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

// Adds a new part to the snake at the given (x, y) position, making it the new head
struct snake* add_snake(struct snake* snake, int x, int y){
    struct snake* new_head = malloc(sizeof(struct snake));
    if(!new_head){
        return NULL;
    }
    new_head->x = x;
    new_head->y = y;
    new_head->next = snake;
    return new_head;
}

// Removes the last part of the snake (tail)
struct snake* remove_snake(struct snake* snake){
    if(!snake || !snake->next){
        free(snake);
        return NULL;
    }

    struct snake* current = snake;
    while (current->next && current->next->next) {
        current = current->next; // Move to the second last part
    }
    free(current->next); // Free the last part (tail)
    current->next = NULL; // Set the second last part's next pointer to NULL
    return snake;
}

// Checks if there is a part of the snake at the given (x, y) coordinates
int is_snake(struct snake* snake, int x, int y){
    while(snake){
        if(snake->x == x && snake->y == y){
            return 1;
        }
        snake = snake->next;
    }
    return 0;
}

// Frees the memory allocated for all parts of the snake
void free_snake(struct snake* sn){
    while(sn){
        struct snake* next = sn->next;
        free(sn);
        sn = next; 
    }
}

// Main function that updates the game state based on the snake's movement
// Returns the game status according to the reason to end the game (enum endgame)
int step_state(struct state* state){
    if (!state || !state->snake) return END_USER;

    int new_x = state->snake->x + state->sx;
    int new_y = state->snake->y + state->sy;

    // Check for collision with wall (end the game if collided)
    if(new_x < 0 || new_x >= state->width || new_y < 0 || new_y >= state->height){
        return END_WALL;
    }

    // Check for collision with itself (end the game if the snake runs into itself)
    if(is_snake(state->snake, new_x, new_y)){
        return END_SNAKE;
    }

    // Check if the snake ate any food
    for(int i = 0; i < FOOD_COUNT; i++) {
        if(state->foodx[i] == new_x && state->foody[i] == new_y){
            // Mark the food as eaten
            state->foodx[i] = -1;
            state->foody[i] = -1;
            // Add a new snake part at the food's location (new head)
            state->snake = add_snake(state->snake, new_x, new_y);

            int food_placed = 0;
            while(!food_placed){
                int food_x = rand() % (state->width - 2) + 1;
                int food_y = rand() % (state->height - 2) + 1;

                if(!is_snake(state->snake, food_x, food_y)){
                    state->foodx[i] = food_x;
                    state->foody[i] = food_y;
                    food_placed = 1; // Successfully placed food
                }
            }

            return END_CONTINUE;
        }
    }

    // Regular snake movement: move the snake by adding a new head and removing the tail
    state->snake = add_snake(state->snake, new_x, new_y);
    state->snake = remove_snake(state->snake);

    return END_CONTINUE; // Continue the game if no other conditions are met
}