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

use num_format::{Locale, ToFormattedString};

const ALL_CHARS: &'static str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789,.<>/?;':\"[]{}\\|-=_+`~!@#$%^&*()";
const LEN: usize = 4;

static mut SOFAR: u128 = 0;
static mut TOTAL: usize = 0;

/// Pseudo main 
/// 
/// Starts the number crunching (blocking on main thread!) and the
/// timer thread which watches the main thread while
/// reporting statistics about it. 
fn start(char_list: &str, output_len: usize) {
    /// Flag to communicate between main (combination crunching) and
    /// timer threads.
    static mut IS_DONE: bool = false;

    let start = Instant::now();

    // Just to report stats
    let timer = thread::spawn(move || {
        let mut out = stderr();

        while unsafe { !IS_DONE } {
            let mut elapsed = start.elapsed().as_secs() as u128;
            // prevent div by zero err
            if elapsed == 0 { elapsed = 1; }

            let sofar = unsafe {SOFAR};
            // output P/s
            let _ = out.write(
                format!("\rCalculated {} possibilities thus far, at {} p/s",
                    sofar.to_formatted_string(&Locale::en_NA),
                    (sofar / elapsed).to_formatted_string(&Locale::en_NA),
                ).as_bytes());
            let _ = out.flush();
            sleep(Duration::from_secs(1));
            
            /*
            // output remaining time
            // I haven't tested to see if this timer is somewhat accurate...
            // This is code I stole of reddit... what am I doing?
            let remaining = unsafe { TOTAL as u128 / (sofar / elapsed) };
            let sec = remaining % 60;
            let min = (remaining / 60) % 60;
            let hrs = (remaining / 60) / 60;
            
            let _ = out.write(
            // TODO clear the whole line, don't just put cursor to the begining...
                format!("\r{}%, {}h:{}m:{}s remaining                       ",
                    unsafe { sofar / TOTAL as u128 },
                    hrs, min, sec
            ).as_bytes());
            let _ = out.flush();
            sleep(Duration::from_secs(1));
            */
        }
    });

    // starting with the blank string is important
    calc(char_list, &"", output_len);

    unsafe { IS_DONE = true; }
    timer.join().unwrap();

    eprintln!("\r{}ms to calculate the permutations (p) for {} chars (n) across {} slots (r).", start.elapsed().as_millis().to_formatted_string(&Locale::en_NA), char_list.len(), output_len);
}

fn main() {
    // All the status messages are printed on stderr
    // This way you can pipe the actual permutations into
    // a file whilst still getting debug messages. 
    let t = (ALL_CHARS.len() as u128).pow(LEN.try_into().unwrap());
    unsafe { TOTAL = t as usize };
    eprintln!(
        "Calculating {} combinations...\n(Number may be trunkated if too large)\n",
        unsafe { TOTAL }.to_formatted_string(&Locale::en_NA)
    );

    start(ALL_CHARS, LEN);
}

/// Recurseively create and print every combination of
/// `choices` chars inside a string of `len` length.
/// 
/// 
/// * `choices` string containing all the chars you wish
/// to build random strings with. 
/// 
/// * `prefix` should be a blank string `""` unless you
/// actually want a prefix on every output. This variable is
/// mainly used within the recursive nature of the funciton.
/// 
/// * `len` the size that all the output strings wil be.
fn calc(choices: &str, prefix: &str, len: usize) {
    let need_to_fill = len - prefix.len();
    match need_to_fill {
        // the last char in the sequence, time to print
        1 => {
            for i in choices.chars() {
                println!("{}{}", prefix, i);
                unsafe { SOFAR = SOFAR + 1 };
            }
        }
        // need to recurse farther into the sequence
        _ => {
            for i in choices.chars() {
                calc(choices, &(prefix.to_string() + &i.to_string()), len);
            }
        }
    }
}