using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;

namespace Common.Infrastructure
{
	public static class ConvertUtils
	{
		/// <summary>
		/// Returns an Object with the specified Type and whose value is equivalent to the specified object.
		/// </summary>
		/// <typeparam name="T">The Type to which value is to be converted.</typeparam>
		/// <returns>An object whose Type is conversionType (or conversionType's underlying type if conversionType
		/// is Nullable&lt;&gt;) and whose value is equivalent to value. -or- a null reference, if value is a null
		/// reference and conversionType is not a value type.</typeparam>
		/// <param name="value">An Object that implements the IConvertible interface.</param>
		/// <returns>An object whose Type is conversionType (or conversionType's underlying type if conversionType
		/// is Nullable&lt;&gt;) and whose value is equivalent to value. -or- a null reference, if value is a null
		/// reference and conversionType is not a value type.</returns>
		/// <remarks>
		/// This method exists as a workaround to System.Convert.ChangeType(Object, Type) which does not handle
		/// nullables as of version 2.0 (2.0.50727.42) of the .NET Framework. The idea is that this method will
		/// be deleted once Convert.ChangeType is updated in a future version of the .NET Framework to handle
		/// nullable types, so we want this to behave as closely to Convert.ChangeType as possible.
		/// This method was written by Peter Johnson at:
		/// http://aspalliance.com/author.aspx?uId=1026.
		/// </remarks>
		public static T ChangeType<T>(object value)
		{
			return (T)ChangeType(value, typeof(T));
		}

		/// <summary>
		/// Returns an Object with the specified Type and whose value is equivalent to the specified object.
		/// </summary>
		/// <param name="value">An Object that implements the IConvertible interface.</param>
		/// <param name="conversionType">The Type to which value is to be converted.</param>
		/// <returns>An object whose Type is conversionType (or conversionType's underlying type if conversionType
		/// is Nullable&lt;&gt;) and whose value is equivalent to value. -or- a null reference, if value is a null
		/// reference and conversionType is not a value type.</returns>
		/// <remarks>
		/// This method exists as a workaround to System.Convert.ChangeType(Object, Type) which does not handle
		/// nullables as of version 2.0 (2.0.50727.42) of the .NET Framework. The idea is that this method will
		/// be deleted once Convert.ChangeType is updated in a future version of the .NET Framework to handle
		/// nullable types, so we want this to behave as closely to Convert.ChangeType as possible.
		/// This method was written by Peter Johnson at:
		/// http://aspalliance.com/author.aspx?uId=1026.
		/// </remarks>
		public static object ChangeType(object value, Type conversionType)
		{
			// Note: This if block was taken from Convert.ChangeType as is, and is needed here since we're
			// checking properties on conversionType below.
			if (conversionType == null)
			{
				throw new ArgumentNullException("conversionType");
			} // end if

			// If it's not a nullable type, just pass through the parameters to Convert.ChangeType

			if (conversionType.IsGenericType &&
			  conversionType.GetGenericTypeDefinition().Equals(typeof(Nullable<>)))
			{
				// It's a nullable type, so instead of calling Convert.ChangeType directly which would throw a
				// InvalidCastException (per http://weblogs.asp.net/pjohnson/archive/2006/02/07/437631.aspx),
				// determine what the underlying type is
				// If it's null, it won't convert to the underlying type, but that's fine since nulls don't really
				// have a type--so just return null
				// Note: We only do this check if we're converting to a nullable type, since doing it outside
				// would diverge from Convert.ChangeType's behavior, which throws an InvalidCastException if
				// value is null and conversionType is a value type.
				if (value == null)
				{
					return null;
				} // end if

				// It's a nullable type, and not null, so that means it can be converted to its underlying type,
				// so overwrite the passed-in conversion type with this underlying type
				NullableConverter nullableConverter = new NullableConverter(conversionType);
				conversionType = nullableConverter.UnderlyingType;
			} // end if

			// Now that we've guaranteed conversionType is something Convert.ChangeType can handle (i.e. not a
			// nullable type), pass the call on to Convert.ChangeType
			return Convert.ChangeType(value, conversionType);
		}
	}
}