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

struct snake* add_snake(struct snake* snake, int x, int y) {
    struct snake* new_part = (struct snake*)malloc(sizeof(struct snake));
    if (new_part == NULL) {
        return 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->next != NULL) {
        current = current->next;
    }
    
    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) {
    if (state == NULL || state->snake == NULL) {
        return END_USER;
    }
    
    int new_x = state->snake->x + state->sx;
    int new_y = state->snake->y + state->sy;
    
    if (new_x < 0 || new_x >= state->width || new_y < 0 || new_y >= state->height) {
        return END_WALL;
    }
    
    int food_index = -1;
    int items_left = 0;
    
    for (int i = 0; i < FOOD_COUNT; i++) {
        if (state->foodx[i] == new_x && state->foody[i] == new_y) {
            food_index = i;
        } else if (state->foodx[i] >= 0 && state->foody[i] >= 0) {
            items_left++;
        }
    }
    
    if (food_index >= 0) {
        state->foodx[food_index] = -1;
        state->foody[food_index] = -1;
        
        if (is_snake(state->snake, new_x, new_y)) {
            state->snake = add_snake(state->snake, new_x, new_y);
            return END_SNAKE;
        }
        
        state->snake = add_snake(state->snake, new_x, new_y);
        
        if (items_left == 0) {
            return END_FOOD;
        }
        return END_CONTINUE;
    } else {
        state->snake = remove_snake(state->snake);
        
        if (is_snake(state->snake, new_x, new_y)) {
            state->snake = add_snake(state->snake, new_x, new_y);
            return END_SNAKE;
        }
        
        state->snake = add_snake(state->snake, new_x, new_y);
        return END_CONTINUE;
    }
}