#include "game_logic.h"

#include <string.h>

static uint8_t game_grid_alpha[GRID_SIDE * GRID_SIDE];
static uint8_t game_grid_beta[GRID_SIDE * GRID_SIDE];

static uint8_t *front_grid = game_grid_alpha;
static uint8_t *back_grid = game_grid_beta;

void swap_grids(void);

void swap_grids(void) {
	uint8_t *temp = front_grid;
	
	front_grid = back_grid;
	back_grid = temp;
}

uint8_t *get_front_grid(void) {
	return front_grid;
}

uint8_t *step_game(step_direction dir) {
	// TODO: Update the grid state calculating the new state in the back grid
	
	uint8_t start_offset;
	int8_t column_step;
	int8_t row_step;
	
	/*
	 *	UP: scans TOP to BOTTOM, RIGHT to LEFT
	 *	DOWN: scans BOTTOM to TOP, RIGHT to LEFT
	 *	LEFT: scans LEFT to RIGHT, TOP to BOTTOM
	 *	RIGHT: scans RIGHT to LEFT, TOP to BOTTOM
	 */
	
	switch(dir) {
		case UP:
			start_offset = GRID_SIDE;
			column_step = GRID_SIDE;
			row_step = -1;
			break;
		case DOWN:
			start_offset = (GRID_SIDE * GRID_SIDE) - 1;
			column_step = -GRID_SIDE;
			row_step = -1;
			break;
		case LEFT:
			start_offset = 0;
			column_step = 1;
			row_step = GRID_SIDE;
			break;
			break;
		case RIGHT:
			start_offset = GRID_SIDE - 1;
			column_step = -1;
			row_step = GRID_SIDE;
			break;
	};
	
	// Clear the back grid
	memset(back_grid, 0, GRID_SIDE * GRID_SIDE);
	
	for (int8_t row = 0; row < GRID_SIDE; row++) {
		for(int8_t col = 0; col < GRID_SIDE; col++) {
			uint8_t current_offset = start_offset + (col * column_step) + (row * row_step);
			uint8_t sub_col;
			
			// Search for the first non-zero value in the front grid and copy it in the current place of the back grid (zeroing it in the front)
			for(sub_col = col; sub_col < GRID_SIDE; sub_col++) {
				uint8_t sub_col_offset = start_offset + (sub_col * column_step) + (row * row_step);
				if(front_grid[sub_col_offset]) {
					back_grid[current_offset] = front_grid[sub_col_offset];
					front_grid[sub_col_offset] = 0;
					break;
				}
			}
			
			// The value is still 0, we found nothing. On to the next row!
			if (!back_grid[current_offset]) break;
			
			// Now search if there is an identical value following this one, so we can merge them
			for(; sub_col < GRID_SIDE; sub_col++) {
				uint8_t sub_col_offset = start_offset + (sub_col * column_step) + (row * row_step);
				if(front_grid[sub_col_offset] == back_grid[current_offset]) {
					back_grid[current_offset]++; // Merge them (by increasing the value of the current square and removing the merged one)
					front_grid[sub_col_offset] = 0;
					break;
				}
			}
		}
	}
	
	swap_grids();
	
	return front_grid;
}