rewot/src/mudlet_replay.rs

use std::io;
use std::io::Read;
use std::thread::sleep;
use std::time::Duration;

type Result<T> = std::result::Result<T, Box<dyn std::error::Error>>;

#[derive(Debug)]
struct Chunk {
	pub delta: i32,
	pub text: String,
}

impl Chunk {
	fn chunk32(chunk: &[u8; 8]) -> Result<(i32, i32)> {
		let (dc, sc) = {
			let (mut dc, mut sc): ([u8; 4], [u8; 4]) = ([0; 4], [0; 4]);
			for i in 0..4 {
				dc[i] = chunk[i];
				sc[i] = chunk[i + 4];
			}
			(dc, sc)
		};

		let delta = i32::from_be_bytes(dc);
		let size = i32::from_be_bytes(sc);

		if delta < 0 || size < 1 || size > 100000 {
			return Err("delta source is not int32_t".into());
		}

		Ok((delta, size))
	}

	fn chunk64(dc: [u8; 8], sc: [u8; 4]) -> Result<(i32, i32)> {
		let delta = i64::from_be_bytes(dc);
		let size = i32::from_be_bytes(sc);

		if delta < 0 || delta > i32::MAX.into() || size < 1 || size > 100000 {
			return Err("delta source is not int64_t".into());
		}

		let delta: i32 = delta.try_into()?;

		Ok((delta, size))
	}

	pub fn read_chunk() -> Result<Self> {
		let mut stdin = io::stdin();

		let mut chunk: [u8; 8] = [0; 8];
		stdin.read_exact(&mut chunk)?;

		let (delta, size) = {
			if let Ok((delta, size)) = Self::chunk32(&chunk) {
				(delta, size)
			} else {
				let mut next_chunk: [u8; 4] = [0; 4];
				stdin.read_exact(&mut next_chunk)?;

				if let Ok((delta, size)) = Self::chunk64(chunk, next_chunk) {
					(delta, size)
				} else {
					return Err("broken".into());
				}
			}
		};

		let mut text_chunk: Vec<u8> = vec![0; size as usize];
		stdin.read_exact(&mut text_chunk)?;
		let text = String::from_utf8(text_chunk)?;

		Ok(Self { delta, text })
	}
}

fn main() -> Result<()> {
	while let Ok(chunk) = Chunk::read_chunk() {
		sleep(Duration::from_millis(chunk.delta.try_into()?));
		print!("{}", chunk.text);
	}

	println!();

	Ok(())
}