AutoMapper.cs

using System;
using System.Reflection;

namespace AutoMapper
{
    public class AutoMapper
    {
        public static TTarget Map<TSource, TTarget>(TSource source)
        where TTarget : new()
        {
            if (source == null) return default!;

            TTarget target = new TTarget();

            var sourceProps = typeof(TSource).GetProperties();
            var targetProps = typeof(TTarget).GetProperties();

            foreach (var tProp in targetProps)
            {
                if (!tProp.CanWrite) continue;

                // Case-insensitive match
                var sProp = sourceProps.FirstOrDefault(
                    sp => string.Equals(sp.Name, tProp.Name, StringComparison.OrdinalIgnoreCase)
                );

                if (sProp == null) continue;

                var sValue = sProp.GetValue(source);

                if (sValue == null)
                {
                    // If nullable → non-nullable, assign default value ("" for string)
                    if (!IsNullable(tProp.PropertyType))
                    {
                        tProp.SetValue(target, GetDefaultValue(tProp.PropertyType));
                    }
                    continue;
                }

                // Type matches → direct assign
                if (tProp.PropertyType == sProp.PropertyType)
                {
                    tProp.SetValue(target, sValue);
                    continue;
                }

                // Try convert types (string ↔ int, etc.)
                try
                {
                    var converted = Convert.ChangeType(sValue, tProp.PropertyType);
                    tProp.SetValue(target, converted);
                }
                catch
                {
                    // ignore conversion errors
                }
            }

            return target;
        }

        private static bool IsNullable(Type t)
        {
            return !t.IsValueType || Nullable.GetUnderlyingType(t) != null;
        }

        private static object GetDefaultValue(Type t)
        {
            if (t == typeof(string)) return string.Empty;
            return Activator.CreateInstance(t)!;
        }
    }
}