function TCKN(number) {
    return {
        toString: function() {
            if(!this.isValid()) throw new Error('TCKN hatalı!');
            return this.no();
        },

        isValid: function() {
            var first9 = this.first9();
            var tenth = this.tenth(first9);
            var eleventh = this.eleventh(first9 + tenth);
            return this.no() == first9 + tenth + eleventh;
        },

        no: function() {
            if(number.toString().split('').length < 9) throw new Error('TCKN hatalı!');
            return number.toString();
        },

        first9: function() {
            return this.no().substring(0, 9);
        },

        tenth: function(first9) {
            var oddSum = parseInt(first9.charAt(0)) + parseInt(first9.charAt(2)) +
                    parseInt(first9.charAt(4)) + parseInt(first9.charAt(6)) + parseInt(first9.charAt(8));
            var evenSum = parseInt(first9.charAt(1)) + parseInt(first9.charAt(3)) +
                    parseInt(first9.charAt(5)) + parseInt(first9.charAt(7));
            return ((oddSum * 7 - evenSum) % 10).toString();
        },

        eleventh: function(first10) {
            var total = 0;
            for(var i = 0; i < first10.split('').length; i++)
                total += parseInt(first10.charAt(i));
            return (total % 10).toString();
        },

        first5: function() {
            return this.no().substring(0, 5);
        },

        last4: function() {
            return this.no().substring(5, 9);
        },

        next: function() {
            var first5 = (parseInt(this.first5()) - 6).toString();
            var last4 = (parseInt(this.last4()) + 2).toString();
            while(true) {
                if(last4.split('').length == 4) break;
                last4 = '0' + last4;
            }

            var first9 = first5 + last4;
            var tenth = this.tenth(first9);
            var eleventh = this.eleventh(first9 + tenth);
            return new TCKN(first9 + tenth + eleventh);
        },

        prev: function() {
            var first5 = (parseInt(this.first5()) + 6).toString();
            var last4 = (parseInt(this.last4()) - 2).toString();
            while(true) {
                if(last4.split('').length == 4) break;
                last4 = '0' + last4;
            }

            var first9 = first5 + last4;
            var tenth = this.tenth(first9);
            var eleventh = this.eleventh(first9 + tenth);
            return new TCKN(first9 + tenth + eleventh);
        }
    };
}