use std::io::{self,Read,Write};
use std::net::{TcpStream,SocketAddr};
use std::process::Child;
use std::sync::{Mutex,Condvar};

use crate::err::Result;


// Returns an error if the argument is not a "Keyword" in the control protocol. The control spec
// mentions several types of "keyword"s; It is used to specify command names, settings and GETINFO
// keys, and each seem to have different parsing rules. This function is intended to validate user
// input in order to prevent protocol injection. It is therefore lenient enough in that it allows
// for the different "keyword" contexts, but should still be strict enough to prevent the string
// from being interpreted as something other than a keyword.
fn is_keyword(s: &str) -> Result<()> {
    if s.contains(|c: char| !c.is_ascii_alphanumeric() && c != '/' && c != '-' && c != '_' && c != '.') {
        return Err(err!(Keyword, s.to_string()))
    }
    Ok(())
}


// A Reply (Sync or Async) consists of any number of intermediate lines (Mid/Data) followed by an
// End line.
type Reply = Vec<ReplyLine>;


#[derive(Debug,PartialEq)]
pub(crate) struct ReplyLine {
    len:    usize, // Length of this reply, in bytes, including the final CRLF
    status: u16,
    end:    bool,  // If this is a Mid/Data or End reply
    text:   String,
    data:   Vec<u8>
}


// Used in error message formatting
impl<'a> std::fmt::Display for ReplyLine {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        write!(f, "{} {}", self.status, self.text)
    }
}


impl ReplyLine {
    fn is_async(&self) -> bool {
        self.status >= 600 && self.status < 700
    }

    fn parse_data(buf: &[u8]) -> Option<(usize,Vec<u8>)> {
        // Yes, this actually does need an optimized find_bytes() implementation; With a naive
        // iterator it will take quite a while to parse `GETINFO md/all`.
        let mut off = match twoway::find_bytes(buf, b"\r\n.\r\n") {
            None => return None,
            Some(i) => i
        };
        let mut data = &buf[..off];
        off += 5;

        // Look for a "\r\n." sequence and remove the dot.
        let mut ndata = Vec::new();
        if data.len() > 0 && data[0] == b'.' {
            data = &data[1..];
        }
        while let Some(idx) = twoway::find_bytes(data, b"\r\n.") {
            ndata.extend_from_slice(&data[..idx+2]);
            data = &data[idx+3..];
        }
        ndata.extend_from_slice(data);
        Some((off, ndata))
    }

    // Returns None if there is not enough data in the buffer.
    fn parse(buf: &[u8]) -> Result<Option<ReplyLine>> {
        let mut off = match twoway::find_bytes(buf, b"\r\n") {
            None => return Ok(None),
            Some(i) if i < 4 => return Err(err!(Parse)),
            Some(i) => i
        };
        let line = &buf[..off];
        off += 2;

        let status : u16 = std::str::from_utf8(&line[..3]).map_err(|_| err!(Parse))?.parse().map_err(|_| err!(Parse))?;
        let end = match line[3] {
            b'-' => false,
            b'+' => false,
            b' ' => true,
            _ => return Err(err!(Parse)),
        };
        let text = std::str::from_utf8(&line[4..]).map_err(|_| err!(Parse))?;

        let data = if line[3] == b'+' {
            if let Some((len, d)) = Self::parse_data(&buf[off..]) {
                off += len;
                d
            } else {
                return Ok(None)
            }
        } else {
            Vec::new()
        };

        Ok(Some(ReplyLine {
            len:    off,
            status: status,
            end:    end,
            text:   text.to_string(),
            data:   data,
        }))
    }
}


/// Authentication method and credentials used to authenticate to the Tor control socket.
/// The `COOKIE` and `SAFECOOKIE` authentication methods are not supported.
pub enum Auth {
    /// Authenticate without credentials.
    Null,
    /// Authenticate with a password, this corresponds to the 'HashedControlPassword' configuration
    /// option in torrc.
    HashedPassword(String)
}


#[derive(Debug)]
pub enum Event {
    // Log messages
    Debug(String),
    Info(String),
    Notice(String),
    Warn(String),
    Err(String),
}



// A double-quoted string where only \ and " are escaped.
// Encoding: QuotedString("hello").to_string()
// Decoding: QuotedString::parse("\"hello\"")
struct QuotedString<'a>(&'a str);

impl<'a> std::fmt::Display for QuotedString<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        use std::fmt::Write;
        f.write_char('"')?;
        for c in self.0.chars() {
            if c == '"' || c == '\\' {
                f.write_char('\\')?;
            }
            f.write_char(c)?;
        }
        f.write_char('"')
    }
}

impl<'a> QuotedString<'a> {
    fn parse(s: &str) -> Result<String> {
        if s.len() < 2 || !s.starts_with('"') || !s.ends_with('"') {
            return Err(err!(Parse))
        }
        let mut out = String::with_capacity(s.len());
        let mut q = false;
        for c in (&s[1..s.len()-1]).chars() {
            match (q, c) {
                (true , _   ) => { q = false; out.push(c) },
                (false, '\\') => q = true,
                (false, _   ) => out.push(c),
            }
        }
        if q {
            return Err(err!(Parse))
        }
        Ok(out)
    }
}




/// Tor control socket.
///
/// A socket is created either by connecting to an existing Tor process using `Sock::connect()`, or
/// by calling `spawn()` to spawn a new Tor process.
///
/// A socket can be used from multiple threads, with the following limitations:
/// - It is possible to run commands simultaneously from multiple threads, but the order in which
///   they are executed is, of course, not deterministic. Running a `setconf()` and `getconf()` on
///   the same keys at the same time may not give reliable results.
/// - You should only read asynchronous events from a single thread at a time. The API allows for
///   multiple threads to read events, but an event will only be received by one thread.
pub struct Sock {
    sock:    TcpStream,
    // Should be set when tor is running as a child process and this socket has "ownership" of the process.
    child:   Option<Child>,
    // Read buffer - only one thread can be reading from the socket at a time.
    rdbuf:   Mutex<Vec<u8>>,
    // Read queue - if multiple threads are interested in reading from the socket, then this
    // structure is used to coordinate which thread gets to read from the socket. If that thread
    // happens to read a reply that it isn't interested in (e.g. it expected a sync reply and got
    // an async one), then that reply is pushed to the queue.
    queue:   Mutex<SockQueue>,
    queuecv: Condvar,
    // Write mutex - this ensures only a single command can be sent at a time. This mutex is
    // currently also held while reading the response of a command, because the read queue itself
    // does not ensure that sync replies are consumed by different threads in the proper order.
    // (Could probably be fixed by keeping track of a command sequence - Tor does support
    // pipelining multiple commands, so this is a potential performance improvement)
    writer:  Mutex<bool>,
}

struct SockQueue {
    queue:   Vec<Reply>,
    reading: bool,
}


impl Drop for Sock {
    fn drop(&mut self) {
        // We have to wait() for the child to shut down, otherwise we get a zombie process. This is
        // a quick-and-dirty approach which doesn't really give Tor the time to do a clean
        // shutdown.  In fact, we kill the process before even shutting down the socket.
        // A cleaner "shut down socket and wait a bit" approach should probably be implemented as a
        // separate method.
        if let Some(mut c) = self.child.take() {
            c.kill().is_ok();
            c.wait().is_ok();
        }
    }
}


impl Sock {
    fn read_line(buf: &mut Vec<u8>, sock: &TcpStream) -> Result<ReplyLine> {
        // This buffer handling isn't very efficient, but that's probably fine.
        loop {
            if let Some(r) = ReplyLine::parse(&buf[..])? {
                buf.drain(..r.len);
                return Ok(r);
            }

            let mut rd = [0u8; 512];
            match (&*sock).read(&mut rd) {
                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => (),
                Err(e) => return Err(e.into()),
                Ok(0) => return Err(io::Error::new(io::ErrorKind::UnexpectedEof, "Unexpected disconnect").into()),
                Ok(l) => buf.extend_from_slice(&rd[..l])
            }
        }
    }

    fn read_reply(buf: &mut Vec<u8>, sock: &TcpStream) -> Result<Reply> {
        let mut reply : Reply = Vec::new();
        while reply.last().map(|r| !r.end).unwrap_or(true) {
            reply.push(Self::read_line(buf, sock)?);
        }
        Ok(reply)
    }

    fn get_reply(&self, async_event: bool) -> Result<Reply> {
        // Check the queue to see if our reply has already been read.
        {
            let mut queue = self.queue.lock().unwrap();
            loop {
                if let Some(idx) = queue.queue.iter().position(|r| r[0].is_async() == async_event) {
                    return Ok(queue.queue.remove(idx))
                }
                // Nothing in the queue, but another thread is currently reading, so let's wait.
                if queue.reading {
                    queue = self.queuecv.wait(queue).unwrap();
                // Nothing in the queue and nobody else is reading, let's read from the socket.
                } else {
                    queue.reading = true;
                    break;
                }
            }
        }

        // We now have the read flag, so keep reading until we have our reply.
        let ret = loop {
            let mut buf = self.rdbuf.lock().unwrap();
            match Self::read_reply(&mut buf, &self.sock) {
                Err(e) => break Err(e),
                Ok(r) => {
                    if r[0].is_async() == async_event {
                        break Ok(r)
                    // This reply isn't for us, add it to the queue
                    } else {
                        self.queue.lock().unwrap().queue.push(r);
                        self.queuecv.notify_one();
                    }
                }
            }
        };
        self.queue.lock().unwrap().reading = false;
        self.queuecv.notify_one();
        ret
    }

    fn cmd<S: AsRef<[u8]>>(&self, cmd: S) -> Result<Reply> {
        let _guard = self.writer.lock().unwrap();
        print!("C: {}", std::str::from_utf8(cmd.as_ref()).unwrap());

        (&self.sock).write_all(cmd.as_ref())?;
        let mut ret = self.get_reply(false)?;
        if ret[0].status >= 200 && ret[0].status < 300 {
            Ok(ret)
        } else {
            Err(err!(Status, ret.remove(0)))
        }
    }

    pub(crate) fn connect_child(s: &SocketAddr, auth: &Auth, child: Option<Child>) -> Result<Sock> {
        let sock = Sock {
            sock:    TcpStream::connect(s)?,
            child:   child,
            rdbuf:   Mutex::new(Vec::new()),
            queue:   Mutex::new(SockQueue {
                queue:   Vec::new(),
                reading: false,
            }),
            queuecv: Condvar::new(),
            writer:  Mutex::new(true),
        };

        match auth {
            Auth::Null => sock.cmd("AUTHENTICATE\r\n")?,
            Auth::HashedPassword(s) => sock.cmd(format!("AUTHENTICATE {}\r\n", QuotedString(s)))?
        };
        Ok(sock)
    }

    /// Connect to a running Tor process and authenticate using the given authentication method.
    pub fn connect(s: &SocketAddr, auth: &Auth) -> Result<Sock> {
        Self::connect_child(s, auth, None)
    }

    /// Send a TAKEOWNERSHIP command. If this command has been acknowledged, the Tor process
    /// will automatically shut down when this control socket is closed.
    ///
    /// Ownership is already implied if this socket has been created with the `spawn()` function,
    /// so in that case you do not have to call this method.
    pub fn takeownership(&self) -> Result<()> {
        self.cmd("TAKEOWNERSHIP\r\n").map(|_|())
    }

    /// Send a DROPOWNERSHIP command. This reverses any earlier TAKEOWNERSHIP command and tells
    /// the Tor process to keep running even after this control socket is closed.
    ///
    /// Note that, if this socket has been created with the `spawn()` function, then the Tor
    /// process will still be killed when the socket is dropped. This method is only useful when
    /// connected to an external Tor process.
    pub fn dropownership(&self) -> Result<()> {
        self.cmd("DROPOWNERSHIP\r\n").map(|_|())
    }

    /// Send a QUIT command. This tells Tor to close this control socket. Any further commands will
    /// likely result in an error.
    ///
    /// The Tor process will exit if this control socket has called `takeownership()` before.
    // TODO: Get rid of this function and implement a more thorough shutdown() instead?
    pub fn quit(&self) -> Result<()> {
        self.cmd("QUIT\r\n").map(|_|())
    }


    // XXX: This IntoIterator works with &[..] and &vec![..]. Haven't tested HashMap/BTreeMap yet,
    // but I suspect their signature doesn't match.
    fn setresetconf<'a,T>(&self, mut msg: String, settings: T) -> Result<()>
        where T: IntoIterator<Item = &'a (&'a str, Option<&'a str>)>,
    {
        use std::fmt::Write;
        for (k, v) in settings {
            is_keyword(k)?;
            msg.push(' ');
            msg.push_str(k);
            if let Some(v) = v {
                write!(msg, "={}", QuotedString(v)).is_ok();
            }
        }
        msg.push_str("\r\n");
        self.cmd(msg).map(|_|())
    }

    /// Send a SETCONF command.
    pub fn setconf<'a,T>(&self, settings: T) -> Result<()>
        where T: IntoIterator<Item = &'a (&'a str, Option<&'a str>)>
    {
        self.setresetconf("SETCONF".to_string(), settings)
    }

    /// Send a RESETCONF command.
    pub fn resetconf<'a,T>(&self, settings: T) -> Result<()>
        where T: IntoIterator<Item = &'a (&'a str, Option<&'a str>)>
    {
        self.setresetconf("RESETCONF".to_string(), settings)
    }

    /// Returns the configuration variables for the requested keys. The values are returned in the
    /// order they were requested. Some keys may return multiple values, these will be listed
    /// multiple times. Some keys may return `None` when are unset or default.  An error is
    /// returned if any of the requested keys does not exist.
    ///
    /// This method corresponds to the GETCONF command.
    pub fn getconf<'a,T: IntoIterator<Item = &'a &'a str>>(&self, keys: T) -> Result<Vec<(String, Option<String>)>> {
        let mut msg = "GETCONF".to_string();
        for k in keys {
            is_keyword(k)?;
            msg.push(' ');
            msg.push_str(k);
        }
        msg.push_str("\r\n");

        let mut res = Vec::new();
        for line in self.cmd(msg)? {
            if let Some(is) = line.text.find('=') {
                let val = &line.text[is+1..];
                let val = if val.starts_with('"') { QuotedString::parse(val)? } else { val.to_string() };
                res.push(( (&line.text[..is]).to_string(), Some(val) ));
            } else {
                res.push((line.text, None));
            }
        }
        Ok(res)
    }

    /// Similar to the `getconf()` method, except this is used to get run-time variables that are
    /// not saved in the configuration. An error is returned if any of the requested keys does not
    /// exist.
    ///
    /// Corresponds to the GETINFO command. Refer to the GETINFO documentation in the [tor-control
    /// specification](https://gitweb.torproject.org/torspec.git/blob/control-spec.txt) for the
    /// list of accepted keys.
    pub fn getinfo<'a,T: IntoIterator<Item = &'a &'a str>>(&self, keys: T) -> Result<Vec<(String, String)>> {
        let mut msg = "GETINFO".to_string();
        for k in keys {
            is_keyword(k)?;
            msg.push(' ');
            msg.push_str(k);
        }
        msg.push_str("\r\n");

        let mut res = Vec::new();
        for line in self.cmd(msg)? {
            if line.text == "OK" {
                break;
            }
            if let Some(is) = line.text.find('=') {
                let val = if line.data.len() > 0 {
                    String::from_utf8(line.data).map_err(|_|err!(Parse))?
                } else {
                    (&line.text[is+1..]).to_string()
                };
                res.push(( (&line.text[..is]).to_string(), val ));
            } else {
                return Err(err!(Parse));
            }
        }
        Ok(res)
    }

    // TODO: Create an enum for supported event types, rather than this string thing. We don't
    // support reading all types of events anyway.
    pub fn setevents<'a,T: IntoIterator<Item = &'a &'a str>>(&self, events: T) -> Result<()> {
        let mut msg = "SETEVENTS".to_string();
        for e in events {
            is_keyword(e)?;
            msg.push(' ');
            msg.push_str(e);
        }
        msg.push_str("\r\n");
        self.cmd(msg).map(|_|())
    }

    /// Read an event from the socket. This method blocks until an event has been received.
    pub fn read_event(&self) -> Result<Event> {
        let mut ret = self.get_reply(true)?;
        let ev = ret.remove(0);

        fn logmsg(r: ReplyLine, skip: usize) -> String {
            if r.data.is_empty() {
                (&r.text[skip..]).trim().to_owned()
            } else {
                String::from_utf8_lossy(&r.data).trim().to_owned()
            }
        }

        if ev.status == 650 && ev.text.starts_with("DEBUG") {
            Ok(Event::Debug(logmsg(ev, 6)))
        } else if ev.status == 650 && ev.text.starts_with("NOTICE") {
            Ok(Event::Notice(logmsg(ev, 7)))
        } else if ev.status == 650 && ev.text.starts_with("INFO") {
            Ok(Event::Info(logmsg(ev, 5)))
        } else if ev.status == 650 && ev.text.starts_with("WARN") {
            Ok(Event::Warn(logmsg(ev, 5)))
        } else if ev.status == 650 && ev.text.starts_with("ERR") {
            Ok(Event::Err(logmsg(ev, 4)))
        } else {
            Err(err!(UnknownEvent, ev.text))
        }
    }
}


#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn parse_replyline() {
        assert!(ReplyLine::parse(b"\r\n").is_err());
        assert!(ReplyLine::parse(b"250\r\n").is_err());
        assert!(ReplyLine::parse(b"2500 Text\r\n").is_err());
        assert!(ReplyLine::parse(b"250.Text\r\n").is_err());
        assert!(ReplyLine::parse(b".50 Text\r\n").is_err());
        assert!(ReplyLine::parse(b"-50 Text\r\n").is_err());
        assert!(ReplyLine::parse(b"01x Text\r\n").is_err());

        assert_eq!(ReplyLine::parse(b"").unwrap(), None);
        assert_eq!(ReplyLine::parse(b"250 Hello\r").unwrap(), None);
        assert_eq!(ReplyLine::parse(b"250+Hello\r\n").unwrap(), None);
        assert_eq!(ReplyLine::parse(b"250+Hello\r\ndata\r\n..a\r\n.\r").unwrap(), None);

        assert_eq!(ReplyLine::parse(b"250 \r\n").unwrap(), Some(ReplyLine { len: 6, status: 250, end: true, text: "".to_string(), data: Vec::new() }) );
        assert_eq!(ReplyLine::parse(b"650-Hello\r\n").unwrap(), Some(ReplyLine { len: 11, status: 650, end: false, text: "Hello".to_string(), data: Vec::new() }) );
        assert_eq!(ReplyLine::parse(b"650+Hello\r\n.data\r\n.\r\n").unwrap(), Some(ReplyLine { len: 21, status: 650, end: false, text: "Hello".to_string(), data: b"data".to_vec() }) );
        assert_eq!(ReplyLine::parse(b"650+Hello\r\ndata\r\n..\r\n.\r\n").unwrap(), Some(ReplyLine { len: 24, status: 650, end: false, text: "Hello".to_string(), data: b"data\r\n.".to_vec() }) );
    }

    #[test]
    fn qs_fmt() {
        assert_eq!(QuotedString("").to_string(), "\"\"".to_string());
        assert_eq!(QuotedString(" \\a\"b \x02").to_string(), "\" \\\\a\\\"b \x02\"".to_string());
    }

    #[test]
    fn qs_parse() {
        assert!(QuotedString::parse("").is_err());
        assert!(QuotedString::parse("\"").is_err());
        assert!(QuotedString::parse("\" \\\"").is_err());
        assert!(QuotedString::parse("abc").is_err());

        assert_eq!(QuotedString::parse("\"\"").unwrap(), "".to_string());
        assert_eq!(QuotedString::parse("\" \\\\a\\\"b \x02\"").unwrap(), " \\a\"b \x02".to_string());
        assert_eq!(QuotedString::parse("\"\\r\\n\"").unwrap(), "rn".to_string());
    }
}