use crate::protocol::ip::{self, IPProtocol};
use nom::bits;
use nom::bytes;
use nom::error::Error;
use nom::number;
use nom::sequence;
use nom::IResult;
use std::convert::TryFrom;
use std::net::Ipv6Addr;

/******************************************************************************
 * Struct
 ******************************************************************************/

/*
 * IPv6 Header Format
 *
 *   0                   1                   2                   3
 *   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *  |Version| Traffic Class |           Flow Label                  |
 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *  |         Payload Length        |  Next Header  |   Hop Limit   |
 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *  |                                                               |
 *  +                                                               +
 *  |                                                               |
 *  +                         Source Address                        +
 *  |                                                               |
 *  +                                                               +
 *  |                                                               |
 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *  |                                                               |
 *  +                                                               +
 *  |                                                               |
 *  +                      Destination Address                      +
 *  |                                                               |
 *  +                                                               +
 *  |                                                               |
 *  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */

#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct IPv6Header {
    pub version: u8,     // 4 bit
    pub dsc: u8,         // Differentiated Services Codepoint: 6 bit
    pub ecn: u8,         // Explicit Congestion Notification:  2 bit
    pub flow_label: u32, // 20 bit
    pub length: u16,
    pub next_header: IPProtocol,
    pub hop_limit: u8,
    pub source_addr: Ipv6Addr,
    pub dest_addr: Ipv6Addr,
}

/******************************************************************************
 * Parse
 ******************************************************************************/

fn parse_byte_to_half(input: &[u8]) -> IResult<&[u8], (u8, u8)> {
    bits::bits::<_, _, Error<_>, _, _>(sequence::pair(
        bits::streaming::take(4u8),
        bits::streaming::take(4u8),
    ))(input)
}

fn parse_ipv6_address(input: &[u8]) -> IResult<&[u8], Ipv6Addr> {
    let (input, ipv6) = bytes::streaming::take(16u8)(input)?;

    Ok((input, Ipv6Addr::from(<[u8; 16]>::try_from(ipv6).unwrap())))
}

pub fn parse_ipv6(input: &[u8]) -> IResult<&[u8], IPv6Header> {
    let (input, ver_tc) = parse_byte_to_half(input)?;
    let (input, tc_fl) = parse_byte_to_half(input)?;
    let (input, fl): (_, u32) =
        bits::bits::<_, _, Error<_>, _, _>(bits::streaming::take(16u8))(input)?;
    let (input, length) = number::streaming::be_u16(input)?;
    let (input, next_header) = ip::protocol(input)?;
    let (input, hop_limit) = number::streaming::be_u8(input)?;
    let (input, source_addr) = parse_ipv6_address(input)?;
    let (input, dest_addr) = parse_ipv6_address(input)?;

    Ok((
        input,
        IPv6Header {
            version: ver_tc.0,
            dsc: (ver_tc.1 << 2) + ((tc_fl.0 & 0b1100) >> 2),
            ecn: tc_fl.0 & 0b11,
            flow_label: (u32::from(tc_fl.1) << 16) + fl,
            length,
            next_header,
            hop_limit,
            source_addr,
            dest_addr,
        },
    ))
}

/******************************************************************************
 * TEST
 ******************************************************************************/

#[cfg(test)]
mod tests {
    use super::parse_ipv6;
    use super::IPv6Header;
    use crate::ip::IPProtocol;
    use std::net::Ipv6Addr;

    const LAST_SLICE: &'static [u8] = &[0xff];

    #[test]
    fn parse_ipv6_works() {
        /*
         * Internet Protocol Version 6, Src: 2409:8034:4025::50:a31, Dst: 2409:8034:4040:5301::204
         *     0110 .... = Version: 6
         *     .... 0000 0000 .... .... .... .... .... = Traffic Class: 0x00 (DSCP: CS0, ECN: Not-ECT)
         *         .... 0000 00.. .... .... .... .... .... = Differentiated Services Codepoint: Default (0)
         *         .... .... ..00 .... .... .... .... .... = Explicit Congestion Notification: Not ECN-Capable Transport (0)
         *     .... 0000 0000 0000 0000 0000 = Flow Label: 0x00000
         *     Payload Length: 1416
         *     Next Header: UDP (17)
         *     Hop Limit: 252
         *     Source Address: 2409:8034:4025::50:a31
         *     Destination Address: 2409:8034:4040:5301::204
         */

        let bytes = [
            0x60, /* Version and Partial Differentiated Services Codepoint */
            0x00, /* Partial Differentiated Services Codepoint and Explicit Congestion Notification and Partial Flow Label */
            0x00, 0x00, /* Partial Flow Label */
            0x05, 0x88, /* Payload Length */
            0x11, /* Next Header */
            0xfc, /* Hop Limit */
            0x24, 0x09, 0x80, 0x34, 0x40, 0x25, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x50,
            0x0a, 0x31, /* Source Address */
            0x24, 0x09, 0x80, 0x34, 0x40, 0x40, 0x53, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
            0x02, 0x04, /* Destination Address */
            0xff, /* Payload */
        ];

        let expectation = IPv6Header {
            version: 6,
            dsc: 0,
            ecn: 0,
            flow_label: 0,
            length: 1416,
            next_header: IPProtocol::UDP,
            hop_limit: 252,
            source_addr: Ipv6Addr::new(
                0x2409, 0x8034, 0x4025, 0x0000, 0x0000, 0x0000, 0x0050, 0x0a31,
            ),
            dest_addr: Ipv6Addr::new(
                0x2409, 0x8034, 0x4040, 0x5301, 0x0000, 0x0000, 0x0000, 0x0204,
            ),
        };

        assert_eq!(parse_ipv6(&bytes), Ok((LAST_SLICE, expectation)));
    }
}