extern crate rand;
use rand::{thread_rng, Rng};
use rand::rngs::ThreadRng;

use std::io::{self, Write};
use std::time::{Duration, Instant};

struct Question {
    query: String,
    answer: String,
}

impl Question {
    fn new(rng: &mut ThreadRng) -> Self {
        let x = rng.gen_range(1, 12);
        let y = rng.gen_range(1, 12);

        let query = format!("What is {} x {}?", x, y);
        // no need to parse user guess and handle non-integer input
        // if we just compare two strings for equality.
        let answer = (x * y).to_string();

        return Question {
            query,
            answer,
        }
    }
}

fn main() {
    let time_limit = Duration::from_secs(30);
    let mut score = 0;
    let mut rng = thread_rng();

    println!("Speedy Multiplication Quiz!");
    println!("Try to answer as many questions as you can in 30 seconds.");

    let instant = Instant::now();
    while instant.elapsed() <= time_limit {
        let question = Question::new(&mut rng);
        print!("{}\n> ", question.query);
        // flush output stream - needed to ensure output emitted immediately
        io::stdout().flush().unwrap();

        let mut guess = String::new();
        io::stdin().read_line(&mut guess)
            .expect("Failed to read line");
        guess.pop(); // get rid of trailing newline character

        if guess == question.answer {
            println!("Correct!");
            score += 1;
        } else {
            println!("Sorry, it was actually {}!", question.answer);
        }
    }
    println!("Bzzzt! Times up!");
    println!("Congratulations, you got a score of {}!", score);
}