Make Enum type emit string or underlying type values to document. Fixed

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We default to underlying type for enums alwasy. Add following attributes. Can be configured as classs level or member level.

[AttributeUsage(AttributeTargets.Class | AttributeTargets.Property, AllowMultiple = true)]
public class EnumAsStringProperty : System.Attribute
{
}
[AttributeUsage(AttributeTargets.Property)] // class leve is default. This used to override EnumAsStringProperty as class level
public class EnumAsUnderlyTypeProperty : System.Attribute
{
}

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Full Code

internal static Document ConvertToDocument<T>(this T instance) where T : IDocument
{
    var document = new Document();

    var enumAsStringClassLevel = System.Attribute.GetCustomAttribute(instance.GetType(), typeof(EnumAsStringProperty));
    var enumAsUnderlyTypeClassLevel = System.Attribute.GetCustomAttribute(instance.GetType(), typeof(EnumAsUnderlyTypeProperty));
    if (enumAsStringClassLevel is not null && enumAsUnderlyTypeClassLevel is not null) throw new ArgumentException();

    foreach (var property in typeof(T).GetProperties())
    {
        var value = property.GetValue(instance) ?? string.Empty;
        var fieldName = property.Name;
        var facetAttribute = System.Attribute.GetCustomAttribute(property, typeof(FacetProperty));

        bool enumAsString = isEnumAsString(enumAsStringClassLevel, property);

        if (!property.PropertyType.IsArray)
        {
            var enumValue = getEnumValue(property, instance);
            if (enumValue is null || enumAsString)
                addField(document, fieldName, facetAttribute, value);
            else
                addField(document, fieldName, facetAttribute, enumValue);
        }
        else
        {
            var array = (Array)value;
            foreach (var arrayItem in array)
            {
                addField(document, fieldName, facetAttribute, arrayItem);
            }
        }
    }

    return document;
}

   ...
}

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Supporting functions:

    private static bool isEnumAsString(System.Attribute? enumAsStringClassLevel, PropertyInfo property)
    {
        var enumAsStringMemberLevel = System.Attribute.GetCustomAttribute(property, typeof(EnumAsStringProperty));
        var enumAsUnderlyTypeMemberLevel = System.Attribute.GetCustomAttribute(property, typeof(EnumAsUnderlyTypeProperty));
        if (enumAsStringMemberLevel is not null && enumAsUnderlyTypeMemberLevel is not null) throw new ArgumentException();

        bool enumAsString = false;
        if (enumAsStringMemberLevel is not null) enumAsString = true;
        else if (enumAsStringClassLevel is not null)
        {
            enumAsString = enumAsUnderlyTypeMemberLevel is null;
        }
        return enumAsString;
    }

    private static void addField(Document document, string fieldName, System.Attribute? facetAttribute, object fieldObj)
    {
        var fieldValue = fieldObj?.ToString() ?? string.Empty;

        document.Add(new TextField(fieldName, fieldValue, Field.Store.YES));

        if (facetAttribute != null)
        {
            document.Add(new FacetField(fieldName, fieldValue));
        }
    }

    private static string? getEnumValue(PropertyInfo property, object instance)
    {
        if (property != null)
        {
            Type typeToCheck = GetUnderlyingType(property);

            if (typeToCheck.IsEnum)
            {
                // Get the value of the property from the instance
                var enumValue = property.GetValue(instance);

                // Convert the enum value to its underlying numerical type (e.g., int or long)
                // Using Convert.ToInt64 is safe as it fits every enum underlying type
                long numericalValue = Convert.ToInt64(enumValue);
                return numericalValue.ToString();
            }
        }
        return null;
    }