moq-dir 0.3.4

use anyhow::Context;
use bytes::BytesMut;
use std::collections::{HashSet, VecDeque};

use moq_transport::serve::{
    ServeError, SubgroupReader, SubgroupWriter, SubgroupsReader, SubgroupsWriter, TrackReader,
    TrackReaderMode, TrackWriter,
};

pub struct ListingWriter {
    track: Option<TrackWriter>,
    subgroups: Option<SubgroupsWriter>,
    subgroup: Option<SubgroupWriter>,

    current: HashSet<String>,
}

impl ListingWriter {
    pub fn new(track: TrackWriter) -> Self {
        Self {
            track: Some(track),
            subgroups: None,
            subgroup: None,
            current: HashSet::new(),
        }
    }

    pub fn insert(&mut self, name: String) -> Result<(), ServeError> {
        if !self.current.insert(name.clone()) {
            return Err(ServeError::Duplicate);
        }

        match self.subgroup {
            // Create a delta if the current subgroup is small enough.
            Some(ref mut subgroup) if self.current.len() < 2 * subgroup.len() => {
                let msg = format!("+{name}");
                subgroup.write(msg.into())?;
            }
            // Otherwise create a snapshot with every element.
            _ => self.subgroup = Some(self.snapshot()?),
        }

        Ok(())
    }

    pub fn remove(&mut self, name: &str) -> Result<(), ServeError> {
        if !self.current.remove(name) {
            return Err(ServeError::NotFound);
        }

        match self.subgroup {
            // Create a delta if the current subgroup is small enough.
            Some(ref mut subgroup) if self.current.len() < 2 * subgroup.len() => {
                let msg = format!("-{name}");
                subgroup.write(msg.into())?;
            }
            // Otherwise create a snapshot with every element.
            _ => self.subgroup = Some(self.snapshot()?),
        }

        Ok(())
    }

    fn snapshot(&mut self) -> Result<SubgroupWriter, ServeError> {
        let mut subgroups = match self.subgroups.take() {
            Some(subgroups) => subgroups,
            None => self.track.take().unwrap().groups()?,
        };

        let priority = 127;
        let mut subgroup = subgroups.append(priority)?;

        let mut msg = BytesMut::new();
        for name in &self.current {
            msg.extend_from_slice(name.as_bytes());
            msg.extend_from_slice(b"\n");
        }

        subgroup.write(msg.freeze())?;
        self.subgroups = Some(subgroups);

        Ok(subgroup)
    }

    pub fn len(&self) -> usize {
        self.current.len()
    }

    pub fn is_empty(&self) -> bool {
        self.current.is_empty()
    }
}

#[derive(Clone)]
pub enum ListingDelta {
    Add(String),
    Rem(String),
}

#[derive(Clone)]
pub struct ListingReader {
    track: TrackReader,

    // Keep track of the current subgroup.
    subgroups: Option<SubgroupsReader>,
    subgroup: Option<SubgroupReader>,

    // The current state of the listing.
    current: HashSet<String>,

    // A list of deltas we need to return
    deltas: VecDeque<ListingDelta>,
}

impl ListingReader {
    pub fn new(track: TrackReader) -> Self {
        Self {
            track,
            subgroups: None,
            subgroup: None,

            current: HashSet::new(),
            deltas: VecDeque::new(),
        }
    }

    pub async fn next(&mut self) -> anyhow::Result<Option<ListingDelta>> {
        if let Some(delta) = self.deltas.pop_front() {
            return Ok(Some(delta));
        }

        if self.subgroups.is_none() {
            self.subgroups = match self.track.mode().await? {
                TrackReaderMode::Subgroups(subgroups) => Some(subgroups),
                _ => anyhow::bail!("expected subgroups mode"),
            };
        };

        if self.subgroup.is_none() {
            self.subgroup = Some(
                self.subgroups
                    .as_mut()
                    .unwrap()
                    .next()
                    .await?
                    .context("empty track")?,
            );
        }

        let mut subgroup_done = false;
        let mut subgroups_done = false;

        loop {
            tokio::select! {
                next = self.subgroups.as_mut().unwrap().next(), if !subgroups_done => {
                    if let Some(next) = next? {
                        self.subgroup = Some(next);
                        subgroup_done = false;
                    } else {
                        subgroups_done = true;
                    }
                },
                object = self.subgroup.as_mut().unwrap().read_next(), if !subgroup_done => {
                    let payload = match object? {
                        Some(object) => object,
                        None => {
                            subgroup_done = true;
                            continue;
                        }
                    };

                    if payload.is_empty() {
                        anyhow::bail!("empty payload");
                    } else if self.subgroup.as_mut().unwrap().pos() == 1 {
                        // This is a full snapshot, not a delta
                        let set = HashSet::from_iter(payload.split(|&b| b == b'\n').map(|s| String::from_utf8_lossy(s).to_string()));

                        for name in set.difference(&self.current) {
                            self.deltas.push_back(ListingDelta::Add(name.clone()));
                        }

                        for name in self.current.difference(&set) {
                            self.deltas.push_back(ListingDelta::Rem(name.clone()));
                        }

                        self.current = set;

                        if let Some(delta) = self.deltas.pop_front() {
                            return Ok(Some(delta));
                        }
                    } else if payload[0] == b'+' {
                        return Ok(Some(ListingDelta::Add(String::from_utf8_lossy(&payload[1..]).to_string())));
                    } else if payload[0] == b'-' {
                        return Ok(Some(ListingDelta::Rem(String::from_utf8_lossy(&payload[1..]).to_string())));
                    } else {
                        anyhow::bail!("invalid delta: {:?}", payload);
                    }
                }
                else => return Ok(None),
            }
        }
    }

    // If you just want to proxy the track
    pub fn into_inner(self) -> TrackReader {
        self.track
    }
}