use std::{
	env::args,
	io::{ stdin, stdout, Error, ErrorKind, Read, Write },
	process::ExitCode,
	vec::Vec
};

extern crate getopt;
use getopt::{ Opt, Parser };

extern crate sysexits;
use sysexits::{ EX_OK, EX_OSERR, EX_USAGE };

fn oserr(s: &str, e: Error) -> ExitCode {
	eprintln!("{}: {}", s, e);
	ExitCode::from(EX_OSERR as u8)
}

fn usage(s: &str) -> ExitCode {
	eprintln!("Usage: {} (-f) (-w [wordsize])", s);
	ExitCode::from(EX_USAGE as u8)
}

fn main() -> ExitCode {
	let argv = args().collect::<Vec<String>>();
	let mut buf: Vec<u8> = Vec::new();
	let mut input = stdin();
	let mut output = stdout().lock();

	let mut opts = Parser::new(&argv, "fw:");
	let mut force = false;
	let mut wordsize: usize = 2;

	loop {
		match opts.next() {
			None => break,
			Some(opt) =>
				match opt {
					Ok(Opt('f', None)) => force = true,
					Ok(Opt('w', Some(arg))) => {
						match arg.parse::<usize>() {
							Ok(w) if w % 2 == 0 => { wordsize = w; () },
							_ => { return usage(&argv[0]); },
						}
					},
					_ => { return usage(&argv[0]); }
				}
		}
	}

	buf.resize(wordsize, 0);

	loop {
		match input.read(&mut buf) {
			Ok(0) => break ExitCode::from(EX_OK as u8),
			Ok(v) if v == wordsize => {
				let (left, right) = buf.split_at(v/2);
				if let Err(e) = output.write(&right)
						.and_then(|_| output.write(&left)) {
					break oserr(&argv[0], e)
				}
			},
			Ok(v) => {
				if let Err(e) = output.write(&buf[..v]) {
					break oserr(&argv[0], e)
				}
			},
			Err(e) if e.kind() == ErrorKind::Interrupted && force => continue,
			Err(e) => break oserr(&argv[0], e)
		}
	}
}