// CalculatorCL.cpp
//
// Illustrates use of numerical command-line arguments.
//
#include <iostream>
#include <iomanip>
#include <string>

using namespace std;

enum ArgStatus {BadOperand1, BadOperator, BadOperand2, AllOK};

void      InvocationError();
void      ArgumentsError(ArgStatus clStatus);
ArgStatus CheckCLArguments(char* argv[]);
int       Calc(int Operand1, char Operator, int Operand2);
void      PrintExpression(int Operand1, char Operator, int Operand2, int Result);

void main(int argc, char* argv[]) {

   // Check for correct number of command-line arguments:
   // (Remember the program name counts as one.)
   if (argc != 4) {
      InvocationError();
      return;
   }

   // Check whether command-line arguments are of correct types:
   ArgStatus clStatus = CheckCLArguments(argv);

   if ( clStatus != AllOK) {
      ArgumentsError(clStatus);
      return;
   }

   // convert command-line arguments to proper types:
   // (atoi converts ascii string to an integer)
   int  Operand1 = atoi(argv[1]);
   char Operator = argv[2][0];
   int  Operand2 = atoi(argv[3]);

   int  Result = Calc(Operand1, Operator, Operand2);

   PrintExpression(Operand1, Operator, Operand2, Result);
}

ArgStatus CheckCLArguments(char* argv[]) {

   bool OperandOK  = true,
        OperatorOK = true;

   OperatorOK = (argv[2][1] == '\0') &&    // check operator length
                ( (argv[2][0] == '+') ||   // check operator symbol
                  (argv[2][0] == '-') ||
                  (argv[2][0] == '*') ||
                  (argv[2][0] == '/') );

   if (!OperatorOK) return BadOperator;

   // Check if first operand is a string of digits:
   for (int Idx = 0; argv[1][Idx] != '\0'; Idx++) {
      //cout << Idx << "  " << argv[1][Idx] << endl;
      if ( !isdigit(argv[1][Idx]) ) {
         OperandOK = false;
         break;
      }
   }

   if (!OperandOK)  return BadOperand1;

   // Check if second operand is a string of digits:
   for (Idx = 0; argv[3][Idx] != '\0'; Idx++) {
      //cout << Idx << "  " << argv[3][Idx] << endl;
      if ( !isdigit(argv[3][Idx]) ) {
         OperandOK = false;
         break;
      }
   }

   if (!OperandOK)  return BadOperand2;

   // No errors detected if we get this far:
   return (AllOK);
}

int Calc(int Operand1, char Operator, int Operand2) {

   switch (Operator) {
   case '+': return (Operand1 + Operand2);
   case '-': return (Operand1 - Operand2);
   case '*': return (Operand1 * Operand2);
   case '/': if (Operand2 == 0)
                return 0;
             else
                return (Operand1 / Operand2);
   default:  return 0;
   }
}

void PrintExpression(int Operand1, char Operator, int Operand2, int Result) {

   cout << Operand1 << ' ' 
        << Operator << ' ' 
        << Operand2 << " = "
        << Result << endl;
}

void InvocationError() {

   string Invocation = "Invocation:  CalculatorCS <integer> <operator> <integer>\n"
                       "where\n"
                       "      <integer> must be an integer value\n"
                       "      <operator> must be one of: '+', '-', '*' or '/'\n\n"
                       "and the expression must be well-formed.\n";

   cout << Invocation;
}

void ArgumentsError(ArgStatus clStatus) {

   string BadOp1Msg      = "The first operand is not an integer.\n"
                           "Please correct the problem.\n\n";
   string BadOp2Msg      = "The second operand is not an integer.\n"
                           "Please correct the problem.\n\n";
   string BadOperatorMsg = "The operand is not + or - or * or /.\n"
                           "Please correct the problem.\n\n";
   string AllOKMsg       = "The command-line arguments are all proper.\n"
                           "Please correct the problem.\n\n";
   string BadStatusMsg   = "Unrecognized command-line status.\n"
                           "Please notify program vendor.\n\n";

   switch (clStatus) {
   case BadOperand1:  cout << BadOp1Msg;
                      break;
   case BadOperand2:  cout << BadOp2Msg;
                      break;
   case BadOperator:  cout << BadOperatorMsg;
                      break;
   case AllOK:        cout << AllOKMsg;
                      break;
   default:           cout << BadStatusMsg;
   }
}