#include <stdio.h>

enum turnstile_state {
    LOCKED,
    UNLOCKED
};


enum turnstile_event {
    COIN,
    PUSH
};


struct turnstile {
    enum turnstile_state state;
};

void transition(struct turnstile *t, enum turnstile_event event) {
    switch (t->state) {
        case LOCKED:
            if (event == COIN) {
                printf("Unlocking turnstile...\n");
                t->state = UNLOCKED;
            } else {
                printf("Turnstile is locked. Please insert a coin to unlock.\n");
            }
            break;
        case UNLOCKED:
            if (event == PUSH) {
                printf("Passing through turnstile...\n");
                t->state = LOCKED;
            } else {
               printf("Turnstile is already unlocked. Please proceed.\n");
            }
            break;
    }
}

extern "C" void app_main (){
    struct turnstile t = { .state = LOCKED };

    enum turnstile_event events[] = {COIN, PUSH, PUSH, COIN};

    for (int i = 0; i < sizeof(events) / sizeof(events[0]); i++) {
        transition(&t, events[i]);
    }
}