CdkShoppingCart.java

package co.in.shoonya.abc.kata;

public class CdkShoppingCart {

    public static void main(String[] args) {
        System.out.println(billAmount(CustomerType.Regular, 15000d));
        System.out.println(billAmount(CustomerType.Premium, 20000d));
    }

    private static double billAmount(CustomerType type, double input) {
        double diff = 0d;
        double disc = 0d;
        double curr = input;
        for (CustomerType.Range range : type.ranges) {
            diff = input >= range.end ? range.end - range.start : curr;
            disc += range.discount == 0d ? 0d : diff * range.discount / 100d;
            curr = curr - diff;
        }
        return input - disc;
    }


    public enum CustomerType {

        Regular(new Range(0, 5000d, 0d),
                new Range(5000d, 10000d, 10d),
                new Range(10000d, Double.MAX_VALUE, 20d)),
        Premium(new Range(0, 4000d, 10d),
                new Range(4000d, 8000d, 15d),
                new Range(8000d, 12000d, 20d),
                new Range(12000d, Double.MAX_VALUE, 30d));

        Range[] ranges;

        CustomerType(Range... ranges) {
            this.ranges = ranges;
        }

        private static class Range {
            double start;
            double end;
            double discount;

            Range(double start, double end, double discount) {
                this.start = start;
                this.end = end;
                this.discount = discount;
            }
        }


    }
}