[ONOS-3871]Yang file-scanner implementation and UT.

Change-Id: I6eb5fd72b8a919ce7776443c59694c5e5411400d

+/*
+ * Copyright 2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.utils.io.impl;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Stack;
+
+/**
+ * Provides the IO services for Yangutils-maven-Plugin.
+ */
+public final class YangFileScanner {
+
+    /**
+     * Default constructor.
+     */
+    private YangFileScanner() {
+    }
+
+    /**
+     * Returns the list of yang files.
+     *
+     * @param root specified directory
+     * @return list of yang files.
+     * @throws IOException when files get deleted while performing the operations.
+     */
+    public static List<String> getYangFiles(String root) throws IOException {
+
+        List<String> store = new LinkedList<>();
+        Stack<String> stack = new Stack<>();
+        stack.push(root);
+        File file;
+        File[] filelist;
+        try {
+            while (!stack.empty()) {
+                root = stack.pop();
+                file = new File(root);
+                filelist = file.listFiles();
+                if (filelist == null) {
+                    continue;
+                }
+                for (File current : filelist) {
+                    if (current.isDirectory()) {
+                        stack.push(current.toString());
+                    } else {
+                        String yangFile = current.getCanonicalPath();
+                        if (yangFile.endsWith(".yang")) {
+                            store.add(yangFile);
+                        }
+                    }
+                }
+            }
+            return store;
+        } catch (IOException e) {
+            throw new IOException("IOException occured");
+        }
+    }
+}

+/*
+ * Copyright 2016 Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.onosproject.yangutils.utils.io.impl;
+
+import java.io.IOException;
+
+import org.junit.Test;
+import java.io.File;
+import java.util.List;
+import org.slf4j.Logger;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Unit tests for searching yang files.
+ */
+public class YangFileScannerTest {
+
+    private final Logger log = getLogger(getClass());
+
+    String baseDir = "target/UnitTestCase";
+
+    /**
+     * Checks an empty directory.
+     */
+    @Test
+    public void testWithSingleEmptyDirectoryInRoot() {
+        try {
+            File dir = new File(baseDir);
+            dir.mkdirs();
+            List<String> list = YangFileScanner.getYangFiles(baseDir.toString());
+        } catch (IOException e) {
+            log.info("IO Exception throwed");
+        }
+    }
+
+    /**
+     * Checks multiple empty directories in root directory.
+     */
+    @Test
+    public void testWithMultiEmptyDirectoriesInRoot() {
+        try {
+            String dir = "emptyDir";
+            String dir1 = "emptyDir1";
+            String dir2 = "emptyDir2";
+            String dir3 = "emptyDir3";
+            String dir4 = "emptyDir4";
+            File firstpath = createDirectory(dir);
+            File firstpath1 = createDirectory(dir1);
+            File firstpath2 = createDirectory(dir2);
+            File firstpath3 = createDirectory(dir3);
+            File firstpath4 = createDirectory(dir4);
+            List<String> list = YangFileScanner.getYangFiles(baseDir.toString());
+        } catch (IOException e) {
+            log.info("IO Exception throwed");
+        }
+    }
+
+    /**
+     * Checks one directory with one .yang file.
+     */
+    @Test
+    public void testWithSingleDirectorySingleFileInRoot() {
+        try {
+            String dir1 = "level1";
+            String firstFileName1 = "secondFile.yang";
+            File firstpath1 = createDirectory(dir1);
+            createFile(firstpath1, firstFileName1);
+            List<String> list = YangFileScanner.getYangFiles(baseDir.toString());
+        } catch (IOException e) {
+            log.info("IO Exception throwed");
+        }
+    }
+
+    /**
+     * Checks one directory with many .yang file.
+     */
+    @Test
+    public void testWithSingleDirectoryMultiFilesInRoot() {
+        try {
+            String dir2 = "level2";
+            String firstFileName2 = "thirdFile.yang";
+            String firstFileName3 = "fourthFile.yang";
+            String firstFileName4 = "fifthFile.yang";
+            String firstFileName5 = "sixthFile.yang";
+            File firstpath2 = createDirectory(dir2);
+            createFile(firstpath2, firstFileName2);
+            createFile(firstpath2, firstFileName3);
+            createFile(firstpath2, firstFileName4);
+            createFile(firstpath2, firstFileName5);
+            List<String> list = YangFileScanner.getYangFiles(baseDir.toString());
+        } catch (IOException e) {
+            log.info("IO Exception throwed");
+        }
+    }
+
+    /**
+     * Checks multi directories with many .yang file.
+     */
+    @Test
+    public void testWithMultiDirectoriesMultiFiles() {
+        try {
+            String dir2 = "newDir1/newDir2/newDir3/newDir4";
+            File dir3 = new File("target/UnitTestCase/newDir1");
+            File dir4 = new File("target/UnitTestCase/newDir1/newDir2");
+            File dir5 = new File("target/UnitTestCase/newDir1/newDir2/newDir3");
+            File dir6 = new File("target/UnitTestCase/newDir1/newDir2/newDir3/newDir4");
+            String firstFileName2 = "thirdFile.yang";
+            String firstFileName3 = "fourthFile.yang";
+            String firstFileName4 = "fifthFile.yang";
+            String firstFileName5 = "sixthFile.yang";
+            File firstpath2 = createDirectory(dir2);
+            createFile(firstpath2, firstFileName2);
+            createFile(firstpath2, firstFileName3);
+            createFile(firstpath2, firstFileName4);
+            createFile(dir3, firstFileName5);
+            createFile(dir3, firstFileName2);
+            createFile(dir3, firstFileName3);
+            createFile(dir3, firstFileName4);
+            createFile(dir3, firstFileName5);
+            createFile(dir4, firstFileName2);
+            createFile(dir4, firstFileName3);
+            createFile(dir4, firstFileName4);
+            createFile(dir4, firstFileName5);
+            createFile(dir5, firstFileName2);
+            createFile(dir5, firstFileName3);
+            createFile(dir5, firstFileName4);
+            createFile(dir5, firstFileName5);
+            createFile(dir6, firstFileName2);
+            createFile(dir6, firstFileName3);
+            createFile(dir6, firstFileName4);
+            createFile(dir6, firstFileName5);
+            List<String> list = YangFileScanner.getYangFiles(baseDir.toString());
+        } catch (IOException e) {
+            log.info("IO Exception throwed");
+        }
+    }
+
+    /**
+     * Method used for creating multiple directories inside the target file.
+     *
+     * @param path directory path
+     * @return directory path
+     */
+    public File createDirectory(String path) {
+        File myDir = new File(baseDir + File.separator + path);
+        myDir.mkdirs();
+        return myDir;
+    }
+
+    /**
+    * Method used for creating file inside the specified directory.
+    *
+    * @param myDir my current dirctory
+    * @param fileName file name
+    * @throws IOException io exception when fails to create a file.
+    */
+    public void createFile(File myDir, String fileName) throws IOException {
+        File file = null;
+        try {
+            file = new File(myDir + File.separator + fileName);
+            file.createNewFile();
+        } catch (final IOException e) {
+            throw new IOException("IOException occured");
+        }
+    }
+}