// FILE: CompuTax.cpp
// DRIVER PROGRAM FOR FUNCTION COMPUTE_TAX

#include <iostream.h>
#include "money.h"

// Functions used ...
// COMPUTES TAX OWED ON ADJUSTED GROSS INCOME
money compute_tax
   (money);	// IN: adjusted gross income

int main ()
{
   // Local data ...
   const money sentinel = -1.0;
   money my_income;	// input: adjusted gross income (taxable)
   money my_tax;		// output: computed tax amount

   // Test compute_tax function -- all possible paths.
   cout << "Driver program for function compute_tax." << endl;
   cout << "Enter income greater than zero (or " << sentinel
        << " to stop test): ";
   cin >> my_income;
   while (my_income != sentinel)
   {
      my_tax = compute_tax (my_income);
      if (my_tax >= 0.0)
      {
         cout << "The tax on " << my_income;
         cout << " is " << my_tax << endl;
      }  // end if
      else
      {
         cout << "Income " << my_income << " was negative. ";
         cout << "Try another value." << endl;
      }  // end else
      cout << endl << endl;
      cout << "Enter income greater than zero (or " << sentinel
           << " to stop test): ";
      cin >> my_income;
   }  // end while

   cout << "A " << sentinel << " was entered.  "
        << "Test execution terminated." << endl;

   return 0;
}

// COMPUTES TAX OWED ON ADJUSTED GROSS INCOME
money compute_tax
  (money adj_income)	// IN: adjusted gross income
// Pre:  adj_income must be assigned a nonnegative value.
// Post: Tax amount computed based on tax category.
// Returns: Tax owed if adj_income is nonnegative; otherwise -1.0.
{
   // Local data ...
   const money cat1_max = 34000.00;
   const money cat2_max = 82150.00;
   const double cat1_rate = 0.15;
   const double cat2_rate = 0.28;
   const double cat3_rate = 0.31;
   const money min_valid_amount = 0.0;
   const money invalid_input = -1.0;

   money tax_amount;     // computed tax amount to be returned

   // Compute and return tax.
   if (adj_income < min_valid_amount)
      return invalid_input;               // return for invalid input
   else if (adj_income > cat2_max)
      tax_amount = cat1_rate * cat1_max
         + cat2_rate * (cat2_max - cat1_max)
         + cat3_rate * (adj_income - cat2_max);
   else if (adj_income > cat1_max)
      tax_amount = cat1_rate * cat1_max
         + cat2_rate * (adj_income - cat1_max);
   else
      tax_amount = cat1_rate * adj_income;

   return tax_amount;
}  // end compute_tax