//! 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::path::PathBuf;
use std::io::{BufReader, BufRead, Write, Read};
use std::fs::File;
use std::collections::HashMap;

use {CgroupError, NetworkResources, Controllers, Controller, Resources, ControllIdentifier, Subsystem};
use CgroupError::*;

/// 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 Controller for NetPrioController {
    fn control_type(self: &Self) -> Controllers { Controllers::NetPrio }
    fn get_path<'a>(self: &'a Self) -> &'a PathBuf { &self.path }
    fn get_path_mut<'a>(self: &'a mut Self) -> &'a mut PathBuf { &mut self.path }
    fn get_base<'a>(self: &'a Self) -> &'a PathBuf { &self.base }

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

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

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);
                    ::std::mem::uninitialized()
                },
            }
        }
    }
}

fn read_u64_from(mut file: File) -> Result<u64, CgroupError> {
    let mut string = String::new();
    match file.read_to_string(&mut string) {
        Ok(_) => string.trim().parse().map_err(|_| ParseError),
        Err(e) => Err(CgroupError::ReadError(e)),
    }
}

impl NetPrioController {
    /// Constructs a new `NetPrioController` with `oroot` serving as the root of the control group.
    pub fn new(oroot: PathBuf) -> Self {
        let mut root = oroot;
        root.push(Self::controller_type().to_string());
        Self {
            base: root.clone(),
            path: root,
        }
    }

    /// Retrieves the current priority of the emitted packets.
    pub fn prio_idx(self: &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: &Self) -> Result<HashMap<String, u64>, CgroupError> {
        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(CgroupError::ParseError)
                    } else {
                        let ifname = ifname.unwrap();
                        let ifprio = ifprio.unwrap().trim().parse();
                        if ifprio.is_err() {
                            Err(CgroupError::ParseError)
                        } else {
                            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: &Self, eif: &String, prio: u64) -> Result<(), CgroupError> {
        self.open_path("net_prio.ifpriomap", true).and_then(|mut file| {
            file.write_all(format!("{} {}", eif, prio).as_ref()).map_err(CgroupError::WriteError)
        })
    }
}