// ***************************************************************************************************************************
// * Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements.  See the NOTICE file *
// * distributed with this work for additional information regarding copyright ownership.  The ASF licenses this file        *
// * to you 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.juneau.cp;

import static org.apache.juneau.internal.IOUtils.*;
import static org.apache.juneau.internal.ObjectUtils.*;

import java.io.*;
import java.util.*;
import java.util.concurrent.*;

import org.apache.juneau.internal.*;
import org.apache.juneau.parser.*;

/**
 * Class for retrieving and caching resource files from the classpath.
 */
public final class ResourceManager {

   // Maps resource names+locales to found resources.
   private final ConcurrentHashMap<ResourceKey,byte[]> byteCache;
   private final ConcurrentHashMap<ResourceKey,String> stringCache;

   private final Class<?> baseClass;
   private final ResourceFinder resourceFinder;
   private final boolean useCache;

   /**
    * Constructor.
    *
    * @param baseClass The default class to use for retrieving resources from the classpath.
    * @param resourceFinder The resource finder implementation.
    * @param useCache If <jk>true</jk>, retrieved resources are stored in an in-memory cache for fast lookup.
    */
   public ResourceManager(Class<?> baseClass, ResourceFinder resourceFinder, boolean useCache) {
      this.baseClass = baseClass;
      this.resourceFinder = resourceFinder;
      this.useCache = useCache;
      if (useCache) {
         this.byteCache = new ConcurrentHashMap<>();
         this.stringCache = new ConcurrentHashMap<>();
      } else {
         this.byteCache = null;
         this.stringCache = null;
      }
   }

   /**
    * Constructor.
    *
    * <p>
    * Uses default {@link BasicResourceFinder} for finding resources.
    *
    * @param baseClass The default class to use for retrieving resources from the classpath.
    */
   public ResourceManager(Class<?> baseClass) {
      this(baseClass, BasicResourceFinder.INSTANCE, false);
   }

   /**
    * Finds the resource with the given name.
    *
    * @param name Name of the desired resource.
    * @return An input stream to the object, or <jk>null</jk> if the resource could not be found.
    * @throws IOException Thrown by underlying stream.
    */
   public InputStream getStream(String name) throws IOException {
      return getStream(name, null);
   }

   /**
    * Finds the resource with the given name for the specified locale and returns it as an input stream.
    *
    * @param name Name of the desired resource.
    * @param locale The locale.  Can be <jk>null</jk>.
    * @return An input stream to the object, or <jk>null</jk> if the resource could not be found.
    * @throws IOException Thrown by underlying stream.
    */
   public InputStream getStream(String name, Locale locale) throws IOException {

      if (isEmpty(name))
         return null;

      if (! useCache)
         return resourceFinder.findResource(baseClass, name, locale);

      ResourceKey key = new ResourceKey(name, locale);

      byte[] r = byteCache.get(key);
      if (r == null) {
         try (InputStream is = resourceFinder.findResource(baseClass, name, locale)) {
            if (is != null)
               byteCache.putIfAbsent(key, IOUtils.readBytes(is, 1024));
         }
      }

      r = byteCache.get(key);
      return r == null ? null : new ByteArrayInputStream(r);
   }

   /**
    * Finds the resource with the given name and converts it to a simple string.
    *
    * @param name Name of the desired resource.
    * @return The resource converted to a string, or <jk>null</jk> if the resource could not be found.
    * @throws IOException Thrown by underlying stream.
    */
   public String getString(String name) throws IOException {
      return getString(name, null);
   }

   /**
    * Finds the resource with the given name and converts it to a simple string.
    *
    * @param name Name of the desired resource.
    * @param locale The locale.  Can be <jk>null</jk>.
    * @return The resource converted to a string, or <jk>null</jk> if the resource could not be found.
    * @throws IOException Thrown by underlying stream.
    */
   public String getString(String name, Locale locale) throws IOException {

      if (isEmpty(name))
         return null;

      if (! useCache) {
         try (InputStream is = resourceFinder.findResource(baseClass, name, locale)) {
            return IOUtils.read(is, IOUtils.UTF8);
         }
      }

      ResourceKey key = new ResourceKey(name, locale);

      String r = stringCache.get(key);
      if (r == null) {
         try (InputStream is = resourceFinder.findResource(baseClass, name, locale)) {
            if (is != null)
               stringCache.putIfAbsent(key, IOUtils.read(is, IOUtils.UTF8));
         }
      }

      return stringCache.get(key);
   }

   /**
    * Reads the input stream and parses it into a POJO using the specified parser.
    *
    * @param c The class type of the POJO to create.
    * @param parser The parser to use to parse the stream.
    * @param name The resource name (e.g. "htdocs/styles.css").
    * @return The parsed resource, or <jk>null</jk> if the resource could not be found.
    * @throws IOException Thrown by underlying stream.
    * @throws ParseException If stream could not be parsed using the specified parser.
    */
   public <T> T getResource(Class<T> c, Parser parser, String name) throws IOException, ParseException {
      return getResource(c, parser, name, null);
   }

   /**
    * Reads the input stream and parses it into a POJO using the specified parser.
    *
    * @param c The class type of the POJO to create.
    * @param parser The parser to use to parse the stream.
    * @param name The resource name (e.g. "htdocs/styles.css").
    * @param locale
    *    Optional locale.
    *    <br>If <jk>null</jk>, won't look for localized file names.
    * @return The parsed resource, or <jk>null</jk> if the resource could not be found.
    * @throws IOException Thrown by underlying stream.
    * @throws ParseException If stream could not be parsed using the specified parser.
    */
   public <T> T getResource(Class<T> c, Parser parser, String name, Locale locale) throws IOException, ParseException {

      InputStream is = getStream(name, locale);
      if (is == null)
         return null;
      try (Closeable in = parser.isReaderParser() ? new InputStreamReader(is, UTF8) : is) {
         return parser.parse(in, c);
      }
   }

   private class ResourceKey {
      final String name;
      final Locale locale;

      ResourceKey(String name, Locale locale) {
         this.name = name;
         this.locale = locale;
      }

      @Override
      public int hashCode() {
         return name.hashCode() + (locale == null ? 0 : locale.hashCode());
      }

      @Override
      public boolean equals(Object o) {
         return eq(this, (ResourceKey)o, (x,y)->eq(x.name, y.name) && eq(x.locale, y.locale));
      }
   }
}