using System;
using System.Globalization;

namespace SyncEngine.Access
{
    /// <summary>Translates Access DefaultValue expressions to T-SQL DEFAULT literals.</summary>
    public static class AccessDefaultTranslator
    {
        public static bool IsNullDefault(string accessDefault)
        {
            if (string.IsNullOrWhiteSpace(accessDefault))
            {
                return false;
            }

            var expr = accessDefault.Trim();
            if (expr.StartsWith("=", StringComparison.Ordinal))
            {
                expr = expr.Substring(1).Trim();
            }

            return string.Equals(expr, "Null", StringComparison.OrdinalIgnoreCase);
        }

        public static bool TryTranslate(string accessDefault, out string sqlExpression)
        {
            sqlExpression = null;
            if (string.IsNullOrWhiteSpace(accessDefault))
            {
                return false;
            }

            if (IsNullDefault(accessDefault))
            {
                return false;
            }

            var expr = accessDefault.Trim();
            if (expr.StartsWith("=", StringComparison.Ordinal))
            {
                expr = expr.Substring(1).Trim();
            }

            if (string.Equals(expr, "Now()", StringComparison.OrdinalIgnoreCase) ||
                string.Equals(expr, "Date()", StringComparison.OrdinalIgnoreCase) ||
                string.Equals(expr, "Time()", StringComparison.OrdinalIgnoreCase))
            {
                sqlExpression = "GETDATE()";
                return true;
            }

            if (TryTranslateAccessDateLiteral(expr, out sqlExpression))
            {
                return true;
            }

            if (string.Equals(expr, "False", StringComparison.OrdinalIgnoreCase) ||
                string.Equals(expr, "No", StringComparison.OrdinalIgnoreCase))
            {
                sqlExpression = "0";
                return true;
            }

            if (string.Equals(expr, "True", StringComparison.OrdinalIgnoreCase) ||
                string.Equals(expr, "Yes", StringComparison.OrdinalIgnoreCase))
            {
                sqlExpression = "1";
                return true;
            }

            if (expr == "\"\"" || expr == "''")
            {
                sqlExpression = "N''";
                return true;
            }

            if (IsQuotedString(expr, '"', out var doubleQuoted))
            {
                sqlExpression = "N'" + doubleQuoted.Replace("'", "''") + "'";
                return true;
            }

            if (IsQuotedString(expr, '\'', out var singleQuoted))
            {
                sqlExpression = "N'" + singleQuoted.Replace("'", "''") + "'";
                return true;
            }

            if (decimal.TryParse(expr, NumberStyles.Number, CultureInfo.InvariantCulture, out _))
            {
                sqlExpression = expr;
                return true;
            }

            return false;
        }

        private static bool TryTranslateAccessDateLiteral(string expr, out string sqlExpression)
        {
            sqlExpression = null;
            if (expr.Length < 3 || expr[0] != '#' || expr[expr.Length - 1] != '#')
            {
                return false;
            }

            var dateText = expr.Substring(1, expr.Length - 2);
            if (!DateTime.TryParse(dateText, CultureInfo.InvariantCulture, DateTimeStyles.None, out var parsed) &&
                !DateTime.TryParse(dateText, CultureInfo.CurrentCulture, DateTimeStyles.None, out parsed))
            {
                return false;
            }

            sqlExpression = "'" + parsed.ToString("yyyy-MM-dd HH:mm:ss.fff", CultureInfo.InvariantCulture) + "'";
            return true;
        }

        private static bool IsQuotedString(string expr, char quote, out string inner)
        {
            inner = null;
            if (expr.Length < 2 || expr[0] != quote || expr[expr.Length - 1] != quote)
            {
                return false;
            }

            inner = expr.Substring(1, expr.Length - 2);
            return true;
        }

        public static string BuildDefaultConstraintName(string tableName, string columnName)
        {
            var name = "DF_" +
                SqlServer.SqlIdentifierHelper.SanitizeConstraintName(tableName) + "_" +
                SqlServer.SqlIdentifierHelper.SanitizeConstraintName(columnName);
            return name.Length <= 128 ? name : name.Substring(0, 128);
        }
    }
}