#include <iostream>
#include <math.h>

int main()
{
	using namespace std;
	
	short reset=1;
	
	while (reset != 0)
	{
		double u=0, v=0, f, m, M, s=0, c=300000000, a=0, t, r=0, t0=0;
		double s0, custDest;
		short dest=10;
		
		cout << "Realistic physics space travel simulation\n";
		cout << "Starting from Earth, where are you going?\n1 = Moon\n2 = Sun\n3 = Pluto\n4 = Proxima Centauri\n5 = Sirius\n";
		cout << "6 = Custom distance in metres\n7 = Custom distance in light seconds\n8 = Custom distance in light years\n";
		while (dest < 1 || dest > 8)
		{
			cin >> dest;
			if (dest == 1)
			{s0 = (384403000 / 2);}
			else if (dest == 2)
			{s0 = (149600000000 / 2);}
			else if (dest == 3)
			{s0 = (5913520000000 / 2);}
			else if (dest == 4)
			{s0 = 18900000000000000;}
			else if (dest == 5)
			{s0 = (81360000000000000 / 2);}
			else if (dest == 6)
			{
				cout << "\nEnter distance in metres:\n";
				cin >> custDest;
				s0 = (custDest / 2);
			}
			else if (dest == 7)
			{
				cout << "\nEnter distance in light seconds:\n";
				cin >> custDest;
				s0 = ( (custDest * 300000000) / 2);
			}
			else if (dest == 8)
			{
				cout << "\nEnter distance in light years:\n";
				cin >> custDest;
				s0 = ( (custDest * 9460000000000000) / 2);
			}
			else
			{cout << "\nInvalid selection, please retry:\n";}
			
		}
		cout << "\nHow heavy is your ship in kg (100000kg is a good starting point)?\n";
		cin >> m;
		cout << "\nAnd what force do your engines produce in N (1000000N is a good starting point)?\n";
		cin >> f;
		cout << "\nAnd every how many seconds should I recalculate (1 is best for the greatest accuracy)?\n";
		cin >> t;
		while (t <= 0)
		{
			cout << "\nRecalculation time must be nonzero and positive, please retry\n";
			cin >> t;
		}
		cout << "\nBeginning simulation...\n";
		
		while (s < s0)
		{
			if (u <= c)
			{
				M = ( m * ( c / ( sqrt( ( c * c ) - ( v * v ) ) ) ) );
				a = ( f / M );
				v = ( u + a * t );
			}
			else
			{
				a = 0;
				u = c;
				v = u;
			}		
			s = s + ( u * t + ( 0.5 * a * ( t * t ) ) );
			u = v;
			t0 = t0 + t;
			r = r + t;
			if (r == 86400)
			{
				r = 0;
				cout << "day " << (t0 / 86400) << " | " << ((s * 100) / s0) << "% | " << (v / c) << "c\n";
			}
			else if (r > 86400)
			{
				r = 0;
				cout << "second " << t0 << " | " << ((s * 100) / s0) << "% | " << (v / c) << "c\n";
			}
			
			
		}
		
		cout << "Halfway point reached in "<< t0 << " seconds or " << (t0 / 86400) << " days or " << (t0 / 31557600) << " years\n";
		cout << "Maximum velocity " << v << " ms^-1 or " << v/c << "c\n";
		cout << "Arrival at destination: " << (t0 * 2) << " seconds or " << (t0 / 43200) << " days or " << (t0 / 15778800) << " years after departing Earth\n";
		cout << "End of simulation\n";
		cout << "Enter 1 to start over or 0 to quit\n";
		cin >> reset;
		cout << "\n\n";
	}
	return 0;
}