#include <stdlib.h>
#include <stdbool.h>
#include <string.h>
#include <inttypes.h>
#include <stdio.h>
#include <math.h>

#include "common.c"


/// This one stores, for each cells, 4 pointers to the west, south,
/// north, and east cells so incrementing them is easy.

typedef struct cell cell;

struct cell {
    cell *west;
    cell *north;
    cell *south;
    cell *east;
    int height;
};


static inline void fire(cell *cell) {
    int div, rest;

    div = cell->height / 4;
    rest = cell->height % 4;
    cell->height = rest;
    cell->west->height += div;
    cell->south->height += div;
    cell->north->height += div;
    cell->east->height += div;
}


void apply_gravity(int width, cell *cells)
{
    bool did_something;

    while (1) {
        did_something = false;
        for (int x = 0; x < width*width; x++) {
            if (cells[x].height >= 4) {
                did_something = true;
                fire(cells+x);
            }
        }
        if (!did_something)
            return;
    }
}

cell *sandpile_new(int width, int height)
{
    cell **terrain = calloc(width, sizeof(cell*));
    cell *data = calloc(width * width, sizeof(cell));
    for (int i = 0; i < width; i++) {
        terrain[i] = data + i * width;
    }
    terrain[width / 2][width / 2].height = height;
    for (int x = 0; x < width; x++) {
        for (int y = 0; y < width; y++) {
            terrain[x][y].west = &terrain[x-1][y];
            terrain[x][y].south = &terrain[x][y-1];
            terrain[x][y].north = &terrain[x][y+1];
            terrain[x][y].east = &terrain[x+1][y];
        }
    }
    return data;
}

int **cells_to_array(int width, cell *cells) {
    // Create terrain:
    int **terrain = calloc(width, sizeof(int*));
    int *data = calloc(width * width, sizeof(int));
    for (int i = 0; i < width; i++) {
        terrain[i] = data + i * width;
    }

    // Organize cells in a 2d structure:
    cell **cell_array = calloc(width, sizeof(cell*));
    for (int i = 0; i < width; i++) {
        cell_array[i] = cells + i * width;
    }

    // Copy cells to terrain:
    for (int x = 0; x < width; x++)
        for (int y = 0; y < width; y++)
            terrain[x][y] = cell_array[x][y].height;
    return terrain;
}

int main(int argc, char **argv)
{
    args args = {0};

    if (parse_args(argc, argv, &args))
        return EXIT_FAILURE;

    int width = sandpile_width(args.height);
    cell *cells = sandpile_new(width, args.height);
    apply_gravity(width, cells);

    if (args.png_filename != NULL || args.print_to_stdout) {
        // Convert to int** for easy display:
        int **terrain = cells_to_array(width, cells);
        save_terrain(width, terrain, &args);
    }

    return EXIT_SUCCESS;
}