	@Test
+	public void testTransformationCallbacksWithoutBackgroundImages() throws IOException {
+		final String css = ".someclass { font-size:small;}";
+		final String expectedOutput = ".someotherclass { font-size:large;}";
+
+		Transform t = new Transform() {
+
+			public String transform(CssToken token) {
+				throw new IllegalStateException("transform should not be called");
+			}
+
+			public String preTransform(String source) {
+				return source.replaceAll("someclass", "someotherclass");
+			}
+
+			public String postTransform(String source) {
+				return source.replaceAll("small", "large");
+			}
+		};
+
+		String output = transform(css, t);
+		assertEquals("Pre and Post transformation not called", expectedOutput, output);
+	}
+
+	@Test
+	public void testMultipleBackgroundImages() throws IOException {
+		final String css = ".firstclass {background-image:url('first.png')} .secondclass {background-image:url('second.png'); .thirdclass{}}";
+		final String expectedOutput = ".firstclass {background-image:url('first.png?version=12');} " +
+				".secondclass {background-image:url('second.png?version=12'); .thirdclass{}}";
+
+		Transform t = new DefaultTransform() {
+			@Override
+			public String transform(CssToken token) {
+				if(token instanceof BackgroundImage) {
+					BackgroundImage image = (BackgroundImage)token;
+					return "background-image:url('" + image.getUrl() + "?version=12');";
+				}
+				throw new IllegalStateException("Unknown token " + token);
+			}
+		};
+
+		String output = transform(css, t);
+		assertEquals(expectedOutput, output);
+	}
+
+	private String transform(String css, Transform t) throws IOException {
+		StringWriter writer = new StringWriter();
+		transformer.transform(new StringReader(css), t, writer);
+		return writer.toString();
+	}
+
+}