/* Programmer: Dylan McDonald
   Class & Section: CS 54, Section <n>
   Date: 18 September 2007
   Purpose: To simulate a broken elevator and what happens to it */

#include <cstdlib>
#include <ctime>
#include <iostream>
using namespace std;

int main()
{
  /* well known constants (some better known than others) */
  const double GRAVITY = 9.80665;
  const double ELEV_IMPULSE = (GRAVITY + 2.0) * 11.5931;
  const double TIME_STEP = .1;
  const double ROOM_HEIGHT = 42 * 3.2;
  const double DRAG_CONSTANT = 7.008;

  /* program variables */
  int randomFall;
  bool fallen = false;
  double impulse = 0, mass, probability;
  double acceleration, fallTime = 0.0;
  double currVelocity, currDisplacement = 0.0;
  double prevVelocity = 0.0, prevDisplacement = 0.0;
  unsigned short i;

  /* run the elevator */
  for (i = 0; i < 4; i++)
  {
    /* add the impulse from each ride */
    do
    {
      cout << "Mass of elevator & passengers: ";
      cin >> mass;
    } while (mass < 100.0 || mass > 1000.0);
    impulse += ELEV_IMPULSE * mass;
  }
  cout << "The elevator has withstood " << impulse
       << " N * s of impulse." << endl;

  /* setup the probability */
  srand(time(NULL));
  randomFall = (rand() % static_cast<int>(impulse)) + 1;
  probability = impulse / (impulse + randomFall);
  
  /* now see if it fell */
  cout << "There is a " << (probability * 100.0)
       << "% chance the cable is broken!" << endl;
  probability *= 1000.0;
  randomFall = rand() % 1000;
  if (randomFall < probability)
  {
    fallen = true;
    cout << "All aboard the injury express! The cable broke!" << endl;
  }

  /* now watch it fall - wheeee! */
  while (fallen && currDisplacement < ROOM_HEIGHT)
  {
    /* calculate our current three */
    acceleration = ((mass * GRAVITY)
                 - (DRAG_CONSTANT * prevVelocity * prevVelocity)) / mass;
    currVelocity = prevVelocity + acceleration * TIME_STEP;
    currDisplacement = prevDisplacement + currVelocity * TIME_STEP;

    /* save them as our previous three & advance time */
    prevVelocity = currVelocity;
    prevDisplacement = currDisplacement;
    fallTime += TIME_STEP;
  }

  /* what happened? */
  if (fallen)
    cout << "The impact velocity of the elevator and peoples was "
         << currVelocity << " m / s and took " << fallTime
         << " s to fall." << endl;

  return 0;
}