use std::fs::File;
use std::io::{BufRead, BufReader, Error, ErrorKind, Read, Write};
use std::net::Shutdown;
use std::os::unix::net::UnixStream;

use crate::options::OPTIONS;

const RESPONSE_NO: [u8; 4] = [0x0, 0x2, b'N', b'O'];
const RESPONSE_OK: [u8; 4] = [0x0, 0x2, b'O', b'K'];

pub struct Server {
    stream: UnixStream,
}

impl Server {
    pub fn new(stream: UnixStream) -> Result<Server, Error> {
        Ok(Server { stream })
    }

    /// The saslauthd protocol transmits strings as
    /// 16-bit unsigned network-byte-order lengths followed
    /// by the string itself.
    ///
    fn read_string(&mut self) -> Result<String, Error> {
        let mut length_buffer = [0u8, 0u8];

        self.stream.read_exact(&mut length_buffer)?;
        let length = u16::from_be_bytes(length_buffer);

        let mut string_buffer = vec![0u8; length as usize];

        self.stream.read_exact(&mut string_buffer)?;

        match String::from_utf8(string_buffer) {
            Ok(str) => Ok(str),
            Err(_err) => Err(Error::new(ErrorKind::Other, "Invalid UTF-8 sent")),
        }
    }

    fn write_string(&mut self, s: &str) -> Result<(), Error> {
        let length = s.len();

        if length > 0xffff {
            return Err(Error::new(ErrorKind::Other, "String too long to write"));
        }

        let length_buffer = [(length >> 8) as u8, (length & 0xff) as u8];

        self.stream.write_all(&length_buffer)?;
        self.stream.write_all(s.as_bytes())?;

        Ok(())
    }

    fn check_auth(&mut self, userid: &str, password: &str) -> Result<bool, Error> {
        // Don't allow empty userids or passwords
        //
        if userid.is_empty() || password.is_empty() {
            return Ok(false);
        }

        let mut password_file = OPTIONS.passwords.clone();
        password_file.push(&userid);

        let file = File::open(password_file)?;

        for line in BufReader::new(file).lines().flatten() {
            if !line.starts_with('#') && line.trim() == password {
                return Ok(true);
            }
        }

        Ok(false)
    }

    fn communicate(&mut self) -> Result<(), Error> {
        let userid = self.read_string()?;
        let password = self.read_string()?;
        let _service = self.read_string()?;
        let _realm = self.read_string()?;

        match self.check_auth(&userid, &password) {
            Ok(true) => self.stream.write_all(&RESPONSE_OK)?,
            Ok(false) => self.stream.write_all(&RESPONSE_NO)?,
            Err(e) => {
                self.stream.write_all(&RESPONSE_NO)?;
                self.stream.shutdown(Shutdown::Both)?;
                return Err(e);
            }
        }

        Ok(())
    }

    pub fn handle_client(&mut self) {
        if let Err(error) = self.communicate() {
            eprint!("{}", error);
        }
    }
}