Add Interfaces to allowed creation of Factory of Mappers

[felpasl]

Change Mapping to Interface to make a Library open to Factory Pattern,

Fix Enum Convert, based on Char values.

[bytefish]

This is a rather large Pull Request. Please give me some time for a review. ✍️

[bytefish]

Could you please describe the reason for the changes? Do you need to mock the CsvMapping for tests? I saw you also changed the EnumConverter, why not implement a different converter if there is a need for a different behavior?

[felpasl]

1 - for the first change, Im using the factory pattern to read an entity from file using generics, with interface we are able to do this:

    public class LoadDataFromFile
    {
        CsvParserOptions csvParserOptions;
        string basePath;

        public LoadDataFromFile(string basePath)
        {
            csvParserOptions = new CsvParserOptions(false, '@');
            this.basePath = basePath;
        }

        public List<T> ReadFile<T>() where T : class, new()
        {
            ICsvMapping<T> mapping = Mapping.MapFactory.Create<T>();
            CsvParser<T> csvParser = new CsvParser<T>(csvParserOptions, mapping);

            List<CsvMappingResult<T>> result = new List<CsvMappingResult<T>>();
            DirectoryInfo d = new DirectoryInfo(basePath);
            var files = d.GetFiles($"{GetFileName(mapping)}").ToList();

            foreach (FileInfo file in files)
            {
                result.AddRange(csvParser.ReadFromFile(file.FullName, Encoding.GetEncoding("ISO-8859-1")).ToList());
            }            

            if (result.Any(r => r.IsValid == false))
                throw new InvalidCastException("Error on reading DNE :" + string.Join("|", result.Where(r => r.IsValid == false)
                    .Select(r => $"row {r.RowIndex}, {r.Error}").ToList()));

            return result.Select(r => r.Result).ToList();
        }

        public string GetFileName(object mapping)
        {
            var fnAttribute = mapping.GetType().GetCustomAttributes(
                typeof(DneFileNameAttribute), true
            ).FirstOrDefault() as DneFileNameAttribute;
            if (fnAttribute != null)
            {
                return fnAttribute.FileName;
            }
            return null;
        }
    }

this is a work in progress code.

2 - From Enum, we have return like 'C', 'D' from file, and Enum with City and District with value 'C' and 'D', this is not unusual for enum types, and I thought it could be an improvement.