/*
 * 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::{
	env::args,
	io::{ Read, stdin, stdout, Write },
	process::{ Command, exit, Stdio },
};

extern crate getopt;
extern crate strerror;
extern crate sysexits;

use getopt::{ Opt, Parser };
use strerror::raw_message;
use sysexits::{ EX_DATAERR, EX_IOERR, EX_UNAVAILABLE, EX_USAGE };

fn main() {
	let argv = args().collect::<Vec<String>>();
	let mut d = '␞';
	let mut arg_parser = Parser::new(&argv, "d:");

	while let Some(opt) = arg_parser.next() {
		match opt {
			Ok(Opt('d', Some(arg))) => {
				let arg_char = arg.chars().collect::<Vec<char>>();
				if arg_char.len() > 1 {
					eprintln!("{}: {}: Not a character.", argv[0], arg);
					exit(EX_USAGE);
				} else { d = arg_char[0]; }
			},
			_ => {},
		};
	}

	let index_arg = arg_parser.index();
	let command_arg = arg_parser.index() + 1;

	argv.get(command_arg).unwrap_or_else(|| {
		eprintln!("Usage: {} [-d delimiter] index command [args...]", argv[0]);
		exit(EX_USAGE);
	});

	let index = argv[index_arg].parse::<usize>().unwrap_or_else(|e| {
		eprintln!("{}: {}: {}", argv[0], argv[1], e);
		exit(EX_DATAERR);
	});

	let mut buf = String::new();
	let _ = stdin().read_to_string(&mut buf);
	let mut fields = buf.split(d).collect::<Vec<&str>>();

	let opts = argv
		.iter()
		.clone()
		.skip(command_arg + 1)
		.collect::<Vec<&String>>();

	let mut spawned = Command::new(argv.get(command_arg).unwrap())
		.args(opts)
		.stdin(Stdio::piped())
		.stdout(Stdio::piped())
		.spawn()
		.unwrap_or_else( |e| {
			eprintln!("{}: {}: {}", argv[0], argv[command_arg], raw_message(e));
			exit(EX_UNAVAILABLE);
		});

	let field = fields.get(index).unwrap_or_else(|| {
		eprintln!(
			"{}: {}: No such index in input",
			argv[0],
			index.to_string(),
		);
		exit(EX_DATAERR);
	});

	if let Some(mut child_stdin) = spawned.stdin.take() {
		let _ = child_stdin.write_all(field.as_bytes());
		drop(child_stdin);
	}

	let output = spawned.wait_with_output().unwrap_or_else(|e| {
		eprintln!("{}: {}: {}", argv[0], argv[command_arg], raw_message(e));
		exit(EX_IOERR);
	});

	let mut replace = output.stdout.clone();

	if replace.pop() != Some(b'\n') { replace = output.stdout; }

	let new_field = String::from_utf8(replace).unwrap_or_else(|e| {
		eprintln!("{}: {}: {}", argv[0], argv[command_arg], e);
		exit(EX_IOERR);
	});

	fields[index] = &new_field;

	stdout().write_all(
		fields.join(&d.to_string()).as_bytes()
	).unwrap_or_else(|e| {
		eprintln!("{}: {}", argv[0], raw_message(e));
		exit(EX_IOERR);
	});
}