use std::borrow::{ Borrow, Cow };
use std::error::Error;
use std::fmt;
use std::path::PathBuf;

use command_runner::CommandRunner;
use symbols::{Action, OwnedSymbolAction, Symbol, SymbolAction, SymbolRunner};

#[derive(Debug)]
pub enum SystemdUserSessionError<E: Error> {
  ExecError(E),
  GenericError
}

impl<E: Error> Error for SystemdUserSessionError<E> {
  fn description(&self) -> &str {
    match self {
      &SystemdUserSessionError::ExecError(ref e) => e.description(),
      &SystemdUserSessionError::GenericError => "Generic error"
    }
  }
  fn cause(&self) -> Option<&Error> {
    match self {
      &SystemdUserSessionError::ExecError(ref e) => Some(e),
      _ => None
    }
  }
}

impl<E: Error> fmt::Display for SystemdUserSessionError<E> {
  fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
    write!(f, "{}", self.description())
  }
}

pub struct SystemdUserSession<'a> {
  user_name: Cow<'a, str>,
  command_runner: &'a CommandRunner
}

impl<'a> SystemdUserSession<'a> {
  pub fn new(user_name: Cow<'a, str>, command_runner: &'a CommandRunner) -> Self {
    SystemdUserSession {
      user_name: user_name,
      command_runner: command_runner
    }
  }
}

impl<'a> Symbol for SystemdUserSession<'a> {
  fn target_reached(&self) -> Result<bool, Box<Error>> {
    let mut path = PathBuf::from("/var/lib/systemd/linger");
    path.push(self.user_name.borrow() as &str);
    Ok(path.exists())
    // Could also do `loginctl show-user ${self.user_name} | grep -F 'Linger=yes`
  }

  fn execute(&self) -> Result<(), Box<Error>> {
    self.command_runner.run_successfully("loginctl", &["enable-linger", self.user_name.borrow()])
  }

  fn as_action<'b>(&'b self, runner: &'b SymbolRunner) -> Box<Action + 'b> {
    Box::new(SymbolAction::new(runner, self))
  }

  fn into_action<'b>(self: Box<Self>, runner: &'b SymbolRunner) -> Box<Action + 'b> where Self: 'b {
    Box::new(OwnedSymbolAction::new(runner, *self))
  }
}

impl<'a> fmt::Display for SystemdUserSession<'a> {
  fn fmt(&self, f: &mut fmt::Formatter) -> Result<(),fmt::Error>{
    write!(f, "Systemd user session for {}", self.user_name)
  }
}