using System.Runtime.InteropServices;

namespace PrivaPub.Infrastructure.Backup
{
	// A second name for a file (.NET has no API for it): a backup links the live media, which costs no disk, since names are
	// random and files never change; deleting the live one leaves the backup's.
	static class HardLink
	{
		// strings go to libc as UTF-8 on Unix
		[DllImport("libc", EntryPoint = "link", SetLastError = true, CharSet = CharSet.Ansi)]
		static extern int Link(string existing, string created);

		/// <summary>Links, or copies where a link can't be made (another disk, a filesystem refusing it).</summary>
		public static bool LinkOrCopy(string existing, string created)
		{
			Directory.CreateDirectory(Path.GetDirectoryName(created)!);
			if (OperatingSystem.IsLinux())
			{
				try
				{
					if (Link(existing, created) == 0)
						return true;
				}
				catch (DllNotFoundException)
				{
				}
				catch (EntryPointNotFoundException)
				{
				}
			}
			File.Copy(existing, created, overwrite: true);
			return false;
		}
	}
}