Use abstract class for extensibility and replace GetAppConfig with specific configuration settings

Author: bahusoid

src/NHibernate/Cfg/AppSettings.cs

@@ -0,0 +1,13 @@
+namespace NHibernate.Cfg
+{
+	/// <summary>
+	/// Configuration App Settings
+	/// </summary>
+	public static class AppSettings
+	{
+		/// <summary>
+		/// Type that implements <see cref="INHibernateLoggerFactory"/>
+		/// </summary>
+		public const string LoggerFactoryClassName = "nhibernate-logger";
+	}
+}

src/NHibernate/Cfg/ConfigurationManagerBase.cs

@@ -0,0 +1,109 @@
+using System;
+using System.Configuration;
+using System.Linq;
+using NHibernate.Cfg.ConfigurationSchema;
+
+namespace NHibernate.Cfg
+{
+	/// <summary>
+	/// Base class for configuration settings that NHibernate might require.
+	/// </summary>
+	public abstract class ConfigurationManagerBase
+	{
+		public abstract IHibernateConfiguration GetConfiguration();
+		public abstract string GetNamedConnectionString(string name);
+
+		/// <summary>
+		/// Type that implements <see cref="INHibernateLoggerFactory"/>
+		/// </summary>
+		public abstract string GetLoggerFactoryClassName();
+	}
+
+	/// <summary>
+	/// Configuration manager that supports user provided configuration
+	/// </summary>
+	public class SystemConfigurationManager : ConfigurationManagerBase
+	{
+		private readonly System.Configuration.Configuration _configuration;
+
+		public SystemConfigurationManager(System.Configuration.Configuration configuration)
+		{
+			_configuration = configuration;
+		}
+
+		public override IHibernateConfiguration GetConfiguration()
+		{
+			ConfigurationSection configurationSection = _configuration.GetSection(CfgXmlHelper.CfgSectionName);
+			var xml = configurationSection?.SectionInformation.GetRawXml();
+			return xml == null ? null : HibernateConfiguration.FromAppConfig(xml);
+		}
+
+		public override string GetNamedConnectionString(string name)
+		{
+			return _configuration.ConnectionStrings.ConnectionStrings[name]?.ConnectionString;
+		}
+
+		public override string GetLoggerFactoryClassName()
+		{
+			return GetAppSetting(AppSettings.LoggerFactoryClassName);
+		}
+
+		private string GetAppSetting(string name)
+		{
+			return  _configuration.AppSettings.Settings[name]?.Value;
+		}
+	}
+
+	class StaticSystemConfigurationManager : ConfigurationManagerBase
+	{
+		public override IHibernateConfiguration GetConfiguration()
+		{
+			//TODO 6.0: Throw if not null and not IHibernateConfiguration
+			return ConfigurationManager.GetSection(CfgXmlHelper.CfgSectionName) as IHibernateConfiguration;
+		}
+
+		public override string GetNamedConnectionString(string name)
+		{
+			return ConfigurationManager.ConnectionStrings[name]?.ConnectionString;
+		}
+
+		public override string GetLoggerFactoryClassName()
+		{
+			var name = AppSettings.LoggerFactoryClassName;
+			var value = ConfigurationManager.AppSettings[name];
+
+			//TODO 6.0:  Return value right away. Don't do ignore case search and document it as possible breaking change.
+			if (value != null)
+				return value;
+
+			return GetAppSettingIgnoreCase(name);
+		}
+
+		//TODO 6.0: Remove it
+		private static string GetAppSettingIgnoreCase(string name)
+		{
+			var key = ConfigurationManager.AppSettings.Keys.Cast<string>().FirstOrDefault(k => name.Equals(k, StringComparison.OrdinalIgnoreCase));
+			return string.IsNullOrEmpty(key)
+				? null
+				: ConfigurationManager.AppSettings[key];
+		}
+	}
+
+	class NullConfigurationManager : ConfigurationManagerBase
+	{
+		public override IHibernateConfiguration GetConfiguration()
+		{
+			return null;
+		}
+
+		public override string GetNamedConnectionString(string name)
+		{
+			return null;
+		}
+
+		public override string GetLoggerFactoryClassName()
+		{
+			return null;
+		}
+	}
+}

src/NHibernate/Cfg/IConfigurationManager.cs

@@ -18,13 +18,13 @@ namespace NHibernate.Cfg
 	/// </summary>
 	public sealed class Settings
 	{
-		private static IConfigurationManager _configurationManager = new StaticSystemConfigurationManager();
+		private static ConfigurationManagerBase _configurationManager = new StaticSystemConfigurationManager();
 
 		/// <summary>
 		/// Provides ability to override default <see cref="System.Configuration.ConfigurationManager"/> with custom implementation.
 		/// Can be set to null if all configuration is specified by code 
 		/// </summary>
-		public static IConfigurationManager ConfigurationManager
+		public static ConfigurationManagerBase ConfigurationManager
 		{
 			get => _configurationManager;
 			set => _configurationManager = value ?? new NullConfigurationManager();

src/NHibernate/Cfg/Settings.cs

@@ -48,7 +48,6 @@ public interface INHibernateLoggerFactory
 	/// </remarks>
 	public static class NHibernateLogger
 	{
-		private const string nhibernateLoggerConfKey = "nhibernate-logger";
 		private static INHibernateLoggerFactory _loggerFactory;
 
 #pragma warning disable 618
@@ -134,7 +133,7 @@ public static INHibernateLogger For(System.Type type)
 
 		private static string GetNhibernateLoggerClass()
 		{
-			var nhibernateLoggerClass = Settings.ConfigurationManager.GetAppSettingIgnoringCase(nhibernateLoggerConfKey);
+			var nhibernateLoggerClass = Settings.ConfigurationManager.GetLoggerFactoryClassName();
 			if (nhibernateLoggerClass == null)
 			{
 				// look for log4net