// File: rocket.cxx
// This program simulates a falling object with a rocket.
#include <algorithm>
#include <iostream>
#include <graphics.h>
using namespace std;

// Physics constants
const double LATERAL_PROP = .5;                               // Proportion
const double GRAVITY = -9.8;                                  // m/s^2
const double LANDER_WEIGHT = 1000;                            // kg 
const double MAX_FUEL = 0.25*LANDER_WEIGHT;                   // kg
const double THRUST_Y = -2*GRAVITY*(LANDER_WEIGHT + MAX_FUEL);// kg m/s^2
const double THRUST_X = THRUST_Y * LATERAL_PROP;              // kg m/s^2
const double MAX_X = 500;                                     // m
const double MAX_Y = 1000;                                    // m     
const double INITIAL_SPEED_X = 0;                             // m/s
const double INITIAL_SPEED_Y = 0;                             // m/s
const double BURN_RATE_Y = MAX_FUEL / 30;                     // kg/s
const double BURN_RATE_X = BURN_RATE_Y * LATERAL_PROP;        // kg/s
const double MAX_LANDING_SPEED = 9.0;                         // m/s
const int TIME_SLICE_MS = 100;                                // ms
const double TIME_SLICE_S = TIME_SLICE_MS/1000.0;             // s

// Graphical constants
const int WINDOW_SIZE_X = 851;        
const int WINDOW_SIZE_Y = 608;
const int GROUND_ZERO_Y = 566;
const int ROCKET_SIZE_X = 86;
const int ROCKET_SIZE_Y = 113;
const int BACKGROUND_BYTES = 2069656; // From the imagesize bgi function
const int ROCKET_BYTES = 38896;       // From the imagesize bgi function

// These functions shows the current state of the lander.
void display_background( );
void display_rocket(
    double x, double y,                                // Position
    bool main_thruster,                                // Thrusters on?
    bool left_thruster,
    bool right_thruster
    );
void display(
    int time,                                          // Simulation time
    double x, double y,                                // Position
    double vx, double vy,                              // Velocity
    double fuel,                                       // Remaining fuel
    bool main_thruster,                                // Thrusters on?
    bool left_thruster,
    bool right_thruster 
    );

// The return value of fuel_use is the amount of fuel that a rocket
// uses during one time slice
double fuel_use(bool is_on, double burn_rate, double fuel);

// The return value of rocket_acceleration is the acceleration
// in m/(sec^2) of a particular rocket.
double rocket_acceleration(bool is_on, double force, double mass);

// This function checks to see whether the user has done anything
// to change the state of the thrusters (on or off).
void interact(bool& main_thruster, bool& left_thruster, bool& right_thruster);

// This function lets you turn the thrusters on or off with mouse clicks.
// But the middle mouse click doesn't work on my machine.
void deal_with_mouse(bool& thruster, int turn_on, int turn_off);

int main( )
{
    // State variables
    bool main_thruster = false;           // Main thruster
    bool left_thruster = false;           // Left thruster
    bool right_thruster = false;          // Right thruster
    double remaining_fuel = MAX_FUEL;     // Remaining fuel
    double mass;                          // Mass of lander + fuel
    double x = 0;                         // X position
    double y = MAX_Y;                     // Y position
    double x_velocity = INITIAL_SPEED_X;  // Lander's X velocity
    double y_velocity = INITIAL_SPEED_Y;  // Lander's Y velocity
    double x_acc = 0;                     // Lander's X acceleration
    double y_acc = 0;                     // Lander's X acceleration
    int current_time = 0;                 // Current time (ms) 

    initwindow(WINDOW_SIZE_X, WINDOW_SIZE_Y, "Crash the Ship!", 0, 0, true);
    bgiout.precision(1);
    bgiout.setf(ios::fixed, ios::floatfield);

    while (y > 0)
    {
	// 1. Modify state variables based on user input:
	interact(main_thruster, left_thruster, right_thruster);

	// 2. Modify state variables based on time passing:
        remaining_fuel -= fuel_use(main_thruster, BURN_RATE_Y, remaining_fuel); 	
        remaining_fuel -= fuel_use(left_thruster, BURN_RATE_X, remaining_fuel); 	
        remaining_fuel -= fuel_use(right_thruster, BURN_RATE_X, remaining_fuel); 	
	mass = LANDER_WEIGHT + remaining_fuel; 

	x_acc = rocket_acceleration(left_thruster, THRUST_X, mass)
              - rocket_acceleration(right_thruster, THRUST_X, mass);
	y_acc = GRAVITY
	      + rocket_acceleration(main_thruster, THRUST_Y, mass);
        x += x_velocity * TIME_SLICE_S
	   + 0.5 * x_acc * TIME_SLICE_S * TIME_SLICE_S;
        y += y_velocity * TIME_SLICE_S
	   + 0.5 * y_acc * TIME_SLICE_S * TIME_SLICE_S;
	x_velocity += x_acc * TIME_SLICE_S;
	y_velocity += y_acc * TIME_SLICE_S;

	current_time += TIME_SLICE_MS;
	
        // 3. Display the current state:
	clearviewport( );
	display(
	    current_time,
	    x, y, x_velocity, y_velocity,
	    remaining_fuel,
	    main_thruster, left_thruster, right_thruster
	    );
	swapbuffers( );
	
	// 4. Delay for the required time:
	delay(TIME_SLICE_MS);
    }

    while (toupper(getch( )) != 'Q')
	delay (TIME_SLICE_MS);
    
    return 0;
}

void display(
    int time,                                          // Simulation time
    double x, double y,                                // Position
    double vx, double vy,                              // Velocity
    double fuel,                                       // Remaining fuel
    bool main_thruster,                                // Thrusters on?
    bool left_thruster,
    bool right_thruster 
    )
{
    display_background( );
    display_rocket(x, y, main_thruster, left_thruster, right_thruster);
    bgiout << "Lander information: \n"
	 << "Time: " << time << "ms\n"
	 << "Position (x: " << x << "m, y: " << y << "m)\n"
	 << "Velocity (x: " << vx << "m/s, y: " << vy << "m/s)\n"
	 << "Remaining fuel: " << fuel << "kg\n"
	 << "Thrusters: ("
	 << "main:" << main_thruster
	 << ", left:" << left_thruster
	 << ", right:" << right_thruster << ")\n"
	   << endl;
    outstreamxy(10, 10);
}

void display_background( )
{
    static bool first = true; // True if this is the first drawing
    static void* buffer;      // Variable sized location for the image

    if (first)
    {
	buffer = malloc(BACKGROUND_BYTES);
	readimagefile("bg.bmp",0, 0, WINDOW_SIZE_X-1, WINDOW_SIZE_Y-1);
	getimage(0, 0, WINDOW_SIZE_X-1, WINDOW_SIZE_Y-1, buffer);
	first = false;
    }
    else
    {
	putimage(0, 0, buffer, COPY_PUT);
    }
}

void display_rocket(
    double x, double y,                                // Position
    bool main_thruster,                                // Thrusters on?
    bool left_thruster,
    bool right_thruster
    )
{
    static bool first = true; // True if this is the first drawing
    static void* buffer[8];   // Variable sized location for the image
    int pixel_x, pixel_y;     // Location to draw the rocket
    int index;                // Loop control variable
    char filename[12] = "rocket?.bmp";
    
    pixel_x = int(x*WINDOW_SIZE_X/(2*MAX_X) + WINDOW_SIZE_X/2.0);
    pixel_y = int(-y*GROUND_ZERO_Y/MAX_Y + GROUND_ZERO_Y);

    if (first)
    {
	for (index = 0; index < 8; ++index)
	{
	    buffer[index] = malloc(ROCKET_BYTES);
	    filename[6] = '0' + index;
	    readimagefile(filename ,0, 0, ROCKET_SIZE_X-1, ROCKET_SIZE_Y-1);
	    getimage(0, 0, ROCKET_SIZE_X-1, ROCKET_SIZE_Y-1, buffer[index]);
	}
	first = false;
	clearviewport( );
    }

    // Figure out which of the 8 images to use...
    index = 4*main_thruster + 2*left_thruster + 1*right_thruster;
    putimage(pixel_x-ROCKET_SIZE_X/2, pixel_y-ROCKET_SIZE_Y/2, buffer[index], OR_PUT);
}

double fuel_use(bool is_on, double burn_rate, double fuel)
{
    if (is_on)
	return min(burn_rate * TIME_SLICE_S, fuel);
    else
	return 0;
}

double rocket_acceleration(bool is_on, double force, double mass)
{
    if (is_on)
	return force / mass;
    else
	return 0;
}


void interact
(bool& main_thruster, bool& left_thruster, bool& right_thruster)
{
    if (kbhit( ))
    {
	switch (getch( ))
	{
	case KEY_UP:
	    main_thruster = !main_thruster;
	    break;
	case KEY_LEFT:
	    right_thruster = !right_thruster;
	    break;
	case KEY_RIGHT:
	    left_thruster = !left_thruster;
	    break;
	}
    }
    deal_with_mouse(main_thruster, WM_MBUTTONDOWN, WM_MBUTTONUP);
    deal_with_mouse(right_thruster, WM_LBUTTONDOWN, WM_LBUTTONUP);
    deal_with_mouse(left_thruster, WM_RBUTTONDOWN, WM_RBUTTONUP);
}

void deal_with_mouse(bool& thruster, int turn_on, int turn_off)
{
    if (ismouseclick(turn_on))
    {
	thruster = true;
	clearmouseclick(turn_on);
    }
    if (ismouseclick(turn_off))
    {
	thruster = false;
	clearmouseclick(turn_off);
    }
}