#include "snake.h"
#include <stdlib.h>

struct snake* add_snake(struct snake* snake, int x, int y) {
    struct snake* head = malloc(sizeof(struct snake));
    if (head == NULL) {
        return NULL;
    }
    head->x=x;
    head->y=y;
    head->next=snake;
    return head;
}

struct snake* remove_snake(struct snake* snake) {
    if (snake == NULL || snake->next == NULL) {
        free(snake);
        return NULL;
    }
    struct snake* lastbo = snake;
    while (lastbo->next->next != NULL) {
        lastbo=lastbo->next;
    }
    free(lastbo->next);
    lastbo->next=NULL;
    return snake;
}

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;
}

void free_snake(struct snake* sn) {
    while (sn != NULL) {
        struct snake* a =sn;
        sn=sn->next;
        free(a);
    }
}

int step_state(struct state* st) {
    int nx = (st->snake->x + st->sx);
    int ny = (st->snake->y + st->sy);

    if (nx<0 || ny<0 || nx>=st->width || ny>=st->height) {
        return END_WALL;
    }

    if (is_snake(st->snake, nx, ny)) {
        return END_SNAKE;
    }

    int ate = 0;
    for (int i = 0; i < FOOD_COUNT; i++) {
        if (st->foodx[i]==nx && st->foody[i] == ny) {
            st->foodx[i]=-1;
            st->foody[i]=-1;
            ate=1;
            break;
        }
    }

    st->snake = add_snake(st->snake, nx, ny);
    if (ate == 0) {
        st->snake=remove_snake(st->snake);
    }

    int foodleft = 0;
    for (int i = 0; i < FOOD_COUNT; i++) {
        if (st->foodx[i] >= 0 && st->foody[i] >= 0) {
            foodleft = 1;
            break;
        }
    }

    if (!foodleft) {
        return END_FOOD;
    }
    return END_CONTINUE;
}