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

struct snake* add_snake(struct snake* head, int x, int y) {
    struct snake* node = (struct snake*)malloc(sizeof(struct snake));
    if (!node) return NULL;

    node->x = x;
    node->y = y;
    node->next = head;
    return node;
}

struct snake* remove_snake(struct snake* head) {
    if (!head) return NULL;
    if (!head->next) {
        free(head);
        return NULL;
    }

    struct snake* current = head;
    while (current->next && current->next->next) {
        current = current->next;
    }

    free(current->next);
    current->next = NULL;
    return head;
}

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

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

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

    // Collision with walls
    if (new_x < 0 || new_y < 0 || new_x >= st->width || new_y >= st->height) {
        return END_WALL;
    }

    // Collision with itself
    if (is_snake(st->snake, new_x, new_y)) {
        return END_SNAKE;
    }

    // Check food collision
    for (int i = 0; i < FOOD_COUNT; ++i) {
        if (st->foodx[i] == new_x && st->foody[i] == new_y) {
            st->foodx[i] = -1;
            st->foody[i] = -1;
            st->snake = add_snake(st->snake, new_x, new_y);

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

            return food_remaining ? END_CONTINUE : END_FOOD;
        }
    }

    // Normal move: add head, remove tail
    st->snake = add_snake(st->snake, new_x, new_y);
    st->snake = remove_snake(st->snake);
    return END_CONTINUE;
}