// Copyright (c) 2018 Levente Kurusa
//
// SPDX-License-Identifier: Apache-2.0 or MIT
//

//! This module contains the implementation of the `net_prio` cgroup subsystem.
//!
//! See the Kernel's documentation for more information about this subsystem, found at:
//!  [Documentation/cgroup-v1/net_prio.txt](https://www.kernel.org/doc/Documentation/cgroup-v1/net_prio.txt)
use std::collections::HashMap;
use std::io::{BufRead, BufReader, Write};
use std::path::PathBuf;

use crate::error::ErrorKind::*;
use crate::error::*;

use crate::read_u64_from;
use crate::{
    ControllIdentifier, ControllerInternal, Controllers, NetworkResources, Resources, Subsystem,
};

/// A controller that allows controlling the `net_prio` subsystem of a Cgroup.
///
/// In essence, using `net_prio` one can set the priority of the packets emitted from the control
/// group's tasks. This can then be used to have QoS restrictions on certain control groups and
/// thus, prioritizing certain tasks.
#[derive(Debug, Clone)]
pub struct NetPrioController {
    base: PathBuf,
    path: PathBuf,
}

impl ControllerInternal for NetPrioController {
    fn control_type(&self) -> Controllers {
        Controllers::NetPrio
    }
    fn get_path(&self) -> &PathBuf {
        &self.path
    }
    fn get_path_mut(&mut self) -> &mut PathBuf {
        &mut self.path
    }
    fn get_base(&self) -> &PathBuf {
        &self.base
    }

    fn apply(&self, res: &Resources) -> Result<()> {
        // get the resources that apply to this controller
        let res: &NetworkResources = &res.network;

        for i in &res.priorities {
            let _ = self.set_if_prio(&i.name, i.priority);
        }

        Ok(())
    }
}

impl ControllIdentifier for NetPrioController {
    fn controller_type() -> Controllers {
        Controllers::NetPrio
    }
}

impl<'a> From<&'a Subsystem> for &'a NetPrioController {
    fn from(sub: &'a Subsystem) -> &'a NetPrioController {
        unsafe {
            match sub {
                Subsystem::NetPrio(c) => c,
                _ => {
                    assert_eq!(1, 0);
                    let v = std::mem::MaybeUninit::uninit();
                    v.assume_init()
                }
            }
        }
    }
}

impl NetPrioController {
    /// Constructs a new `NetPrioController` with `root` serving as the root of the control group.
    pub fn new(root: PathBuf) -> Self {
        Self {
            base: root.clone(),
            path: root,
        }
    }

    /// Retrieves the current priority of the emitted packets.
    pub fn prio_idx(&self) -> u64 {
        self.open_path("net_prio.prioidx", false)
            .and_then(read_u64_from)
            .unwrap_or(0)
    }

    /// A map of priorities for each network interface.
    pub fn ifpriomap(&self) -> Result<HashMap<String, u64>> {
        self.open_path("net_prio.ifpriomap", false)
            .and_then(|file| {
                let bf = BufReader::new(file);
                bf.lines().fold(Ok(HashMap::new()), |acc, line| {
                    if acc.is_err() {
                        acc
                    } else {
                        let mut acc = acc.unwrap();
                        let l = line.unwrap();
                        let mut sp = l.split_whitespace();
                        let ifname = sp.nth(0);
                        let ifprio = sp.nth(1);
                        if ifname.is_none() || ifprio.is_none() {
                            Err(Error::new(ParseError))
                        } else {
                            let ifname = ifname.unwrap();
                            let ifprio = ifprio.unwrap().trim().parse();
                            match ifprio {
                                Err(e) => Err(Error::with_cause(ParseError, e)),
                                Ok(_) => {
                                    acc.insert(ifname.to_string(), ifprio.unwrap());
                                    Ok(acc)
                                }
                            }
                        }
                    }
                })
            })
    }

    /// Set the priority of the network traffic on `eif` to be `prio`.
    pub fn set_if_prio(&self, eif: &str, prio: u64) -> Result<()> {
        self.open_path("net_prio.ifpriomap", true)
            .and_then(|mut file| {
                file.write_all(format!("{} {}", eif, prio).as_ref())
                    .map_err(|e| Error::with_cause(WriteFailed, e))
            })
    }
}
