/*
    * 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.logging.log4j;
  
  import java.io.Serializable;
  import java.util.AbstractCollection;
  import java.util.Collection;
  import java.util.Collections;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.NoSuchElementException;
  
  import org.apache.logging.log4j.message.ParameterizedMessage;
  import org.apache.logging.log4j.spi.DefaultThreadContextMap;
  import org.apache.logging.log4j.spi.DefaultThreadContextStack;
  import org.apache.logging.log4j.spi.Provider;
  import org.apache.logging.log4j.spi.ThreadContextMap;
  import org.apache.logging.log4j.spi.ThreadContextStack;
  import org.apache.logging.log4j.status.StatusLogger;
  import org.apache.logging.log4j.util.PropertiesUtil;
  import org.apache.logging.log4j.util.ProviderUtil;
  
  /**
   * The ThreadContext allows applications to store information either in a Map or a Stack.
   * <p>
   * <b><em>The MDC is managed on a per thread basis</em></b>. A child thread automatically inherits a <em>copy</em> of
   * the mapped diagnostic context of its parent.
   * </p>
   */
  public final class ThreadContext {
  
      /**
       * An empty read-only ThreadContextStack.
       */
      private static class EmptyThreadContextStack extends AbstractCollection<String> implements ThreadContextStack {
  
          private static final long serialVersionUID = 1L;
  
          private static final Iterator<String> EMPTY_ITERATOR = new EmptyIterator<>();
  
          @Override
          public String pop() {
              return null;
          }
  
          @Override
          public String peek() {
              return null;
          }
  
          @Override
          public void push(final String message) {
              throw new UnsupportedOperationException();
          }
  
          @Override
          public int getDepth() {
              return 0;
          }
  
          @Override
          public List<String> asList() {
              return Collections.emptyList();
          }
  
          @Override
          public void trim(final int depth) {
              // Do nothing
          }
  
          @Override
          public boolean equals(final Object o) {
              // Similar to java.util.Collections.EmptyList.equals(Object)
              return (o instanceof Collection) && ((Collection<?>) o).isEmpty();
          }
  
          @Override
          public int hashCode() {
              // Same as java.util.Collections.EmptyList.hashCode()
              return 1;
          }
  
          @Override
         public ContextStack copy() {
             return this;
         }
 
         @Override
         public <T> T[] toArray(final T[] a) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public boolean add(final String e) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public boolean containsAll(final Collection<?> c) {
             return false;
         }
 
         @Override
         public boolean addAll(final Collection<? extends String> c) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public boolean removeAll(final Collection<?> c) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public boolean retainAll(final Collection<?> c) {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public Iterator<String> iterator() {
             return EMPTY_ITERATOR;
         }
 
         @Override
         public int size() {
             return 0;
         }
 
         @Override
         public ContextStack getImmutableStackOrNull() {
             return this;
         }
     }
 
     /**
      * An empty iterator. Since Java 1.7 added the Collections.emptyIterator() method, we have to make do.
      * 
      * @param <E> the type of the empty iterator
      */
     private static class EmptyIterator<E> implements Iterator<E> {
 
         @Override
         public boolean hasNext() {
             return false;
         }
 
         @Override
         public E next() {
             throw new NoSuchElementException("This is an empty iterator!");
         }
 
         @Override
         public void remove() {
             // no-op
         }
     }
 
     /**
      * Empty, immutable Map.
      */
     // ironically, this annotation gives an "unsupported @SuppressWarnings" warning in Eclipse
     @SuppressWarnings("PublicStaticCollectionField")
     // I like irony, so I won't delete it...
     public static final Map<String, String> EMPTY_MAP = Collections.emptyMap();
 
     /**
      * Empty, immutable ContextStack.
      */
     // ironically, this annotation gives an "unsupported @SuppressWarnings" warning in Eclipse
     @SuppressWarnings("PublicStaticCollectionField")
     public static final ThreadContextStack EMPTY_STACK = new EmptyThreadContextStack();
 
     private static final String DISABLE_MAP = "disableThreadContextMap";
     private static final String DISABLE_STACK = "disableThreadContextStack";
     private static final String DISABLE_ALL = "disableThreadContext";
     private static final String THREAD_CONTEXT_KEY = "log4j2.threadContextMap";
 
     private static boolean disableAll;
     private static boolean useMap;
     private static boolean useStack;
     private static ThreadContextMap contextMap;
     private static ThreadContextStack contextStack;
     private static final Logger LOGGER = StatusLogger.getLogger();
 
     static {
         init();
     }
 
     private ThreadContext() {
         // empty
     }
 
     /**
      * <em>Consider private, used for testing.</em>
      */
     static void init() {
         contextMap = null;
         final PropertiesUtil managerProps = PropertiesUtil.getProperties();
         disableAll = managerProps.getBooleanProperty(DISABLE_ALL);
         useStack = !(managerProps.getBooleanProperty(DISABLE_STACK) || disableAll);
         useMap = !(managerProps.getBooleanProperty(DISABLE_MAP) || disableAll);
 
         contextStack = new DefaultThreadContextStack(useStack);
         final String threadContextMapName = managerProps.getStringProperty(THREAD_CONTEXT_KEY);
         final ClassLoader cl = ProviderUtil.findClassLoader();
         if (threadContextMapName != null) {
             try {
                 final Class<?> clazz = cl.loadClass(threadContextMapName);
                 if (ThreadContextMap.class.isAssignableFrom(clazz)) {
                     contextMap = (ThreadContextMap) clazz.newInstance();
                 }
             } catch (final ClassNotFoundException cnfe) {
                 LOGGER.error("Unable to locate configured ThreadContextMap {}", threadContextMapName);
             } catch (final Exception ex) {
                 LOGGER.error("Unable to create configured ThreadContextMap {}", threadContextMapName, ex);
             }
         }
         if (contextMap == null && ProviderUtil.hasProviders()) {
             final String factoryClassName = LogManager.getFactory().getClass().getName();
             for (final Provider provider : ProviderUtil.getProviders()) {
                 if (factoryClassName.equals(provider.getClassName())) {
                     final Class<? extends ThreadContextMap> clazz = provider.loadThreadContextMap();
                     if (clazz != null) {
                         try {
                             contextMap = clazz.newInstance();
                             break;
                         } catch (final Exception e) {
                             LOGGER.error("Unable to locate or load configured ThreadContextMap {}",
                                     provider.getThreadContextMap(), e);
                             contextMap = new DefaultThreadContextMap(useMap);
                         }
                     }
                 }
             }
         }
         if (contextMap == null) {
             contextMap = new DefaultThreadContextMap(useMap);
         }
     }
 
     /**
      * Puts a context value (the <code>value</code> parameter) as identified with the <code>key</code> parameter into
      * the current thread's context map.
      *
      * <p>
      * If the current thread does not have a context map it is created as a side effect.
      * </p>
      * 
      * @param key The key name.
      * @param value The key value.
      */
     public static void put(final String key, final String value) {
         contextMap.put(key, value);
     }
 
     /**
      * Gets the context value identified by the <code>key</code> parameter.
      *
      * <p>
      * This method has no side effects.
      * </p>
      * 
      * @param key The key to locate.
      * @return The value associated with the key or null.
      */
     public static String get(final String key) {
         return contextMap.get(key);
     }
 
     /**
      * Removes the context value identified by the <code>key</code> parameter.
      * 
      * @param key The key to remove.
      */
     public static void remove(final String key) {
         contextMap.remove(key);
     }
 
     /**
      * Clears the context map.
      */
     public static void clearMap() {
         contextMap.clear();
     }
 
     /**
      * Clears the context map and stack.
      */
     public static void clearAll() {
         clearMap();
         clearStack();
     }
 
     /**
      * Determines if the key is in the context.
      * 
      * @param key The key to locate.
      * @return True if the key is in the context, false otherwise.
      */
     public static boolean containsKey(final String key) {
         return contextMap.containsKey(key);
     }
 
     /**
      * Returns a mutable copy of current thread's context Map.
      * 
      * @return a mutable copy of the context.
      */
     public static Map<String, String> getContext() {
         return contextMap.getCopy();
     }
 
     /**
      * Returns an immutable view of the current thread's context Map.
      * 
      * @return An immutable view of the ThreadContext Map.
      */
     public static Map<String, String> getImmutableContext() {
         final Map<String, String> map = contextMap.getImmutableMapOrNull();
         return map == null ? EMPTY_MAP : map;
     }
 
     /**
      * Returns true if the Map is empty.
      * 
      * @return true if the Map is empty, false otherwise.
      */
     public static boolean isEmpty() {
         return contextMap.isEmpty();
     }
 
     /**
      * Clears the stack for this thread.
      */
     public static void clearStack() {
         contextStack.clear();
     }
 
     /**
      * Returns a copy of this thread's stack.
      * 
      * @return A copy of this thread's stack.
      */
     public static ContextStack cloneStack() {
         return contextStack.copy();
     }
 
     /**
      * Gets an immutable copy of this current thread's context stack.
      * 
      * @return an immutable copy of the ThreadContext stack.
      */
     public static ContextStack getImmutableStack() {
         final ContextStack result = contextStack.getImmutableStackOrNull();
         return result == null ? EMPTY_STACK : result;
     }
 
     /**
      * Sets this thread's stack.
      * 
      * @param stack The stack to use.
      */
     public static void setStack(final Collection<String> stack) {
         if (stack.isEmpty() || !useStack) {
             return;
         }
         contextStack.clear();
         contextStack.addAll(stack);
     }
 
     /**
      * Gets the current nesting depth of this thread's stack.
      * 
      * @return the number of items in the stack.
      *
      * @see #trim
      */
     public static int getDepth() {
         return contextStack.getDepth();
     }
 
     /**
      * Returns the value of the last item placed on the stack.
      *
      * <p>
      * The returned value is the value that was pushed last. If no context is available, then the empty string "" is
      * returned.
      * </p>
      *
      * @return String The innermost diagnostic context.
      */
     public static String pop() {
         return contextStack.pop();
     }
 
     /**
      * Looks at the last diagnostic context at the top of this NDC without removing it.
      *
      * <p>
      * The returned value is the value that was pushed last. If no context is available, then the empty string "" is
      * returned.
      * </p>
      *
      * @return String The innermost diagnostic context.
      */
     public static String peek() {
         return contextStack.peek();
     }
 
     /**
      * Pushes new diagnostic context information for the current thread.
      *
      * <p>
      * The contents of the <code>message</code> parameter is determined solely by the client.
      * </p>
      *
      * @param message The new diagnostic context information.
      */
     public static void push(final String message) {
         contextStack.push(message);
     }
 
     /**
      * Pushes new diagnostic context information for the current thread.
      *
      * <p>
      * The contents of the <code>message</code> and args parameters are determined solely by the client. The message
      * will be treated as a format String and tokens will be replaced with the String value of the arguments in
      * accordance with ParameterizedMessage.
      * </p>
      *
      * @param message The new diagnostic context information.
      * @param args Parameters for the message.
      */
     public static void push(final String message, final Object... args) {
         contextStack.push(ParameterizedMessage.format(message, args));
     }
 
     /**
      * Removes the diagnostic context for this thread.
      *
      * <p>
      * Each thread that created a diagnostic context by calling {@link #push} should call this method before exiting.
      * Otherwise, the memory used by the <b>thread</b> cannot be reclaimed by the VM.
      * </p>
      *
      * <p>
      * As this is such an important problem in heavy duty systems and because it is difficult to always guarantee that
      * the remove method is called before exiting a thread, this method has been augmented to lazily remove references
      * to dead threads. In practice, this means that you can be a little sloppy and occasionally forget to call
      * {@link #remove} before exiting a thread. However, you must call <code>remove</code> sometime. If you never call
      * it, then your application is sure to run out of memory.
      * </p>
      */
     public static void removeStack() {
         contextStack.clear();
     }
 
     /**
      * Trims elements from this diagnostic context. If the current depth is smaller or equal to <code>maxDepth</code>,
      * then no action is taken. If the current depth is larger than newDepth then all elements at maxDepth or higher are
      * discarded.
      *
      * <p>
      * This method is a convenient alternative to multiple {@link #pop} calls. Moreover, it is often the case that at
      * the end of complex call sequences, the depth of the ThreadContext is unpredictable. The <code>trim</code> method
      * circumvents this problem.
      * </p>
      *
      * <p>
      * For example, the combination
      * </p>
      * 
      * <pre>
      * void foo() {
      *     final int depth = ThreadContext.getDepth();
      * 
      *     // ... complex sequence of calls
      * 
      *     ThreadContext.trim(depth);
      * }
      * </pre>
      *
      * <p>
      * ensures that between the entry and exit of {@code foo} the depth of the diagnostic stack is conserved.
      * </p>
      *
      * @see #getDepth
      * @param depth The number of elements to keep.
      */
     public static void trim(final int depth) {
         contextStack.trim(depth);
     }
 
     /**
      * The ThreadContext Stack interface.
      */
     public interface ContextStack extends Serializable, Collection<String> {
 
         /**
          * Returns the element at the top of the stack.
          * 
          * @return The element at the top of the stack.
          * @throws java.util.NoSuchElementException if the stack is empty.
          */
         String pop();
 
         /**
          * Returns the element at the top of the stack without removing it or null if the stack is empty.
          * 
          * @return the element at the top of the stack or null if the stack is empty.
          */
         String peek();
 
         /**
          * Pushes an element onto the stack.
          * 
          * @param message The element to add.
          */
         void push(String message);
 
         /**
          * Returns the number of elements in the stack.
          * 
          * @return the number of elements in the stack.
          */
         int getDepth();
 
         /**
          * Returns all the elements in the stack in a List.
          * 
          * @return all the elements in the stack in a List.
          */
         List<String> asList();
 
         /**
          * Trims elements from the end of the stack.
          * 
          * @param depth The maximum number of items in the stack to keep.
          */
         void trim(int depth);
 
         /**
          * Returns a copy of the ContextStack.
          * 
          * @return a copy of the ContextStack.
          */
         ContextStack copy();
 
         /**
          * Returns a ContextStack with the same contents as this ContextStack or {@code null}. Attempts to modify the
          * returned stack may or may not throw an exception, but will not affect the contents of this ContextStack.
          * 
          * @return a ContextStack with the same contents as this ContextStack or {@code null}.
          */
         ContextStack getImmutableStackOrNull();
     }
 }