using System;
using System.Collections.Generic;
using System.Data.SqlClient;
using System.Linq;

// ReSharper disable UnusedMember.Global

namespace Tapeti.Flow.SQL
{
    internal static class SqlExceptionHelper
    {
        // 2601: Cannot insert duplicate key row in object '%.*ls' with unique index '%.*ls'. The duplicate key value is %ls.
        // 2627: Violation of %ls constraint '%.*ls'. Cannot insert duplicate key in object '%.*ls'. The duplicate key value is %ls.
        public static bool IsDuplicateKey(SqlException e)
        {
            return e != null && (e.Number == 2601 || e.Number == 2627);
        }


        public static bool IsTransientError(Exception e)
        {
            switch (e)
            {
                case TimeoutException _:
                    return true;

                case Exception exception:
                    {
                        var sqlExceptions = ExtractSqlExceptions(exception);
                        return sqlExceptions.Select(UnwrapSqlErrors).Any(IsRecoverableSQLError);
                    }

                default:
                    return false;
            }
        }

        /// <summary>
        /// Extracts alls SqlExceptions from the main and inner or aggregate exceptions
        /// </summary>
        public static IEnumerable<SqlException> ExtractSqlExceptions(Exception e)
        {
            while (e != null)
            {
                switch (e)
                {
                    case AggregateException aggregateException:
                        foreach (var innerException in aggregateException.InnerExceptions)
                        {
                            foreach (var extractedSqlException in ExtractSqlExceptions(innerException))
                                yield return extractedSqlException;
                        }
                        break;

                    case SqlException sqlException:
                        yield return sqlException;
                        break;
                }
                e = e.InnerException;
            }
        }


        /// <summary>
        /// Goes through all errors in a SqlException, and any InnerException that is also a SqlException.
        /// </summary>
        public static IEnumerable<SqlError> UnwrapSqlErrors(SqlException exception)
        {
            while (exception != null)
            {
                foreach (SqlError error in exception.Errors)
                    yield return error;

                exception = exception.InnerException as SqlException;
            }
        }

        // Mostly borrowed from EF:
        // https://github.com/aspnet/EntityFrameworkCore/blob/d8b7ebbfabff3d2e8560c24b1ff14d1f4244ca6a/src/EFCore.SqlServer/Storage/Internal/SqlServerTransientExceptionDetector.cs
        private static bool IsRecoverableSQLError(IEnumerable<SqlError> sqlErrors)
        {
            foreach (var err in sqlErrors)
            {
                switch (err.Number)
                {
                    // This exception can be thrown even if the operation completed succesfully, so it's safer to let the application fail.
                    // DBNETLIB Error Code: -2
                    // Timeout expired. The timeout period elapsed prior to completion of the operation or the server is not responding. The statement has been terminated.
                    // In onze situatie mag elke repository operation nogmaals uitgevoerd worden dus gaan we deze retry-en, ook al vind EF van niet.
                    case -2:


                    // EF doesn't recognize this one for some reason, but it occurs when I stop the SQL Server service
                    case 2:

                    // I had this occur once as well, even though all credentials were valid, so assume it's transient as well
                    case 4060:


                    // SQL Error Code: 49920
                    // Cannot process request. Too many operations in progress for subscription "%ld".
                    // The service is busy processing multiple requests for this subscription.
                    // Requests are currently blocked for resource optimization. Query sys.dm_operation_status for operation status.
                    // Wait until pending requests are complete or delete one of your pending requests and retry your request later.
                    case 49920:
                    // SQL Error Code: 49919
                    // Cannot process create or update request. Too many create or update operations in progress for subscription "%ld".
                    // The service is busy processing multiple create or update requests for your subscription or server.
                    // Requests are currently blocked for resource optimization. Query sys.dm_operation_status for pending operations.
                    // Wait till pending create or update requests are complete or delete one of your pending requests and
                    // retry your request later.
                    case 49919:
                    // SQL Error Code: 49918
                    // Cannot process request. Not enough resources to process request.
                    // The service is currently busy.Please retry the request later.
                    case 49918:
                    // SQL Error Code: 41839
                    // Transaction exceeded the maximum number of commit dependencies.
                    case 41839:
                    // SQL Error Code: 41325
                    // The current transaction failed to commit due to a serializable validation failure.
                    case 41325:
                    // SQL Error Code: 41305
                    // The current transaction failed to commit due to a repeatable read validation failure.
                    case 41305:
                    // SQL Error Code: 41302
                    // The current transaction attempted to update a record that has been updated since the transaction started.
                    case 41302:
                    // SQL Error Code: 41301
                    // Dependency failure: a dependency was taken on another transaction that later failed to commit.
                    case 41301:
                    // SQL Error Code: 40613
                    // Database XXXX on server YYYY is not currently available. Please retry the connection later.
                    // If the problem persists, contact customer support, and provide them the session tracing ID of ZZZZZ.
                    case 40613:
                    // SQL Error Code: 40501
                    // The service is currently busy. Retry the request after 10 seconds. Code: (reason code to be decoded).
                    case 40501:
                    // SQL Error Code: 40197
                    // The service has encountered an error processing your request. Please try again.
                    case 40197:
                    // SQL Error Code: 10929
                    // Resource ID: %d. The %s minimum guarantee is %d, maximum limit is %d and the current usage for the database is %d.
                    // However, the server is currently too busy to support requests greater than %d for this database.
                    // For more information, see http://go.microsoft.com/fwlink/?LinkId=267637. Otherwise, please try again.
                    case 10929:
                    // SQL Error Code: 10928
                    // Resource ID: %d. The %s limit for the database is %d and has been reached. For more information,
                    // see http://go.microsoft.com/fwlink/?LinkId=267637.
                    case 10928:
                    // SQL Error Code: 10060
                    // A network-related or instance-specific error occurred while establishing a connection to SQL Server.
                    // The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server
                    // is configured to allow remote connections. (provider: TCP Provider, error: 0 - A connection attempt failed
                    // because the connected party did not properly respond after a period of time, or established connection failed
                    // because connected host has failed to respond.)"}
                    case 10060:
                    // SQL Error Code: 10054
                    // A transport-level error has occurred when sending the request to the server.
                    // (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by the remote host.)
                    case 10054:
                    // SQL Error Code: 10053
                    // A transport-level error has occurred when receiving results from the server.
                    // An established connection was aborted by the software in your host machine.
                    case 10053:
                    // SQL Error Code: 1205
                    // Deadlock
                    case 1205:
                    // SQL Error Code: 233
                    // The client was unable to establish a connection because of an error during connection initialization process before login.
                    // Possible causes include the following: the client tried to connect to an unsupported version of SQL Server;
                    // the server was too busy to accept new connections; or there was a resource limitation (insufficient memory or maximum
                    // allowed connections) on the server. (provider: TCP Provider, error: 0 - An existing connection was forcibly closed by
                    // the remote host.)
                    case 233:
                    // SQL Error Code: 121
                    // The semaphore timeout period has expired
                    case 121:
                    // SQL Error Code: 64
                    // A connection was successfully established with the server, but then an error occurred during the login process.
                    // (provider: TCP Provider, error: 0 - The specified network name is no longer available.)
                    case 64:
                    // DBNETLIB Error Code: 20
                    // The instance of SQL Server you attempted to connect to does not support encryption.
                    case 20:
                        return true;
                }
            }

            return false;
        }
    }
}