use std::{collections::HashMap, ops::Deref as _};

use tokio_stream::StreamExt as _;
use tracing::{Instrument, debug, debug_span, error, trace, warn};
use zbus::{
    Connection, ObjectServer,
    fdo::Result,
    names::OwnedUniqueName,
    object_server::SignalEmitter,
    proxy::ProxyImpl,
    zvariant::{self, OwnedObjectPath},
};

pub const RESPONSE_SUCCESS: u32 = 0;
// pub const RESPONSE_CANCELLED: u32 = 1;
pub const RESPONSE_OTHER: u32 = 2;

/// A handler for the org.freedesktop.portal.Request interface, proxying to another
/// instance of the same interface.
struct Request {
    host: RequestProxy<'static>,
}

#[zbus::interface(
    name = "org.freedesktop.portal.Request",
    proxy(default_service = "org.freedesktop.portal.Desktop")
)]
impl Request {
    #[zbus(signal)]
    async fn response(
        signal_emitter: &SignalEmitter<'_>,
        response: u32,
        results: HashMap<&str, zvariant::Value<'_>>,
    ) -> zbus::Result<()>;

    async fn close(&self) -> Result<()> {
        self.host.close().await
    }
}

pub trait ResultTransformer {
    fn apply<'a>(
        self,
        response: u32,
        results: HashMap<&'a str, zvariant::Value<'a>>,
    ) -> impl std::future::Future<Output = Result<(u32, HashMap<&'a str, zvariant::Value<'a>>)>>
    + std::marker::Send;
}

impl ResultTransformer for () {
    async fn apply<'a>(
        self,
        response: u32,
        results: HashMap<&'a str, zvariant::Value<'a>>,
    ) -> Result<(u32, HashMap<&'a str, zvariant::Value<'a>>)> {
        Ok((response, results))
    }
}

pub struct ReqHandler<T: ResultTransformer> {
    token: String,
    sender: Option<OwnedUniqueName>,
    conn: Connection,
    server: ObjectServer,
    host_conn: Connection,
    transformer: T,
}

impl ReqHandler<()> {
    pub fn prepare<'a>(
        host: &impl ProxyImpl<'a>,
        hdr: zbus::message::Header<'_>,
        server: &ObjectServer,
        conn: &Connection,
        options: &HashMap<&str, zvariant::Value<'_>>,
    ) -> Self {
        ReqHandler {
            token: get_token(options),
            sender: hdr.sender().map(|s| s.to_owned().into()),
            conn: conn.to_owned(),
            server: server.to_owned(),
            host_conn: host.inner().connection().to_owned(),
            transformer: (),
        }
    }
}

impl<T: ResultTransformer> ReqHandler<T> {
    pub fn with_transform<T1: ResultTransformer>(self, transformer: T1) -> ReqHandler<T1> {
        ReqHandler {
            transformer,
            token: self.token,
            sender: self.sender,
            conn: self.conn,
            server: self.server,
            host_conn: self.host_conn,
        }
    }
}

impl<T: ResultTransformer + Send + 'static> ReqHandler<T> {
    pub async fn perform(
        self,
        call: impl AsyncFnOnce() -> Result<OwnedObjectPath>,
    ) -> Result<OwnedObjectPath> {
        let sender = self.sender.ok_or_else(|| zbus::Error::MissingField)?;
        let sender_str = sender.trim_start_matches(':').replace('.', "_");
        let token = self.token;
        let path = zvariant::ObjectPath::try_from(format!(
            "/org/freedesktop/portal/desktop/request/{sender_str}/{token}"
        ))
        .map_err(zbus::Error::from)?;

        let host_path = call().await?;
        let imp = Request {
            host: RequestProxy::builder(&self.host_conn)
                .path(host_path)?
                .build()
                .await?,
        };
        let stream = imp.host.receive_response().await?;
        if !self.server.at(&path, imp).await? {
            return Err(zbus::fdo::Error::Failed(
                "Duplicate request object path".to_owned(),
            ));
        }

        let path_1: OwnedObjectPath = path.clone().into();
        let sender = sender.to_owned().into();
        tokio::spawn(
            forward_response(stream, self.conn.clone(), path_1, sender, self.transformer)
                .instrument(debug_span!("response proxy", ?path)),
        );
        Ok(path.into())
    }
}

fn get_token(options: &HashMap<&str, zvariant::Value<'_>>) -> String {
    match options.get("handle_token") {
        Some(zvariant::Value::Str(str)) => {
            trace!("extracted token from handle_token option");
            return String::from(str.deref());
        }
        Some(value) => warn!(?value, "handle_token option provided but not a string"),
        None => trace!("handle_token not provided"),
    };
    use rand::distr::{Alphanumeric, SampleString};
    Alphanumeric.sample_string(&mut rand::rng(), 16)
}

async fn forward_response(
    mut stream: ResponseStream,
    conn: Connection,
    path: zvariant::OwnedObjectPath,
    sender: zbus::names::OwnedUniqueName,
    transform: impl ResultTransformer,
) -> Result<()> {
    let signal_emitter = SignalEmitter::new(&conn, path)?
        .set_destination(zbus::names::BusName::Unique(sender.into()))
        .into_owned();
    let Some(resp) = stream.next().await else {
        debug!("response stream gone");
        return Ok(());
    };
    debug!(?resp, "got resp");
    let (response, results) = match resp.0.deserialize() {
        Ok((response, results)) => match transform.apply(response, results).await {
            Ok(res) => res,
            Err(err) => {
                error!(%err, "transform error");
                (RESPONSE_OTHER, HashMap::new())
            }
        },
        Err(err) => {
            error!(%err, "signal body type mismatch");
            (RESPONSE_OTHER, HashMap::new())
        }
    };
    if let Err(err) = Request::response(&signal_emitter, response, results).await {
        error!(%err, "signal forwarding failed");
    }
    Ok(())
}