/*-------------------------------------------------------------------------
  A modification of the program in Fig. C.7 for computing wages for 
  several employees.  Permanent employee information is read from a file.

  Input (file):     Id-number, number of dependents, and hourly rate 
                      for each of several employees
  Input (keyboard): Hours worked by employees
  Output (screen):  Prompts to user, including id-numbers.
  Output (file):    Id-numbers, hours worked, gross pay, taxes withheld
                      and net pay
--------------------------------------------------------------------------*/

#include <iostream>
#include <fstream>
#include <iomanip>
#include <string>
#include <cassert>
using namespace std;

void instruct();
void getEmployeeInfo(ifstream & in, int & empNumber, int & dependents,
                     double & hours, double & rate, bool & done);
double grossWages(int dependents, double hours, double rate);
void computeNetPay(double grossPay, int dependents,
                   double & tax, double & netPay);
void printEmpInfo(ofstream & out, int idNumber, double hours, 
                  double grossPay, double taxes, double netPay);
int main()
{
  string inFilename,
         outFilename;
  cout << "Enter names of input and output files: ";
  cin >> inFilename >> outFilename;
  ifstream inStream(inFilename.data());
  assert( inStream.is_open() );
  ofstream outStream(outFilename.data());
  assert( outStream.is_open() );
  int idNumber,              // employee's id-number
       numDependents;        //   number of dependents
  double hoursWorked,        //   hours worked for this pay period
         hourlyRate,         //   dollars per hour
         grossPay,           //   gross pay (before taxes)
         taxWithheld,        //   amount of tax withheld
         netPay;             //   grossPay - taxWithheld
  bool endOfData;            // signals end of data
  instruct();
  for (;;)
  {
    getEmployeeInfo(inStream, idNumber, numDependents,
                    hoursWorked, hourlyRate, endOfData);
    if (endOfData) break;
    grossPay = grossWages(numDependents, hoursWorked, hourlyRate);
    computeNetPay(grossPay, numDependents, taxWithheld, netPay);
    printEmpInfo(outStream, idNumber, hoursWorked, grossPay,
                 taxWithheld, netPay);
  }
}

void instruct()
/*-------------------------------------------------------------------------
  Display instructions to the user.

  Output: Instructions
 -------------------------------------------------------------------------*/
{
  cout <<
       "This program computes gross pay, tax withheld, and net pay for "
       "employees.\n\tWhen prompted, enter hours worked and hourly rate"
       "\n\t(separated by spaces) for the indicated employee.\n\n";
}

void getEmployeeInfo(ifstream & in, int & empNumber, int & dependents,
                     double & hours, double & rate, bool & done)
/*-------------------------------------------------------------------------
  Get employee information and/or signal there is no more.

  Receive:          ifstream
  Input (file):     Id-number, number of dependents, and hourly rate
  Input (keyboard): Hours worked by employee
  Output (screen):  Prompts to user, including id-number
  Pass back:        Modified ifstream, the four input values, done is
                      true if end of data was signaled, false otherwise
 -------------------------------------------------------------------------*/
{
  in >> empNumber;                      // get employee number from file
  done = in.eof();
  if (done) return;                     // if end of file, return
                                        // else
  in >> dependents >> rate;             // get other info from file
  cout << "Enter hours worked by " << empNumber << ": ";
  cin >> hours;                         // get hours worked from user
}

double grossWages(int dependents, double hours, double rate)
/*-------------------------------------------------------------------------
  Compute gross wages as determined by number of hours employee worked 
  plus a dependency allowance for each dependent.

  Receive:  Number of dependents, hours worked, hourly rate
  Return:   Gross wages
 -------------------------------------------------------------------------*/
{
  const double DEP_ALLOWANCE = 100; // bonus per dependent
  double wages;                     // wages earned
  if (hours <= 40)                  // no overtime
    wages = hours * rate;
  else                              // overtime
    wages = 40 * rate + 1.5 * rate * (hours - 40);

                                   // return wages + allowance for deps
  return wages + DEP_ALLOWANCE * dependents;
}

void computeNetPay(double grossPay, int dependents,
                   double & tax, double & netPay)
/*-------------------------------------------------------------------------
  Compute taxes withheld and net pay as gross pay minus taxes withheld.

  Receive:  Gross pay and number of dependents
  Return:   Taxes withheld and net pay (via parameters)
 -------------------------------------------------------------------------*/
{
  const double
    DEDUCTION = 25.00,        // deduction per dependent
    TAX_RATE = 0.12;          // withholding rate
  tax = TAX_RATE * (grossPay - DEDUCTION * dependents);
  if (tax < 0)                // check if any tax to be withheld
    tax = 0;

  netPay = grossPay - tax;    // compute net pay
}

void printEmpInfo(ofstream & out, int idNumber, double hours,
                  double grossPay, double taxes, double netPay)
/*-------------------------------------------------------------------------
  Write employee information to a file.

  Receive:    ofstream, employee's id number, hours worked, gross pay,
              taxes withheld, and net pay
  Pass back:  the modified ofstream
 -------------------------------------------------------------------------*/
{
  out << setprecision(2) << setiosflags(ios::showpoint | ios::fixed)
      << "Employee " << idNumber << ":\n"
      << "\tHours worked:    " << setw(6) << hours << endl
      << "\tGross Pay:      $" << setw(6) << grossPay << endl
      << "\tTaxes withheld: $" << setw(6) << taxes << endl
      << "\tNet Pay:        $" << setw(6) << netPay << endl;
}