ConfigurationReader.cs

using System.Reflection;
using System.Runtime.CompilerServices;
using System.Text.RegularExpressions;

using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.Primitives;

using Serilog.Configuration;
using Serilog.Core;
using Serilog.Debugging;
using Serilog.Events;
using Serilog.Settings.Configuration.Assemblies;

namespace Serilog.Settings.Configuration;

class ConfigurationReader : IConfigurationReader
{
    const string LevelSwitchNameRegex = @"^\${0,1}[A-Za-z]+[A-Za-z0-9]*$";

    // Section names that can be handled by Serilog itself (hence builtin) without requiring any additional assemblies.
    static readonly string[] BuiltinSectionNames = ["LevelSwitches", "MinimumLevel", "Properties"];

    readonly IConfiguration _section;
    readonly IReadOnlyCollection<Assembly> _configurationAssemblies;
    readonly ResolutionContext _resolutionContext;
    readonly IConfigurationRoot? _configurationRoot;

    public ConfigurationReader(IConfiguration configSection, AssemblyFinder assemblyFinder, ConfigurationReaderOptions readerOptions, IConfiguration? configuration = null)
    {
        _section = configSection ?? throw new ArgumentNullException(nameof(configSection));
        _configurationAssemblies = LoadConfigurationAssemblies(_section, assemblyFinder);
        _resolutionContext = new ResolutionContext(configuration, readerOptions);
        _configurationRoot = configuration as IConfigurationRoot;
    }

    // Used internally for processing nested configuration sections -- see GetMethodCalls below.
    internal ConfigurationReader(IConfiguration configSection, IReadOnlyCollection<Assembly> configurationAssemblies, ResolutionContext resolutionContext)
    {
        _section = configSection ?? throw new ArgumentNullException(nameof(configSection));
        _configurationAssemblies = configurationAssemblies ?? throw new ArgumentNullException(nameof(configurationAssemblies));
        _resolutionContext = resolutionContext ?? throw new ArgumentNullException(nameof(resolutionContext));
        _configurationRoot = resolutionContext.HasAppConfiguration ? resolutionContext.AppConfiguration as IConfigurationRoot : null;
    }

    public void Configure(LoggerConfiguration loggerConfiguration)
    {
        ProcessLevelSwitchDeclarations();
        ProcessFilterSwitchDeclarations();

        ApplyMinimumLevel(loggerConfiguration);
        ApplyEnrichment(loggerConfiguration);
        ApplyFilters(loggerConfiguration);
        ApplyDestructuring(loggerConfiguration);
        ApplySinks(loggerConfiguration);
        ApplyAuditSinks(loggerConfiguration);
    }

    void ProcessFilterSwitchDeclarations()
    {
        var filterSwitchesDirective = _section.GetSection("FilterSwitches");

        foreach (var filterSwitchDeclaration in filterSwitchesDirective.GetChildren())
        {
            var filterSwitch = LoggingFilterSwitchProxy.Create();
            if (filterSwitch == null)
            {
                SelfLog.WriteLine($"FilterSwitches section found, but neither Serilog.Expressions nor Serilog.Filters.Expressions is referenced.");
                break;
            }

            var switchName = filterSwitchDeclaration.Key;
            // switchName must be something like $switch to avoid ambiguities
            if (!IsValidSwitchName(switchName))
            {
                throw new FormatException($"\"{switchName}\" is not a valid name for a Filter Switch declaration. The first character of the name must be a letter or '$' sign, like \"FilterSwitches\" : {{\"$switchName\" : \"{{FilterExpression}}\"}}");
            }

            SetFilterSwitch(throwOnError: true);
            SubscribeToFilterExpressionChanges();

            _resolutionContext.AddFilterSwitch(switchName, filterSwitch);
            _resolutionContext.ReaderOptions.OnFilterSwitchCreated?.Invoke(switchName, filterSwitch);

            void SubscribeToFilterExpressionChanges()
            {
                ChangeToken.OnChange(filterSwitchDeclaration.GetReloadToken, () => SetFilterSwitch(throwOnError: false));
            }

            void SetFilterSwitch(bool throwOnError)
            {
                var filterExpr = filterSwitchDeclaration.Value;
                if (string.IsNullOrWhiteSpace(filterExpr))
                {
                    filterSwitch.Expression = null;
                    return;
                }

                try
                {
                    filterSwitch.Expression = filterExpr;
                }
                catch (Exception e)
                {
                    var errMsg = $"The expression '{filterExpr}' is invalid filter expression: {e.Message}.";
                    if (throwOnError)
                    {
                        throw new InvalidOperationException(errMsg, e);
                    }

                    SelfLog.WriteLine(errMsg);
                }
            }
        }
    }

    void ProcessLevelSwitchDeclarations()
    {
        var levelSwitchesDirective = _section.GetSection("LevelSwitches");
        foreach (var levelSwitchDeclaration in levelSwitchesDirective.GetChildren())
        {
            var switchName = levelSwitchDeclaration.Key;
            var switchInitialLevel = levelSwitchDeclaration.Value;
            // switchName must be something like $switch to avoid ambiguities
            if (!IsValidSwitchName(switchName))
            {
                throw new FormatException($"\"{switchName}\" is not a valid name for a Level Switch declaration. The first character of the name must be a letter or '$' sign, like \"LevelSwitches\" : {{\"$switchName\" : \"InitialLevel\"}}");
            }

            LoggingLevelSwitch newSwitch;
            if (string.IsNullOrEmpty(switchInitialLevel))
            {
                newSwitch = new LoggingLevelSwitch();
            }
            else
            {
                var initialLevel = ParseLogEventLevel(switchInitialLevel!);
                newSwitch = new LoggingLevelSwitch(initialLevel);
            }

            SubscribeToLoggingLevelChanges(levelSwitchDeclaration, newSwitch);

            // make them available later on when resolving argument values
            var referenceName = _resolutionContext.AddLevelSwitch(switchName, newSwitch);
            _resolutionContext.ReaderOptions.OnLevelSwitchCreated?.Invoke(referenceName, newSwitch);
        }
    }

    void ApplyMinimumLevel(LoggerConfiguration loggerConfiguration)
    {
        var minimumLevelDirective = _section.GetSection("MinimumLevel");

        IConfigurationSection? defaultMinLevelDirective = GetDefaultMinLevelDirective();
        if (defaultMinLevelDirective?.Value != null)
        {
            ApplyMinimumLevelConfiguration(defaultMinLevelDirective, (configuration, levelSwitch) => configuration.ControlledBy(levelSwitch));
        }

        var minLevelControlledByDirective = minimumLevelDirective.GetSection("ControlledBy");
        if (minLevelControlledByDirective.Value != null)
        {
            var globalMinimumLevelSwitch = _resolutionContext.LookUpLevelSwitchByName(minLevelControlledByDirective.Value);
            // not calling ApplyMinimumLevel local function because here we have a reference to a LogLevelSwitch already
            loggerConfiguration.MinimumLevel.ControlledBy(globalMinimumLevelSwitch);
        }

        foreach (var overrideDirective in minimumLevelDirective.GetSection("Override").GetChildren())
        {
            var overridePrefix = overrideDirective.Key;
            var overridenLevelOrSwitch = overrideDirective.Value;
            if (Enum.TryParse(overridenLevelOrSwitch, ignoreCase: true, out LogEventLevel _))
            {
                ApplyMinimumLevelConfiguration(overrideDirective, (configuration, levelSwitch) =>
                {
                    configuration.Override(overridePrefix, levelSwitch);
                    _resolutionContext.ReaderOptions.OnLevelSwitchCreated?.Invoke(overridePrefix, levelSwitch);
                });
            }
            else if (!string.IsNullOrEmpty(overridenLevelOrSwitch))
            {
                var overrideSwitch = _resolutionContext.LookUpLevelSwitchByName(overridenLevelOrSwitch!);
                // not calling ApplyMinimumLevel local function because here we have a reference to a LogLevelSwitch already
                loggerConfiguration.MinimumLevel.Override(overridePrefix, overrideSwitch);
            }
        }

        void ApplyMinimumLevelConfiguration(IConfigurationSection directive, Action<LoggerMinimumLevelConfiguration, LoggingLevelSwitch> applyConfigAction)
        {
            var minimumLevel = ParseLogEventLevel(directive.Value!);

            var levelSwitch = new LoggingLevelSwitch(minimumLevel);
            applyConfigAction(loggerConfiguration.MinimumLevel, levelSwitch);

            SubscribeToLoggingLevelChanges(directive, levelSwitch);
        }

        IConfigurationSection? GetDefaultMinLevelDirective()
        {
            var defaultLevelDirective = minimumLevelDirective.GetSection("Default");
            if (_configurationRoot != null && minimumLevelDirective.Value != null && defaultLevelDirective.Value != null)
            {
                foreach (var provider in _configurationRoot.Providers.Reverse())
                {
                    if (provider.TryGet(minimumLevelDirective.Path, out _))
                    {
                        return _configurationRoot.GetSection(minimumLevelDirective.Path);
                    }

                    if (provider.TryGet(defaultLevelDirective.Path, out _))
                    {
                        return _configurationRoot.GetSection(defaultLevelDirective.Path);
                    }
                }

                return null;
            }

            return minimumLevelDirective.Value != null ? minimumLevelDirective : minimumLevelDirective.GetSection("Default");
        }
    }

    static void SubscribeToLoggingLevelChanges(IConfigurationSection levelSection, LoggingLevelSwitch levelSwitch)
    {
        ChangeToken.OnChange(
            levelSection.GetReloadToken,
            () =>
            {
                if (Enum.TryParse(levelSection.Value, ignoreCase: true, out LogEventLevel minimumLevel))
                    levelSwitch.MinimumLevel = minimumLevel;
                else
                    SelfLog.WriteLine($"The value {levelSection.Value} is not a valid Serilog level.");
            });
    }

    void ApplyFilters(LoggerConfiguration loggerConfiguration)
    {
        var filterDirective = _section.GetSection("Filter");
        if (filterDirective.GetChildren().Any())
        {
            var methodCalls = GetMethodCalls(filterDirective);
            CallConfigurationMethods(methodCalls, FindFilterConfigurationMethods(_configurationAssemblies, _resolutionContext.ReaderOptions.AllowInternalTypes, _resolutionContext.ReaderOptions.AllowInternalMethods), loggerConfiguration.Filter);
        }
    }

    void ApplyDestructuring(LoggerConfiguration loggerConfiguration)
    {
        var destructureDirective = _section.GetSection("Destructure");
        if (destructureDirective.GetChildren().Any())
        {
            var methodCalls = GetMethodCalls(destructureDirective);
            CallConfigurationMethods(methodCalls, FindDestructureConfigurationMethods(_configurationAssemblies, _resolutionContext.ReaderOptions.AllowInternalTypes, _resolutionContext.ReaderOptions.AllowInternalMethods), loggerConfiguration.Destructure);
        }
    }

    void ApplySinks(LoggerConfiguration loggerConfiguration)
    {
        var writeToDirective = _section.GetSection("WriteTo");
        if (writeToDirective.GetChildren().Any())
        {
            var methodCalls = GetMethodCalls(writeToDirective);
            CallConfigurationMethods(methodCalls, FindSinkConfigurationMethods(_configurationAssemblies, _resolutionContext.ReaderOptions.AllowInternalTypes, _resolutionContext.ReaderOptions.AllowInternalMethods), loggerConfiguration.WriteTo);
        }
    }

    void ApplyAuditSinks(LoggerConfiguration loggerConfiguration)
    {
        var auditToDirective = _section.GetSection("AuditTo");
        if (auditToDirective.GetChildren().Any())
        {
            var methodCalls = GetMethodCalls(auditToDirective);
            CallConfigurationMethods(methodCalls, FindAuditSinkConfigurationMethods(_configurationAssemblies, _resolutionContext.ReaderOptions.AllowInternalTypes, _resolutionContext.ReaderOptions.AllowInternalMethods), loggerConfiguration.AuditTo);
        }
    }

    void IConfigurationReader.ApplySinks(LoggerSinkConfiguration loggerSinkConfiguration)
    {
        var methodCalls = GetMethodCalls(_section);
        CallConfigurationMethods(methodCalls, FindSinkConfigurationMethods(_configurationAssemblies, _resolutionContext.ReaderOptions.AllowInternalTypes, _resolutionContext.ReaderOptions.AllowInternalMethods), loggerSinkConfiguration);
    }

    void IConfigurationReader.ApplyEnrichment(LoggerEnrichmentConfiguration loggerEnrichmentConfiguration)
    {
        var methodCalls = GetMethodCalls(_section);
        CallConfigurationMethods(methodCalls, FindEventEnricherConfigurationMethods(_configurationAssemblies, _resolutionContext.ReaderOptions.AllowInternalTypes, _resolutionContext.ReaderOptions.AllowInternalMethods), loggerEnrichmentConfiguration);
    }

    void ApplyEnrichment(LoggerConfiguration loggerConfiguration)
    {
        var enrichDirective = _section.GetSection("Enrich");
        if (enrichDirective.GetChildren().Any())
        {
            var methodCalls = GetMethodCalls(enrichDirective);
            CallConfigurationMethods(methodCalls, FindEventEnricherConfigurationMethods(_configurationAssemblies, _resolutionContext.ReaderOptions.AllowInternalTypes, _resolutionContext.ReaderOptions.AllowInternalMethods), loggerConfiguration.Enrich);
        }

        var propertiesDirective = _section.GetSection("Properties");
        if (propertiesDirective.GetChildren().Any())
        {
            foreach (var enrichPropertyDirective in propertiesDirective.GetChildren())
            {
                // Null is an acceptable value here; annotations on Serilog need updating.
                loggerConfiguration.Enrich.WithProperty(enrichPropertyDirective.Key, enrichPropertyDirective.Value!);
            }
        }
    }

    internal ILookup<string, Dictionary<string, IConfigurationArgumentValue>> GetMethodCalls(IConfiguration directive)
    {
        var children = directive.GetChildren().ToList();

        var result =
            (from child in children
             where child.Value != null // Plain string
             select new { Name = child.Value, Args = new Dictionary<string, IConfigurationArgumentValue>() })
                 .Concat(
            (from child in children
             where child.Value == null
             let name = GetSectionName(child)
             let callArgs = (from argument in child.GetSection("Args").GetChildren()
                             select new
                             {
                                 Name = argument.Key,
                                 Value = GetArgumentValue(argument, _configurationAssemblies)
                             }).ToDictionary(p => p.Name, p => p.Value)
             select new { Name = name, Args = callArgs }))
                 .ToLookup(p => p.Name, p => p.Args);

        return result;

        static string GetSectionName(IConfigurationSection s)
        {
            var name = s.GetSection("Name");
            if (name.Value == null)
                throw new InvalidOperationException($"The configuration value in {name.Path} has no 'Name' element.");

            return name.Value;
        }
    }

    internal static IConfigurationArgumentValue GetArgumentValue(IConfigurationSection argumentSection, IReadOnlyCollection<Assembly> configurationAssemblies)
    {
        IConfigurationArgumentValue argumentValue;

        // Reject configurations where an element has both scalar and complex
        // values as a result of reading multiple configuration sources.
        if (argumentSection.Value != null && argumentSection.GetChildren().Any())
            throw new InvalidOperationException(
                $"The value for the argument '{argumentSection.Path}' is assigned different value " +
                "types in more than one configuration source. Ensure all configurations consistently " +
                "use either a scalar (int, string, boolean) or a complex (array, section, list, " +
                "POCO, etc.) type for this argument value.");

        if (argumentSection.Value != null)
        {
            argumentValue = new StringArgumentValue(argumentSection.Value);
        }
        else
        {
            argumentValue = new ObjectArgumentValue(argumentSection, configurationAssemblies);
        }

        return argumentValue;
    }

    static IReadOnlyCollection<Assembly> LoadConfigurationAssemblies(IConfiguration section, AssemblyFinder assemblyFinder)
    {
        var serilogAssembly = typeof(ILogger).Assembly;
        var assemblies = new HashSet<Assembly> { serilogAssembly };

        var usingSection = section.GetSection("Using");
        if (usingSection.GetChildren().Any())
        {
            foreach (var simpleName in usingSection.GetChildren().Select(c => c.Value))
            {
                if (string.IsNullOrWhiteSpace(simpleName))
                    throw new InvalidOperationException(
                        $"A zero-length or whitespace assembly name was supplied to a {usingSection.Path} configuration statement.");

                var assembly = Assembly.Load(new AssemblyName(simpleName));
                assemblies.Add(assembly);
            }
        }

        foreach (var assemblyName in assemblyFinder.FindAssembliesContainingName("serilog"))
        {
            var assumed = Assembly.Load(assemblyName);
            assemblies.Add(assumed);
        }

        // We don't want to throw if the configuration contains only sections that can be handled by Serilog itself, without requiring any additional assembly.
        // See https://github.com/serilog/serilog-settings-configuration/issues/389
        var requiresAdditionalAssemblies = section.GetChildren().Select(e => e.Key).Except(BuiltinSectionNames).Any();
        if (assemblies.Count == 1 && requiresAdditionalAssemblies)
        {
            var message = $"""
                No {usingSection.Path} configuration section is defined and no Serilog assemblies were found.
                This is most likely because the application is published as single-file.
                Either add a {usingSection.Path} section or explicitly specify assemblies that contains sinks and other types through the reader options. For example:
                var options = new ConfigurationReaderOptions(typeof(ConsoleLoggerConfigurationExtensions).Assembly, typeof(SerilogExpression).Assembly);
                new LoggerConfiguration().ReadFrom.Configuration(configuration, options);
                """;
            throw new InvalidOperationException(message);
        }

        return assemblies;
    }

    void CallConfigurationMethods(ILookup<string, Dictionary<string, IConfigurationArgumentValue>> methods, IReadOnlyCollection<MethodInfo> configurationMethods, object receiver)
    {
        foreach (var method in methods.SelectMany(g => g.Select(x => new { g.Key, Value = x })))
        {
            var methodInfo = SelectConfigurationMethod(configurationMethods, method.Key, method.Value.Keys.ToList());

            if (methodInfo != null)
            {
                var call = (from p in methodInfo.GetParameters().Skip(1)
                            let directive = method.Value.FirstOrDefault(s => ParameterNameMatches(p.Name, s.Key))
                            select directive.Key == null
                                ? GetImplicitValueForNotSpecifiedKey(p, methodInfo)
                                : directive.Value.ConvertTo(p.ParameterType, _resolutionContext)).ToList();

                call.Insert(0, receiver);
                methodInfo.Invoke(null, call.ToArray());
            }
        }
    }

    static bool HasImplicitValueWhenNotSpecified(ParameterInfo paramInfo)
    {
        return paramInfo.HasDefaultValue
           // parameters of type IConfiguration are implicitly populated with provided Configuration
           || paramInfo.ParameterType == typeof(IConfiguration);
    }

    object? GetImplicitValueForNotSpecifiedKey(ParameterInfo parameter, MethodInfo methodToInvoke)
    {
        if (!HasImplicitValueWhenNotSpecified(parameter))
        {
            throw new InvalidOperationException("GetImplicitValueForNotSpecifiedKey() should only be called for parameters for which HasImplicitValueWhenNotSpecified() is true. " +
                                                "This means something is wrong in the Serilog.Settings.Configuration code.");
        }

        if (parameter.ParameterType == typeof(IConfiguration))
        {
            if (_resolutionContext.HasAppConfiguration)
            {
                return _resolutionContext.AppConfiguration;
            }
            if (parameter.HasDefaultValue)
            {
                return parameter.DefaultValue;
            }

            throw new InvalidOperationException("Trying to invoke a configuration method accepting a `IConfiguration` argument. " +
                                                          $"This is not supported when only a `IConfigSection` has been provided. (method '{methodToInvoke}')");
        }

        return parameter.DefaultValue;
    }

    internal static MethodInfo? SelectConfigurationMethod(IReadOnlyCollection<MethodInfo> candidateMethods, string name, IReadOnlyCollection<string> suppliedArgumentNames)
    {
        // Per issue #111, it is safe to use case-insensitive matching on argument names. The CLR doesn't permit this type
        // of overloading, and the Microsoft.Extensions.Configuration keys are case-insensitive (case is preserved with some
        // config sources, but key-matching is case-insensitive and case-preservation does not appear to be guaranteed).
        var selectedMethod = candidateMethods
            .Where(m => m.Name == name)
            .Where(m => m.GetParameters()
                        .Skip(1)
                        .All(p => HasImplicitValueWhenNotSpecified(p) ||
                                  ParameterNameMatches(p.Name, suppliedArgumentNames)))
            .OrderByDescending(m =>
            {
                var matchingArgs = m.GetParameters().Where(p => ParameterNameMatches(p.Name, suppliedArgumentNames)).ToList();

                // Prefer the configuration method with most number of matching arguments and of those the ones with
                // the most string type parameters to predict best match with least type casting
                return new Tuple<int, int>(
                    matchingArgs.Count,
                    matchingArgs.Count(p => p.ParameterType == typeof(string)));
            })
            .FirstOrDefault();

        if (selectedMethod == null)
        {
            var methodsByName = candidateMethods
                .Where(m => m.Name == name)
                .Select(m => $"{m.Name}({string.Join(", ", m.GetParameters().Skip(1).Select(p => p.Name))})")
                .ToList();

            if (!methodsByName.Any())
            {
                if (candidateMethods.Any())
                {
                    SelfLog.WriteLine($"Unable to find a method called {name}. Candidate methods are:{Environment.NewLine}{string.Join(Environment.NewLine, candidateMethods)}");
                }
                else
                {
                    SelfLog.WriteLine($"Unable to find a method called {name}. No candidates found.");
                }
            }
            else
            {
                SelfLog.WriteLine($"Unable to find a method called {name} "
                + (suppliedArgumentNames.Any()
                    ? "for supplied arguments: " + string.Join(", ", suppliedArgumentNames)
                    : "with no supplied arguments")
                + ". Candidate methods are:"
                + Environment.NewLine
                + string.Join(Environment.NewLine, methodsByName));
            }
        }
        return selectedMethod;
    }

    static bool ParameterNameMatches(string? actualParameterName, string suppliedName)
    {
        return suppliedName.Equals(actualParameterName, StringComparison.OrdinalIgnoreCase);
    }

    static bool ParameterNameMatches(string? actualParameterName, IEnumerable<string> suppliedNames)
    {
        return suppliedNames.Any(s => ParameterNameMatches(actualParameterName, s));
    }

    static IReadOnlyCollection<MethodInfo> FindSinkConfigurationMethods(IReadOnlyCollection<Assembly> configurationAssemblies, bool allowInternalTypes, bool allowInternalMethods)
    {
        var found = FindConfigurationExtensionMethods(configurationAssemblies, typeof(LoggerSinkConfiguration), allowInternalTypes, allowInternalMethods);
        if (configurationAssemblies.Contains(typeof(LoggerSinkConfiguration).GetTypeInfo().Assembly))
            found.AddRange(SurrogateConfigurationMethods.WriteTo);

        return found;
    }

    static IReadOnlyCollection<MethodInfo> FindAuditSinkConfigurationMethods(IReadOnlyCollection<Assembly> configurationAssemblies, bool allowInternalTypes, bool allowInternalMethods)
    {
        var found = FindConfigurationExtensionMethods(configurationAssemblies, typeof(LoggerAuditSinkConfiguration), allowInternalTypes, allowInternalMethods);
        if (configurationAssemblies.Contains(typeof(LoggerAuditSinkConfiguration).GetTypeInfo().Assembly))
            found.AddRange(SurrogateConfigurationMethods.AuditTo);
        return found;
    }

    static IReadOnlyCollection<MethodInfo> FindFilterConfigurationMethods(IReadOnlyCollection<Assembly> configurationAssemblies, bool allowInternalTypes, bool allowInternalMethods)
    {
        var found = FindConfigurationExtensionMethods(configurationAssemblies, typeof(LoggerFilterConfiguration), allowInternalTypes, allowInternalMethods);
        if (configurationAssemblies.Contains(typeof(LoggerFilterConfiguration).GetTypeInfo().Assembly))
            found.AddRange(SurrogateConfigurationMethods.Filter);

        return found;
    }

    static IReadOnlyCollection<MethodInfo> FindDestructureConfigurationMethods(IReadOnlyCollection<Assembly> configurationAssemblies, bool allowInternalTypes, bool allowInternalMethods)
    {
        var found = FindConfigurationExtensionMethods(configurationAssemblies, typeof(LoggerDestructuringConfiguration), allowInternalTypes, allowInternalMethods);
        if (configurationAssemblies.Contains(typeof(LoggerDestructuringConfiguration).GetTypeInfo().Assembly))
            found.AddRange(SurrogateConfigurationMethods.Destructure);

        return found;
    }

    static IReadOnlyCollection<MethodInfo> FindEventEnricherConfigurationMethods(IReadOnlyCollection<Assembly> configurationAssemblies, bool allowInternalTypes, bool allowInternalMethods)
    {
        var found = FindConfigurationExtensionMethods(configurationAssemblies, typeof(LoggerEnrichmentConfiguration), allowInternalTypes, allowInternalMethods);
        if (configurationAssemblies.Contains(typeof(LoggerEnrichmentConfiguration).GetTypeInfo().Assembly))
            found.AddRange(SurrogateConfigurationMethods.Enrich);

        return found;
    }

    static List<MethodInfo> FindConfigurationExtensionMethods(IReadOnlyCollection<Assembly> configurationAssemblies, Type configType, bool allowInternalTypes, bool allowInternalMethods)
    {
        // ExtensionAttribute can be polyfilled to support extension methods
        static bool HasCustomExtensionAttribute(MethodInfo m)
        {
            try
            {
                return m.CustomAttributes.Any(a => a.AttributeType.FullName == "System.Runtime.CompilerServices.ExtensionAttribute");
            }
            catch (CustomAttributeFormatException)
            {
                return false;
            }
        }

        return configurationAssemblies
            .SelectMany(a => (allowInternalTypes ? a.GetTypes() : a.ExportedTypes)
                .Select(t => t.GetTypeInfo())
                .Where(t => t.IsSealed && t.IsAbstract && !t.IsNested && (t.IsPublic || allowInternalTypes && !t.IsVisible)))
            .SelectMany(t => t.DeclaredMethods)
            .Where(m => m.IsStatic && (m.IsPublic || allowInternalMethods && m.IsAssembly) && (m.IsDefined(typeof(ExtensionAttribute), false) || HasCustomExtensionAttribute(m)))
            .Where(m => m.GetParameters()[0].ParameterType == configType)
            .ToList();
    }

    internal static bool IsValidSwitchName(string input)
    {
        return Regex.IsMatch(input, LevelSwitchNameRegex);
    }

    static LogEventLevel ParseLogEventLevel(string value)
        => Enum.TryParse(value, ignoreCase: true, out LogEventLevel parsedLevel)
            ? parsedLevel
            : throw new InvalidOperationException($"The value {value} is not a valid Serilog level.");
}