using System.Globalization;

namespace PrivaPub.Federation.Crawler
{
	public static class PeerHosts
	{
		static readonly IdnMapping Idn = new();
		static readonly string[] Unreachable = { ".onion", ".i2p", ".local", ".localhost", ".internal" };
		static readonly string[] Reserved = { ".test", ".invalid", ".example" };

		//names from a peers list we could ever talk to: DNS names, ASCII (punycode), no addresses, ports or hidden services;
		//the reserved test names only on a test network
		public static IEnumerable<string> Filter(IEnumerable<string> names, Func<string, bool> allowed, bool testNetwork = false) =>
			names
				.Select(Normalise)
				.Where(host => host != default && (testNetwork || !Reserved.Any(suffix => host.EndsWith(suffix, StringComparison.Ordinal))) && allowed(host))
				.Distinct(StringComparer.Ordinal);

		public static string Normalise(string name)
		{
			var host = name?.Trim().TrimEnd('.').ToLowerInvariant();
			if (string.IsNullOrEmpty(host) || host.Length > 253 || !host.Contains('.') || host.Contains(':') || host.Contains('/'))
				return default;
			try
			{
				host = Idn.GetAscii(host);
			}
			catch (ArgumentException)
			{
				return default;
			}
			if (Uri.CheckHostName(host) != UriHostNameType.Dns || Unreachable.Any(suffix => host.EndsWith(suffix, StringComparison.Ordinal)))
				return default;
			return host;
		}
	}
}