use chrono::Local;
use rand::Rng;
use spamassassin_milter::{Config, ConfigBuilder};
use std::{
    io::{self, ErrorKind},
    net::{Ipv4Addr, Ipv6Addr, SocketAddr},
    time::Duration,
};
use tokio::{
    io::{AsyncReadExt, AsyncWriteExt},
    net::{TcpListener, ToSocketAddrs},
    sync::oneshot,
    task::JoinHandle,
    time,
};

pub const LOCALHOST: (Ipv4Addr, u16) = (Ipv4Addr::LOCALHOST, 0);

/// Configures the builder for integration testing with `spamc`. Most
/// importantly, this isolates `spamc` from any configuration file
/// `/etc/spamassassin/spamc.conf` present on the host, as this configuration is
/// read by default and may break the integration tests.
pub fn configure_spamc(builder: ConfigBuilder) -> ConfigBuilder {
    // Note: Must use `-F` instead of `--config` due to a bug in `spamc`.
    // `--no-safe-fallback` prevents connection attempts from failing silently,
    // and `--log-to-stderr` avoids polluting syslog with test output.
    builder.spamc_args(["-F", "/dev/null", "--no-safe-fallback", "--log-to-stderr"])
}

pub const SPAMD_PORT: u16 = 3783;  // mock port

pub type HamOrSpam = Result<String, String>;

/// Spawns a mock `spamd` server that echoes what it is sent after applying
/// transformation `f` to the message content and mock-classifying it as ham or
/// spam.
pub async fn spawn_mock_spamd_server<F>(port: u16, f: F) -> io::Result<JoinHandle<io::Result<()>>>
where
    F: Fn(String) -> HamOrSpam + Send + 'static,
{
    let socket_addr = (Ipv6Addr::LOCALHOST, port);
    let listener = TcpListener::bind(socket_addr).await?;

    Ok(tokio::spawn(async move {
        // This server expects and handles only a single connection, so that we
        // can `join` this task in the tests and detect errors and panics.
        let (mut stream, _) = time::timeout(Duration::from_secs(10), listener.accept())
            .await
            .map_err(|e| io::Error::new(ErrorKind::Other, e))??;

        let mut buf = Vec::new();

        stream.read_to_end(&mut buf).await?;

        let msg = process_message(buf, &f);

        stream.write_all(msg.as_bytes()).await?;

        Ok(())
    }))
}

// The SpamAssassin client/server protocol is here reverse-engineered in a very
// rudimentary fashion: Both client and server send a protocol header containing
// a content length indication and terminated with "\r\n\r\n". The payload is
// the email message itself with CRLF line endings.

const SPAMD_PROTOCOL_OK: &str = "SPAMD/1.1 0 EX_OK";

fn process_message<F>(buf: Vec<u8>, f: &F) -> String
where
    F: Fn(String) -> HamOrSpam + Send + 'static,
{
    let mut msg = String::from_utf8(buf).unwrap();

    // Crude handling of the `spamc` client protocol: strip off everything
    // before and including the first "\r\n\r\n".
    let i = msg.find("\r\n\r\n").expect("spamc protocol header missing");
    msg.drain(..i + 4);

    match f(msg) {
        // Again very basic handling of the `spamd` server protocol: add a
        // forged protocol header terminated with "\r\n\r\n". (This is currently
        // not used in tests.)
        Ok(ham) => format!(
            "{}\r\nContent-length: {}\r\nSpam: False ; 4.0 / 5.0\r\n\r\n{}",
            SPAMD_PROTOCOL_OK,
            ham.len(),
            ham
        ),
        Err(spam) => format!(
            "{}\r\nContent-length: {}\r\nSpam: True ; 6.0 / 5.0\r\n\r\n{}",
            SPAMD_PROTOCOL_OK,
            spam.len(),
            spam
        ),
    }
}

pub fn rand_msg_id() -> String {
    let n = rand::thread_rng().gen_range(1..=999999);
    format!("<{n:06}@gluet.ch>")
}

pub fn current_date() -> String {
    Local::now().to_rfc2822()
}

pub struct SpamAssassinMilter {
    milter_handle: JoinHandle<io::Result<()>>,
    shutdown: oneshot::Sender<()>,
    addr: SocketAddr,
}

impl SpamAssassinMilter {
    pub async fn spawn(addr: impl ToSocketAddrs, config: Config) -> io::Result<Self> {
        let listener = TcpListener::bind(addr).await?;

        let addr = listener.local_addr()?;

        let (shutdown_tx, shutdown_rx) = oneshot::channel();

        let milter = tokio::spawn(spamassassin_milter::run(listener, config, shutdown_rx));

        Ok(Self {
            milter_handle: milter,
            shutdown: shutdown_tx,
            addr,
        })
    }

    pub fn addr(&self) -> SocketAddr {
        self.addr
    }

    pub async fn shutdown(self) -> io::Result<()> {
        let _ = self.shutdown.send(());

        self.milter_handle.await?
    }
}