/*
 *  Copyright 2004 Clinton Begin
 *
 *  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 com.ibatis.common.resources;

import java.io.*;
import java.net.URL;
import java.net.URLConnection;
import java.nio.charset.Charset;
import java.util.Properties;

/**
 * A class to simplify access to resources through the classloader.
 */
public class Resources extends Object {

  private static ClassLoader defaultClassLoader;
  
  /**
   * Charset to use when calling getResourceAsReader.
   * null means use the system default.
   */
  private static Charset charset;

  private Resources() {
  }

  /**
   * Returns the default classloader (may be null).
   *
   * @return The default classloader
   */
  public static ClassLoader getDefaultClassLoader() {
    return defaultClassLoader;
  }

  /**
   * Sets the default classloader
   *
   * @param defaultClassLoader - the new default ClassLoader
   */
  public static void setDefaultClassLoader(ClassLoader defaultClassLoader) {
    Resources.defaultClassLoader = defaultClassLoader;
  }

  /**
   * Returns the URL of the resource on the classpath
   *
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static URL getResourceURL(String resource) throws IOException {
    return getResourceURL(getClassLoader(), resource);
  }

  /**
   * Returns the URL of the resource on the classpath
   *
   * @param loader   The classloader used to load the resource
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static URL getResourceURL(ClassLoader loader, String resource) throws IOException {
    URL url = null;
    if (loader != null) url = loader.getResource(resource);
    if (url == null) url = ClassLoader.getSystemResource(resource);
    if (url == null) throw new IOException("Could not find resource " + resource);
    return url;
  }

  /**
   * Returns a resource on the classpath as a Stream object
   *
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static InputStream getResourceAsStream(String resource) throws IOException {
    return getResourceAsStream(getClassLoader(), resource);
  }

  /**
   * Returns a resource on the classpath as a Stream object
   *
   * @param loader   The classloader used to load the resource
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static InputStream getResourceAsStream(ClassLoader loader, String resource) throws IOException {
    InputStream in = null;
    if (loader != null) in = loader.getResourceAsStream(resource);
    if (in == null) in = ClassLoader.getSystemResourceAsStream(resource);
    if (in == null) throw new IOException("Could not find resource " + resource);
    return in;
  }

  /**
   * Returns a resource on the classpath as a Properties object
   *
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static Properties getResourceAsProperties(String resource)
      throws IOException {
    Properties props = new Properties();
    InputStream in = null;
    String propfile = resource;
    in = getResourceAsStream(propfile);
    props.load(in);
    in.close();
    return props;
  }

  /**
   * Returns a resource on the classpath as a Properties object
   *
   * @param loader   The classloader used to load the resource
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static Properties getResourceAsProperties(ClassLoader loader, String resource)
      throws IOException {
    Properties props = new Properties();
    InputStream in = null;
    String propfile = resource;
    in = getResourceAsStream(loader, propfile);
    props.load(in);
    in.close();
    return props;
  }

  /**
   * Returns a resource on the classpath as a Reader object
   *
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static Reader getResourceAsReader(String resource) throws IOException {
    Reader reader;
    if (charset == null) {
      reader = new InputStreamReader(getResourceAsStream(resource));
    } else {
      reader = new InputStreamReader(getResourceAsStream(resource), charset);
    }
    
    return reader;
  }

  /**
   * Returns a resource on the classpath as a Reader object
   *
   * @param loader   The classloader used to load the resource
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static Reader getResourceAsReader(ClassLoader loader, String resource) throws IOException {
    Reader reader;
    if (charset == null) {
      reader = new InputStreamReader(getResourceAsStream(loader, resource));
    } else {
      reader = new InputStreamReader(getResourceAsStream(loader, resource), charset);
    }
    
    return reader;
  }

  /**
   * Returns a resource on the classpath as a File object
   *
   * @param resource The resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static File getResourceAsFile(String resource) throws IOException {
    return new File(getResourceURL(resource).getFile());
  }

  /**
   * Returns a resource on the classpath as a File object
   *
   * @param loader   - the classloader used to load the resource
   * @param resource - the resource to find
   * @return The resource
   * @throws IOException If the resource cannot be found or read
   */
  public static File getResourceAsFile(ClassLoader loader, String resource) throws IOException {
    return new File(getResourceURL(loader, resource).getFile());
  }

  /**
   * Gets a URL as an input stream
   *
   * @param urlString - the URL to get
   * @return An input stream with the data from the URL
   * @throws IOException If the resource cannot be found or read
   */
  public static InputStream getUrlAsStream(String urlString) throws IOException {
    URL url = new URL(urlString);
    URLConnection conn = url.openConnection();
    return conn.getInputStream();
  }

  /**
   * Gets a URL as a Reader
   *
   * @param urlString - the URL to get
   * @return A Reader with the data from the URL
   * @throws IOException If the resource cannot be found or read
   */
  public static Reader getUrlAsReader(String urlString) throws IOException {
    return new InputStreamReader(getUrlAsStream(urlString));
  }

  /**
   * Gets a URL as a Properties object
   *
   * @param urlString - the URL to get
   * @return A Properties object with the data from the URL
   * @throws IOException If the resource cannot be found or read
   */
  public static Properties getUrlAsProperties(String urlString) throws IOException {
    Properties props = new Properties();
    InputStream in = null;
    String propfile = urlString;
    in = getUrlAsStream(propfile);
    props.load(in);
    in.close();
    return props;
  }

  /**
   * Loads a class
   *
   * @param className - the class to load
   * @return The loaded class
   * @throws ClassNotFoundException If the class cannot be found (duh!)
   */
  public static Class classForName(String className) throws ClassNotFoundException {
    Class clazz = null;
    try {
      clazz = getClassLoader().loadClass(className);
    } catch (Exception e) {
      // Ignore.  Failsafe below.
    }
    if (clazz == null) {
      clazz = Class.forName(className);
    }
    return clazz;
  }

  /**
   * Creates an instance of a class
   *
   * @param className - the class to create
   * @return An instance of the class
   * @throws ClassNotFoundException If the class cannot be found (duh!)
   * @throws InstantiationException If the class cannot be instantiaed
   * @throws IllegalAccessException If the class is not public, or other access problems arise
   */
  public static Object instantiate(String className)
      throws ClassNotFoundException, InstantiationException, IllegalAccessException {
    return instantiate(classForName(className));
  }

  /**
   * Creates an instance of a class
   *
   * @param clazz - the class to create
   * @return An instance of the class
   * @throws InstantiationException If the class cannot be instantiaed
   * @throws IllegalAccessException If the class is not public, or other access problems arise
   */
  public static Object instantiate(Class clazz)
      throws InstantiationException, IllegalAccessException {
    return clazz.newInstance();
  }

  private static ClassLoader getClassLoader() {
    if (defaultClassLoader != null) {
      return defaultClassLoader;
    } else {
      return Thread.currentThread().getContextClassLoader();
    }
  }

  public static Charset getCharset() {
    return charset;
  }

  /**
   * Use this method to set the Charset to be used when
   * calling the getResourceAsReader methods.  This will
   * allow iBATIS to function properly when the system default
   * encoding doesn't deal well with unicode (IBATIS-340, IBATIS-349)
   * 
   * @param charset
   */
  public static void setCharset(Charset charset) {
    Resources.charset = charset;
  }

}