#include "snake.h"
#include <stdlib.h>
 
struct snake* add_snake(struct snake* snake, int x, int y){
    struct snake* head = malloc(sizeof(struct snake));
    head->x = x;
    head->y = y;
    head->next = snake;
    return head;
}
 
struct snake* remove_snake(struct snake* snake){
    if(snake == NULL) return NULL;
    if(snake->next == NULL){
        free(snake);
        return NULL;
    }
    struct snake* cur = snake;
    while(cur->next->next != NULL)
        cur = cur->next;
    free(cur->next);
    cur->next = NULL;
    return snake;
}
 
void free_snake(struct snake* sn){
    while(sn != NULL){
        struct snake* tmp = sn->next;
        free(sn);
        sn = tmp;
    }
}
 
int is_snake(struct snake* snake, int x, int y){
    while(snake != NULL){
        if(snake->x == x && snake->y == y) return 1;
        snake = snake->next;
    }
    return 0;
}
 
int step_state(struct state* st){
    int nx = st->snake->x + st->sx;
    int ny = st->snake->y + st->sy;
 
    if(nx < 0 || nx >= st->width || ny < 0 || ny >= st->height)
        return END_WALL;
 
    if(is_snake(st->snake, nx, ny))
        return END_SNAKE;
 
    for(int i = 0; i < FOOD_COUNT; i++){
        if(st->foodx[i] == nx && st->foody[i] == ny){
            st->snake = add_snake(st->snake, nx, ny);
            st->foodx[i] = -1;
            st->foody[i] = -1;
            for(int j = 0; j < FOOD_COUNT; j++)
                if(st->foodx[j] >= 0) return END_CONTINUE;
            return END_FOOD;
        }
    }
 
    st->snake = add_snake(st->snake, nx, ny);
    st->snake = remove_snake(st->snake);
    return END_CONTINUE;
}