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using MySql.Data.Authentication.GSSAPI.Native;
using MySql.Data.Authentication.GSSAPI.Utility;
using MySql.Data.MySqlClient;
using System;
using System.Runtime.InteropServices;

namespace MySql.Data.Authentication.GSSAPI
{
    internal enum CredentialUsage
    {
        Both = 0,
        Initiate = 1,
        Accept = 2
    }

    /// <summary>
    /// Credentials to use to establish the context
    /// </summary>
    internal class GssCredentials : IDisposable
    {
        internal IntPtr _credentials;
        private IntPtr _gssUsername;

        internal string UserName { get; set; }

        /// <summary>
        /// Acquires credentials for the supplied principal using the supplied password
        /// </summary>
        /// <param name="username">Username</param>
        /// <param name="password">Password</param>
        /// <param name="usage">GSS_C_BOTH - Credentials may be used either to initiate or accept security contexts. 
        /// GSS_C_INITIATE - Credentials will only be used to initiate security contexts. 
        /// GSS_C_ACCEPT - Credentials will only be used to accept security contexts.</param>
        /// <returns>An object containing the credentials</returns>
        internal GssCredentials(string username, string password, CredentialUsage usage = CredentialUsage.Initiate)
        {
            this.UserName = username;

            uint minorStatus = 0;
            uint majorStatus = 0;

            // copy the principal name to a gss_buffer
            using (var gssUsernameBuffer = GssType.GetBufferFromString(username))
            using (var gssPasswordBuffer = GssType.GetBufferFromString(password))
            {
                // use the buffer to import the name into a gss_name
                majorStatus = NativeMethods.gss_import_name(
                    out minorStatus,
                    ref gssUsernameBuffer.Value,
                    ref Const.GssNtUserName,
                    out this._gssUsername
                );
                if (majorStatus != Const.GSS_S_COMPLETE)
                {
                    throw new MySqlException(ExceptionMessages.FormatGssMessage(
                        "GSSAPI: Unable to import the supplied user name.",
              majorStatus, minorStatus, Const.GssNtHostBasedService));
                }

                majorStatus = NativeMethods.gss_acquire_cred_with_password(
                  out minorStatus,
                  this._gssUsername,
                  ref gssPasswordBuffer.Value,
                  0,
                  ref Const.GssKrb5MechOidSet,
                  (int)usage,
                  ref this._credentials,
                  IntPtr.Zero,
                  out var actualExpiry);

                if (majorStatus != Const.GSS_S_COMPLETE)
                {
                    throw new MySqlException(ExceptionMessages.FormatGssMessage(
                        "GSSAPI: Unable to acquire credentials for authentication.",
              majorStatus, minorStatus, Const.GssKrb5MechOidDesc));
                }
            }
        }

        /// <summary>
        /// Acquires credentials for the supplied principal using material stored in a valid keytab
        /// </summary>
        /// <param name="username">Username</param>
        /// <param name="usage">GSS_C_BOTH - Credentials may be used either to initiate or accept security contexts. 
        /// GSS_C_INITIATE - Credentials will only be used to initiate security contexts. 
        /// GSS_C_ACCEPT - Credentials will only be used to accept security contexts.</param>
        /// <returns>An object containing the credentials</returns>
        internal GssCredentials(string username, CredentialUsage usage = CredentialUsage.Initiate)
        {
            this.UserName = username;

            // allocate a gss buffer and copy the principal name to it
            using (var gssNameBuffer = GssType.GetBufferFromString(username))
            {
                uint minorStatus = 0;
                uint majorStatus = 0;

                // use the buffer to import the name into a gss_name
                majorStatus = NativeMethods.gss_import_name(
                    out minorStatus,
                    ref gssNameBuffer.Value,
                    ref Const.GssNtUserName,
                    out var _gssUsername
                );
                if (majorStatus != Const.GSS_S_COMPLETE)
                {
                    throw new MySqlException(ExceptionMessages.FormatGssMessage(
                        "GSSAPI: Unable to import the supplied user name.",
              majorStatus, minorStatus, Const.GssNtHostBasedService));
                }

                majorStatus = NativeMethods.gss_acquire_cred(
                    out minorStatus,
                    _gssUsername,
                    Const.GSS_C_INDEFINITE,
                    ref Const.GssKrb5MechOidSet,
                    (int)usage,
                    ref this._credentials,
                    IntPtr.Zero,
                    out var actualExpiry);

                if (majorStatus != Const.GSS_S_COMPLETE)
                {
                    throw new MySqlException(ExceptionMessages.FormatGssMessage(
                        "GSSAPI: Unable acquire credentials for authentication.",
              majorStatus, minorStatus, Const.GssKrb5MechOidDesc));
                }
            }
        }

        /// <summary>
        /// Acquires default credentials stored in the cache
        /// </summary>
        /// <param name="usage">GSS_C_BOTH - Credentials may be used either to initiate or accept security contexts. 
        /// GSS_C_INITIATE - Credentials will only be used to initiate security contexts. 
        /// GSS_C_ACCEPT - Credentials will only be used to accept security contexts.</param>
        /// <returns>An object containing the credentials</returns>
        internal GssCredentials(CredentialUsage usage = CredentialUsage.Initiate)
        {
            uint minorStatus, lifetime = 0;
            int credentialUsage;
            IntPtr name, mechs;

            var majorStatus = NativeMethods.gss_acquire_cred(
                out minorStatus,
                Const.GSS_C_NO_NAME,
                Const.GSS_C_INDEFINITE,
                ref Const.GssKrb5MechOidSet,
                (int)usage,
                ref this._credentials,
                IntPtr.Zero,
                out var actualExpiry);

            if (majorStatus != Const.GSS_S_COMPLETE)
            {
                throw new MySqlException(ExceptionMessages.FormatGssMessage(
                    "GSSAPI: Unable acquire credentials for authentication.",
            majorStatus, minorStatus, Const.GssKrb5MechOidDesc));
            }

            majorStatus = NativeMethods.gss_inquire_cred(
              out minorStatus,
              this._credentials,
              out name,
              out lifetime,
              out credentialUsage,
              out mechs);

            if (majorStatus != Const.GSS_S_COMPLETE)
            {
                throw new MySqlException(ExceptionMessages.FormatGssMessage(
                    "GSSAPI: Unable to obtain information about the credentials provided.",
            majorStatus, minorStatus, Const.GssKrb5MechOidDesc));
            }

            this.UserName = TranslateDisplayName(name);
        }

        /// <summary>
        /// Translates a name in internal form to a textual representation.
        /// </summary>
        /// <param name="name">Name in internal form (GSSAPI).</param>
        /// <returns></returns>
        private static string TranslateDisplayName(IntPtr name)
        {
            string userName;

            GssBufferDescStruct buffer;
            NativeMethods.gss_display_name(out _, name, out buffer, out _);

            userName = buffer.value == IntPtr.Zero ? string.Empty : Marshal.PtrToStringAnsi(buffer.value);

            var majorStatus = NativeMethods.gss_release_buffer(out var minorStatus, ref buffer);
            if (majorStatus != Const.GSS_S_COMPLETE)
            {
                throw new MySqlException(ExceptionMessages.FormatGssMessage(
                    "GSSAPI: An error occurred releasing a buffer.",
                majorStatus, minorStatus, Const.GSS_C_NO_OID));
            }

            return userName;
        }

        public void Dispose()
        {
            uint minorStatus = 0;
            uint majorStatus = 0;

            majorStatus = NativeMethods.gss_release_name(out minorStatus, ref this._gssUsername);
            if (majorStatus != Const.GSS_S_COMPLETE)
            {
                throw new MySqlException(ExceptionMessages.FormatGssMessage(
                    "GSSAPI: Unable to release the user name handle.",
          majorStatus, minorStatus, Const.GssNtHostBasedService));
            }

            majorStatus = NativeMethods.gss_release_cred(out minorStatus, ref this._credentials);
            if (majorStatus != Const.GSS_S_COMPLETE)
            {
                throw new MySqlException(ExceptionMessages.FormatGssMessage(
                    "GSSAPI: Unable to release the credential handle.",
          majorStatus, minorStatus, Const.GssNtHostBasedService));
            }
        }
    }
}