use std::io::{stdin, stdout, Write};

use std::sync::Mutex;

use lazy_static::lazy_static;

lazy_static! {
    static ref CACHE: Mutex<Vec<u64>> = Mutex::new(vec![1, 1]);
}

fn main() {
    loop {
        print!("Enter a positive integer: ");
        stdout().flush().expect("could not flush buffer");

        let mut input = String::new();
        let read = stdin().read_line(&mut input).expect("failed to read line");
        // EOF
        if read == 0 || input.trim() == "quit" {
            break;
        }

        let num: usize = match input.trim().parse() {
            Ok(num) => num,
            Err(e) => {
                println!("error parsing integer: {}", e);
                continue;
            }
        };

        println!("fibonacci of {} is {}", num, fib(num));
    }
}

fn fib(n: usize) -> u64 {
    CACHE.lock().unwrap().reserve(n);
    if CACHE.lock().unwrap().len() <= n {
        let result = match n {
            0 => 1,
            1 => 1,
            _ => fib(n - 1) + fib(n - 2)
        };
        CACHE.lock().unwrap().push(result);
    }
    return CACHE.lock().unwrap()[n];
}