using System.Security.Cryptography;
using System.Text;
using RadicadeServer.DB;

namespace RadicadeServer.Utils
{
	public static class AdminUtils
	{
		/// <summary>
		/// The ceiling every admin upload is held to, on the request and on the multipart form.
		///
		/// Kestrel's own default is 30 MB, and no room import fits under it: an .assetbundle or
		/// a .room save routinely runs to tens or hundreds of megabytes. A route that does not
		/// raise the limit has its connection killed part-way through the body, so the panel sees
		/// a broken connection instead of an answer - which is what made importing a large room
		/// look like an authentication failure. Named once here so the next upload route cannot
		/// quietly forget it.
		/// </summary>
		public const long MaxUploadBytes = 256L * 1024 * 1024;

		/// <summary>
		/// A room file being assembled from parts lives beside its final name under this suffix
		/// until the last part lands. Nothing serves or lists one, so a half-imported bundle can
		/// never be fetched by the client, and a name ending in this suffix is refused outright.
		/// </summary>
		public const string PartSuffix = ".uploading";

		/// The multipart ceiling this server answers with, in the words the panel shows an admin.
		public const string MaxUploadLabel = "256 MiB";

		public static bool IsUploadPart(string? name) =>
			!string.IsNullOrEmpty(name) && name.EndsWith(PartSuffix, StringComparison.OrdinalIgnoreCase);

		private static bool SecretMatches(string? given, string? stored)
		{
			if (string.IsNullOrEmpty(given) || string.IsNullOrEmpty(stored))
				return false;

			return CryptographicOperations.FixedTimeEquals(
				Encoding.UTF8.GetBytes(given),
				Encoding.UTF8.GetBytes(stored));
		}

		public static bool IsAdminKey(this string? key)
		{
			return SecretMatches(key, DBConfig.AdminApiKey);
		}

		public static bool IsSupportKey(this string? key)
		{
			return SecretMatches(key, DBConfig.AdminApiKey)
				|| SecretMatches(key, DBConfig.SupportApiKey);
		}

		public static bool TryResolveUploadName(string? requested, out string? name, out string? error)
		{
			name = null;
			error = null;

			if (string.IsNullOrWhiteSpace(requested)) return true;

			var trimmed = requested.Trim();

			if (trimmed.Length > 128)
			{
				error = "Name is too long.";
				return false;
			}

			if (trimmed != Path.GetFileName(trimmed) || trimmed.Contains(".."))
			{
				error = "Name must be a bare file name.";
				return false;
			}

			foreach (var c in trimmed)
			{
				if (!char.IsLetterOrDigit(c) && c != '-' && c != '_' && c != '.')
				{
					error = "Name may only contain letters, digits, '-', '_' and '.'.";
					return false;
				}
			}

			name = trimmed;
			return true;
		}

		/// A subroom's Unity bundle is served under the name it is stored as
		/// (RoomServerAPI's unity_assets route hands the client that file name, and
		/// the client then fetches it from the CDN by name), so binding accepts any
		/// uploaded '<name>.assetbundle'. That is deliberately wider than
		/// StudioUnityAssetRegistry.IsValidAssetId, which only covers the
		/// 40-character manifest ids the Studio pipeline mints.
		public static bool TryResolveBundleName(string? requested, out string? name, out string? error)
		{
			if (!TryResolveUploadName(requested, out name, out error)) return false;

			if (name == null)
			{
				error = "A bundle file name is required.";
				return false;
			}

			if (!name.EndsWith(".assetbundle", StringComparison.OrdinalIgnoreCase))
			{
				error = $"'{name}' is not a .assetbundle file.";
				name = null;
				return false;
			}

			if (!System.IO.File.Exists(Path.Join(DBConfig.CDNStorage, name)))
			{
				error = $"No uploaded bundle named '{name}'.";
				name = null;
				return false;
			}

			return true;
		}
	}
}