#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

using System;
using System.IO;
using System.Xml;

using log4net.Util;
using log4net.Core;
using log4net.Layout.Internal;

namespace log4net.Layout
{
  /// <summary>
  /// Layout that formats the log events as XML elements.
  /// </summary>
  /// <remarks>
  /// <para>
  /// This is an abstract class that must be subclassed by an implementation 
  /// to conform to a specific schema.
  /// </para>
  /// <para>
  /// Deriving classes must implement the <see cref="FormatXml"/> method.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  /// <author>Gert Driesen</author>
  public abstract class XmlLayoutBase : LayoutSkeleton
  {
    /// <summary>
    /// Protected constructor to support subclasses
    /// </summary>
    /// <remarks>
    /// <para>
    /// Initializes a new instance of the <see cref="XmlLayoutBase" /> class
    /// with no location info.
    /// </para>
    /// </remarks>
    protected XmlLayoutBase() : this(false)
    {
      IgnoresException = false;
    }

    /// <summary>
    /// Protected constructor to support subclasses
    /// </summary>
    /// <remarks>
    /// <para>
    /// The <paramref name="locationInfo" /> parameter determines whether 
    /// location information will be output by the layout. If 
    /// <paramref name="locationInfo" /> is set to <c>true</c>, then the 
    /// file name and line number of the statement at the origin of the log 
    /// statement will be output. 
    /// </para>
    /// <para>
    /// If you are embedding this layout within an SMTPAppender
    /// then make sure to set the <b>LocationInfo</b> option of that 
    /// appender as well.
    /// </para>
    /// </remarks>
    protected XmlLayoutBase(bool locationInfo)
    {
      IgnoresException = false;
      LocationInfo = locationInfo;
    }

    /// <summary>
    /// Gets a value indicating whether to include location information in 
    /// the XML events.
    /// </summary>
    /// <value>
    /// <c>true</c> if location information should be included in the XML 
    /// events; otherwise, <c>false</c>.
    /// </value>
    /// <remarks>
    /// <para>
    /// If <see cref="LocationInfo" /> is set to <c>true</c>, then the file 
    /// name and line number of the statement at the origin of the log 
    /// statement will be output. 
    /// </para>
    /// <para>
    /// If you are embedding this layout within an <c>SMTPAppender</c>
    /// then make sure to set the <b>LocationInfo</b> option of that 
    /// appender as well.
    /// </para>
    /// </remarks>
    public bool LocationInfo { get; set; }

    /// <summary>
    /// The string to replace characters that can not be expressed in XML with.
    /// <remarks>
    /// <para>
    /// Not all characters may be expressed in XML. This property contains the
    /// string to replace those that can not with. This defaults to a ?. Set it
    /// to the empty string to simply remove offending characters. For more
    /// details on the allowed character ranges see http://www.w3.org/TR/REC-xml/#charsets
    /// Character replacement will occur in  the log message, the property names 
    /// and the property values.
    /// </para>
    /// </remarks>
    /// </summary>
    public string InvalidCharReplacement { get; set; } = "?";

    /// <summary>
    /// Initialize layout options
    /// </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>
    public override void ActivateOptions()
    {
      // nothing to do
    }

    /// <summary>
    /// Gets the content type output by this layout. 
    /// </summary>
    /// <value>
    /// As this is the XML layout, the value is always <c>"text/xml"</c>.
    /// </value>
    /// <remarks>
    /// <para>
    /// As this is the XML layout, the value is always <c>"text/xml"</c>.
    /// </para>
    /// </remarks>
    public override string ContentType => "text/xml";

    /// <summary>
    /// Produces a formatted string.
    /// </summary>
    /// <param name="loggingEvent">The event being logged.</param>
    /// <param name="writer">The TextWriter to write the formatted event to</param>
    /// <remarks>
    /// <para>
    /// Format the <see cref="LoggingEvent"/> and write it to the <see cref="TextWriter"/>.
    /// </para>
    /// <para>
    /// This method creates an <see cref="XmlTextWriter"/> that writes to the
    /// <paramref name="writer"/>. The <see cref="XmlTextWriter"/> is passed 
    /// to the <see cref="FormatXml"/> method. Subclasses should override the
    /// <see cref="FormatXml"/> method rather than this method.
    /// </para>
    /// </remarks>
    public override void Format(TextWriter writer, LoggingEvent loggingEvent)
    {
      if (loggingEvent is null)
      {
        throw new ArgumentNullException(nameof(loggingEvent));
      }
      using XmlWriter xmlWriter = XmlWriterExtensions.CreateXmlWriter(writer);
      // Write the event to the writer
      FormatXml(xmlWriter, loggingEvent);

      xmlWriter.WriteWhitespace(SystemInfo.NewLine);

      // Close on xmlWriter will ensure xml is flushed
      // the protected writer will ignore the actual close
      // -> Dispose from using var will close & flush
    }

    /// <summary>
    /// Does the actual writing of the XML.
    /// </summary>
    /// <param name="writer">The writer to use to output the event to.</param>
    /// <param name="loggingEvent">The event to write.</param>
    /// <remarks>
    /// <para>
    /// Subclasses should override this method to format
    /// the <see cref="LoggingEvent"/> as XML.
    /// </para>
    /// </remarks>
    protected abstract void FormatXml(XmlWriter writer, LoggingEvent loggingEvent);
  }
}