#![deny(missing_docs)]
//! This library provides basically two functions for querying Minecraft
//! servers. For increased stability, an extra function for handshakes
//! is not provided.
//! 
//! ## Usage
//! To perform a query, call [`Query::get_basic`] or [`Query::get_full`].
//! The returned response will either be a [`BasicQueryResponse`] or a
//! [`FullQueryResponse`] respectively.
//! 
//! ## Development resources
//! Thank you to the [Tokio project] and the [Minecraft Developer Wiki] for
//! providing a great asynchronous runtime and useful documentation!
//!
//! Without them, this crate wouldn't be possible.
//!
//! [Tokio project]: https://tokio.rs/
//! [Minecraft Developer Wiki]: https://wiki.vg/

use std::{
    collections::HashMap,
    io,
    time::Duration
};
use tokio::{
    net::{ ToSocketAddrs, UdpSocket },
    time::timeout as tokioTimeout,
};

/// Bitmask to validate a session ID
///
/// Usually you don't need this.
///
/// # Example
/// ```
/// use mcquery::SESSION_ID_MASK;
/// 
/// # #[allow(unused_variables)]
/// # fn main() {
/// let session_id = 0x12345678_u32;
/// let valid_session_id = session_id & SESSION_ID_MASK;
/// # }
/// ```
pub const SESSION_ID_MASK: u32 = 0x0F0F0F0F;
const REQUEST_HEADER: [u8; 2] = [0xFE, 0xFD];

static mut SESSION_ID_COUNTER: u16 = 0;

fn gen_session_id() -> u32 {
    unsafe {
        SESSION_ID_COUNTER = SESSION_ID_COUNTER.wrapping_add(1);
    }

    let mut session_id_bytes = [0; 4];
    for (i, b) in unsafe { SESSION_ID_COUNTER }.to_be_bytes().iter().enumerate() {
        session_id_bytes[i * 2] = b >> 4;
        session_id_bytes[i * 2 + 1] = b & 0x0F;
    }
    u32::from_be_bytes(session_id_bytes)
}

/// Encountered when the buffer is full.
///
/// # Desciption
/// The response may be incomplete, if the buffer has been filled up,
/// because excess bytes that don't fit into it are discarded.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub struct MaybeIncompleteDataError(usize);

impl std::error::Error for MaybeIncompleteDataError {}

impl core::fmt::Display for MaybeIncompleteDataError {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        write!(f, "Buffer filled up")
    }
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
enum PacketType {
    Handshake = 0x09,
    Query = 0x00,
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct HandshakeRequest {
    session_id: u32,
}

impl HandshakeRequest {
    const PACKET_TYPE: PacketType = PacketType::Handshake;

    fn bytes(&self) -> Vec<u8> {
        let mut vec = Vec::new();
        vec.extend_from_slice(&REQUEST_HEADER);
        vec.push(Self::PACKET_TYPE as u8);
        vec.extend_from_slice(&self.session_id.to_be_bytes());

        vec
    }

    async fn send(&self, socket: &UdpSocket, timeout: Duration) -> io::Result<HandshakeResponse> {
        // Sending
        tokioTimeout(timeout, socket.send(self.bytes().as_slice())).await??;

        // Receiving
        let mut response_buffer = [0; 16];
        let bytes_read = tokioTimeout(timeout, socket.recv(&mut response_buffer)).await??;

        // Parsing
        let mut response_buffer = response_buffer[..bytes_read].to_owned();
        let res_packet_type = response_buffer.remove(0);
        let mut res_session_id = [0; 4];

        for (i, b) in response_buffer.drain(..4).enumerate() {
            res_session_id[i] = b;
        }

        let res_session_id = u32::from_be_bytes(res_session_id);
        let res_challenge_token =
            String::from_utf8(
                response_buffer
                    .into_iter()
                    .take_while(|x| x != &0x00)
                    .collect()
            ).map_err(|_| io::ErrorKind::InvalidData)?
            .parse()
            .map_err(|_| io::ErrorKind::InvalidData)?;

        if res_packet_type != Self::PACKET_TYPE as u8 || res_session_id != self.session_id {
            Err(io::ErrorKind::InvalidData.into())
        } else {
            Ok(HandshakeResponse {
                session_id: res_session_id,
                challenge_token: res_challenge_token,
            })
        }
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct HandshakeResponse {
    session_id: u32,
    challenge_token: i32,
}

impl From<HandshakeResponse> for BasicQueryRequest {
    fn from(res: HandshakeResponse) -> Self {
        BasicQueryRequest {
            session_id: res.session_id,
            challenge_token: res.challenge_token,
        }
    }
}

impl From<HandshakeResponse> for FullQueryRequest {
    fn from(res: HandshakeResponse) -> Self {
        FullQueryRequest {
            session_id: res.session_id,
            challenge_token: res.challenge_token,
        }
    }
}

#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct BasicQueryRequest {
    session_id: u32,
    challenge_token: i32,
}

impl BasicQueryRequest {
    const PACKET_TYPE: PacketType = PacketType::Query;

    fn bytes(&self) -> Vec<u8> {
        let mut vec = Vec::new();
        vec.extend_from_slice(&REQUEST_HEADER);
        vec.push(Self::PACKET_TYPE as u8);
        vec.extend_from_slice(&self.session_id.to_be_bytes());
        vec.extend_from_slice(&self.challenge_token.to_be_bytes());

        vec
    }

    async fn send(&self, socket: &UdpSocket, timeout: Duration, buffer: &mut [u8]) -> io::Result<BasicQueryResponse> {
        // Sending
        tokioTimeout(timeout, socket.send(self.bytes().as_slice())).await??;

        // Receiving
        let bytes_read = tokioTimeout(timeout, socket.recv(buffer)).await??;
        if bytes_read == buffer.len() {
            return Err(io::Error::new(io::ErrorKind::Other, MaybeIncompleteDataError(bytes_read)));
        }

        // Parsing
        let mut response_buffer: String = buffer[0..bytes_read].iter().map(|b| *b as char).collect();

        // Packet type
        let res_packet_type = response_buffer.remove(0) as u8;

        // Session ID
        let mut res_session_id = [0; 4];
        for (i, b) in response_buffer.drain(..4).enumerate() {
            res_session_id[i] = b as u8;
        }
        let res_session_id = u32::from_be_bytes(res_session_id);

        let (
            res_motd,
            res_gametype,
            res_map,
            res_num_players,
            res_max_players,
            mut res_address
        ) = {
            let mut i = 0;
            let vec: Vec<_> = response_buffer
                .split_terminator(|c| {
                    if i < 5 {
                        if c == '\0' {
                            i += 1;
                        }
                        c == '\0'
                    } else {
                        i += 1;
                        i > 7 && c == '\0'
                    }
                })
                .collect();
            (
                vec[0].clone(),
                vec[1].clone(),
                vec[2].clone(),
                vec[3].clone(),
                vec[4].clone(),
                vec[5].chars().map(|c| c as u8).collect::<Vec<_>>(),
            )
        };

        // Number of players
        let res_num_players = res_num_players.parse().map_err(|_| io::ErrorKind::InvalidData)?;

        // Max number of players
        let res_max_players = res_max_players.parse().map_err(|_| io::ErrorKind::InvalidData)?;

        // Host port
        let mut res_port = [0; 2];
        for (i, b) in res_address.drain(..2).enumerate() {
            res_port[i] = b;
        }
        let res_port = u16::from_le_bytes(res_port);

        // Host IP
        let res_ip = String::from_utf8(res_address).map_err(|_| io::ErrorKind::InvalidData)?;

        if res_packet_type != Self::PACKET_TYPE as u8 || res_session_id != self.session_id {
            Err(io::ErrorKind::InvalidData.into())
        } else {
            Ok(BasicQueryResponse {
                session_id: res_session_id,
                motd: res_motd.to_owned(),
                gametype: res_gametype.to_owned(),
                map: res_map.to_owned(),
                num_players: res_num_players,
                max_players: res_max_players,
                port: res_port,
                ip: res_ip,
            })
        }
    }
}

/// Response to a basic query
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
pub struct BasicQueryResponse {
    session_id: u32,
    /// The Motto of the Day
    pub motd: String,
    /// Should always be `"SMP"`
    pub gametype: String,
    /// The default map
    pub map: String,
    /// Number of players currently online
    pub num_players: u32,
    /// Maximum player capacity
    pub max_players: u32,
    /// The host port. Default is `25565`
    pub port: u16,
    /// The host ip. This is the localhost by default
    pub ip: String,
}

struct FullQueryRequest {
    session_id: u32,
    challenge_token: i32,
}

impl FullQueryRequest {
    const PACKET_TYPE: PacketType = PacketType::Query;

    fn bytes(&self) -> Vec<u8> {
        let mut vec = Vec::new();
        vec.extend_from_slice(&REQUEST_HEADER);
        vec.push(Self::PACKET_TYPE as u8);
        vec.extend_from_slice(&self.session_id.to_be_bytes());
        vec.extend_from_slice(&self.challenge_token.to_be_bytes());
        vec.extend_from_slice(&[0; 4]);

        vec
    }

    async fn send(&self, socket: &UdpSocket, timeout: Duration, buffer: &mut [u8]) -> io::Result<FullQueryResponse> {
        // Sending
        tokioTimeout(timeout, socket.send(self.bytes().as_slice())).await??;

        // Receiving
        let bytes_read = tokioTimeout(timeout, socket.recv(buffer)).await??;
        if bytes_read == buffer.len() {
            return Err(io::Error::new(io::ErrorKind::Other, MaybeIncompleteDataError(bytes_read)));
        }

        // Parsing
        let mut response_buffer = buffer[0..bytes_read].to_vec();

        // Packet type
        let res_packet_type = response_buffer.remove(0);

        // Session ID
        let mut res_session_id = [0; 4];
        for (i, b) in response_buffer.drain(..4).enumerate() {
            res_session_id[i] = b
        }
        let res_session_id = u32::from_be_bytes(res_session_id);

        // Key value section
        let mut res_kv = HashMap::<String, String>::new();
        loop {
            let key: Vec<u8> = response_buffer.iter()
                .take_while(|b| **b != 0x00)
                .map(|&b| b)
                .collect();
            response_buffer.drain(0..key.len() + 1);
            if key.len() == 0 {
                break;
            }

            let value: Vec<u8> = response_buffer.iter()
                .take_while(|b| **b != 0x00)
                .map(|&b| b)
                .collect();
            response_buffer.drain(0..value.len() + 1);

            res_kv.insert(
                key.iter()
                    .map(|b| *b as char)
                    .collect(), 
                value.iter()
                    .map(|b| *b as char)
                    .collect()
            );
        }
        res_kv.remove("splitnum").ok_or(io::ErrorKind::InvalidData)?;

        // Plugins and server software
        let (
            res_software,
            res_plugins
        ) = if let Some(mut plugins) = res_kv.get("plugins")
            .map(|s| s.clone())
        {
            res_kv.remove("plugins");
            // let mut plugin_string = plugin_string;
            let software: String = plugins.chars().take_while(|c| *c != ':').collect();
            plugins.drain(0..software.len() + 1);

            let plugins = if plugins.len() > 0 {
                Some(plugins.split(';').map(|s| s.trim().to_owned()).collect())
            } else {
                None
            };

            (Some(software), plugins)
        } else {
            (None, None)
        };

        // Players
        {
            let player_header = "\x01player_\0\0";
            if !response_buffer.starts_with(player_header.as_bytes()) {
                return Err(io::ErrorKind::InvalidData.into());
            } else {
                response_buffer.drain(0..player_header.len());
            }
        }
        let mut res_players = Vec::new();
        loop {
            let player: Vec<u8> = response_buffer.iter()
                .take_while(|b| **b != 0x00)
                .map(|&b| b)
                .collect();
            response_buffer.drain(0..player.len() + 1);
            if player.len() == 0 {
                break;
            }

            res_players.push(
                player.iter()
                    .map(|b| *b as char)
                    .collect()
            );
        }

        if res_packet_type != Self::PACKET_TYPE as u8 || res_session_id != self.session_id {
            Err(io::ErrorKind::InvalidData.into())
        } else {
            Ok(FullQueryResponse {
                session_id: res_session_id,
                kv: res_kv,
                players: res_players,
                software: res_software,
                plugins: res_plugins,
            })
        }
    }
}

/// Response to a full query
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct FullQueryResponse {
    session_id: u32,
    /// Additional server information
    pub kv: HashMap<String, String>,
    /// Names of players currently online
    pub players: Vec<String>,
    /// The software string. Empty if vanilla server or not supported
    pub software: Option<String>,
    /// Plugins used on the server. Empty if vanilla server or not supported
    pub plugins: Option<Vec<String>>
}

/// The main data structure in this crate
/// 
/// # Description
/// Basic queries are enabled by default. They can be diabled in the server's
/// `server.properties` with `enable-status=true`. This is what is used in the
/// server list inside Minecraft.
/// 
/// Full queries are diabled by default. They can be enabled in the server's
/// `server.properties` with `enable-query=true`.
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum Query {
    /// Response to a basic query. Can be obtained with [`Query::get_basic()`]
    /// 
    /// See [`BasicQueryResponse`] for more
    Basic(BasicQueryResponse),
    /// Response to a full query. Can be obtained with [`Query::get_full()`]
    /// 
    /// See [`FullQueryResponse`] for more
    Full(FullQueryResponse),
}

impl Query {
    /// Connects with the Minecraft server at `address` and performs a basic query.
    /// `timeout` is used as a response timeout. The specified buffer needs to be big
    /// enough to hold all response bytes, else this function will return a
    /// [`MaybeIncompleteDataError`] wrapped in an [`std::io::Error`]. The [`Ok`] value
    /// will be [`Query::Basic`].
    pub async fn get_basic<A: ToSocketAddrs>(address: A, timeout: Duration, buffer: &mut [u8]) -> io::Result<Self> {
        let socket = UdpSocket::bind("0.0.0.0:0").await?;
        socket.connect(address).await?;

        let handshake_req = HandshakeRequest {
            session_id: gen_session_id(),
        };

        let handshake_res = handshake_req.send(&socket, timeout).await?;

        let query_req: BasicQueryRequest = handshake_res.into();

        buffer.iter_mut().for_each(|b| *b = 0);
        let query_res = query_req.send(&socket, timeout, buffer).await?;

        Ok(Query::Basic(query_res))
    }

    /// Connects with the Minecraft server at `address` and performs a full query.
    /// `timeout` is used as a response timeout. The specified buffer needs to be big
    /// enough to hold all response bytes, else this function will return a
    /// [`MaybeIncompleteDataError`] wrapped in an [`std::io::Error`]. The [`Ok`] vlaue
    /// will be [`Query::Full`].
    pub async fn get_full<A: ToSocketAddrs>(address: A, timeout: Duration, buffer: &mut [u8]) -> io::Result<Self> {
        let socket = UdpSocket::bind("0.0.0.0:0").await?;
        socket.connect(address).await?;

        let handshake_req = HandshakeRequest {
            session_id: gen_session_id(),
        };

        let handshake_res = handshake_req.send(&socket, timeout).await?;

        let query_req: FullQueryRequest = handshake_res.into();

        buffer.iter_mut().for_each(|b| *b = 0);
        let query_res = query_req.send(&socket, timeout, buffer).await?;

        Ok(Query::Full(query_res))
    }
}