#region Apache License
//
// 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.
//
#endregion

// .NET Compact Framework 1.0 has no support for Marshal.StringToHGlobalAnsi
// SSCLI 1.0 has no support for Marshal.StringToHGlobalAnsi
#if !NETCF && !SSCLI

using System;
using System.Runtime.InteropServices;

using log4net.Core;
using log4net.Appender;
using log4net.Util;
using log4net.Layout;

namespace log4net.Appender 
{
	/// <summary>
	/// Logs events to a local syslog service.
	/// </summary>
	/// <remarks>
	/// <note>
	/// This appender uses the POSIX libc library functions <c>openlog</c>, <c>syslog</c>, and <c>closelog</c>.
	/// If these functions are not available on the local system then this appender will not work!
	/// </note>
	/// <para>
	/// The functions <c>openlog</c>, <c>syslog</c>, and <c>closelog</c> are specified in SUSv2 and 
	/// POSIX 1003.1-2001 standards. These are used to log messages to the local syslog service.
	/// </para>
	/// <para>
	/// This appender talks to a local syslog service. If you need to log to a remote syslog
	/// daemon and you cannot configure your local syslog service to do this you may be
	/// able to use the <see cref="RemoteSyslogAppender"/> to log via UDP.
	/// </para>
	/// <para>
	/// Syslog messages must have a facility and and a severity. The severity
	/// is derived from the Level of the logging event.
	/// The facility must be chosen from the set of defined syslog 
	/// <see cref="SyslogFacility"/> values. The facilities list is predefined
	/// and cannot be extended.
	/// </para>
	/// <para>
	/// An identifier is specified with each log message. This can be specified
	/// by setting the <see cref="Identity"/> property. The identity (also know 
	/// as the tag) must not contain white space. The default value for the
	/// identity is the application name (from <see cref="SystemInfo.ApplicationFriendlyName"/>).
	/// </para>
	/// </remarks>
	/// <author>Rob Lyon</author>
	/// <author>Nicko Cadell</author>
	public class LocalSyslogAppender : AppenderSkeleton 
	{
		#region Enumerations

		/// <summary>
		/// syslog severities
		/// </summary>
		/// <remarks>
		/// <para>
		/// The log4net Level maps to a syslog severity using the
		/// <see cref="LocalSyslogAppender.AddMapping"/> method and the <see cref="LevelSeverity"/>
		/// class. The severity is set on <see cref="LevelSeverity.Severity"/>.
		/// </para>
		/// </remarks>
		public enum SyslogSeverity
		{
			/// <summary>
			/// system is unusable
			/// </summary>
			Emergency = 0,

			/// <summary>
			/// action must be taken immediately
			/// </summary>
			Alert = 1,

			/// <summary>
			/// critical conditions
			/// </summary>
			Critical = 2,

			/// <summary>
			/// error conditions
			/// </summary>
			Error = 3,

			/// <summary>
			/// warning conditions
			/// </summary>
			Warning = 4,

			/// <summary>
			/// normal but significant condition
			/// </summary>
			Notice = 5,

			/// <summary>
			/// informational
			/// </summary>
			Informational = 6,

			/// <summary>
			/// debug-level messages
			/// </summary>
			Debug = 7
		};

		/// <summary>
		/// syslog facilities
		/// </summary>
		/// <remarks>
		/// <para>
		/// The syslog facility defines which subsystem the logging comes from.
		/// This is set on the <see cref="Facility"/> property.
		/// </para>
		/// </remarks>
		public enum SyslogFacility
		{
			/// <summary>
			/// kernel messages
			/// </summary>
			Kernel = 0,

			/// <summary>
			/// random user-level messages
			/// </summary>
			User = 1,

			/// <summary>
			/// mail system
			/// </summary>
			Mail = 2,

			/// <summary>
			/// system daemons
			/// </summary>
			Daemons = 3,

			/// <summary>
			/// security/authorization messages
			/// </summary>
			Authorization = 4,

			/// <summary>
			/// messages generated internally by syslogd
			/// </summary>
			Syslog = 5,

			/// <summary>
			/// line printer subsystem
			/// </summary>
			Printer = 6,

			/// <summary>
			/// network news subsystem
			/// </summary>
			News = 7,

			/// <summary>
			/// UUCP subsystem
			/// </summary>
			Uucp = 8,

			/// <summary>
			/// clock (cron/at) daemon
			/// </summary>
			Clock = 9,

			/// <summary>
			/// security/authorization  messages (private)
			/// </summary>
			Authorization2 = 10,

			/// <summary>
			/// ftp daemon
			/// </summary>
			Ftp = 11,

			/// <summary>
			/// NTP subsystem
			/// </summary>
			Ntp = 12,

			/// <summary>
			/// log audit
			/// </summary>
			Audit = 13,

			/// <summary>
			/// log alert
			/// </summary>
			Alert = 14,

			/// <summary>
			/// clock daemon
			/// </summary>
			Clock2 = 15,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local0 = 16,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local1 = 17,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local2 = 18,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local3 = 19,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local4 = 20,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local5 = 21,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local6 = 22,

			/// <summary>
			/// reserved for local use
			/// </summary>
			Local7 = 23
		}

		#endregion // Enumerations

		#region Public Instance Constructors

		/// <summary>
		/// Initializes a new instance of the <see cref="LocalSyslogAppender" /> class.
		/// </summary>
		/// <remarks>
		/// This instance of the <see cref="LocalSyslogAppender" /> class is set up to write 
		/// to a local syslog service.
		/// </remarks>
		public LocalSyslogAppender() 
		{
		}

		#endregion // Public Instance Constructors

		#region Public Instance Properties
		
		/// <summary>
		/// Message identity
		/// </summary>
		/// <remarks>
		/// <para>
		/// An identifier is specified with each log message. This can be specified
		/// by setting the <see cref="Identity"/> property. The identity (also know 
		/// as the tag) must not contain white space. The default value for the
		/// identity is the application name (from <see cref="SystemInfo.ApplicationFriendlyName"/>).
		/// </para>
		/// </remarks>
		public string Identity
		{
			get { return m_identity; }
			set { m_identity = value; }
		}

		/// <summary>
		/// Syslog facility
		/// </summary>
		/// <remarks>
		/// Set to one of the <see cref="SyslogFacility"/> values. The list of
		/// facilities is predefined and cannot be extended. The default value
		/// is <see cref="SyslogFacility.User"/>.
		/// </remarks>
		public SyslogFacility Facility
		{
			get { return m_facility; }
			set { m_facility = value; }
		}
		
		#endregion // Public Instance Properties

		/// <summary>
		/// Add a mapping of level to severity
		/// </summary>
		/// <param name="mapping">The mapping to add</param>
		/// <remarks>
		/// <para>
		/// Adds a <see cref="LevelSeverity"/> to this appender.
		/// </para>
		/// </remarks>
		public void AddMapping(LevelSeverity mapping)
		{
			m_levelMapping.Add(mapping);
		}

		#region IOptionHandler Implementation

		/// <summary>
		/// Initialize the appender based on the options set.
		/// </summary>
		/// <remarks>
		/// <para>
		/// This is part of the <see cref="IOptionHandler"/> delayed object
		/// activation scheme. The <see cref="ActivateOptions"/> method must 
		/// be called on this object after the configuration properties have
		/// been set. Until <see cref="ActivateOptions"/> is called this
		/// object is in an undefined state and must not be used. 
		/// </para>
		/// <para>
		/// If any of the configuration properties are modified then 
		/// <see cref="ActivateOptions"/> must be called again.
		/// </para>
		/// </remarks>
#if NET_4_0 || MONO_4_0 || NETSTANDARD1_3
        [System.Security.SecuritySafeCritical]
#endif
        public override void ActivateOptions()
		{
			base.ActivateOptions();
			
			m_levelMapping.ActivateOptions();

			string identString = m_identity;
			if (identString == null)
			{
				// Set to app name by default
				identString = SystemInfo.ApplicationFriendlyName;
			}

			// create the native heap ansi string. Note this is a copy of our string
			// so we do not need to hold on to the string itself, holding on to the
			// handle will keep the heap ansi string alive.
			m_handleToIdentity = Marshal.StringToHGlobalAnsi(identString);

			// open syslog
			openlog(m_handleToIdentity, 1, m_facility);
		}

		#endregion // IOptionHandler Implementation

		#region AppenderSkeleton Implementation

		/// <summary>
		/// This method is called by the <see cref="M:AppenderSkeleton.DoAppend(LoggingEvent)"/> method.
		/// </summary>
		/// <param name="loggingEvent">The event to log.</param>
		/// <remarks>
		/// <para>
		/// Writes the event to a remote syslog daemon.
		/// </para>
		/// <para>
		/// The format of the output will depend on the appender's layout.
		/// </para>
		/// </remarks>
#if NET_4_0 || MONO_4_0 || NETSTANDARD1_3
        [System.Security.SecuritySafeCritical]
#endif
#if !NETSTANDARD1_3
        [System.Security.Permissions.SecurityPermission(System.Security.Permissions.SecurityAction.Demand, UnmanagedCode = true)]
#endif
        protected override void Append(LoggingEvent loggingEvent) 
		{
			int priority = GeneratePriority(m_facility, GetSeverity(loggingEvent.Level));
			string message = RenderLoggingEvent(loggingEvent);

			// Call the local libc syslog method
			// The second argument is a printf style format string
			syslog(priority, "%s", message);
		}

		/// <summary>
		/// Close the syslog when the appender is closed
		/// </summary>
		/// <remarks>
		/// <para>
		/// Close the syslog when the appender is closed
		/// </para>
		/// </remarks>
#if NET_4_0 || MONO_4_0 || NETSTANDARD1_3
        [System.Security.SecuritySafeCritical]
#endif
        protected override void OnClose()
		{
			base.OnClose();

			try
			{
				// close syslog
				closelog();
			}
			catch(DllNotFoundException)
			{
				// Ignore dll not found at this point
			}
		
			if (m_handleToIdentity != IntPtr.Zero)
			{
				// free global ident
				Marshal.FreeHGlobal(m_handleToIdentity);
			}
		}

		/// <summary>
		/// This appender requires a <see cref="AppenderSkeleton.Layout"/> to be set.
		/// </summary>
		/// <value><c>true</c></value>
		/// <remarks>
		/// <para>
		/// This appender requires a <see cref="AppenderSkeleton.Layout"/> to be set.
		/// </para>
		/// </remarks>
		override protected bool RequiresLayout
		{
			get { return true; }
		}

		#endregion // AppenderSkeleton Implementation

		#region Protected Members

		/// <summary>
		/// Translates a log4net level to a syslog severity.
		/// </summary>
		/// <param name="level">A log4net level.</param>
		/// <returns>A syslog severity.</returns>
		/// <remarks>
		/// <para>
		/// Translates a log4net level to a syslog severity.
		/// </para>
		/// </remarks>
		virtual protected SyslogSeverity GetSeverity(Level level)
		{
			LevelSeverity levelSeverity = m_levelMapping.Lookup(level) as LevelSeverity;
			if (levelSeverity != null)
			{
				return levelSeverity.Severity;
			}

			//
			// Fallback to sensible default values
			//

			if (level >= Level.Alert) 
			{
				return SyslogSeverity.Alert;
			} 
			else if (level >= Level.Critical) 
			{
				return SyslogSeverity.Critical;
			} 
			else if (level >= Level.Error) 
			{
				return SyslogSeverity.Error;
			} 
			else if (level >= Level.Warn) 
			{
				return SyslogSeverity.Warning;
			} 
			else if (level >= Level.Notice) 
			{
				return SyslogSeverity.Notice;
			} 
			else if (level >= Level.Info) 
			{
				return SyslogSeverity.Informational;
			} 
			// Default setting
			return SyslogSeverity.Debug;
		}

		#endregion // Protected Members

		#region Public Static Members

		/// <summary>
		/// Generate a syslog priority.
		/// </summary>
		/// <param name="facility">The syslog facility.</param>
		/// <param name="severity">The syslog severity.</param>
		/// <returns>A syslog priority.</returns>
		private static int GeneratePriority(SyslogFacility facility, SyslogSeverity severity)
		{
			return ((int)facility * 8) + (int)severity;
		}

		#endregion // Public Static Members

		#region Private Instances Fields

		/// <summary>
		/// The facility. The default facility is <see cref="SyslogFacility.User"/>.
		/// </summary>
		private SyslogFacility m_facility = SyslogFacility.User;

		/// <summary>
		/// The message identity
		/// </summary>
		private string m_identity;

		/// <summary>
		/// Marshaled handle to the identity string. We have to hold on to the
		/// string as the <c>openlog</c> and <c>syslog</c> APIs just hold the
		/// pointer to the ident and dereference it for each log message.
		/// </summary>
		private IntPtr m_handleToIdentity = IntPtr.Zero;

		/// <summary>
		/// Mapping from level object to syslog severity
		/// </summary>
		private LevelMapping m_levelMapping = new LevelMapping();

		#endregion // Private Instances Fields

		#region External Members
		
		/// <summary>
		/// Open connection to system logger.
		/// </summary>
		[DllImport("libc")]
		private static extern void openlog(IntPtr ident, int option, SyslogFacility facility);

		/// <summary>
		/// Generate a log message.
		/// </summary>
		/// <remarks>
		/// <para>
		/// The libc syslog method takes a format string and a variable argument list similar
		/// to the classic printf function. As this type of vararg list is not supported
		/// by C# we need to specify the arguments explicitly. Here we have specified the
		/// format string with a single message argument. The caller must set the format 
		/// string to <c>"%s"</c>.
		/// </para>
		/// </remarks>
		[DllImport("libc", CharSet=CharSet.Ansi, CallingConvention=CallingConvention.Cdecl)]
		private static extern void syslog(int priority, string format, string message);

		/// <summary>
		/// Close descriptor used to write to system logger.
		/// </summary>
		[DllImport("libc")]
		private static extern void closelog();

		#endregion // External Members

		#region LevelSeverity LevelMapping Entry

		/// <summary>
		/// A class to act as a mapping between the level that a logging call is made at and
		/// the syslog severity that is should be logged at.
		/// </summary>
		/// <remarks>
		/// <para>
		/// A class to act as a mapping between the level that a logging call is made at and
		/// the syslog severity that is should be logged at.
		/// </para>
		/// </remarks>
		public class LevelSeverity : LevelMappingEntry
		{
			private SyslogSeverity m_severity;

			/// <summary>
			/// The mapped syslog severity for the specified level
			/// </summary>
			/// <remarks>
			/// <para>
			/// Required property.
			/// The mapped syslog severity for the specified level
			/// </para>
			/// </remarks>
			public SyslogSeverity Severity
			{
				get { return m_severity; }
				set { m_severity = value; }
			}
		}

		#endregion // LevelSeverity LevelMapping Entry
	}
}

#endif