use std::collections::HashMap;
use std::process::Command;

use std::io;

#[derive(Debug, PartialEq, Eq)]
pub struct Unit {
    pub name: String,
    pub type_: String,
    pub active_state: String,
    pub sub_state: String,
}

pub fn parse_key_value(line: &str) -> Option<(String, String)> {
    let pos = line.find('=');
    pos.map(|pos| {
        let (k, v) = line.split_at(pos);
        (k.to_owned(), v[1..].to_owned())
    })
}

#[test]
fn test_parse_key_value() {
    assert_eq!(None, parse_key_value("ab"));
    assert_eq!(Some(("a".to_owned(), "b".to_owned())), parse_key_value("a=b"));
    assert_eq!(Some(("a".to_owned(), "b=c".to_owned())), parse_key_value("a=b=c"));
}

fn make_unit(info: HashMap<String, String>) -> Option<Unit> {
    fn from_id(id: &str) -> Option<String> {
        id.rsplit('.').next().map(|t| t.to_owned())
    };
    fn cloned(s: &String) -> String { s.clone() }
    let id = info.get("Id").map(cloned);
    let type_ = id.as_ref().and_then(|id| from_id(&id));
    let active_state = info.get("ActiveState").map(cloned);
    let sub_state = info.get("SubState").map(cloned);
    
    if let (Some(id), Some(type_), Some(active_state), Some(sub_state)) =
        (id, type_, active_state, sub_state) {
        Some(Unit { name: id, type_: type_, active_state: active_state, sub_state: sub_state })
    } else {
        None
    }
}

#[test]
fn test_make_unit() {
    let s = |s: &str| -> String { s.to_owned() };
    let info = [
        (s("Id"), s("Test.service")),
        (s("ActiveState"), s("active")),
        (s("SubState"), s("running")),
    ]
        .iter().cloned().collect::<HashMap<String, String>>();
    let actual = make_unit(info).unwrap();;
    assert_eq!(s("Test.service"), actual.name);

    let info = HashMap::new();
    assert_eq!(None, make_unit(info));
}

pub fn get_units(filter: &str) -> io::Result<Vec<Unit>> {
    let mut units = Vec::new();
    let status = try!(Command::new("systemctl")
        .args(&["show", filter]).output());

    let mut unit_info = HashMap::new();
    for line in String::from_utf8_lossy(&status.stdout).split('\n') {
        if let Some((k, v)) = parse_key_value(line) {
            unit_info.insert(k, v);
        } else {
            make_unit(unit_info).map(|u| units.push(u));
            unit_info = HashMap::new();
        }
    }
    return Ok(units);
}