#include <stdio.h>
#include <stdlib.h>

#define FOOD_COUNT 5

struct snake {
    int x;
    int y;
    struct snake* next;
};

enum endgame {
    END_CONTINUE = 0,
    END_WALL,
    END_SNAKE,
    END_FOOD,
    END_USER
};

struct state {
    struct snake* snake;
    int foodx[FOOD_COUNT];
    int foody[FOOD_COUNT];
    int sx;
    int sy;
    int width;
    int height;
};

struct snake* add_snake(struct snake* snake, int x, int y);
struct snake* remove_snake(struct snake* snake);
int is_snake(struct snake* snake, int x, int y);
void free_snake(struct snake* sn);
int step_state(struct state* state);

struct snake* add_snake(struct snake* snake, int x, int y) {
    struct snake* new_part = (struct snake*)malloc(sizeof(struct 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 != NULL && current->next->next != NULL) {
        current = current->next;
    }
    
    if (current->next != NULL) {
        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) {
    int newX = state->snake->x + state->sx;
    int newY = state->snake->y + state->sy;
    
    if (newX < 0 || newX >= state->width || newY < 0 || newY >= state->height) {
        return END_WALL;
    }
    
    if (is_snake(state->snake->next, newX, newY)) {
        return END_SNAKE;
    }
    
    int foodIdx = -1;
    for (int i = 0; i < FOOD_COUNT; i++) {
        if (state->foodx[i] == newX && state->foody[i] == newY) {
            foodIdx = i;
            break;
        }
    }
    
    if (foodIdx != -1) {
        state->foodx[foodIdx] = -1;
        state->foody[foodIdx] = -1;
        
        state->snake = add_snake(state->snake, newX, newY);
        
        int foodLeft = 0;
        for (int i = 0; i < FOOD_COUNT; i++) {
            if (state->foodx[i] >= 0) {
                foodLeft = 1;
                break;
            }
        }
        
        return foodLeft ? END_CONTINUE : END_FOOD;
    }
    
    state->snake = add_snake(state->snake, newX, newY);
    state->snake = remove_snake(state->snake);
    
    return END_CONTINUE;
}

void display_game(struct state* game) {
    printf("SNAKE GAME\n");
    
    for (int y = 0; y < 10; y++) {
        for (int x = 0; x < 20; x++) {
            int head = (game->snake->x == x && game->snake->y == y);
            int body = is_snake(game->snake->next, x, y);
            int food = 0;
            
            for (int i = 0; i < FOOD_COUNT; i++) {
                if (game->foodx[i] == x && game->foody[i] == y) {
                    food = 1;
                    break;
                }
            }
            
            if (head) printf("S");
            else if (body) printf("+");
            else if (food) printf("F");
            else printf(" ");
        }
        printf("\n");
    }
}

void start_game(struct state* game) {
    game->snake = add_snake(NULL, 10, 5);
    game->snake = add_snake(game->snake, 9, 5);
    
    game->sx = 1;
    game->sy = 0;
    game->width = 20;
    game->height = 10;
    
    for (int i = 0; i < FOOD_COUNT; i++) {
        game->foodx[i] = 5 + i * 2;
        game->foody[i] = 3 + i;
    }
}

int main(void) {
    struct state game;
    start_game(&game);
    
    display_game(&game);
    
    int status = step_state(&game);
    
    printf("Game status: %d\n", status);
    
    free_snake(game.snake);
    
    return 0;
}