/*
    * Copyright (C) 2007 The Guava 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 com.google.common.io;
  
  import static com.google.common.base.Preconditions.checkArgument;
  import static com.google.common.base.Preconditions.checkNotNull;
  
  import com.google.common.annotations.Beta;
  import com.google.common.base.Charsets;
  import com.google.common.base.MoreObjects;
  import com.google.common.collect.Lists;
  
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.OutputStream;
  import java.net.URL;
  import java.nio.charset.Charset;
  import java.util.List;
  
  /**
   * Provides utility methods for working with resources in the classpath.
   * Note that even though these methods use {@link URL} parameters, they
   * are usually not appropriate for HTTP or other non-classpath resources.
   *
   * <p>All method parameters must be non-null unless documented otherwise.
   *
   * @author Chris Nokleberg
   * @author Ben Yu
   * @author Colin Decker
   * @since 1.0
   */
  @Beta
  public final class Resources {
    private Resources() {}
  
    /**
     * Returns a {@link ByteSource} that reads from the given URL.
     *
     * @since 14.0
     */
    public static ByteSource asByteSource(URL url) {
      return new UrlByteSource(url);
    }
  
    /**
     * A byte source that reads from a URL using {@link URL#openStream()}.
     */
    private static final class UrlByteSource extends ByteSource {
  
      private final URL url;
  
      private UrlByteSource(URL url) {
        this.url = checkNotNull(url);
      }
  
      @Override
      public InputStream openStream() throws IOException {
        return url.openStream();
      }
  
      @Override
      public String toString() {
        return "Resources.asByteSource(" + url + ")";
      }
    }
  
    /**
     * Returns a {@link CharSource} that reads from the given URL using the given
     * character set.
     *
     * @since 14.0
     */
    public static CharSource asCharSource(URL url, Charset charset) {
      return asByteSource(url).asCharSource(charset);
    }
  
    /**
     * Reads all bytes from a URL into a byte array.
     *
     * @param url the URL to read from
     * @return a byte array containing all the bytes from the URL
     * @throws IOException if an I/O error occurs
     */
    public static byte[] toByteArray(URL url) throws IOException {
      return asByteSource(url).read();
   }
 
   /**
    * Reads all characters from a URL into a {@link String}, using the given
    * character set.
    *
    * @param url the URL to read from
    * @param charset the charset used to decode the input stream; see {@link
    *     Charsets} for helpful predefined constants
    * @return a string containing all the characters from the URL
    * @throws IOException if an I/O error occurs.
    */
   public static String toString(URL url, Charset charset) throws IOException {
     return asCharSource(url, charset).read();
   }
 
   /**
    * Streams lines from a URL, stopping when our callback returns false, or we
    * have read all of the lines.
    *
    * @param url the URL to read from
    * @param charset the charset used to decode the input stream; see {@link
    *     Charsets} for helpful predefined constants
    * @param callback the LineProcessor to use to handle the lines
    * @return the output of processing the lines
    * @throws IOException if an I/O error occurs
    */
   public static <T> T readLines(URL url, Charset charset,
       LineProcessor<T> callback) throws IOException {
     return asCharSource(url, charset).readLines(callback);
   }
 
   /**
    * Reads all of the lines from a URL. The lines do not include
    * line-termination characters, but do include other leading and trailing
    * whitespace.
    *
    * <p>This method returns a mutable {@code List}. For an
    * {@code ImmutableList}, use
    * {@code Resources.asCharSource(url, charset).readLines()}.
    *
    * @param url the URL to read from
    * @param charset the charset used to decode the input stream; see {@link
    *     Charsets} for helpful predefined constants
    * @return a mutable {@link List} containing all the lines
    * @throws IOException if an I/O error occurs
    */
   public static List<String> readLines(URL url, Charset charset)
       throws IOException {
     // don't use asCharSource(url, charset).readLines() because that returns
     // an immutable list, which would change the behavior of this method
     return readLines(url, charset, new LineProcessor<List<String>>() {
       final List<String> result = Lists.newArrayList();
 
       @Override
       public boolean processLine(String line) {
         result.add(line);
         return true;
       }
 
       @Override
       public List<String> getResult() {
         return result;
       }
     });
   }
 
   /**
    * Copies all bytes from a URL to an output stream.
    *
    * @param from the URL to read from
    * @param to the output stream
    * @throws IOException if an I/O error occurs
    */
   public static void copy(URL from, OutputStream to) throws IOException {
     asByteSource(from).copyTo(to);
   }
   
   /**
    * Returns a {@code URL} pointing to {@code resourceName} if the resource is
    * found using the {@linkplain Thread#getContextClassLoader() context class
    * loader}. In simple environments, the context class loader will find
    * resources from the class path. In environments where different threads can
    * have different class loaders, for example app servers, the context class
    * loader will typically have been set to an appropriate loader for the
    * current thread.
    *
    * <p>In the unusual case where the context class loader is null, the class
    * loader that loaded this class ({@code Resources}) will be used instead.
    * 
    * @throws IllegalArgumentException if the resource is not found
    */
   public static URL getResource(String resourceName) {
     ClassLoader loader = MoreObjects.firstNonNull(
         Thread.currentThread().getContextClassLoader(),
         Resources.class.getClassLoader());
     URL url = loader.getResource(resourceName);
     checkArgument(url != null, "resource %s not found.", resourceName);
     return url;
   }
 
   /**
    * Given a {@code resourceName} that is relative to {@code contextClass},
    * returns a {@code URL} pointing to the named resource.
    * 
    * @throws IllegalArgumentException if the resource is not found
    */
   public static URL getResource(Class<?> contextClass, String resourceName) {
     URL url = contextClass.getResource(resourceName);
     checkArgument(url != null, "resource %s relative to %s not found.",
         resourceName, contextClass.getName());
     return url;
   }
 }