namespace RelayClient.Crypto;

/// <summary>
/// Per-user RSA keypair persistence. Keys live as base64-encoded files in
/// {AppData}/keys/{username}.{public|private}.key
///
/// Plaintext on disk. For now this is fine because the only attack model is "someone else
/// has access to your filesystem" — at which point everything is compromised. A future
/// enhancement could encrypt the private key with a passphrase derived from the user's
/// password, similar to how SSH/PGP do it.
/// </summary>
public static class KeyStorage
{
    /// <summary>Returns (and creates if needed) the per-app keys directory.</summary>
    private static string GetKeyFolder()
    {
        var folder = Path.Combine(FileSystem.AppDataDirectory, "keys");
        Directory.CreateDirectory(folder);
        return folder;
    }

    /// <summary>Writes the base64 RSA private key to disk. Used at first-launch after GenerateRsaKeyPair.</summary>
    public static void SavePrivateKey(string username, string privateKey)
    {
        File.WriteAllText(Path.Combine(GetKeyFolder(), $"{username}.private.key"), privateKey);
    }

    /// <summary>Writes the base64 RSA public key to disk. Sent to the server via WsAction.RegisterKey.</summary>
    public static void SavePublicKey(string username, string publicKey)
    {
        File.WriteAllText(Path.Combine(GetKeyFolder(), $"{username}.public.key"), publicKey);
    }

    /// <summary>Reads the user's RSA private key. Used by TryDecryptAndParseContent on every inbound message.</summary>
    public static string LoadPrivateKey(string username)
    {
        return File.ReadAllText(Path.Combine(GetKeyFolder(), $"{username}.private.key"));
    }

    /// <summary>Reads the user's RSA public key. Used during the boot handshake to send to the server.</summary>
    public static string LoadPublicKey(string username)
    {
        return File.ReadAllText(Path.Combine(GetKeyFolder(), $"{username}.public.key"));
    }

    /// <summary>True if BOTH halves of the user's keypair already exist on disk. False means we need to generate.</summary>
    public static bool HasKeys(string username)
    {
        return File.Exists(Path.Combine(GetKeyFolder(), $"{username}.private.key")) &&
               File.Exists(Path.Combine(GetKeyFolder(), $"{username}.public.key"));
    }
}