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

namespace Vanara.Extensions
{
	/// <summary>Extensions for enumerated types.</summary>
	public static class EnumExtensions
	{
		/// <summary>Gets the bit position of a flag that has a single bit, starting at 0.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="flags">The enumerated value.</param>
		/// <returns>The bit position, starting at 0, of the single bit flag specified in <paramref name="flags"/>.</returns>
		/// <exception cref="ArgumentException">The flag value is zero and has no bit position.</exception>
		/// <exception cref="ArithmeticException">The flag value has more than a single bit set.</exception>
		public static byte BitPosition<T>(this T flags) where T : struct, System.Enum
		{
			CheckHasFlags<T>();
			var flagValue = Convert.ToInt64(flags);
			if (flagValue == 0) throw new ArgumentException("The flag value is zero and has no bit position.");
			var r = Math.Log(flagValue, 2);
			if (r % 1 > 0) throw new ArithmeticException("The flag value has more than a single bit set.");
			return Convert.ToByte(r);
		}

		/// <summary>Throws an exception if a flag value does not exist in a specified enumeration.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="value">The value to check.</param>
		/// <param name="argName">Name of the argument to display in the exception. "value" is used if no value or <c>null</c> is supplied.</param>
		/// <exception cref="InvalidEnumArgumentException"></exception>
		public static void CheckHasValue<T>(T value, string argName = null) where T : struct, System.Enum
		{
			if (!IsValid(value))
				throw new InvalidEnumArgumentException(argName ?? "value", Convert.ToInt32(value), typeof(T));
		}

		/// <summary>Clears the specified flags from an enumerated value and returns the new value.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="flags">The enumerated value.</param>
		/// <param name="flag">The flags to clear or unset.</param>
		/// <returns>The resulting enumerated value after the <paramref name="flag"/> has been unset.</returns>
		public static T ClearFlags<T>(this T flags, T flag) where T : struct, System.Enum => flags.SetFlags(flag, false);

		/// <summary>Combines enumerated list of values into a single enumerated value.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="flags">The flags to combine.</param>
		/// <returns>A single enumerated value.</returns>
		public static T CombineFlags<T>(this IEnumerable<T> flags) where T : struct, System.Enum
		{
			CheckHasFlags<T>();
			long lValue = 0;
			foreach (var flag in flags)
			{
				var lFlag = Convert.ToInt64(flag);
				lValue |= lFlag;
			}
			return (T)Enum.ToObject(typeof(T), lValue);
		}

		/// <summary>Gets the description supplied by a <see cref="DescriptionAttribute"/> if one is set.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="value">The enumerated value.</param>
		/// <returns>The description, or <c>null</c> if one is not set.</returns>
		public static string GetDescription<T>(this T value) where T : struct, System.Enum
		{
			// If this is flag, return flags if there are more than one.
			if (IsFlags<T>() && value.GetFlags().Count() > 1)
				return value.ToString();
			// Get the name or description of the single enum value.
			var name = Enum.GetName(typeof(T), value);
			if (name != null)
			{
				var field = typeof(T).GetField(name);
				if (field != null && Attribute.GetCustomAttribute(field, typeof(DescriptionAttribute)) is DescriptionAttribute attr)
					return attr.Description;
			}
			return name;
		}

		/// <summary>Gets the flags of an enumerated value as an enumerated list.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="value">The enumerated value.</param>
		/// <returns>An enumeration of individual flags that compose the <paramref name="value"/>.</returns>
		public static IEnumerable<T> GetFlags<T>(this T value) where T : struct, System.Enum
		{
			CheckHasFlags<T>();
			foreach (T flag in Enum.GetValues(typeof(T)))
			{
				if (value.IsFlagSet(flag))
					yield return flag;
			}
		}

		/// <summary>Determines whether the enumerated flag value has the specified flag set.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="flags">The enumerated flag value.</param>
		/// <param name="flag">The flag value to check.</param>
		/// <returns><c>true</c> if is flag set; otherwise, <c>false</c>.</returns>
		public static bool IsFlagSet<T>(this T flags, T flag) where T : struct, System.Enum
		{
			CheckHasFlags<T>();
			var flagValue = Convert.ToInt64(flag);
			return (Convert.ToInt64(flags) & flagValue) == flagValue;
		}

		/// <summary>Returns an indication if the enumerated value is either defined or can be defined by a set of known flags.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="value">The enumerated value.</param>
		/// <returns><c>true</c> if the specified value is valid; otherwise, <c>false</c>.</returns>
		public static bool IsValid<T>(this T value) where T : struct, System.Enum
		{
			if (IsFlags<T>())
			{
				long mask = 0, lValue = Convert.ToInt64(value);
				foreach (T flag in Enum.GetValues(typeof(T)))
					mask |= Convert.ToInt64(flag);
				return (mask & lValue) == lValue;
			}
			return Enum.IsDefined(typeof(T), value);
		}

		/// <summary>Set or unsets flags in a referenced enumerated value.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="flags">A reference to an enumerated value.</param>
		/// <param name="flag">The flag to set or unset.</param>
		/// <param name="set">if set to <c>true</c> sets the flag; otherwise the flag is unset.</param>
		public static void SetFlags<T>(ref T flags, T flag, bool set = true) where T : struct, System.Enum
		{
			CheckHasFlags<T>();
			var flagsValue = Convert.ToInt64(flags);
			var flagValue = Convert.ToInt64(flag);
			if (set)
				flagsValue |= flagValue;
			else
				flagsValue &= (~flagValue);
			flags = (T)Enum.ToObject(typeof(T), flagsValue);
		}

		/// <summary>Set or unsets flags in an enumerated value and returns the new value.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="flags">The enumerated value.</param>
		/// <param name="flag">The flag to set or unset.</param>
		/// <param name="set">if set to <c>true</c> sets the flag; otherwise the flag is unset.</param>
		/// <returns>The resulting enumerated value after the <paramref name="flag"/> has been set or unset.</returns>
		public static T SetFlags<T>(this T flags, T flag, bool set = true) where T : struct, System.Enum
		{
			var ret = flags;
			SetFlags(ref ret, flag, set);
			return ret;
		}

		/// <summary>Converts an enumerated value to another fixed type.</summary>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <typeparam name="TResult">The type of the result.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		/// <exception cref="System.ArgumentException">The size of TResult cannot be smaller than the size of TEnum.</exception>
		public static TResult To<TEnum, TResult>(this TEnum value) where TEnum : unmanaged, System.Enum where TResult : unmanaged, IConvertible
		{
			unsafe
			{
				if (sizeof(TResult) < sizeof(TEnum)) throw new ArgumentException("The size of TResult cannot be smaller than the size of TEnum.");
				return *(TResult*)(void*)&value;
			}
		}

		/// <summary>Converts a fixed type to an enumerated value.</summary>
		/// <typeparam name="TValue">The type of the value to convert.</typeparam>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		/// <exception cref="System.ArgumentException">The size of TEnum cannot be smaller than the size of TValue.</exception>
		public static TEnum ToEnum<TValue, TEnum>(this TValue value) where TEnum : unmanaged, System.Enum where TValue : unmanaged, IConvertible
		{
			unsafe
			{
				if (sizeof(TEnum) < sizeof(TValue)) throw new ArgumentException("The size of TEnum cannot be smaller than the size of TValue.");
				return *(TEnum*)(void*)&value;
			}
		}

		/// <summary>Converts a fixed type to an enumerated value.</summary>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		public static TEnum ToEnum<TEnum>(this byte value) where TEnum : unmanaged, System.Enum => ToEnum<byte, TEnum>(value);

		/// <summary>Converts a fixed type to an enumerated value.</summary>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		public static TEnum ToEnum<TEnum>(this sbyte value) where TEnum : unmanaged, System.Enum => ToEnum<sbyte, TEnum>(value);

		/// <summary>Converts a fixed type to an enumerated value.</summary>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		public static TEnum ToEnum<TEnum>(this ushort value) where TEnum : unmanaged, System.Enum => ToEnum<ushort, TEnum>(value);

		/// <summary>Converts a fixed type to an enumerated value.</summary>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		public static TEnum ToEnum<TEnum>(this short value) where TEnum : unmanaged, System.Enum => ToEnum<short, TEnum>(value);

		/// <summary>Converts a fixed type to an enumerated value.</summary>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		public static TEnum ToEnum<TEnum>(this uint value) where TEnum : unmanaged, System.Enum => ToEnum<uint, TEnum>(value);

		/// <summary>Converts a fixed type to an enumerated value.</summary>
		/// <typeparam name="TEnum">The enumerated type.</typeparam>
		/// <param name="value">The value to convert.</param>
		/// <returns>The converted value.</returns>
		public static TEnum ToEnum<TEnum>(this int value) where TEnum : unmanaged, System.Enum => ToEnum<int, TEnum>(value);

		/// <summary>Checks if <typeparamref name="T"/> represents an enumeration and throws an exception if not.</summary>
		/// <typeparam name="T">The <see cref="Type"/> to validate.</typeparam>
		/// <exception cref="System.ArgumentException"></exception>
		private static void CheckHasFlags<T>() where T : struct, System.Enum
		{
			if (!IsFlags<T>())
				throw new ArgumentException($"Type '{typeof(T).FullName}' doesn't have the 'Flags' attribute");
		}

		/// <summary>Determines whether this enumerations has the <see cref="FlagsAttribute"/> set.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <returns><c>true</c> if this instance has the <see cref="FlagsAttribute"/> set; otherwise, <c>false</c>.</returns>
		private static bool IsFlags<T>() where T : struct, System.Enum => Attribute.IsDefined(typeof(T), typeof(FlagsAttribute));

		/*/// <summary>Returns an indication if the enumerated value is either defined or can be defined by a set of known flags.</summary>
		/// <typeparam name="T">The enumerated type.</typeparam>
		/// <param name="value">The enumerated value.</param>
		/// <param name="validValues">The valid values.</param>
		/// <returns><c>true</c> if the specified value is valid; otherwise, <c>false</c>.</returns>
		private static bool IsValid<T>(this T value, params T[] validValues) where T : struct, IConvertible
		{
			CheckIsEnum<T>();
			foreach (var vval in validValues)
				if (value.Equals(vval))
					return true;
			return false;
		}*/
	}
}