#include<stdio.h>
#include<stdlib.h>
#include<time.h>
#include<unistd.h>
#include<termios.h>
/*
 *macro for random number from 0, up to but not including x, however this does
 *not guarantee absolute equal distribution as RAND_MAX % x isn't guaranteed to
 *be x-1, so all values up to and including RAND_MAX %x will have a slight
 *advantage
 */
#define r(x) (rand() % x)
/*
 * Stores the state of the game
 */
unsigned int field[4][4] = {0};
//if victory is 1, then 2048 has been found, if -1, then we ran out of space
int victory = 0;
//loop var
int loop = 1;
/*
 * Adds another value randomly to board, if this can not be done declare lose
 * condition. It also looks for 2048 and handles the win condition
 */
void addlose() {
	// Number of empty spaces left, it this is 0 then this function will
	// handle the lose condition/ death screen
	int empty = 0;
	//loops through and counts empty spaces
	for (int i = 0; i <4 ; i++) {
		for (int j =0; j < 4; j++) {
			if (field[i][j] == 0) {
				empty++;
			}
			//victory detected
			if (field[i][j] == 2048) {
				loop = 0;
				victory = 1;
				return;
			}
		}
	}
	//no empty spaces left, lose
	if (empty == 0) {
		loop = 0;
		victory = -1;
		return;
	}
	int  addfield  = r(empty);
	int k = 0;
	for (int i = 0; i < 4; i++) {
		for (int j = 0; j < 4; j++) {
			//the kth empty field has been found
			if (field[i][j] == 0) {
				if ( k == addfield) {
					field[i][j] = 2;
				}
				k++;
			}
		}
	}
}
/*
 * Shifts the values in field according to dx and dy, handles all logic even for
 * the case where there is no shift. Returns 1 if it has shifted, return 0 if
 * not.
 */
int shift (int dx, int dy) {
	//if there is no shift, return
	if (dx == 0 && dy == 0) {
		return 0;
	}
	int shift = 0;
	//initial and final x and y values
	int xi, xf, yi, yf = 0;
	//increment values, default to going low to high
	int di, dj = 1;
	/*
	 * We want it to go from highest x to lowest x if dx is positive, and
	 * the opposite if it's negative, likewise for y values
	 */
	if (dx > 0) {
		di = -1;
		xi = 3;
		xf = -1;
	} else {
		di = 1;
		xi = 0;
		xf = 4;
	}
	if (dy > 0) {
		dj = -1;
		yi = 3;
		yf = -1;
	} else {
		dj = 1;
		yi = 0;
		yf = 4;
	}
	//loops through and does all the shifting
	for (int i = xi; i != xf; i += di) {
		for (int j = yi; j != yf; j += dj) {
			//finds prime field to compare to
			int xp = i + dx;
			int yp = j + dy;
			//checks that there's an actual shift and that it's in
			//bounds
			if (xp == i && yp == j) {
				//don't do anything
			} else if (xp < 0 || xp > 3 || yp < 0 || yp > 3) {
				//don't do anythign either
			} else {
				//it shifts and it's in bound
				//check to see if you should merge
				if (field[xp][yp] == 0 || 
					field[xp][yp] == field[i][j]) {
					//make shift not 0 if that wasn't a zero
					//being shifted
					if (field[i][j] != 0) {
						shift = 1;
					}
					//add the current field to the
					//transformed field, then set current
					//field to 0 so somebody else can move
					//in.
					field[xp][yp] += field[i][j];
					field[i][j] = 0;
				}
			}

		}
	}
	return shift;
}
int main (int argc, char * argv[]) {
	//seeding RNG with time
	srand(time(NULL));
	//initializes the game board
	field[r(4)][r(4)] = 2;
	//sets raw tty mode
	struct termios term;
	tcgetattr(STDIN_FILENO, &term);
	struct termios old_term = term;
	cfmakeraw(&term);
	tcsetattr(STDIN_FILENO, TCSANOW, &term);
	while (loop) {
		//clears the screen
		printf("\033[2J");
		//homes the cursor
		printf("\033[H");
		//displays the field
		for (int i =0; i < 4; i ++) {
			for (int j = 0; j < 4; j++) {
				//adds color
				switch (field[j][i]) {
					case 0:
						printf("\033[31m");
					break;
					case 2:
						printf("\033[32m");
					break;
					case 4:
						printf("\033[33m");
					break;
					case 8:
						printf("\033[34m");
					break;
					case 16:
						printf("\033[35m");
					break;
					case 32:
						printf("\033[36m");
					break;
					case 64:
						printf("\033[1;31m");
					break;
					case 128:
						printf("\033[1;32m");
					break;
					case 256:
						printf("\033[30m\033[41m");
					break;
					case 512:
						printf("\033[30m\033[42m");
					break;
					case 1024:
						printf("\033[30m\033[43m");
					break;
					case 2048:
						printf("\033[30m\033[44m");
					break;
				}
				printf("%.3X\033[0;39m\033[49m ",field[j][i]);
			}
			printf("\r\n\n");
		}
		//Determines the direction that blocks will attempt to move
		int dx = 0;
		int dy = 0;
		//only reads one byte, may get messy with utf-8
		char input;
		read(STDIN_FILENO, &input, 1);
		//write(STDOUT_FILENO, &input, 1);
		//input handling
		switch (input) {
			case 'q':
				loop = 0;
			break;
			
			case 'h':
				dx = -1;
			break;
			
			case 'j':
				dy = 1;
			break;
			
			case 'k':
				dy = -1;
			break;
			
			case 'l':
				dx = 1;
			break;

			default:
			break;
		}
		//shifts until it can't shift anymore
		while ( shift(dx,dy) ) {
			//pass
		}
		//detects win/lose state, add another '2' to field otherwise
		if (dx != 0 || dy != 0) {
			addlose();
		}
	}
	//Prints victory or defeat
	if (victory == 1) {
		printf("YOU WIN\r\n");
	} else if (victory == -1) {
		printf("YOU LOSE\r\n");
	} else {
		printf("Goodbye!\r\n");
	}
	//restores terminal state
	printf("\033[0;39m\033[49m");
	tcsetattr(STDIN_FILENO, TCSANOW, &old_term);
	return 0;
}