use std::error::Error;
use std::ffi::OsStr;
use std::io::{Result as IoResult, Write};
use std::process::Command;
use std::process::Output;
use std::process::Stdio;

pub trait CommandRunner {
  fn run_with_args_and_stdin<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
    stdin: &str,
  ) -> IoResult<Output>;
  fn run_with_args<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
  ) -> IoResult<Output> {
    self.run_with_args_and_stdin(program, args, "")
  }
  fn get_output<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
  ) -> Result<Vec<u8>, Box<dyn Error>> {
    let output = try!(self.run_with_args(program, args));
    if !output.status.success() {
      return Err(try!(String::from_utf8(output.stderr)).into());
    }
    Ok(output.stdout)
  }
  fn get_stderr<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
  ) -> Result<Vec<u8>, Box<dyn Error>> {
    let output = try!(self.run_with_args(program, args));
    if !output.status.success() {
      return Err(try!(String::from_utf8(output.stderr)).into());
    }
    Ok(output.stderr)
  }
  fn run_successfully<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
  ) -> Result<(), Box<dyn Error>> {
    let output = try!(self.run_with_args(program, args));
    if output.status.success() {
      Ok(())
    } else {
      Err(try!(String::from_utf8(output.stderr)).into())
    }
  }
}

#[derive(Debug)]
pub struct StdCommandRunner;

impl CommandRunner for StdCommandRunner {
  fn run_with_args_and_stdin<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
    input: &str,
  ) -> IoResult<Output> {
    // FIXME: logger
    //println!("{} {:?}", program, args);
    let mut child = Command::new(program)
      .args(args)
      .stdin(Stdio::piped())
      .stdout(Stdio::piped())
      .stderr(Stdio::piped())
      .spawn()
      .expect("Failed to spawn child process");
    let stdin = child.stdin.as_mut().expect("Failed to open stdin");
    stdin
      .write_all(input.as_bytes())
      .expect("Failed to write to stdin");
    let res = child.wait_with_output();
    println!("{:?}", res);
    res
  }
}

#[derive(Debug)]
pub struct SetuidCommandRunner<'a, C>
where
  C: 'a + CommandRunner,
{
  command_runner: &'a C,
  user_name: &'a str,
}

impl<'a, C> SetuidCommandRunner<'a, C>
where
  C: 'a + CommandRunner,
{
  pub fn new(user_name: &'a str, command_runner: &'a C) -> SetuidCommandRunner<'a, C> {
    SetuidCommandRunner {
      command_runner,
      user_name,
    }
  }
}

use std::env;
use std::os::unix::process::CommandExt;
use users::get_user_by_name;

struct TempSetEnv<'a> {
  name: &'a str,
  old_value: Option<String>,
}

impl<'a> TempSetEnv<'a> {
  fn new(name: &'a str, new_value: String) -> TempSetEnv<'a> {
    let old_value = env::var(name);
    env::set_var(name, new_value);
    TempSetEnv {
      name,
      old_value: old_value.ok(),
    }
  }
}

impl<'a> Drop for TempSetEnv<'a> {
  fn drop(&mut self) {
    match self.old_value {
      Some(ref val) => env::set_var(self.name, val),
      None => env::remove_var(self.name),
    }
  }
}

impl<'a, C> CommandRunner for SetuidCommandRunner<'a, C>
where
  C: 'a + CommandRunner,
{
  fn run_with_args_and_stdin<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
    input: &str,
  ) -> IoResult<Output> {
    let uid = get_user_by_name(self.user_name)
      .expect("User does not exist")
      .uid();
    let set_home = TempSetEnv::new("HOME", format!("/home/{}", self.user_name));
    let set_dbus = TempSetEnv::new("XDG_RUNTIME_DIR", format!("/run/user/{}", uid));
    //println!("{} {:?}", program, args);
    let mut child = Command::new(program)
      .args(args)
      .stdin(Stdio::piped())
      .uid(uid)
      .gid(uid)
      .stdout(Stdio::piped())
      .stderr(Stdio::piped())
      .spawn()
      .expect("Failed to spawn child process");
    let stdin = child.stdin.as_mut().expect("Failed to open stdin");
    stdin
      .write_all(input.as_bytes())
      .expect("Failed to write to stdin");
    let res = child.wait_with_output();
    println!("{:?}", res);
    res
  }
}

#[derive(Debug)]
pub struct SuCommandRunner<'a, C>
where
  C: 'a + CommandRunner,
{
  command_runner: &'a C,
  user_name: &'a str,
}

impl<'a, C> SuCommandRunner<'a, C>
where
  C: 'a + CommandRunner,
{
  pub fn new(user_name: &'a str, command_runner: &'a C) -> SuCommandRunner<'a, C> {
    SuCommandRunner {
      command_runner,
      user_name,
    }
  }
}

// Su doesn't set XDG_RUNTIME_DIR
// https://github.com/systemd/systemd/blob/master/src/login/pam_systemd.c#L439
impl<'a, C> CommandRunner for SuCommandRunner<'a, C>
where
  C: 'a + CommandRunner,
{
  fn run_with_args_and_stdin<S: AsRef<OsStr> + ?Sized>(
    &self,
    program: &str,
    args: &[&S],
    input: &str,
  ) -> IoResult<Output> {
    let raw_new_args = [self.user_name, "-s", "/usr/bin/env", "--", program];
    let mut new_args: Vec<&OsStr> = raw_new_args.iter().map(|s| s.as_ref()).collect();
    let old_args: Vec<&OsStr> = args.iter().map(|s| s.as_ref()).collect();
    new_args.extend_from_slice(&old_args);
    self
      .command_runner
      .run_with_args_and_stdin("su", &new_args, input)
  }
}

#[cfg(test)]
mod test {}