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/*
   Copyright The containerd Authors.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

use std::{
    collections::HashMap,
    sync::{
        mpsc::{channel, Receiver, Sender},
        Mutex,
    },
};

use lazy_static::lazy_static;
use log::{error, warn};

use crate::{
    monitor::{ExitEvent, Subject, Topic},
    Result,
};

lazy_static! {
    pub static ref MONITOR: Mutex<Monitor> = {
        let monitor = Monitor {
            seq_id: 0,
            subscribers: HashMap::new(),
            topic_subs: HashMap::new(),
        };
        Mutex::new(monitor)
    };
}

pub fn monitor_subscribe(topic: Topic) -> Result<Subscription> {
    let mut monitor = MONITOR.lock().unwrap();
    let s = monitor.subscribe(topic)?;
    Ok(s)
}

pub fn monitor_notify_by_pid(pid: i32, exit_code: i32) -> Result<()> {
    let monitor = MONITOR.lock().unwrap();
    monitor.notify_by_pid(pid, exit_code)
}

pub fn monitor_notify_by_exec(id: &str, exec_id: &str, exit_code: i32) -> Result<()> {
    let monitor = MONITOR.lock().unwrap();
    monitor.notify_by_exec(id, exec_id, exit_code)
}

pub struct Monitor {
    pub(crate) seq_id: i64,
    pub(crate) subscribers: HashMap<i64, Subscriber>,
    pub(crate) topic_subs: HashMap<Topic, Vec<i64>>,
}

pub(crate) struct Subscriber {
    pub(crate) topic: Topic,
    pub(crate) tx: Sender<ExitEvent>,
}

pub struct Subscription {
    pub id: i64,
    pub rx: Receiver<ExitEvent>,
}

impl Monitor {
    pub fn subscribe(&mut self, topic: Topic) -> Result<Subscription> {
        let (tx, rx) = channel::<ExitEvent>();
        let id = self.seq_id;
        self.seq_id += 1;
        let subscriber = Subscriber {
            tx,
            topic: topic.clone(),
        };
        self.subscribers.insert(id, subscriber);
        self.topic_subs
            .entry(topic)
            .or_insert_with(Vec::new)
            .push(id);
        Ok(Subscription { id, rx })
    }

    pub fn notify_by_pid(&self, pid: i32, exit_code: i32) -> Result<()> {
        let subject = Subject::Pid(pid);
        self.notify_topic(&Topic::Pid, &subject, exit_code);
        self.notify_topic(&Topic::All, &subject, exit_code);
        Ok(())
    }

    pub fn notify_by_exec(&self, cid: &str, exec_id: &str, exit_code: i32) -> Result<()> {
        let subject = Subject::Exec(cid.into(), exec_id.into());
        self.notify_topic(&Topic::Exec, &subject, exit_code);
        self.notify_topic(&Topic::All, &subject, exit_code);
        Ok(())
    }

    fn notify_topic(&self, topic: &Topic, subject: &Subject, exit_code: i32) {
        self.topic_subs.get(topic).map_or((), |subs| {
            for i in subs {
                self.subscribers.get(i).and_then(|sub| {
                    sub.tx
                        .send(ExitEvent {
                            subject: subject.clone(),
                            exit_code,
                        })
                        .map_err(|e| warn!("failed to send {}", e))
                        .ok()
                });
            }
        })
    }

    pub fn unsubscribe(&mut self, id: i64) -> Result<()> {
        let sub = self.subscribers.remove(&id);
        if let Some(s) = sub {
            self.topic_subs.get_mut(&s.topic).map(|v| {
                v.iter().position(|&x| x == id).map(|i| {
                    v.remove(i);
                })
            });
        }
        Ok(())
    }
}

impl Drop for Subscription {
    fn drop(&mut self) {
        let mut monitor = MONITOR.lock().unwrap();
        monitor.unsubscribe(self.id).unwrap_or_else(|e| {
            error!("failed to unsubscribe the subscription {}, {}", self.id, e);
        });
    }
}

pub fn wait_pid(pid: i32, s: Subscription) -> i32 {
    loop {
        if let Ok(ExitEvent {
            subject: Subject::Pid(epid),
            exit_code: code,
        }) = s.rx.recv()
        {
            if pid == epid {
                return code;
            }
        }
    }
}