#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.Globalization;
using System.Reflection;
using System.Text;

using log4net.Core;
using log4net.Util.TypeConverters;

namespace log4net.Util
{
  /// <summary>
  /// A convenience class to convert property values to specific types.
  /// </summary>
  /// <remarks>
  /// <para>
  /// Utility functions for converting types and parsing values.
  /// </para>
  /// </remarks>
  /// <author>Nicko Cadell</author>
  /// <author>Gert Driesen</author>
  public static class OptionConverter
  {
    /// <summary>
    /// Converts a string to a <see cref="bool" /> value.
    /// </summary>
    /// <param name="argValue">String to convert.</param>
    /// <param name="defaultValue">The default value.</param>
    /// <returns>The <see cref="bool" /> value of <paramref name="argValue" />.</returns>
    /// <remarks>
    /// <para>
    /// If <paramref name="argValue"/> is "true", then <c>true</c> is returned. 
    /// If <paramref name="argValue"/> is "false", then <c>false</c> is returned. 
    /// Otherwise, <paramref name="defaultValue"/> is returned.
    /// </para>
    /// </remarks>
    public static bool ToBoolean(string? argValue, bool defaultValue)
    {
      if (!string.IsNullOrEmpty(argValue))
      {
        try
        {
          return bool.Parse(argValue);
        }
        catch (Exception e)
        {
          LogLog.Error(declaringType, $"[{argValue}] is not in proper bool form.", e);
        }
      }
      return defaultValue;
    }

    /// <summary>
    /// Parses a file size into a number.
    /// </summary>
    /// <param name="argValue">String to parse.</param>
    /// <param name="defaultValue">The default value.</param>
    /// <returns>The <see cref="long" /> value of <paramref name="argValue" />.</returns>
    /// <remarks>
    /// <para>
    /// Parses a file size of the form: number[KB|MB|GB] into a
    /// long value. It is scaled with the appropriate multiplier.
    /// </para>
    /// <para>
    /// <paramref name="defaultValue"/> is returned when <paramref name="argValue"/>
    /// cannot be converted to a <see cref="long" /> value.
    /// </para>
    /// </remarks>
    public static long ToFileSize(string? argValue, long defaultValue)
    {
      if (argValue is null)
      {
        return defaultValue;
      }

      string s = argValue.Trim().ToUpperInvariant();
      long multiplier = 1;
      int index;

      if ((index = s.IndexOf("KB", StringComparison.Ordinal)) != -1)
      {
        multiplier = 1024;
        s = s.Substring(0, index);
      }
      else if ((index = s.IndexOf("MB", StringComparison.Ordinal)) != -1)
      {
        multiplier = 1024 * 1024;
        s = s.Substring(0, index);
      }
      else if ((index = s.IndexOf("GB", StringComparison.Ordinal)) != -1)
      {
        multiplier = 1024 * 1024 * 1024;
        s = s.Substring(0, index);
      }

      // Try again to remove whitespace between the number and the size specifier
      s = s.Trim();

      if (SystemInfo.TryParse(s, out long longVal))
      {
        return longVal * multiplier;
      }
      else
      {
        LogLog.Error(declaringType, $"OptionConverter: [{s}] is not in the correct file size syntax.");
      }
      return defaultValue;
    }

    /// <summary>
    /// Converts a string to an object.
    /// </summary>
    /// <param name="target">The target type to convert to.</param>
    /// <param name="txt">The string to convert to an object.</param>
    /// <returns>
    /// The object converted from a string or <c>null</c> when the 
    /// conversion failed.
    /// </returns>
    /// <remarks>
    /// <para>
    /// Converts a string to an object. Uses the converter registry to try
    /// to convert the string value into the specified target type.
    /// </para>
    /// </remarks>
    public static object? ConvertStringTo(Type target, string txt)
    {
      if (target is null)
      {
        throw new ArgumentNullException(nameof(target));
      }

      // If we want a string we already have the correct type
      if (typeof(string) == target || typeof(object) == target)
      {
        return txt;
      }

      // First lets try to find a type converter
      IConvertFrom? typeConverter = ConverterRegistry.GetConvertFrom(target);
      if (typeConverter is not null && typeConverter.CanConvertFrom(typeof(string)))
      {
        // Found appropriate converter
        return typeConverter.ConvertFrom(txt);
      }
      else
      {
        if (target.IsEnum)
        {
          // Target type is an enum.

          // Use the Enum.Parse(EnumType, string) method to get the enum value
          return ParseEnum(target, txt, true);
        }
        else
        {
          // We essentially make a guess that to convert from a string
          // to an arbitrary type T there will be a static method defined on type T called Parse
          // that will take an argument of type string. i.e. T.Parse(string)->T we call this
          // method to convert the string to the type required by the property.
          if (target.GetMethod("Parse", new[] { typeof(string) }) is MethodInfo meth)
          {
            // Call the Parse method
            return meth.Invoke(null, BindingFlags.InvokeMethod, null, new object[] { txt }, CultureInfo.InvariantCulture);
          }
          else
          {
            // No Parse() method found.
          }
        }
      }
      return null;
    }

    /// <summary>
    /// Checks if there is an appropriate type conversion from the source type to the target type.
    /// </summary>
    /// <param name="sourceType">The type to convert from.</param>
    /// <param name="targetType">The type to convert to.</param>
    /// <returns><c>true</c> if there is a conversion from the source type to the target type.</returns>
    /// <remarks>
    /// Checks if there is an appropriate type conversion from the source type to the target type.
    /// <para>
    /// </para>
    /// </remarks>
    public static bool CanConvertTypeTo(Type? sourceType, Type? targetType)
    {
      if (sourceType is null || targetType is null)
      {
        return false;
      }

      // Check if we can assign directly from the source type to the target type
      if (targetType.IsAssignableFrom(sourceType))
      {
        return true;
      }

      // Look for a To converter
      if (ConverterRegistry.GetConvertTo(sourceType, targetType) is IConvertTo tcSource)
      {
        if (tcSource.CanConvertTo(targetType))
        {
          return true;
        }
      }

      // Look for a From converter
      if (ConverterRegistry.GetConvertFrom(targetType) is IConvertFrom tcTarget)
      {
        if (tcTarget.CanConvertFrom(sourceType))
        {
          return true;
        }
      }

      return false;
    }

    /// <summary>
    /// Converts an object to the target type.
    /// </summary>
    /// <param name="sourceInstance">The object to convert to the target type.</param>
    /// <param name="targetType">The type to convert to.</param>
    /// <returns>The converted object.</returns>
    /// <remarks>
    /// <para>
    /// Converts an object to the target type.
    /// </para>
    /// </remarks>
    public static object ConvertTypeTo(object sourceInstance, Type targetType)
    {
      Type sourceType = sourceInstance.GetType();

      // Check if we can assign directly from the source type to the target type
      if (targetType.IsAssignableFrom(sourceType))
      {
        return sourceInstance;
      }

      // Look for a TO converter
      if (ConverterRegistry.GetConvertTo(sourceType, targetType) is IConvertTo tcSource)
      {
        if (tcSource.CanConvertTo(targetType))
        {
          return tcSource.ConvertTo(sourceInstance, targetType);
        }
      }

      // Look for a FROM converter
      if (ConverterRegistry.GetConvertFrom(targetType) is IConvertFrom tcTarget)
      {
        if (tcTarget.CanConvertFrom(sourceType))
        {
          return tcTarget.ConvertFrom(sourceInstance);
        }
      }

      throw new ArgumentException($"Cannot convert source object [{sourceInstance}] to target type [{targetType.Name}]", nameof(sourceInstance));
    }

    /// <summary>
    /// Instantiates an object given a class name.
    /// </summary>
    /// <param name="className">The fully qualified class name of the object to instantiate.</param>
    /// <param name="superClass">The class to which the new object should belong.</param>
    /// <param name="defaultValue">The object to return in case of non-fulfillment.</param>
    /// <returns>
    /// An instance of the <paramref name="className"/> or <paramref name="defaultValue"/>
    /// if the object could not be instantiated.
    /// </returns>
    /// <remarks>
    /// <para>
    /// Checks that the <paramref name="className"/> is a subclass of
    /// <paramref name="superClass"/>. If that test fails or the object could
    /// not be instantiated, then <paramref name="defaultValue"/> is returned.
    /// </para>
    /// </remarks>
    public static object? InstantiateByClassName(string? className, Type superClass, object? defaultValue)
    {
      if (className is not null)
      {
        try
        {
          Type? classObj = SystemInfo.GetTypeFromString(className, true, true);
          if (classObj is not null)
          {
            if (!superClass.IsAssignableFrom(classObj))
            {
              LogLog.Error(declaringType, $"OptionConverter: A [{className}] object is not assignable to a [{superClass.FullName}] variable.");
              return defaultValue;
            }
            return Activator.CreateInstance(classObj);
          }

          LogLog.Error(declaringType, $"Could not find class [{className}].");
        }
        catch (Exception e)
        {
          LogLog.Error(declaringType, $"Could not instantiate class [{className}].", e);
        }
      }
      return defaultValue;
    }

    /// <summary>
    /// Performs variable substitution in string <paramref name="value"/> from the 
    /// values of keys found in <paramref name="props"/>.
    /// </summary>
    /// <param name="value">The string on which variable substitution is performed.</param>
    /// <param name="props">The dictionary to use to lookup variables.</param>
    /// <returns>The result of the substitutions.</returns>
    /// <remarks>
    /// <para>
    /// The variable substitution delimiters are <b>${</b> and <b>}</b>.
    /// </para>
    /// <para>
    /// For example, if props contains <c>key=value</c>, then the call
    /// </para>
    /// <para>
    /// <code lang="C#">
    /// string s = OptionConverter.SubstituteVariables("Value of key is ${key}.");
    /// </code>
    /// </para>
    /// <para>
    /// will set the variable <c>s</c> to "Value of key is value.".
    /// </para>
    /// <para>
    /// If no value could be found for the specified key, then substitution 
    /// defaults to an empty string.
    /// </para>
    /// <para>
    /// For example, if system properties contains no value for the key
    /// "nonExistentKey", then the call
    /// </para>
    /// <para>
    /// <code lang="C#">
    /// string s = OptionConverter.SubstituteVariables("Value of nonExistentKey is [${nonExistentKey}]");
    /// </code>
    /// </para>
    /// <para>
    /// will set <s>s</s> to "Value of nonExistentKey is []".   
    /// </para>
    /// <para>
    /// An Exception is thrown if <paramref name="value"/> contains a start 
    /// delimiter "${" which is not balanced by a stop delimiter "}". 
    /// </para>
    /// </remarks>
    public static string SubstituteVariables(string value, System.Collections.IDictionary props)
    {
      StringBuilder buf = new StringBuilder();

      int i = 0;
      int j, k;

      while (true)
      {
        j = value.IndexOf(DELIM_START, i, StringComparison.Ordinal);
        if (j == -1)
        {
          if (i == 0)
          {
            return value;
          }
          else
          {
            buf.Append(value.Substring(i, value.Length - i));
            return buf.ToString();
          }
        }
        else
        {
          buf.Append(value.Substring(i, j - i));
          k = value.IndexOf(DELIM_STOP, j);
          if (k == -1)
          {
            throw new LogException("[" + value + "] has no closing brace. Opening brace at position [" + j + "]");
          }
          else
          {
            j += DELIM_START_LEN;
            string key = value.Substring(j, k - j);

            if (props[key] is string replacement)
            {
              buf.Append(replacement);
            }
            i = k + DELIM_STOP_LEN;
          }
        }
      }
    }

    /// <summary>
    /// Converts the string representation of the name or numeric value of one or 
    /// more enumerated constants to an equivalent enumerated object.
    /// </summary>
    /// <param name="enumType">The type to convert to.</param>
    /// <param name="value">The enum string value.</param>
    /// <param name="ignoreCase">If <c>true</c>, ignore case; otherwise, regard case.</param>
    /// <returns>An object of type <paramref name="enumType" /> whose value is represented by <paramref name="value" />.</returns>
    private static object ParseEnum(Type enumType, string value, bool ignoreCase)
    {
      return Enum.Parse(enumType, value, ignoreCase);
    }

    /// <summary>
    /// The fully qualified type of the OptionConverter class.
    /// </summary>
    /// <remarks>
    /// Used by the internal logger to record the Type of the
    /// log message.
    /// </remarks>
    private static readonly Type declaringType = typeof(OptionConverter);

    private const string DELIM_START = "${";
    private const char DELIM_STOP = '}';
    private const int DELIM_START_LEN = 2;
    private const int DELIM_STOP_LEN = 1;
  }
}