using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.Data.SqlClient;
using System.Linq;
using System.Text.RegularExpressions;
using NPoco;
using Umbraco.Core.Persistence.SqlSyntax;

namespace Umbraco.Core.Persistence
{
    /// <summary>
    /// Provides extension methods to NPoco Database class.
    /// </summary>
    public static class NPocoDatabaseExtensions
    {
        // NOTE
        //
        // proper way to do it with TSQL and SQLCE
        //   IF EXISTS (SELECT ... FROM table WITH (UPDLOCK,HOLDLOCK)) WHERE ...)
        //   BEGIN
        //     UPDATE table SET ... WHERE ...
        //   END
        //   ELSE
        //   BEGIN
        //     INSERT INTO table (...) VALUES (...)
        //   END
        //
        // works in READ COMMITED, TSQL & SQLCE lock the constraint even if it does not exist, so INSERT is OK
        //
        // proper way to do it with MySQL
        //   IF EXISTS (SELECT ... FROM table WHERE ... FOR UPDATE)
        //   BEGIN
        //     UPDATE table SET ... WHERE ...
        //   END
        //   ELSE
        //   BEGIN
        //     INSERT INTO table (...) VALUES (...)
        //   END
        //
        // MySQL locks the constraint ONLY if it exists, so INSERT may fail...
        //   in theory, happens in READ COMMITTED but not REPEATABLE READ
        //   http://www.percona.com/blog/2012/08/28/differences-between-read-committed-and-repeatable-read-transaction-isolation-levels/
        //   but according to
        //   http://dev.mysql.com/doc/refman/5.0/en/set-transaction.html
        //   it won't work for exact index value (only ranges) so really...
        //
        // MySQL should do
        //   INSERT INTO table (...) VALUES (...) ON DUPLICATE KEY UPDATE ...
        //
        // also the lock is released when the transaction is committed
        // not sure if that can have unexpected consequences on our code?
        //
        // so... for the time being, let's do with that somewhat crazy solution below...
        // todo: use the proper database syntax, not this kludge

        /// <summary>
        /// Safely inserts a record, or updates if it exists, based on a unique constraint.
        /// </summary>
        /// <param name="db"></param>
        /// <param name="poco"></param>
        /// <returns>The action that executed, either an insert or an update. If an insert occurred and a PK value got generated, the poco object
        /// passed in will contain the updated value.</returns>
        /// <remarks>
        /// <para>We cannot rely on database-specific options such as MySql ON DUPLICATE KEY UPDATE or MSSQL MERGE WHEN MATCHED because SQLCE
        /// does not support any of them. Ideally this should be achieved with proper transaction isolation levels but that would mean revisiting
        /// isolation levels globally. We want to keep it simple for the time being and manage it manually.</para>
        /// <para>We handle it by trying to update, then insert, etc. until something works, or we get bored.</para>
        /// <para>Note that with proper transactions, if T2 begins after T1 then we are sure that the database will contain T2's value
        /// once T1 and T2 have completed. Whereas here, it could contain T1's value.</para>
        /// </remarks>
        internal static RecordPersistenceType InsertOrUpdate<T>(this IDatabase db, T poco)
            where T : class
        {
            return db.InsertOrUpdate(poco, null, null);
        }

        /// <summary>
        /// Safely inserts a record, or updates if it exists, based on a unique constraint.
        /// </summary>
        /// <param name="db"></param>
        /// <param name="poco"></param>
        /// <param name="updateArgs"></param>
        /// <param name="updateCommand">If the entity has a composite key they you need to specify the update command explicitly</param>
        /// <returns>The action that executed, either an insert or an update. If an insert occurred and a PK value got generated, the poco object
        /// passed in will contain the updated value.</returns>
        /// <remarks>
        /// <para>We cannot rely on database-specific options such as MySql ON DUPLICATE KEY UPDATE or MSSQL MERGE WHEN MATCHED because SQLCE
        /// does not support any of them. Ideally this should be achieved with proper transaction isolation levels but that would mean revisiting
        /// isolation levels globally. We want to keep it simple for the time being and manage it manually.</para>
        /// <para>We handle it by trying to update, then insert, etc. until something works, or we get bored.</para>
        /// <para>Note that with proper transactions, if T2 begins after T1 then we are sure that the database will contain T2's value
        /// once T1 and T2 have completed. Whereas here, it could contain T1's value.</para>
        /// </remarks>
        internal static RecordPersistenceType InsertOrUpdate<T>(this IDatabase db,
            T poco,
            string updateCommand,
            object updateArgs)
            where T : class
        {
            if (poco == null)
                throw new ArgumentNullException(nameof(poco));

            // try to update
            var rowCount = updateCommand.IsNullOrWhiteSpace()
                    ? db.Update(poco)
                    : db.Update<T>(updateCommand, updateArgs);
            if (rowCount > 0)
                return RecordPersistenceType.Update;

            // failed: does not exist, need to insert
            // RC1 race cond here: another thread may insert a record with the same constraint

            var i = 0;
            while (i++ < 4)
            {
                try
                {
                    // try to insert
                    db.Insert(poco);
                    return RecordPersistenceType.Insert;
                }
                catch (SqlException) // assuming all db engines will throw that exception
                {
                    // failed: exists (due to race cond RC1)
                    // RC2 race cond here: another thread may remove the record

                    // try to update
                    rowCount = updateCommand.IsNullOrWhiteSpace()
                        ? db.Update(poco)
                        : db.Update<T>(updateCommand, updateArgs);
                    if (rowCount > 0)
                        return RecordPersistenceType.Update;

                    // failed: does not exist (due to race cond RC2), need to insert
                    // loop
                }
            }

            // this can go on forever... have to break at some point and report an error.
            throw new DataException("Record could not be inserted or updated.");
        }

        /// <summary>
        /// This will escape single @ symbols for npoco values so it doesn't think it's a parameter
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static string EscapeAtSymbols(string value)
        {
            if (value.Contains("@") == false) return value;

            //this fancy regex will only match a single @ not a double, etc...
            var regex = new Regex("(?<!@)@(?!@)");
            return regex.Replace(value, "@@");
        }

        // todo: review NPoco native InsertBulk to replace the code below

        public static void BulkInsertRecordsWithTransaction<T>(this IDatabase db, ISqlSyntaxProvider sqlSyntax, IEnumerable<T> records)
        {
            var recordsA = records.ToArray();
            if (recordsA.Length == 0)
                return;

            // no need to "try...catch", if the transaction is not completed it will rollback!
            using (var tr = db.GetTransaction())
            {
                db.BulkInsertRecords(sqlSyntax, recordsA);
                tr.Complete();
            }
        }

        /// <summary>
        /// Performs the bulk insertion in the context of a current transaction with an optional parameter to complete the transaction
        /// when finished
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="db"></param>
        /// <param name="sqlSyntax"></param>
        /// <param name="records"></param>
        public static void BulkInsertRecords<T>(this IDatabase db, ISqlSyntaxProvider sqlSyntax, IEnumerable<T> records)
        {
            var recordsA = records.ToArray();
            if (recordsA.Length == 0)
                return;

            // if it is sql ce or it is a sql server version less than 2008, we need to do individual inserts.
            var sqlServerSyntax = sqlSyntax as SqlServerSyntaxProvider;
            if ((sqlServerSyntax != null && (int) sqlServerSyntax.ServerVersion.ProductVersionName < (int) SqlServerSyntaxProvider.VersionName.V2008)
                || sqlSyntax is SqlCeSyntaxProvider)
            {
                // SqlCe doesn't support bulk insert statements!
                foreach (var poco in recordsA)
                    db.Insert(poco);
            }
            else
            {
                string[] sqlStatements;
                var cmds = db.GenerateBulkInsertCommand(recordsA, db.Connection, out sqlStatements);
                for (var i = 0; i < sqlStatements.Length; i++)
                {
                    using (var cmd = cmds[i])
                    {
                        cmd.CommandText = sqlStatements[i];
                        cmd.ExecuteNonQuery();
                    }
                }
            }
        }

        private static bool IncludeColumn(PocoData pocoData, string columnKey, PocoColumn column)
        {
            // exclude result columns,
            // exclude primary key column if auto-increment
            return column.ResultColumn == false && (pocoData.TableInfo.AutoIncrement == false || columnKey != pocoData.TableInfo.PrimaryKey);
        }

        /// <summary>
        /// Creates a bulk insert command
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="db"></param>
        /// <param name="records"></param>
        /// <param name="connection"></param>
        /// <param name="sql"></param>
        /// <returns>Sql commands with populated command parameters required to execute the sql statement</returns>
        /// <remarks>
        /// The limits for number of parameters are 2100 (in sql server, I think there's many more allowed in mysql). So
        /// we need to detect that many params and split somehow.
        /// For some reason the 2100 limit is not actually allowed even though the exception from sql server mentions 2100 as a max, perhaps it is 2099
        /// that is max. I've reduced it to 2000 anyways.
        /// </remarks>
        internal static IDbCommand[] GenerateBulkInsertCommand<T>(
            this IDatabase db,
            T[] records,
            DbConnection connection,
            out string[] sql)
        {
            var pocoData = db.PocoDataFactory.ForType(typeof(T));

            // get columns to include, = number of parameters per row
            var columns = pocoData.Columns.Where(c => IncludeColumn(pocoData, c.Key, c.Value)).ToArray();
            var paramsPerRow = columns.Length;

            // format columns to sql
            var tableName = db.DatabaseType.EscapeTableName(pocoData.TableInfo.TableName);
            var columnNames = string.Join(", ", columns.Select(c => tableName + "." + db.DatabaseType.EscapeSqlIdentifier(c.Key)));

            // example calc:
            // given: we have 4168 items in the collection, each item contains 8 command parameters (values to be inserted)
            // 2100 / 8 = 262.5
            // Math.Floor(2100 / 8) = 262 items per trans
            // 4168 / 262 = 15.908... = there will be 16 trans in total

            // if we have disabled db parameters, then all items will be included, in only one transaction
            var rowsPerCommand = paramsPerRow == 0 ? int.MaxValue : Convert.ToInt32(Math.Floor(2000.00 / paramsPerRow));
            var commandsCount = Convert.ToInt32(Math.Ceiling((double) records.Length / rowsPerCommand));

            sql = new string[commandsCount];
            var commands = new IDbCommand[commandsCount];

            for (var commandIndex = 0; commandIndex < commandsCount; commandIndex++)
            {
                var itemsForTrans = records
                    .Skip(commandIndex * rowsPerCommand)
                    .Take(rowsPerCommand);

                var cmd = db.CreateCommand(connection, CommandType.Text,  "");
                var prefix = db.DatabaseType.GetParameterPrefix(cmd.Connection.ConnectionString);
                var pocoValues = new List<string>();
                var index = 0;
                foreach (var poco in itemsForTrans)
                {
                    var values = new List<string>();
                    foreach (var column in columns)
                    {
                        db.AddParameter(cmd, column.Value.GetValue(poco));
                        values.Add(prefix + index++);
                    }
                    pocoValues.Add("(" + string.Join(",", values.ToArray()) + ")");
                }

                sql[commandIndex] = $"INSERT INTO {tableName} ({columnNames}) VALUES {string.Join(", ", pocoValues)}";
                commands[commandIndex] = cmd;
            }

            return commands;
        }

        public static void TruncateTable(this IDatabase db, ISqlSyntaxProvider sqlSyntax, string tableName)
        {
            var sql = new Sql(string.Format(
                sqlSyntax.TruncateTable,
                sqlSyntax.GetQuotedTableName(tableName)));
            db.Execute(sql);
        }

        public static IsolationLevel GetCurrentTransactionIsolationLevel(this IDatabase database)
        {
            var transaction = database.Transaction;
            return transaction?.IsolationLevel ?? IsolationLevel.Unspecified;
        }

        public static IEnumerable<TResult> FetchByGroups<TResult, TSource>(this IDatabase db, IEnumerable<TSource> source, int groupSize, Func<IEnumerable<TSource>, Sql<SqlContext>> sqlFactory)
        {
            return source.SelectByGroups(x => db.Fetch<TResult>(sqlFactory(x)), groupSize);
        }
    }
}