use std::error::Error;
use std::fmt;
use std::io::Error as IoError;
use std::path::PathBuf;
use std::str::from_utf8;

use command_runner::CommandRunner;
use symbols::Symbol;

#[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: &'a str,
  command_runner: &'a CommandRunner
}

impl<'a> SystemdUserSession<'a> {
  pub fn new(user_name: &'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);
    Ok(path.exists())
    // Could also do `loginctl show-user ${self.user_name} | grep -F 'Linger=yes`
  }

  fn execute(&self) -> Result<(), Box<Error>> {
    match self.command_runner.run_with_args("loginctl", &["enable-linger", self.user_name]) {
      Ok(output) => { println!("{:?} {:?}", from_utf8(&output.stdout).unwrap(), from_utf8(&output.stderr).unwrap() ); match output.status.code() {
        Some(0) => Ok(()),
        _ => Err(Box::new(SystemdUserSessionError::GenericError as SystemdUserSessionError<IoError>))
      } },
      Err(e) => Err(Box::new(SystemdUserSessionError::ExecError(e)))
    }
  }
}

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)
  }
}