#include <stdio.h>
#include <stdlib.h>

#define FOOD_COUNT 5

struct snake {
    int x;
    int y;
    struct snake* next;
};

enum endgame {
    END_CONTINUE = 0,
    END_WALL,
    END_SNAKE,
    END_FOOD,
    END_USER
};

struct state {
    struct snake* snake;
    int foodx[FOOD_COUNT];
    int foody[FOOD_COUNT];
    int sx;
    int sy;
    int width;
    int height;
};

struct snake* add_snake(struct snake* snake, int x, int y);
struct snake* remove_snake(struct snake* snake);
int is_snake(struct snake* snake, int x, int y);
void free_snake(struct snake* sn);
int step_state(struct state* state);

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

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

int is_snake(struct snake* snake, int x, int y) {
    struct snake* current = snake;
    while (current != NULL) {
        if (current->x == x && current->y == y) {
            return 1;
        }
        current = current->next;
    }
    return 0;
}

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

int step_state(struct state* state) {
    int newX = state->snake->x + state->sx;
    int newY = state->snake->y + state->sy;
    
    if (newX < 0 || newX >= state->width || newY < 0 || newY >= state->height) {
        return END_WALL;
    }
    
    if (is_snake(state->snake->next, newX, newY)) {
        return END_SNAKE;
    }
    
    int foodIdx = -1;
    for (int i = 0; i < FOOD_COUNT; i++) {
        if (state->foodx[i] == newX && state->foody[i] == newY) {
            foodIdx = i;
            break;
        }
    }
    
    if (foodIdx != -1) {
        state->foodx[foodIdx] = -1;
        state->foody[foodIdx] = -1;
        
        state->snake = add_snake(state->snake, newX, newY);
        
        int foodLeft = 0;
        for (int i = 0; i < FOOD_COUNT; i++) {
            if (state->foodx[i] >= 0) {
                foodLeft = 1;
                break;
            }
        }
        
        return foodLeft ? END_CONTINUE : END_FOOD;
    }
    
    state->snake = add_snake(state->snake, newX, newY);
    state->snake = remove_snake(state->snake);
    
    return END_CONTINUE;
}