// VpnCloud - Peer-to-Peer VPN
// Copyright (C) 2015-2016  Dennis Schwerdel
// This software is licensed under GPL-3 or newer (see LICENSE.md)

use std::fmt;
use std::net::{SocketAddr, SocketAddrV4, Ipv4Addr, SocketAddrV6, Ipv6Addr};

use super::types::{NodeId, Error, NetworkId, Range, NODE_ID_BYTES};
use super::util::{bytes_to_hex, Encoder};
use super::crypto::Crypto;

const MAGIC: [u8; 3] = [0x76, 0x70, 0x6e];
pub const VERSION: u8 = 1;

const NETWORK_ID_BYTES: usize = 8;

#[derive(Clone, Copy)]
#[repr(packed)]
struct TopHeader {
    magic: [u8; 3],
    version: u8,
    crypto_method : u8,
    _reserved: u8,
    flags: u8,
    msgtype: u8
}

impl TopHeader {
    #[inline]
    pub fn size() -> usize {
        8
    }

    pub fn read_from(data: &[u8]) -> Result<(TopHeader, usize), Error> {
        if data.len() < TopHeader::size() {
            return Err(Error::ParseError("Empty message"));
        }
        let mut header = TopHeader::default();
        header.magic.clone_from_slice(&data[0..3]);
        header.version = data[3];
        header.crypto_method = data[4];
        header.flags = data[6];
        header.msgtype = data[7];
        Ok((header, TopHeader::size()))
    }

    pub fn write_to(&self, data: &mut [u8]) -> usize {
        data[0..3].clone_from_slice(&self.magic);
        data[3] = self.version;
        data[4] = self.crypto_method;
        data[6] = self.flags;
        data[7] = self.msgtype;
        TopHeader::size()
    }
}

impl Default for TopHeader {
    fn default() -> Self {
        TopHeader{magic: MAGIC, version: VERSION, crypto_method: 0, _reserved: 0, flags: 0, msgtype: 0}
    }
}

#[derive(Default, Debug, PartialEq, Eq)]
pub struct Options {
    pub network_id: Option<NetworkId>,
}

pub enum Message<'a> {
    Data(&'a mut[u8], usize, usize), // data, start, end
    Peers(Vec<SocketAddr>), // peers
    Init(u8, NodeId, Vec<Range>), // step, node_id, ranges
    Close,
}

impl<'a> fmt::Debug for Message<'a> {
    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        match *self {
            Message::Data(_, start, end) => write!(formatter, "Data({} bytes)", end-start),
            Message::Peers(ref peers) => {
                try!(write!(formatter, "Peers ["));
                let mut first = true;
                for p in peers {
                    if !first {
                        try!(write!(formatter, ", "));
                    }
                    first = false;
                    try!(write!(formatter, "{}", p));
                }
                write!(formatter, "]")
            },
            Message::Init(stage, ref node_id, ref peers) => write!(formatter, "Init(stage={}, node_id={}, {:?})", stage, bytes_to_hex(node_id), peers),
            Message::Close => write!(formatter, "Close"),
        }
    }
}

#[allow(needless_range_loop)]
pub fn decode<'a>(data: &'a mut [u8], crypto: &mut Crypto) -> Result<(Options, Message<'a>), Error> {
    let mut end = data.len();
    let (header, mut pos) = try!(TopHeader::read_from(&data[..end]));
    if header.magic != MAGIC {
        return Err(Error::ParseError("Wrong protocol"));
    }
    if header.version != VERSION {
        return Err(Error::ParseError("Wrong version"));
    }
    if header.crypto_method != crypto.method() {
        return Err(Error::CryptoError("Wrong crypto method"));
    }
    if crypto.method() > 0 {
        let len = crypto.nonce_bytes();
        if end < pos + len {
            return Err(Error::ParseError("Truncated crypto header"));
        }
        {
            let (before, after) = data.split_at_mut(pos);
            let (nonce, crypto_data) = after.split_at_mut(len);
            pos += len;
            end = try!(crypto.decrypt(crypto_data, nonce, &before[..TopHeader::size()])) + pos;
        }
        assert_eq!(end, data.len()-crypto.additional_bytes());
    }
    let mut options = Options::default();
    if header.flags & 0x01 > 0 {
        if end < pos + NETWORK_ID_BYTES {
            return Err(Error::ParseError("Truncated options"));
        }
        options.network_id = Some(Encoder::read_u64(&data[pos..pos+NETWORK_ID_BYTES]));
        pos += NETWORK_ID_BYTES;
    }
    let msg = match header.msgtype {
        0 => Message::Data(data, pos, end),
        1 => {
            if end < pos + 1 {
                return Err(Error::ParseError("Empty peers"));
            }
            let mut peers = Vec::new();
            let count = data[pos];
            pos += 1;
            let len = count as usize * 6;
            if end < pos + len {
                return Err(Error::ParseError("Peer data too short"));
            }
            for _ in 0..count {
                let ip = &data[pos..];
                pos += 4;
                let port = Encoder::read_u16(&data[pos..]);
                pos += 2;
                let addr = SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::new(ip[0], ip[1], ip[2], ip[3]), port));
                peers.push(addr);
            }
            let count = data[pos];
            pos += 1;
            let len = count as usize * 18;
            if end < pos + len {
                return Err(Error::ParseError("Peer data too short"));
            }
            for _ in 0..count {
                let mut ip = [0u16; 8];
                for i in 0..8 {
                    ip[i] = Encoder::read_u16(&data[pos..]);
                    pos += 2;
                }
                let port = Encoder::read_u16(&data[pos..]);
                pos += 2;
                let addr = SocketAddr::V6(SocketAddrV6::new(Ipv6Addr::new(ip[0], ip[1], ip[2],
                    ip[3], ip[4], ip[5], ip[6], ip[7]), port, 0, 0));
                peers.push(addr);
            }
            Message::Peers(peers)
        },
        2 => {
            if end < pos + 2 + NODE_ID_BYTES {
                return Err(Error::ParseError("Init data too short"));
            }
            let stage = data[pos];
            pos += 1;
            let mut node_id = [0; NODE_ID_BYTES];
            node_id.clone_from_slice(&data[pos..pos+NODE_ID_BYTES]);
            pos += NODE_ID_BYTES;
            let count = data[pos] as usize;
            pos += 1;
            let mut addrs = Vec::with_capacity(count);
            for _ in 0..count {
                let (range, read) = try!(Range::read_from(&data[pos..end]));
                pos += read;
                addrs.push(range);
            }
            Message::Init(stage, node_id, addrs)
        },
        3 => Message::Close,
        _ => return Err(Error::ParseError("Unknown message type"))
    };
    Ok((options, msg))
}

#[allow(needless_range_loop)]
pub fn encode<'a>(options: &Options, msg: &'a mut Message, mut buf: &'a mut [u8], crypto: &mut Crypto) -> &'a mut [u8] {
    let mut start = 64;
    let mut end = 64;
    match *msg {
        Message::Data(ref mut data, data_start, data_end) => {
            buf = data;
            start = data_start;
            end = data_end;
        },
        Message::Peers(ref peers) => {
            let mut v4addrs = Vec::new();
            let mut v6addrs = Vec::new();
            for p in peers {
                match *p {
                    SocketAddr::V4(addr) => v4addrs.push(addr),
                    SocketAddr::V6(addr) => v6addrs.push(addr)
                }
            };
            assert!(v4addrs.len() <= 255);
            assert!(v6addrs.len() <= 255);
            let mut pos = start;
            assert!(buf.len() >= pos + 2 + v4addrs.len() * 6 + v6addrs.len() * 18);
            buf[pos] = v4addrs.len() as u8;
            pos += 1;
            for addr in v4addrs {
                let ip = addr.ip().octets();
                buf[pos..pos+4].clone_from_slice(&ip);
                pos += 4;
                Encoder::write_u16(addr.port(), &mut buf[pos..]);
                pos += 2;
            };
            buf[pos] = v6addrs.len() as u8;
            pos += 1;
            for addr in v6addrs {
                let ip = addr.ip().segments();
                for i in 0..8 {
                    Encoder::write_u16(ip[i], &mut buf[pos..]);
                    pos += 2;
                }
                Encoder::write_u16(addr.port(), &mut buf[pos..]);
                pos += 2;
            };
            end = pos;
        },
        Message::Init(stage, ref node_id, ref ranges) => {
            let mut pos = start;
            assert!(buf.len() >= pos + 2 + NODE_ID_BYTES);
            buf[pos] = stage;
            pos += 1;
            buf[pos..pos+NODE_ID_BYTES].clone_from_slice(node_id);
            pos += NODE_ID_BYTES;
            assert!(ranges.len() <= 255);
            buf[pos] = ranges.len() as u8;
            pos += 1;
            for range in ranges {
                pos += range.write_to(&mut buf[pos..]);
            }
            end = pos;
        },
        Message::Close => {
        }
    }
    assert!(start >= 64);
    assert!(buf.len() >= end + 64);
    if let Some(id) = options.network_id {
        assert!(start >= NETWORK_ID_BYTES);
        Encoder::write_u64(id, &mut buf[start-NETWORK_ID_BYTES..]);
        start -= NETWORK_ID_BYTES;
    }
    let crypto_start = start;
    start -= crypto.nonce_bytes();
    let mut header = TopHeader::default();
    header.msgtype = match *msg {
        Message::Data(_, _, _) => 0,
        Message::Peers(_) => 1,
        Message::Init(_, _, _) => 2,
        Message::Close => 3
    };
    header.crypto_method = crypto.method();
    if options.network_id.is_some() {
        header.flags |= 0x01;
    }
    start -= TopHeader::size();
    header.write_to(&mut buf[start..]);
    if crypto.method() > 0 {
        let (junk_before, rest) = buf.split_at_mut(start);
        let (header, rest) = rest.split_at_mut(TopHeader::size());
        let (nonce, rest) = rest.split_at_mut(crypto.nonce_bytes());
        debug_assert_eq!(junk_before.len() + header.len() + crypto.nonce_bytes(), crypto_start);
        assert!(rest.len() >= end - crypto_start + crypto.additional_bytes());
        end = crypto.encrypt(rest, end-crypto_start, nonce, header) + crypto_start;
    }
    &mut buf[start..end]
}