/*
    * 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.core.appender.db;
  
  import java.io.Flushable;
  import java.util.ArrayList;
  import java.util.concurrent.TimeUnit;
  
  import org.apache.logging.log4j.core.LogEvent;
  import org.apache.logging.log4j.core.appender.AbstractManager;
  import org.apache.logging.log4j.core.appender.ManagerFactory;
  
  /**
   * Manager that allows database appenders to have their configuration reloaded without losing events.
   */
  public abstract class AbstractDatabaseManager extends AbstractManager implements Flushable {
      private final ArrayList<LogEvent> buffer;
      private final int bufferSize;
  
      private boolean running = false;
  
      /**
       * Instantiates the base manager.
       *
       * @param name The manager name, which should include any configuration details that one might want to be able to
       *             reconfigure at runtime, such as database name, username, (hashed) password, etc.
       * @param bufferSize The size of the log event buffer.
       */
      protected AbstractDatabaseManager(final String name, final int bufferSize) {
          super(null, name);
          this.bufferSize = bufferSize;
          this.buffer = new ArrayList<>(bufferSize + 1);
      }
  
      /**
       * Implementations should implement this method to perform any proprietary startup operations. This method will
       * never be called twice on the same instance. It is safe to throw any exceptions from this method. This method
       * does not necessarily connect to the database, as it is generally unreliable to connect once and use the same
       * connection for hours.
       */
      protected abstract void startupInternal() throws Exception;
  
      /**
       * This method is called within the appender when the appender is started. If it has not already been called, it
       * calls {@link #startupInternal()} and catches any exceptions it might throw.
       */
      public final synchronized void startup() {
          if (!this.isRunning()) {
              try {
                  this.startupInternal();
                  this.running = true;
              } catch (final Exception e) {
                  logError("Could not perform database startup operations", e);
              }
          }
      }
  
      /**
       * Implementations should implement this method to perform any proprietary disconnection / shutdown operations. This
       * method will never be called twice on the same instance, and it will only be called <em>after</em>
       * {@link #startupInternal()}. It is safe to throw any exceptions from this method. This method does not
       * necessarily disconnect from the database for the same reasons outlined in {@link #startupInternal()}.
       * @return true if all resources were closed normally, false otherwise.
       */
      protected abstract boolean shutdownInternal() throws Exception;
  
      /**
       * This method is called from the {@link #close()} method when the appender is stopped or the appender's manager
       * is replaced. If it has not already been called, it calls {@link #shutdownInternal()} and catches any exceptions
       * it might throw.
       * @return true if all resources were closed normally, false otherwise.
       */
      public final synchronized boolean shutdown() {
          boolean closed = true;
          this.flush();
          if (this.isRunning()) {
              try {
                  closed &= this.shutdownInternal();
              } catch (final Exception e) {
                  logWarn("Caught exception while performing database shutdown operations", e);
                  closed = false;
              } finally {
                  this.running = false;
              }
         }
         return closed;
     }
 
     /**
      * Indicates whether the manager is currently connected {@link #startup()} has been called and {@link #shutdown()}
      * has not been called).
      *
      * @return {@code true} if the manager is connected.
      */
     public final boolean isRunning() {
         return this.running;
     }
 
     /**
      * Connects to the database and starts a transaction (if applicable). With buffering enabled, this is called when
      * flushing the buffer begins, before the first call to {@link #writeInternal}. With buffering disabled, this is
      * called immediately before every invocation of {@link #writeInternal}.
      */
     protected abstract void connectAndStart();
 
     /**
      * Performs the actual writing of the event in an implementation-specific way. This method is called immediately
      * from {@link #write(LogEvent)} if buffering is off, or from {@link #flush()} if the buffer has reached its limit.
      *
      * @param event The event to write to the database.
      */
     protected abstract void writeInternal(LogEvent event);
 
     /**
      * Commits any active transaction (if applicable) and disconnects from the database (returns the connection to the
      * connection pool). With buffering enabled, this is called when flushing the buffer completes, after the last call
      * to {@link #writeInternal}. With buffering disabled, this is called immediately after every invocation of
      * {@link #writeInternal}.
      * @return true if all resources were closed normally, false otherwise.
      */
     protected abstract boolean commitAndClose();
 
     /**
      * This method is called automatically when the buffer size reaches its maximum or at the beginning of a call to
      * {@link #shutdown()}. It can also be called manually to flush events to the database.
      */
     @Override
     public final synchronized void flush() {
         if (this.isRunning() && this.buffer.size() > 0) {
             this.connectAndStart();
             try {
                 for (final LogEvent event : this.buffer) {
                     this.writeInternal(event);
                 }
             } finally {
                 this.commitAndClose();
                 // not sure if this should be done when writing the events failed
                 this.buffer.clear();
             }
         }
     }
 
     /**
      * This method manages buffering and writing of events.
      *
      * @param event The event to write to the database.
      */
     public final synchronized void write(final LogEvent event) {
         if (this.bufferSize > 0) {
             this.buffer.add(event.toImmutable());
             if (this.buffer.size() >= this.bufferSize || event.isEndOfBatch()) {
                 this.flush();
             }
         } else {
             this.connectAndStart();
             try {
                 this.writeInternal(event);
             } finally {
                 this.commitAndClose();
             }
         }
     }
 
     @Override
     public final boolean releaseSub(final long timeout, final TimeUnit timeUnit) {
         return this.shutdown();
     }
 
     @Override
     public final String toString() {
         return this.getName();
     }
 
     /**
      * Implementations should define their own getManager method and call this method from that to create or get
      * existing managers.
      *
      * @param name The manager name, which should include any configuration details that one might want to be able to
      *             reconfigure at runtime, such as database name, username, (hashed) password, etc.
      * @param data The concrete instance of {@link AbstractFactoryData} appropriate for the given manager.
      * @param factory A factory instance for creating the appropriate manager.
      * @param <M> The concrete manager type.
      * @param <T> The concrete {@link AbstractFactoryData} type.
      * @return a new or existing manager of the specified type and name.
      */
     protected static <M extends AbstractDatabaseManager, T extends AbstractFactoryData> M getManager(
             final String name, final T data, final ManagerFactory<M, T> factory
     ) {
         return AbstractManager.getManager(name, factory, data);
     }
 
     /**
      * Implementations should extend this class for passing data between the getManager method and the manager factory
      * class.
      */
     protected abstract static class AbstractFactoryData {
         private final int bufferSize;
 
         /**
          * Constructs the base factory data.
          *
          * @param bufferSize The size of the buffer.
          */
         protected AbstractFactoryData(final int bufferSize) {
             this.bufferSize = bufferSize;
         }
 
         /**
          * Gets the buffer size.
          *
          * @return the buffer size.
          */
         public int getBufferSize() {
             return bufferSize;
         }
     }
 }