/*	Program written by Michael Hoshino and Howard Li
 *
 *	Assignment 1
 */

#include<stdlib.h>
#include<stdio.h>
#include<math.h>
#include<time.h>
#define DELTA 0.01
#define G 9.81
#define PI 3.14159265

double simulate (double, double, double, double);

int main (void)
{
	double d, v, angle_in_deg = 0, angle_in_rad;
	double x0, y0, vx0, vy0, distance_of_throw, precise_angle_1, precise_angle_2;
	char test_random, guess_again;

	/*
	 * Uses the system time as an argument for srand to set the seed used for randomly generated values
	 */
	srand(time(0));

	printf("Enter the letter 'y' if you would like to use random values>  ");
	scanf(" %c", &test_random);

	if (test_random == 'y')
	{
		d = 60 * (rand()*1.0)/RAND_MAX + 60;
		v = 20 * (rand()*1.0)/RAND_MAX + sqrt(d*G);
	}
	else
	{
		d = 100;
		v = sqrt(d*G) + 10;
	}

	/*
	 * Keeps asking user for angle of throw until the ball lands within 10 meters of home plate or until user quits
	 */
	do
	{
		printf("\nThe fielder is %5.1lf meters from home plate.\n", d);
		printf("He throws the ball at a speed of %5.2lfm/s (%6.2lfkm/hr).\n\n", v, (v*3.6));
		angle_in_deg = 0;
		while (angle_in_deg <= 0 || angle_in_deg >= 90)
		{
			printf("Please enter the angle of the throw, between 0 and 90 degrees, so that\n");
			printf("the ball lands at the home plate. > ");
			scanf("%lf", &angle_in_deg);
			
			if (angle_in_deg <= 0 || angle_in_deg >= 90)
			{
				printf("\nThe angle of the throw MUST be between 0 and 90 degrees, NOT including 0 and 90.\n");
			}
		}
		angle_in_rad = (PI * angle_in_deg)/180.0;

		x0 = d * -1;
		y0 = 0.0;
		vx0 = v * cos(angle_in_rad);
		vy0 = v * sin(angle_in_rad);
		
		distance_of_throw = simulate (x0, y0, vx0, vy0);
		
		if (distance_of_throw > 10)
		{	
			printf("\n\nThe ball flew long by %6.1lf meters.", distance_of_throw);
			printf("\n\nEnter the letter 'y' if you would like to guess again. > ");
			scanf(" %c", &guess_again);
		}	
		else
			if (distance_of_throw < -10)
			{
				printf("\n\nThe ball landed short by %6.1lf meters.", distance_of_throw * -1.0);
				printf("\n\nEnter the letter 'y' if you would like to guess again. > ");
				scanf(" %c", &guess_again);
			}
			else
			{
				printf("\n\nCongratulations! You picked a great angle!\n");
			}
	}
	while(guess_again == 'y');

/*
 *Calculates the precise angles such that the ball lands directly on the home plate
 */
	precise_angle_1 = 0.5 * (180.0/PI) * asin((d*G)/pow(v, 2));
	precise_angle_2 = 90.0 - precise_angle_1;
	printf("\nThe calculated angles are %5.2lf degrees and %5.2lf degrees.\n", precise_angle_1, precise_angle_2);

}

/*
 * The "simulate" method calculates the distance and height of the ball every DELTA seconds
 */
double simulate (double x0, double y0, double vx0, double vy0)
{
	double x = x0, y = y0, vy = vy0, t = 0, xlast, ylast, tlast;
	while(y >= 0)
	{
		if ((int)(t * 100) % 100 == 0)
			printf("\nt = %-5.2lf x = %-7.1lf y = %-5.2lf", t, x, y);
		xlast = x;
		ylast = y;
		tlast = t;
		t += DELTA;
		vy -= G * DELTA;
		x += vx0 * DELTA;
		y += vy * DELTA;
	}
		printf("\nt = %-5.2lf x = %-7.1lf y = %-5.2lf", tlast, xlast, ylast);
	return xlast;
}