// SPDX-FileCopyrightText: V <v@unfathomable.blue>
// SPDX-License-Identifier: OSL-3.0

use {
	anyhow::{anyhow, Error, Result},
	git2::{Oid, Repository, Sort},
	irc::client::prelude::*,
	pin_utils::pin_mut,
	std::{
		collections::{HashMap, HashSet},
		env,
		fs::{remove_file, File},
		io::{ErrorKind, Read},
		path::Path,
	},
	tokio::{
		io::{AsyncBufRead, AsyncBufReadExt, BufReader, Lines},
		net::UnixListener,
		select, spawn,
		sync::{mpsc, mpsc::UnboundedSender},
	},
	tokio_stream::{wrappers::UnboundedReceiverStream, StreamExt},
};

#[derive(Debug)]
struct Batch {
	repository: String,
	lines: Vec<String>,
}

#[tokio::main]
async fn main() -> Result<()> {
	let repo_by_channel = {
		let mut buf = vec![];
		File::open(env::var("NAUT_CONFIG")?)?.read_to_end(&mut buf)?;
		let tmp: HashMap<String, Vec<String>> = toml::from_slice(&buf)?;
		if tmp.is_empty() {
			return Err(anyhow!("No channels configured!"));
		}
		tmp
	};

	let channels: Vec<String> = repo_by_channel
		.keys()
		.clone()
		.map(ToOwned::to_owned)
		.collect();

	// Invert the config, so we have a map of repositories to channel names
	let channel_by_repo = {
		let mut tmp = HashMap::new();
		for (channel, repos) in repo_by_channel {
			for repo in repos {
				tmp.entry(repo)
					.or_insert_with(Vec::new)
					.push(channel.to_string());
			}
		}
		tmp
	};

	let repositories: HashSet<_> = channel_by_repo
		.keys()
		.clone()
		.map(ToOwned::to_owned)
		.collect();

	let (tx, rx) = mpsc::unbounded_channel::<Batch>();

	let listener = bind(env::var("NAUT_SOCK")?.as_str())?;
	spawn(async move {
		loop {
			let (stream, _) = listener.accept().await.unwrap();

			let tx = tx.clone();
			let repositories = repositories.clone();

			let conn = async move {
				let mut lines = BufReader::new(stream).lines();
				let path = lines.next_line().await?.unwrap();

				let repo_name = Path::new(&path).file_name().unwrap().to_str().unwrap();
				if !repositories.contains(repo_name) {
					return Err(anyhow!(
						"Received a request for an unmanaged repository: {}",
						repo_name
					));
				}

				let repo = Repository::open(&path)?;

				handle(repo, repo_name, lines, tx).await?;
				Ok::<(), Error>(())
			};

			spawn(async move {
				if let Err(e) = conn.await {
					eprintln!("Failed to handle request: {}", e);
				}
			});
		}
	});

	let client_config = Config {
		server: Some("irc.libera.chat".to_owned()),
		password: Some(env::var("NAUT_PASS")?),
		nickname: Some("naut".to_owned()),
		realname: Some("blub blub".to_owned()),
		version: Some(format!("naut {}", env!("CARGO_PKG_VERSION"))),
		source: Some("https://src.unfathomable.blue/nixos-config/tree/pkgs/naut".to_owned()),
		channels,
		..Default::default()
	};

	let rx = UnboundedReceiverStream::new(rx).fuse();
	pin_mut!(rx);

	loop {
		let mut client = Client::from_config(client_config.clone()).await?;
		client.identify()?;

		let sender = client.sender();

		let stream = client.stream()?.fuse();
		pin_mut!(stream);

		loop {
			select! {
				message = stream.next() => match message {
					Some(_) => {},
					None => break,
				},
				Some(batch) = rx.next() => {
					let channels = channel_by_repo.get(&batch.repository).unwrap();
					for line in batch.lines {
						for channel in channels {
							sender.send_privmsg(channel.to_owned(), line.to_owned())?;
						}
					}
				},
			}
		}
	}
}

fn bind(path: &str) -> Result<UnixListener> {
	match remove_file(path) {
		Ok(()) => (),
		Err(e) if e.kind() == ErrorKind::NotFound => (),
		Err(e) => return Err(e.into()),
	}

	UnixListener::bind(path).map_err(Error::from)
}

async fn handle(
	repo: Repository,
	repo_name: &str,
	mut lines: Lines<impl AsyncBufRead + Unpin>,
	tx: UnboundedSender<Batch>,
) -> Result<()> {
	while let Some(line) = lines.next_line().await? {
		let args: Vec<_> = line.splitn(3, ' ').collect();

		let old = Oid::from_str(args[0])?;
		let new = Oid::from_str(args[1])?;
		let r#ref = repo.find_reference(args[2])?;
		let ref_name = r#ref.shorthand().unwrap();

		let mut lines = vec![];

		if r#ref.is_branch() {
			if new.is_zero() {
				lines.push(format!(
					"[{}] branch {} deleted (was {})",
					repo_name, ref_name, old
				));
			} else {
				let mut walker = repo.revwalk()?;
				walker.set_sorting(Sort::REVERSE)?;
				walker.push(new)?;

				if old.is_zero() {
					lines.push(format!("[{}] new branch created: {}", repo_name, ref_name));

					// We cannot use repo.head directly, as that comes resolved already.
					let head = repo.find_reference("HEAD")?;

					// Hide commits also present from HEAD (unless this *is* HEAD, in which we do want them).
					// This avoids duplicating notifications for commits that we've already seen, provided we
					// only push branches that are forked directly from HEAD (or one of its ancestors).
					if ref_name != head.symbolic_target().unwrap() {
						if let Ok(base) = repo.merge_base(head.resolve()?.target().unwrap(), new) {
							walker.hide(base)?;
						}
					}
				} else {
					walker.hide(old)?;
				}

				let commits: Vec<_> = walker
					.map(|x| repo.find_commit(x.unwrap()).unwrap())
					.collect();

				lines.push(format!(
					"[{}] {} {} pushed to {}",
					repo_name,
					commits.len(),
					if commits.len() == 1 {
						"commit"
					} else {
						"commits"
					},
					ref_name
				));

				for commit in commits {
					lines.push(format!(
						"  {} \"{}\" by {}",
						commit.as_object().short_id()?.as_str().unwrap(),
						commit.summary().unwrap(),
						commit.author().name().unwrap()
					));
				}
			}
		} else if r#ref.is_tag() {
			if new.is_zero() {
				lines.push(format!(
					"[{}] tag {} deleted (was {})",
					repo_name, ref_name, old
				))
			} else if old.is_zero() {
				lines.push(format!(
					"[{}] commit {} tagged as {}",
					repo_name, new, ref_name
				))
			} else {
				lines.push(format!(
					"[{}] tag {} modified (was {}, now {})",
					repo_name, ref_name, old, new
				))
			}
		} else {
			return Err(anyhow!(
				"Received a reference that's neither a branch nor tag: {}",
				args[2]
			));
		}

		tx.send(Batch {
			repository: repo_name.to_owned(),
			lines,
		})?;
	}

	Ok(())
}