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

struct snake* add_snake(struct snake* snake, int x, int y) {
    struct snake* head = calloc(1, sizeof(struct snake));
    if (head == NULL) {
        return NULL; // Handle memory allocation failure
    }
    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* this = snake;
    struct snake* prev = NULL;
    while (this->next != NULL) {
        prev = this;
        this = this->next;
    }

    free(this);
    prev->next = NULL;
    return snake;
}

void free_snake(struct snake* sn) {
    if (sn == NULL) {
        return;
    }
    free_snake(sn->next);
    free(sn);
}

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

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

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

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

    // Check if food is eaten
    int ate_food = 0;
    int food_left = 0;
    for (int i = 0; i < FOOD_COUNT; i++) {
        if (st->foodx[i] >= 0 && st->foody[i] >= 0) {
            food_left++;
            if (st->foodx[i] == nx && st->foody[i] == ny) {
                // Eat food
                st->foodx[i] = -1;
                st->foody[i] = -1;
                ate_food = 1;
                food_left--; // This food is now eaten
            }
        }
    }

    // Add new head
    st->snake = add_snake(st->snake, nx, ny);

    if (ate_food) {
        // If all food eaten, end game
        if (food_left == 0) {
            return END_FOOD;
        }
        // Do not remove tail (snake grows)
    } else {
        // Remove tail (snake moves)
        st->snake = remove_snake(st->snake);
    }

    return END_CONTINUE;
}