using System;
using System.Data;
using System.Collections.Generic;

public class CustomerComparer : IComparer<Customer>
{
    // Instance variables
    private string sortColumn;
    private bool reverse;

    public CustomerComparer(string sortExpression)
    {
        reverse = sortExpression.ToLowerInvariant().EndsWith(" desc");
        if (reverse)
        {
            sortColumn = sortExpression.Substring(0, sortExpression.Length - 5);
        }
        else
        {
            sortColumn = sortExpression;
        }
    }

    public int Compare(Customer a, Customer b)
    {
        int retVal = 0;
        switch (sortColumn)
        {
            case "CustomerId":
                if (a.CustomerId > b.CustomerId) retVal = 1;
                else if (a.CustomerId < b.CustomerId) retVal = -1;
                else retVal = 0;
                break;
            case "LastName":
                retVal = String.Compare(a.LastName, b.LastName, StringComparison.InvariantCultureIgnoreCase);
                break;
            case "FirstName":
                retVal = String.Compare(a.FirstName, b.FirstName, StringComparison.InvariantCultureIgnoreCase);
                break;
            case "CreditLimit":
                if (a.CreditLimit > b.CreditLimit) retVal = 1;
                else if (a.CreditLimit < b.CreditLimit) retVal = -1;
                else retVal = 0;
                break;
            case "PhoneNumber":
                retVal = String.Compare(a.PhoneNumber, b.PhoneNumber, StringComparison.InvariantCultureIgnoreCase);
                break;
        }
        return (retVal * (reverse ? -1 : 1));
    }
}