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

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

struct snake* remove_snake(struct snake* snake){
    if (snake == NULL) {
        return NULL;
    }
    
    // If snake has only one part
    if (snake->next == NULL) {
        free(snake);
        return NULL;
    }
    
    // Find the second-to-last part
    struct snake* current = snake;
    while (current->next->next != NULL) {
        current = current->next;
    }
    
    // Free the last part
    free(current->next);
    current->next = NULL;
    
    return snake;
}

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

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;
}

int step_state(struct state* st){
    int nx = (st->snake->x + st->sx);
    int ny = (st->snake->y + st->sy);
    
    // Check if new position is on the wall
    if (nx < 0 || nx >= st->width || ny < 0 || ny >= st->height) {
        return END_WALL;
    }
    
    // Check if new position is on the snake (excluding the head)
    struct snake* current = st->snake->next;
    while (current != NULL) {
        if (current->x == nx && current->y == ny) {
            return END_SNAKE;
        }
        current = current->next;
    }
    
    // Check if new position is on food
    int food_index = -1;
    for (int i = 0; i < FOOD_COUNT; i++) {
        if (st->foodx[i] == nx && st->foody[i] == ny) {
            food_index = i;
            break;
        }
    }
    
    if (food_index != -1) {
        // Mark food as eaten
        st->foodx[food_index] = -1;
        st->foody[food_index] = -1;
        // Add new snake part at food position
        st->snake = add_snake(st->snake, nx, ny);
        
        // Check if there is any food left
        int food_left = 0;
        for (int i = 0; i < FOOD_COUNT; i++) {
            if (st->foodx[i] >= 0) {
                food_left = 1;
                break;
            }
        }
        
        if (!food_left) {
            return END_FOOD;
        }
        return END_CONTINUE;
    }
    
    // Normal move: add new head and remove tail
    st->snake = add_snake(st->snake, nx, ny);
    st->snake = remove_snake(st->snake);
    
    return END_CONTINUE;
}