namespace System.Threading;

public static class LazyInitializer
{
	public static T EnsureInitialized<T>(ref T target) where T : class
	{
		return target ?? EnsureInitialized(ref target, GetDefaultCtorValue<T>);
	}

	public static T EnsureInitialized<T>(ref T target, Func<T> valueFactory) where T : class
	{
		if (target == null)
		{
			T val = valueFactory();
			if (val == null)
			{
				throw new InvalidOperationException();
			}
			Interlocked.CompareExchange(ref target, val, null);
		}
		return target;
	}

	public static T EnsureInitialized<T>(ref T target, ref bool initialized, ref object syncLock)
	{
		return EnsureInitialized(ref target, ref initialized, ref syncLock, GetDefaultCtorValue<T>);
	}

	public static T EnsureInitialized<T>(ref T target, ref bool initialized, ref object syncLock, Func<T> valueFactory)
	{
		if (initialized)
		{
			return target;
		}
		if (syncLock == null)
		{
			Interlocked.CompareExchange(ref syncLock, new object(), null);
		}
		lock (syncLock)
		{
			if (initialized)
			{
				return target;
			}
			initialized = true;
			Thread.MemoryBarrier();
			target = valueFactory();
		}
		return target;
	}

	private static T GetDefaultCtorValue<T>()
	{
		try
		{
			return Activator.CreateInstance<T>();
		}
		catch
		{
			throw new MissingMemberException("The type being lazily initialized does not have a public, parameterless constructor.");
		}
	}
}