#include "stdstuff.h"
#include "GasTank.h"

// constructs a GasTank object (for a car) that gets 400km on a tank of gas, with the tank currently empty
GasTank::GasTank() {
   kmPerTank = 400;
   kmAvail = 0; // tank is empty 
}

// constructs a GasTank object (for a car) that gets the given number of km on a tank of gas, with the tank currently
// empty.  .
// Throws invalid_argument exception if argument is less than or equal to 0.
GasTank::GasTank(int numKms) {
   if (numKms <= 0) { // **must** set fields to get full marks!!
      kmPerTank = 400;
      kmAvail = 0; // tank is empty 
          // I used the default -- doesn't really matter as long as they are set to something
      throw invalid_argument("GasTank::GasTank -- numKms must be greater than 0.");
   }
   kmPerTank = numKms;
   kmAvail = 0; // tank is empty
}

// the GasTank object has its gas tank filled
void GasTank::fill() {
   kmAvail = kmPerTank; // tank is now full
}

// the GasTank object drives the given number of kms.  If unsuccessful (not enough gas), this method has no effect.
// Throws invalid_argument exception if argument is less than 0.
void GasTank::drive(int numKms) {
   if (numKms < 0) 
      throw invalid_argument("GasTank::drive -- numKms must be greater than or equal to 0.");
   if (numKms > kmAvail)
      return; // do nothing, as there's not enough gas for that drive
   // otherwise subtract the number of kilometers driven from the number available
   kmAvail -= numKms; 
}

// returns the number of kilometers that this GasTank object can drive before running out of gas.
// (Does not change the state of the GasTank.) 
int GasTank::kmLeft() const {
   return kmAvail;
}

// prints the percent level of the GasTank object, i.e. 100 = full, 0 = empty, etc.
// (Does not change the state of the GasTank.)
void GasTank::printLevel() const {
   cout << 100.0* kmAvail / kmPerTank;
}