implement event based parser like SAX

Author: KengoTODA

README.md

@@ -7,3 +7,5 @@ A fork of [java-diff-utils](https://code.google.com/p/java-diff-utils/)
 - switch from JDK5 to JDK7
 - add Guava to dependency
 - let user uses other string to represent line which does not exist
+- implement event based parser like SAX (in difflib.event package)
+

src/main/java/difflib/event/PatchHandler.java

@@ -0,0 +1,10 @@
+package difflib.event;
+
+import difflib.Patch;
+
+/**
+ * Interface to handle list of patch about specific file.
+ */
+public interface PatchHandler<T> {
+    void handle(String originalPath, String revisedPath, Patch<T> patch);
+}

src/main/java/difflib/event/UnifiedPatchParser.java

@@ -0,0 +1,52 @@
+package difflib.event;
+
+import java.io.BufferedReader;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.List;
+
+import javax.annotation.Nonnull;
+
+import com.google.common.base.Charsets;
+import com.google.common.collect.Lists;
+import com.google.common.io.Files;
+
+import difflib.DiffUtils;
+import difflib.Patch;
+
+public class UnifiedPatchParser {
+
+    void parse(File unifiedPatch, @Nonnull PatchHandler<String> handler) throws FileNotFoundException, IOException {
+        try (BufferedReader reader = Files.newReader(unifiedPatch, Charsets.UTF_8)) {
+            String line = reader.readLine();
+            do {
+                List<String> patch = Lists.newArrayList();
+                while (!line.startsWith("---")) {
+                    // in prelude: skip all lines
+                    line = reader.readLine();
+                }
+                assert line.startsWith("---");
+                patch.add(line);
+                final String originalFileName = line.substring(4);
+    
+                line = reader.readLine();
+                assert line.startsWith("+++");
+                patch.add(line);
+                final String revisedFileName = line.substring(4);
+    
+                line = reader.readLine();
+                do {
+                    patch.add(line);
+                    line = reader.readLine();
+                } while (
+                        line != null &&
+                        (line.startsWith("@@ ") || line.startsWith(" ") || line.startsWith("+") || line.startsWith("-")) // TODO this implementation expects that we have comment between 2 diffs. 
+                        );
+
+                Patch<String> parsed = DiffUtils.parseUnifiedDiff(patch);
+                handler.handle(originalFileName, revisedFileName, parsed);
+            } while (line != null);
+        }
+    }
+}

src/test/java/difflib/event/UnifiedPatchParserTest.java

@@ -0,0 +1,49 @@
+package difflib.event;
+
+import static org.hamcrest.CoreMatchers.hasItem;
+import static org.hamcrest.CoreMatchers.hasItems;
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.CoreMatchers.startsWith;
+import static org.junit.Assert.assertThat;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.junit.Test;
+
+import difflib.Delta;
+import difflib.Patch;
+
+public class UnifiedPatchParserTest {
+
+    @Test
+    public void test() throws FileNotFoundException, IOException {
+        final AtomicInteger visited = new AtomicInteger(0);
+        PatchHandler<String> handler = new PatchHandler<String>() {
+            @Override
+            public void handle(String originalPath, String revisedPath,
+                    Patch<String> patch) {
+                visited.incrementAndGet();
+
+                Delta<String> delta = patch.getDeltas().get(0);
+                assertThat(delta.getOriginal().getPosition(), is(0));
+                if (originalPath.startsWith("test/a.txt")) {
+                    assertThat(revisedPath, startsWith("test2/a.txt"));
+                    assertThat(patch.getDeltas().size(), is(1));
+                    assertThat(delta.getOriginal().getLines(), hasItem("hello, world"));
+                    assertThat(delta.getRevised().getLines(), hasItem("hello"));
+                } else {
+                    assertThat(originalPath, startsWith("test/b.txt"));
+                    assertThat(revisedPath,  startsWith("test2/b.txt"));
+                    assertThat(patch.getDeltas().size(), is(1));
+                    assertThat(delta.getOriginal().getLines(), hasItems("hello! 1", "hello! 2"));
+                    assertThat(delta.getRevised().getLines(), hasItem("hello"));
+                }
+            }
+        };
+        new UnifiedPatchParser().parse(new File("src/test/resources/event",  "2files.diff"), handler);
+        assertThat(visited.intValue(), is(2));
+    }
+}

src/test/resources/event/2files.diff

@@ -0,0 +1,13 @@
+diff -u test/a.txt test2/a.txt
+--- test/a.txt  2013-12-31 19:37:09.000000000 +0800
++++ test2/a.txt 2013-12-31 19:37:02.000000000 +0800
+@@ -1 +1 @@
+-hello, world
++hello
+diff -u test/b.txt test2/b.txt
+--- test/b.txt  2013-12-31 19:37:20.000000000 +0800
++++ test2/b.txt 2013-12-31 19:37:02.000000000 +0800
+@@ -1,2 +1 @@
+-hello! 1
+-hello! 2
++hello