// Copyright 2025 Dillution <hskimse1@gmail.com>.
//
// This file is part of DPIBreak.
//
// DPIBreak is free software: you can redistribute it and/or modify it
// under the terms of the GNU General Public License as published by the
// Free Software Foundation, either version 3 of the License, or (at your
// option) any later version.
//
// DPIBreak is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
// for more details.
//
// You should have received a copy of the GNU General Public License
// along with DPIBreak. If not, see <https://www.gnu.org/licenses/>.

use anyhow::Result;
use etherparse::{IpSlice, TcpSlice};
use anyhow::anyhow;
use std::sync::OnceLock;

/// www.microsoft.com
/// Stolen from github.com/bol-van/zapret/blob/master/nfq/desync.c
const DEFAULT_FAKE_TLS_CLIENTHELLO: &'static [u8] = &[
    0x16, 0x03, 0x01, 0x02, 0xa3, 0x01, 0x00, 0x02, 0x9f, 0x03, 0x03, 0x41,
    0x88, 0x82, 0x2d, 0x4f, 0xfd, 0x81, 0x48, 0x9e, 0xe7, 0x90, 0x65, 0x1f,
    0xba, 0x05, 0x7b, 0xff, 0xa7, 0x5a, 0xf9, 0x5b, 0x8a, 0x8f, 0x45, 0x8b,
    0x41, 0xf0, 0x3d, 0x1b, 0xdd, 0xe3, 0xf8, 0x20, 0x9b, 0x23, 0xa5, 0xd2,
    0x21, 0x1e, 0x9f, 0xe7, 0x85, 0x6c, 0xfc, 0x61, 0x80, 0x3a, 0x3f, 0xba,
    0xb9, 0x60, 0xba, 0xb3, 0x0e, 0x98, 0x27, 0x6c, 0xf7, 0x38, 0x28, 0x65,
    0x80, 0x5d, 0x40, 0x38, 0x00, 0x22, 0x13, 0x01, 0x13, 0x03, 0x13, 0x02,
    0xc0, 0x2b, 0xc0, 0x2f, 0xcc, 0xa9, 0xcc, 0xa8, 0xc0, 0x2c, 0xc0, 0x30,
    0xc0, 0x0a, 0xc0, 0x09, 0xc0, 0x13, 0xc0, 0x14, 0x00, 0x9c, 0x00, 0x9d,
    0x00, 0x2f, 0x00, 0x35, 0x01, 0x00, 0x02, 0x34, 0x00, 0x00, 0x00, 0x16,
    0x00, 0x14, 0x00, 0x00, 0x11, 0x77, 0x77, 0x77, 0x2e, 0x6d, 0x69, 0x63,
    0x72, 0x6f, 0x73, 0x6f, 0x66, 0x74, 0x2e, 0x63, 0x6f, 0x6d, 0x00, 0x17,
    0x00, 0x00, 0xff, 0x01, 0x00, 0x01, 0x00, 0x00, 0x0a, 0x00, 0x0e, 0x00,
    0x0c, 0x00, 0x1d, 0x00, 0x17, 0x00, 0x18, 0x00, 0x19, 0x01, 0x00, 0x01,
    0x01, 0x00, 0x0b, 0x00, 0x02, 0x01, 0x00, 0x00, 0x23, 0x00, 0x00, 0x00,
    0x10, 0x00, 0x0e, 0x00, 0x0c, 0x02, 0x68, 0x32, 0x08, 0x68, 0x74, 0x74,
    0x70, 0x2f, 0x31, 0x2e, 0x31, 0x00, 0x05, 0x00, 0x05, 0x01, 0x00, 0x00,
    0x00, 0x00, 0x00, 0x22, 0x00, 0x0a, 0x00, 0x08, 0x04, 0x03, 0x05, 0x03,
    0x06, 0x03, 0x02, 0x03, 0x00, 0x12, 0x00, 0x00, 0x00, 0x33, 0x00, 0x6b,
    0x00, 0x69, 0x00, 0x1d, 0x00, 0x20, 0x69, 0x15, 0x16, 0x29, 0x6d, 0xad,
    0xd5, 0x68, 0x88, 0x27, 0x2f, 0xde, 0xaf, 0xac, 0x3c, 0x4c, 0xa4, 0xe4,
    0xd8, 0xc8, 0xfb, 0x41, 0x87, 0xf4, 0x76, 0x4e, 0x0e, 0xfa, 0x64, 0xc4,
    0xe9, 0x29, 0x00, 0x17, 0x00, 0x41, 0x04, 0xfe, 0x62, 0xb9, 0x08, 0xc8,
    0xc3, 0x2a, 0xb9, 0x87, 0x37, 0x84, 0x42, 0x6b, 0x5c, 0xcd, 0xc9, 0xca,
    0x62, 0x38, 0xd3, 0xd9, 0x99, 0x8a, 0xc4, 0x2d, 0xc6, 0xd0, 0xa3, 0x60,
    0xb2, 0x12, 0x54, 0x41, 0x8e, 0x52, 0x5e, 0xe3, 0xab, 0xf9, 0xc2, 0x07,
    0x81, 0xdc, 0xf8, 0xf2, 0x6a, 0x91, 0x40, 0x2f, 0xcb, 0xa4, 0xff, 0x6f,
    0x24, 0xc7, 0x4d, 0x77, 0x77, 0x2d, 0x6f, 0xe0, 0x77, 0xaa, 0x92, 0x00,
    0x2b, 0x00, 0x05, 0x04, 0x03, 0x04, 0x03, 0x03, 0x00, 0x0d, 0x00, 0x18,
    0x00, 0x16, 0x04, 0x03, 0x05, 0x03, 0x06, 0x03, 0x08, 0x04, 0x08, 0x05,
    0x08, 0x06, 0x04, 0x01, 0x05, 0x01, 0x06, 0x01, 0x02, 0x03, 0x02, 0x01,
    0x00, 0x2d, 0x00, 0x02, 0x01, 0x01, 0x00, 0x1c, 0x00, 0x02, 0x40, 0x01,
    0x00, 0x1b, 0x00, 0x07, 0x06, 0x00, 0x01, 0x00, 0x02, 0x00, 0x03, 0xfe,
    0x0d, 0x01, 0x19, 0x00, 0x00, 0x01, 0x00, 0x03, 0x21, 0x00, 0x20, 0x62,
    0xe8, 0x83, 0xd8, 0x97, 0x05, 0x8a, 0xbe, 0xa1, 0xf2, 0x63, 0x4e, 0xce,
    0x93, 0x84, 0x8e, 0xcf, 0xe7, 0xdd, 0xb2, 0xe4, 0x87, 0x06, 0xac, 0x11,
    0x19, 0xbe, 0x0e, 0x71, 0x87, 0xf1, 0xa6, 0x00, 0xef, 0xd8, 0x6b, 0x27,
    0x5e, 0xc0, 0xa7, 0x5d, 0x42, 0x4e, 0x8c, 0xdc, 0xf3, 0x9f, 0x1c, 0x51,
    0x62, 0xef, 0xff, 0x5b, 0xed, 0xc8, 0xfd, 0xee, 0x6f, 0xbb, 0x88, 0x9b,
    0xb1, 0x30, 0x9c, 0x66, 0x42, 0xab, 0x0f, 0x66, 0x89, 0x18, 0x8b, 0x11,
    0xc1, 0x6d, 0xe7, 0x2a, 0xeb, 0x96, 0x3b, 0x7f, 0x52, 0x78, 0xdb, 0xf8,
    0x6d, 0x04, 0xf7, 0x95, 0x1a, 0xa8, 0xf0, 0x64, 0x52, 0x07, 0x39, 0xf0,
    0xa8, 0x1d, 0x0d, 0x16, 0x36, 0xb7, 0x18, 0x0e, 0xc8, 0x44, 0x27, 0xfe,
    0xf3, 0x31, 0xf0, 0xde, 0x8c, 0x74, 0xf5, 0xa1, 0xd8, 0x8f, 0x6f, 0x45,
    0x97, 0x69, 0x79, 0x5e, 0x2e, 0xd4, 0xb0, 0x2c, 0x0c, 0x1a, 0x6f, 0xcc,
    0xce, 0x90, 0xc7, 0xdd, 0xc6, 0x60, 0x95, 0xf3, 0xc2, 0x19, 0xde, 0x50,
    0x80, 0xbf, 0xde, 0xf2, 0x25, 0x63, 0x15, 0x26, 0x63, 0x09, 0x1f, 0xc5,
    0xdf, 0x32, 0xf5, 0xea, 0x9c, 0xd2, 0xff, 0x99, 0x4e, 0x67, 0xa2, 0xe5,
    0x1a, 0x94, 0x85, 0xe3, 0xdf, 0x36, 0xa5, 0x83, 0x4b, 0x0a, 0x1c, 0xaf,
    0xd7, 0x48, 0xc9, 0x4b, 0x8a, 0x27, 0xdd, 0x58, 0x7f, 0x95, 0xf2, 0x6b,
    0xde, 0x2b, 0x12, 0xd3, 0xec, 0x4d, 0x69, 0x37, 0x9c, 0x13, 0x9b, 0x16,
    0xb0, 0x45, 0x52, 0x38, 0x77, 0x69, 0xef, 0xaa, 0x65, 0x19, 0xbc, 0xc2,
    0x93, 0x4d, 0xb0, 0x1b, 0x7f, 0x5b, 0x41, 0xff, 0xaf, 0xba, 0x50, 0x51,
    0xc3, 0xf1, 0x27, 0x09, 0x25, 0xf5, 0x60, 0x90, 0x09, 0xb1, 0xe5, 0xc0,
    0xc7, 0x42, 0x78, 0x54, 0x3b, 0x23, 0x19, 0x7d, 0x8e, 0x72, 0x13, 0xb4,
    0xd3, 0xcd, 0x63, 0xb6, 0xc4, 0x4a, 0x28, 0x3d, 0x45, 0x3e, 0x8b, 0xdb,
    0x84, 0x4f, 0x78, 0x64, 0x30, 0x69, 0xe2, 0x1b
];

pub static OPT_FAKE_TTL: OnceLock<u8> = OnceLock::new();

fn fake_ttl() -> u8 {
    *OPT_FAKE_TTL.get().expect("OPT_FAKE_TTL not initialized")
}

pub struct PktView<'a> {
    pub ip: IpSlice<'a>,
    pub tcp: TcpSlice<'a>
}

impl<'a> PktView<'a> {
    #[inline]
    pub fn from_raw(raw: &'a [u8]) -> Result<Self> {
        let ip = IpSlice::from_slice(raw)?;
        let tcp = TcpSlice::from_slice(ip.payload().payload)?;

        Ok(Self { ip, tcp })
    }
}

/// Write TCP/IP packet (payload = view.tcp.payload[start..Some(end)])
/// to out_buf, explicitly clearing before.
///
/// If payload or ttl is given, override view's one.
pub fn split_packet_0(
    view: &PktView,
    start: u32,
    end: Option<u32>,
    out_buf: &mut Vec<u8>,
    payload: Option<&[u8]>,
    ttl: Option<u8>
) -> Result<()> {
    use etherparse::*;

    let ip = &view.ip;
    let tcp = &view.tcp;
    let payload = payload.unwrap_or(tcp.payload());

    let end = end.unwrap_or(payload.len().try_into()?);

    if start > end || payload.len() < end as usize {
        return Err(anyhow!("invalid index"));
    }

    let opts = tcp.options();
    let mut tcp_hdr = tcp.to_header();
    tcp_hdr.sequence_number += start;

    let builder = match ip {
        IpSlice::Ipv4(hdr) => {
            let mut ip_hdr = hdr.header().to_header();
            if let Some(t) = ttl { ip_hdr.time_to_live = t; };

            PacketBuilder::ip(IpHeaders::Ipv4(
                ip_hdr,
                hdr.extensions().to_header()
            ))
        },

        IpSlice::Ipv6(hdr) => {
            let mut ip6_hdr = hdr.header().to_header();
            if let Some(t) = ttl { ip6_hdr.hop_limit = t; };

            PacketBuilder::ip(IpHeaders::Ipv6(
                ip6_hdr,
                Default::default()
            ))
        }
    }.tcp_header(tcp_hdr).options_raw(opts)?;

    let payload = &payload[start as usize..end as usize];

    out_buf.clear();
    builder.write(out_buf, payload)?;

    Ok(())
}

pub fn fake_clienthello(
    view: &PktView,
    start: u32,
    end: Option<u32>,
    out_buf: &mut Vec<u8>
) -> Result<()> {
    split_packet_0(view, start, end, out_buf,
                   Some(DEFAULT_FAKE_TLS_CLIENTHELLO), Some(fake_ttl()))
}