using System;
using System.IO;
using System.Net.Sockets;
using MySqlConnector;

namespace SyncEngine.MySql
{
    public static class MySqlConnectionFailures
    {
        public static bool IsReconnectable(Exception ex)
        {
            if (ex == null)
            {
                return false;
            }

            var mysql = FindException<MySqlException>(ex);
            if (mysql != null)
            {
                return IsReconnectableMySql(mysql);
            }

            if (ex is ObjectDisposedException)
            {
                return true;
            }

            if (ex is InvalidOperationException invalidOp &&
                invalidOp.Message.IndexOf("connection", StringComparison.OrdinalIgnoreCase) >= 0)
            {
                return true;
            }

            if (FindException<IOException>(ex) != null || FindException<SocketException>(ex) != null)
            {
                return true;
            }

            return false;
        }

        /// <summary>Classifies a MySQL exception for reconnect retry (testable without a live server).</summary>
        public static bool IsReconnectableMySql(MySqlException mysql)
        {
            if (mysql == null)
            {
                return false;
            }

            return IsReconnectableMySql(mysql.ErrorCode, mysql.IsTransient);
        }

        /// <summary>Classifies MySQL error codes for reconnect retry.</summary>
        public static bool IsReconnectableMySql(MySqlErrorCode errorCode, bool isTransient)
        {
            if (errorCode == MySqlErrorCode.AccessDenied
                || errorCode == MySqlErrorCode.UnknownDatabase
                || errorCode == MySqlErrorCode.NoSuchTable
                || errorCode == MySqlErrorCode.TableAccessDenied)
            {
                return false;
            }

            return isTransient || IsConnectionLostErrorCode(errorCode);
        }

        private static bool IsConnectionLostErrorCode(MySqlErrorCode code)
        {
            // MySQL server/client disconnect codes (incl. ServerShutdown during restart)
            if (code == MySqlErrorCode.UnableToConnectToHost
                || code == MySqlErrorCode.ServerShutdown
                || code == MySqlErrorCode.ShutdownComplete
                || code == MySqlErrorCode.ConnectionCountError)
            {
                return true;
            }

            // 2006 = server has gone away, 2013 = lost connection during query
            var numeric = (int)code;
            return numeric == 0 || numeric == 2006 || numeric == 2013;
        }

        private static T FindException<T>(Exception ex) where T : Exception
        {
            var current = ex;
            while (current != null)
            {
                var typed = current as T;
                if (typed != null)
                {
                    return typed;
                }

                current = current.InnerException;
            }

            return null;
        }
    }
}