/**
    *    Copyright 2009-2015 the original author or authors.
    *
    *    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.apache.ibatis.io;
  
  import java.io.IOException;
  import java.lang.reflect.InvocationTargetException;
  import java.lang.reflect.Method;
  import java.net.URL;
  import java.util.ArrayList;
  import java.util.Arrays;
  import java.util.Collections;
  import java.util.List;
  
  import org.apache.ibatis.logging.Log;
  import org.apache.ibatis.logging.LogFactory;
  
  /**
   * Provides a very simple API for accessing resources within an application server.
   * 
   * @author Ben Gunter
   */
  public abstract class VFS {
    private static final Log log = LogFactory.getLog(ResolverUtil.class);
  
    /** The built-in implementations. */
    public static final Class<?>[] IMPLEMENTATIONS = { JBoss6VFS.class, DefaultVFS.class };
  
    /** The list to which implementations are added by {@link #addImplClass(Class)}. */
    public static final List<Class<? extends VFS>> USER_IMPLEMENTATIONS = new ArrayList<Class<? extends VFS>>();
  
    /** Singleton instance. */
    private static VFS instance;
  
    /**
     * Get the singleton {@link VFS} instance. If no {@link VFS} implementation can be found for the
     * current environment, then this method returns null.
     */
    @SuppressWarnings("unchecked")
    public static VFS getInstance() {
      if (instance != null) {
        return instance;
      }
  
      // Try the user implementations first, then the built-ins
      List<Class<? extends VFS>> impls = new ArrayList<Class<? extends VFS>>();
      impls.addAll(USER_IMPLEMENTATIONS);
      impls.addAll(Arrays.asList((Class<? extends VFS>[]) IMPLEMENTATIONS));
  
      // Try each implementation class until a valid one is found
      VFS vfs = null;
      for (int i = 0; vfs == null || !vfs.isValid(); i++) {
        Class<? extends VFS> impl = impls.get(i);
        try {
          vfs = impl.newInstance();
          if (vfs == null || !vfs.isValid()) {
            if (log.isDebugEnabled()) {
              log.debug("VFS implementation " + impl.getName() +
                " is not valid in this environment.");
            }
          }
        } catch (InstantiationException e) {
          log.error("Failed to instantiate " + impl, e);
          return null;
        } catch (IllegalAccessException e) {
          log.error("Failed to instantiate " + impl, e);
          return null;
        }
      }
  
      if (log.isDebugEnabled()) {
        log.debug("Using VFS adapter " + vfs.getClass().getName());
      }
      VFS.instance = vfs;
      return VFS.instance;
    }
  
    /**
     * Adds the specified class to the list of {@link VFS} implementations. Classes added in this
     * manner are tried in the order they are added and before any of the built-in implementations.
     * 
     * @param clazz The {@link VFS} implementation class to add.
     */
    public static void addImplClass(Class<? extends VFS> clazz) {
      if (clazz != null) {
        USER_IMPLEMENTATIONS.add(clazz);
      }
   }
 
   /** Get a class by name. If the class is not found then return null. */
   protected static Class<?> getClass(String className) {
     try {
       return Thread.currentThread().getContextClassLoader().loadClass(className);
 //      return ReflectUtil.findClass(className);
     } catch (ClassNotFoundException e) {
       if (log.isDebugEnabled()) {
         log.debug("Class not found: " + className);
       }
       return null;
     }
   }
 
   /**
    * Get a method by name and parameter types. If the method is not found then return null.
    * 
    * @param clazz The class to which the method belongs.
    * @param methodName The name of the method.
    * @param parameterTypes The types of the parameters accepted by the method.
    */
   protected static Method getMethod(Class<?> clazz, String methodName, Class<?>... parameterTypes) {
     if (clazz == null) {
       return null;
     }
     try {
       return clazz.getMethod(methodName, parameterTypes);
     } catch (SecurityException e) {
       log.error("Security exception looking for method " + clazz.getName() + "." + methodName + ".  Cause: " + e);
       return null;
     } catch (NoSuchMethodException e) {
       log.error("Method not found " + clazz.getName() + "." + methodName + "." + methodName + ".  Cause: " + e);
       return null;
     }
   }
 
   /**
    * Invoke a method on an object and return whatever it returns.
    * 
    * @param method The method to invoke.
    * @param object The instance or class (for static methods) on which to invoke the method.
    * @param parameters The parameters to pass to the method.
    * @return Whatever the method returns.
    * @throws IOException If I/O errors occur
    * @throws StripesRuntimeException If anything else goes wrong
    */
   @SuppressWarnings("unchecked")
   protected static <T> T invoke(Method method, Object object, Object... parameters)
       throws IOException, RuntimeException {
     try {
       return (T) method.invoke(object, parameters);
     } catch (IllegalArgumentException e) {
       throw new RuntimeException(e);
     } catch (IllegalAccessException e) {
       throw new RuntimeException(e);
     } catch (InvocationTargetException e) {
       if (e.getTargetException() instanceof IOException) {
         throw (IOException) e.getTargetException();
       } else {
         throw new RuntimeException(e);
       }
     }
   }
 
   /**
    * Get a list of {@link URL}s from the context classloader for all the resources found at the
    * specified path.
    * 
    * @param path The resource path.
    * @return A list of {@link URL}s, as returned by {@link ClassLoader#getResources(String)}.
    * @throws IOException If I/O errors occur
    */
   protected static List<URL> getResources(String path) throws IOException {
     return Collections.list(Thread.currentThread().getContextClassLoader().getResources(path));
   }
 
   /** Return true if the {@link VFS} implementation is valid for the current environment. */
   public abstract boolean isValid();
 
   /**
    * Recursively list the full resource path of all the resources that are children of the
    * resource identified by a URL.
    * 
    * @param url The URL that identifies the resource to list.
    * @param forPath The path to the resource that is identified by the URL. Generally, this is the
    *            value passed to {@link #getResources(String)} to get the resource URL.
    * @return A list containing the names of the child resources.
    * @throws IOException If I/O errors occur
    */
   protected abstract List<String> list(URL url, String forPath) throws IOException;
 
   /**
    * Recursively list the full resource path of all the resources that are children of all the
    * resources found at the specified path.
    * 
    * @param path The path of the resource(s) to list.
    * @return A list containing the names of the child resources.
    * @throws IOException If I/O errors occur
    */
   public List<String> list(String path) throws IOException {
     List<String> names = new ArrayList<String>();
     for (URL url : getResources(path)) {
       names.addAll(list(url, path));
     }
     return names;
   }
 }