// Copyright 2009-2024 Josh Close
// This file is a part of CsvHelper and is dual licensed under MS-PL and Apache 2.0.
// See LICENSE.txt for details or visit http://www.opensource.org/licenses/ms-pl.html for MS-PL and http://opensource.org/licenses/Apache-2.0 for Apache 2.0.
// https://github.com/JoshClose/CsvHelper
using CsvHelper.Configuration;

namespace CsvHelper.TypeConversion;

/// <summary>
/// Converts a <see cref="Nullable{T}"/> to and from a <see cref="string"/>.
/// </summary>
public class NullableConverter : DefaultTypeConverter
{
	/// <summary>
	/// Gets the type of the nullable.
	/// </summary>
	/// <value>
	/// The type of the nullable.
	/// </value>
	public Type NullableType { get; private set; }

	/// <summary>
	/// Gets the underlying type of the nullable.
	/// </summary>
	/// <value>
	/// The underlying type.
	/// </value>
	public Type? UnderlyingType { get; private set; }

	/// <summary>
	/// Gets the type converter for the underlying type.
	/// </summary>
	/// <value>
	/// The type converter.
	/// </value>
	public ITypeConverter UnderlyingTypeConverter { get; private set; }

	/// <summary>
	/// Creates a new <see cref="NullableConverter"/> for the given <see cref="Nullable{T}"/> <see cref="Type"/>.
	/// </summary>
	/// <param name="type">The nullable type.</param>
	/// <param name="typeConverterFactory">The type converter factory.</param>
	/// <exception cref="System.ArgumentException">type is not a nullable type.</exception>
	public NullableConverter(Type type, TypeConverterCache typeConverterFactory)
	{
		NullableType = type;
		UnderlyingType = Nullable.GetUnderlyingType(type);
		if (UnderlyingType == null)
		{
			throw new ArgumentException("type is not a nullable type.");
		}

		UnderlyingTypeConverter = typeConverterFactory.GetConverter(UnderlyingType);
	}

	/// <summary>
	/// Converts the string to an object.
	/// </summary>
	/// <param name="text">The string to convert to an object.</param>
	/// <param name="row">The <see cref="IReaderRow"/> for the current record.</param>
	/// <param name="memberMapData">The <see cref="MemberMapData"/> for the member being created.</param>
	/// <returns>The object created from the string.</returns>
	public override object? ConvertFromString(string? text, IReaderRow row, MemberMapData memberMapData)
	{
		if (string.IsNullOrEmpty(text))
		{
			return null;
		}

		foreach (var nullValue in memberMapData.TypeConverterOptions.NullValues)
		{
			if (text == nullValue)
			{
				return null;
			}
		}

		return UnderlyingTypeConverter.ConvertFromString(text, row, memberMapData);
	}

	/// <summary>
	/// Converts the object to a string.
	/// </summary>
	/// <param name="value">The object to convert to a string.</param>
	/// <param name="row"></param>
	/// <param name="memberMapData"></param>
	/// <returns>The string representation of the object.</returns>
	public override string? ConvertToString(object? value, IWriterRow row, MemberMapData memberMapData)
	{
		return UnderlyingTypeConverter.ConvertToString(value, row, memberMapData);
	}
}
