using System;
using System.Collections.Generic;
using System.Linq;
using System.Linq.Expressions;
using System.Text;
namespace Google.Protobuf
{
public class EnumHelper<T> where T : struct, IComparable, IFormattable
{
// TODO(jonskeet): For snmall enums, use something lighter-weight than a dictionary?
private static readonly Dictionary<int, T> _byNumber;
private static readonly Dictionary<string, T> _byName;
private static readonly Func<T, long> toRawValue;
private static readonly Func<long, T> fromRawValue;
private const long UnknownValueBase = 0x100000000L;
static EnumHelper()
{
if (!typeof(T).IsEnum)
{
throw new InvalidOperationException(string.Format("{0} is not an enum type", typeof(T).FullName));
}
if (Enum.GetUnderlyingType(typeof(T)) != typeof(long))
{
throw new InvalidOperationException(string.Format("{0} does not have long as an underlying type", typeof(T).FullName));
}
// It will actually be a T[], but the CLR will let us convert.
long[] array = (long[])Enum.GetValues(typeof(T));
_byNumber = new Dictionary<int, T>(array.Length);
foreach (long i in array)
{
_byNumber[(int) i] = (T)(object)i;
}
string[] names = (string[])Enum.GetNames(typeof(T));
_byName = new Dictionary<string, T>();
foreach (var name in names)
{
_byName[name] = (T) Enum.Parse(typeof(T), name, false);
}
ParameterExpression param1 = Expression.Parameter(typeof(T), "x");
ParameterExpression param2 = Expression.Parameter(typeof(long), "x");
Expression convertedParam1 = Expression.Convert(param1, typeof(long));
Expression convertedParam2 = Expression.Convert(param2, typeof(T));
toRawValue = Expression.Lambda<Func<T, long>>(convertedParam1, param1).Compile();
fromRawValue = Expression.Lambda<Func<long, T>>(convertedParam2, param2).Compile();
}
/// <summary>
/// Converts the given 32-bit integer into a value of the enum type.
/// If the integer is a known, named value, that is returned; otherwise,
/// a value which is outside the range of 32-bit integers but which preserves
/// the original integer is returned.
/// </summary>
public static T FromInt32(int value)
{
T validValue;
return _byNumber.TryGetValue(value, out validValue) ? validValue : FromRawValue((long) value | UnknownValueBase);
}
/// <summary>
/// Converts a value of the enum type to a 32-bit integer. This reverses
/// <see cref="Int32"/>.
/// </summary>
public static int ToInt32(T value)
{
return (int)GetRawValue(value);
}
public static bool IsKnownValue(T value)
{
long raw = GetRawValue(value);
if (raw >= int.MinValue && raw <= int.MaxValue)
{
return _byNumber.ContainsKey((int)raw);
}
return false;
}
private static long GetRawValue(T value)
{
return toRawValue(value);
}
private static T FromRawValue(long value)
{
return fromRawValue(value);
}
}
}
