/*
 * Copyright (c) 2023–2024 Emma Tebibyte <emma@tebibyte.media>
 * SPDX-License-Identifier: AGPL-3.0-or-later
 *
 * This program is free software: you can redistribute it and/or modify it under
 * the terms of the GNU Affero General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option) any
 * later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
 * details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see https://www.gnu.org/licenses/.
 */

use std::{
	cmp::Ordering,
	env::args,
	io::{ stdin, stdout, Write },
	process::{ ExitCode, exit },
};

extern crate strerror;
extern crate sysexits;

use strerror::c_error;
use sysexits::{ EX_DATAERR, EX_IOERR, EX_SOFTWARE };

const LIST: [(u32, &str); 10] = [
	(3, "k"),
	(6, "M"),
	(9, "G"),
	(12, "T"),
	(15, "P"),
	(18, "E"),
	(21, "Z"),
	(24, "Y"),
	(27, "R"),
	(30, "Q")
];

fn convert(input: u128) -> Result<(f64, (u32, &'static str)), String> {

	let mut out = (input as f64, (0_u32, ""));
	if input < 1000 { return Ok(out); }

	for (n, p) in LIST {
		let c = match 10_u128.checked_pow(n) {
			Some(c) => c,
			None => {
				return Err(format!("10^{}: Integer overflow", n.to_string()));
			},
		};

		match c.cmp(&input) {
			Ordering::Less => {
				out = (input as f64 / c as f64, (n, p));
			},
			Ordering::Equal => {
				return Ok((input as f64 / c as f64, (n, p)));
			},
			Ordering::Greater => {},
		};
	}

	Ok(out)
}

fn main() -> ExitCode {
	let argv = args().collect::<Vec<String>>();
	let mut buf = String::new();
	while let Ok(_) = stdin().read_line(&mut buf) {
		if buf.is_empty() { return ExitCode::SUCCESS; }

		let n: u128 = match buf.trim().parse() {
			Ok(f) => {
				buf.clear();
				f
			},
			Err(err) => {
				eprintln!("{}: {}", argv[0], err);
				return ExitCode::from(EX_DATAERR as u8);
			},
		};

		let (number, prefix) = match convert(n) {
			Ok(x) => x,
			Err(err) => {
				eprintln!("{}: {}", argv[0], err);
				return ExitCode::from(EX_SOFTWARE as u8);
			},
		};

		let si_prefix = format!("{}B", prefix.1);

		let out = ((number * 10.0).round() / 10.0).to_string();

		stdout().write_all(format!("{} {}\n", out, si_prefix).as_bytes())
			.unwrap_or_else(|e| {
				eprintln!("{}: {}", argv[0], c_error(e));
				exit(EX_IOERR);
			});
	}

	ExitCode::SUCCESS
}