// lesavka-uvc - minimal UVC control handler for the gadget node.

use anyhow::{Context, Result};
use std::env;
use std::fs::OpenOptions;
use std::os::unix::fs::OpenOptionsExt;
use std::os::unix::io::AsRawFd;
use std::thread;
use std::time::Duration;

const STREAM_CTRL_SIZE: usize = 34;
const UVC_DATA_SIZE: usize = 60;

const V4L2_EVENT_PRIVATE_START: u32 = 0x0800_0000;
const UVC_EVENT_CONNECT: u32 = V4L2_EVENT_PRIVATE_START + 0;
const UVC_EVENT_DISCONNECT: u32 = V4L2_EVENT_PRIVATE_START + 1;
const UVC_EVENT_STREAMON: u32 = V4L2_EVENT_PRIVATE_START + 2;
const UVC_EVENT_STREAMOFF: u32 = V4L2_EVENT_PRIVATE_START + 3;
const UVC_EVENT_SETUP: u32 = V4L2_EVENT_PRIVATE_START + 4;
const UVC_EVENT_DATA: u32 = V4L2_EVENT_PRIVATE_START + 5;

const UVC_STRING_CONTROL_IDX: u8 = 0;
const UVC_STRING_STREAMING_IDX: u8 = 1;

const USB_DIR_IN: u8 = 0x80;

const UVC_SET_CUR: u8 = 0x01;
const UVC_GET_CUR: u8 = 0x81;
const UVC_GET_MIN: u8 = 0x82;
const UVC_GET_MAX: u8 = 0x83;
const UVC_GET_RES: u8 = 0x84;
const UVC_GET_LEN: u8 = 0x85;
const UVC_GET_INFO: u8 = 0x86;
const UVC_GET_DEF: u8 = 0x87;

const UVC_VS_PROBE_CONTROL: u8 = 0x01;
const UVC_VS_COMMIT_CONTROL: u8 = 0x02;
const UVC_VC_REQUEST_ERROR_CODE_CONTROL: u8 = 0x02;

#[repr(C)]
struct V4l2EventSubscription {
    type_: u32,
    id: u32,
    flags: u32,
    reserved: [u32; 5],
}

#[repr(C)]
union V4l2EventUnion {
    data: [u8; 64],
    _align: u64,
}

#[repr(C)]
struct V4l2Event {
    type_: u32,
    u: V4l2EventUnion,
    pending: u32,
    sequence: u32,
    timestamp: libc::timespec,
    id: u32,
    reserved: [u32; 8],
}

#[repr(C)]
#[derive(Clone, Copy)]
struct UsbCtrlRequest {
    b_request_type: u8,
    b_request: u8,
    w_value: u16,
    w_index: u16,
    w_length: u16,
}

#[repr(C)]
#[derive(Clone, Copy)]
struct UvcRequestData {
    length: i32,
    data: [u8; UVC_DATA_SIZE],
}

#[derive(Clone, Copy)]
struct UvcConfig {
    width: u32,
    height: u32,
    fps: u32,
    interval: u32,
    max_packet: u32,
}

struct UvcState {
    cfg: UvcConfig,
    default: [u8; STREAM_CTRL_SIZE],
    probe: [u8; STREAM_CTRL_SIZE],
    commit: [u8; STREAM_CTRL_SIZE],
}

#[derive(Clone, Copy)]
struct PendingRequest {
    interface: u8,
    selector: u8,
}

fn main() -> Result<()> {
    let (dev, cfg) = parse_args()?;
    eprintln!("[lesavka-uvc] starting (dev={dev})");

    let debug = env::var("LESAVKA_UVC_DEBUG").is_ok();
    let mut setup_seen: u64 = 0;
    let mut data_seen: u64 = 0;
    let mut dq_err_seen: u64 = 0;
    let mut dq_err_last: Option<i32> = None;

    loop {
        let file = open_with_retry(&dev)?;
        let fd = file.as_raw_fd();
        let vidioc_subscribe = ioctl_write::<V4l2EventSubscription>(b'V', 90);
        let vidioc_dqevent = ioctl_read::<V4l2Event>(b'V', 89);
        let uvc_send_response = ioctl_write::<UvcRequestData>(b'U', 1);

        subscribe_event(fd, vidioc_subscribe, UVC_EVENT_SETUP)?;
        subscribe_event(fd, vidioc_subscribe, UVC_EVENT_DATA)?;
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_CONNECT);
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_DISCONNECT);
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_STREAMON);
        let _ = subscribe_event(fd, vidioc_subscribe, UVC_EVENT_STREAMOFF);

        let mut state = UvcState::new(cfg);
        let mut pending: Option<PendingRequest> = None;

        loop {
            let mut ev = unsafe { std::mem::zeroed::<V4l2Event>() };
            let rc = unsafe { libc::ioctl(fd, vidioc_dqevent, &mut ev) };
            if rc < 0 {
                let err = std::io::Error::last_os_error();
                match err.raw_os_error() {
                    Some(libc::EAGAIN) | Some(libc::EINTR) | Some(libc::ENOENT) => {
                        if debug {
                            let code = err.raw_os_error();
                            if dq_err_seen < 10 || code != dq_err_last {
                                eprintln!("[lesavka-uvc] dqevent idle: {err}");
                                dq_err_seen += 1;
                                dq_err_last = code;
                            }
                        }
                        thread::sleep(Duration::from_millis(10));
                        continue;
                    }
                    Some(libc::ENODEV) | Some(libc::EBADF) | Some(libc::EIO) => {
                        eprintln!("[lesavka-uvc] device reset ({err}); reopening");
                        break;
                    }
                    _ => {
                        eprintln!("[lesavka-uvc] dqevent failed: {err}");
                        thread::sleep(Duration::from_millis(100));
                        continue;
                    }
                }
            }

            match ev.type_ {
                UVC_EVENT_CONNECT => {
                    let speed = u32::from_le_bytes(event_bytes(&ev)[0..4].try_into().unwrap());
                    eprintln!("[lesavka-uvc] UVC connect (speed={speed})");
                }
                UVC_EVENT_DISCONNECT => eprintln!("[lesavka-uvc] UVC disconnect"),
                UVC_EVENT_STREAMON => eprintln!("[lesavka-uvc] stream on"),
                UVC_EVENT_STREAMOFF => eprintln!("[lesavka-uvc] stream off"),
                UVC_EVENT_SETUP => {
                    let req = parse_ctrl_request(event_bytes(&ev));
                    setup_seen += 1;
                    if debug || setup_seen <= 10 {
                        eprintln!(
                            "[lesavka-uvc] setup #{setup_seen} rt=0x{:02x} rq=0x{:02x} val=0x{:04x} idx=0x{:04x} len={}",
                            req.b_request_type,
                            req.b_request,
                            req.w_value,
                            req.w_index,
                            req.w_length
                        );
                    }
                    handle_setup(
                        fd,
                        uvc_send_response,
                        &mut state,
                        &mut pending,
                        req,
                    );
                }
                UVC_EVENT_DATA => {
                    let data = parse_request_data(event_bytes(&ev));
                    data_seen += 1;
                    if debug || data_seen <= 10 {
                        eprintln!(
                            "[lesavka-uvc] data #{data_seen} len={}",
                            data.length
                        );
                    }
                    handle_data(fd, uvc_send_response, &mut state, &mut pending, data);
                }
                _ => {
                    if debug {
                        eprintln!("[lesavka-uvc] event type=0x{:08x}", ev.type_);
                    }
                }
            }
        }
    }
}

fn parse_args() -> Result<(String, UvcConfig)> {
    let mut args = env::args().skip(1);
    let mut dev: Option<String> = None;

    while let Some(arg) = args.next() {
        match arg.as_str() {
            "--device" | "-d" => dev = args.next(),
            _ => dev = Some(arg),
        }
    }

    let dev = dev
        .or_else(|| env::var("LESAVKA_UVC_DEV").ok())
        .context("missing --device (or LESAVKA_UVC_DEV)")?;

    Ok((dev, UvcConfig::from_env()))
}

impl UvcConfig {
    fn from_env() -> Self {
        let width = env_u32("LESAVKA_UVC_WIDTH", 640);
        let height = env_u32("LESAVKA_UVC_HEIGHT", 480);
        let fps = env_u32("LESAVKA_UVC_FPS", 30).max(1);
        let interval = env_u32("LESAVKA_UVC_INTERVAL", 0);
        let mut max_packet = env_u32("LESAVKA_UVC_MAXPACKET", 3072);
        if env::var("LESAVKA_UVC_BULK").is_ok() {
            max_packet = max_packet.min(512);
        } else {
            max_packet = max_packet.min(1024);
        }

        let interval = if interval == 0 {
            10_000_000 / fps
        } else {
            interval
        };

        Self {
            width,
            height,
            fps,
            interval,
            max_packet,
        }
    }
}

impl UvcState {
    fn new(cfg: UvcConfig) -> Self {
        let default = build_streaming_control(&cfg);
        Self {
            cfg,
            default,
            probe: default,
            commit: default,
        }
    }
}

fn open_with_retry(path: &str) -> Result<std::fs::File> {
    for attempt in 1..=200 {
        let mut opts = OpenOptions::new();
        opts.read(true).write(true);
        if env::var("LESAVKA_UVC_NONBLOCK").is_ok() {
            opts.custom_flags(libc::O_NONBLOCK);
        }
        match opts.open(path) {
            Ok(f) => {
                eprintln!("[lesavka-uvc] opened {path} (attempt {attempt})");
                return Ok(f);
            }
            Err(err) if err.raw_os_error() == Some(libc::ENOENT) => {
                thread::sleep(Duration::from_millis(50));
            }
            Err(err) => return Err(err).with_context(|| format!("open {path}")),
        }
    }
    Err(anyhow::anyhow!("timeout opening {path}"))
}

fn subscribe_event(fd: i32, req: libc::c_ulong, event: u32) -> Result<()> {
    let mut sub = V4l2EventSubscription {
        type_: event,
        id: 0,
        flags: 0,
        reserved: [0; 5],
    };
    let rc = unsafe { libc::ioctl(fd, req, &mut sub) };
    if rc < 0 {
        return Err(std::io::Error::last_os_error()).with_context(|| {
            format!("subscribe event {event:#x} (fd={fd})")
        });
    }
    Ok(())
}

fn handle_setup(
    fd: i32,
    uvc_send_response: libc::c_ulong,
    state: &mut UvcState,
    pending: &mut Option<PendingRequest>,
    req: UsbCtrlRequest,
) {
    let interface = (req.w_index & 0xff) as u8;
    let selector = (req.w_value >> 8) as u8;
    let is_in = (req.b_request_type & USB_DIR_IN) != 0;

    if !is_in && req.b_request == UVC_SET_CUR {
        *pending = Some(PendingRequest { interface, selector });
        let len = req.w_length as usize;
        let payload = vec![0u8; len.min(UVC_DATA_SIZE)];
        let _ = send_response(fd, uvc_send_response, &payload);
        return;
    }

    if !is_in {
        let _ = send_stall(fd, uvc_send_response);
        return;
    }

    let payload = build_in_response(state, interface, selector, req.b_request);
    match payload {
        Some(bytes) => {
            let _ = send_response(fd, uvc_send_response, &bytes);
        }
        None => {
            let _ = send_stall(fd, uvc_send_response);
        }
    }
}

fn handle_data(
    fd: i32,
    uvc_send_response: libc::c_ulong,
    state: &mut UvcState,
    pending: &mut Option<PendingRequest>,
    data: UvcRequestData,
) {
    let Some(p) = pending.take() else {
        return;
    };

    if data.length < 0 {
        return;
    }

    let len = data.length as usize;
    let slice = &data.data[..len.min(data.data.len())];

    if p.interface == UVC_STRING_STREAMING_IDX
        && matches!(p.selector, UVC_VS_PROBE_CONTROL | UVC_VS_COMMIT_CONTROL)
    {
        let sanitized = sanitize_streaming_control(slice, state);
        if p.selector == UVC_VS_PROBE_CONTROL {
            state.probe = sanitized;
        } else {
            state.commit = sanitized;
        }
    }
}

fn build_in_response(
    state: &UvcState,
    interface: u8,
    selector: u8,
    request: u8,
) -> Option<Vec<u8>> {
    match interface {
        UVC_STRING_STREAMING_IDX => build_streaming_response(state, selector, request),
        UVC_STRING_CONTROL_IDX => build_control_response(selector, request),
        _ => None,
    }
}

fn build_streaming_response(
    state: &UvcState,
    selector: u8,
    request: u8,
) -> Option<Vec<u8>> {
    let current = match selector {
        UVC_VS_PROBE_CONTROL => state.probe,
        UVC_VS_COMMIT_CONTROL => state.commit,
        _ => return None,
    };

    match request {
        UVC_GET_INFO => Some(vec![0x03]),
        UVC_GET_LEN => Some((STREAM_CTRL_SIZE as u16).to_le_bytes().to_vec()),
        UVC_GET_CUR => Some(current.to_vec()),
        UVC_GET_MIN | UVC_GET_MAX | UVC_GET_DEF | UVC_GET_RES => Some(state.default.to_vec()),
        _ => None,
    }
}

fn build_control_response(selector: u8, request: u8) -> Option<Vec<u8>> {
    match request {
        UVC_GET_INFO => Some(vec![0x01]),
        UVC_GET_LEN => Some(1u16.to_le_bytes().to_vec()),
        UVC_GET_CUR | UVC_GET_MIN | UVC_GET_MAX | UVC_GET_DEF | UVC_GET_RES => {
            if selector == UVC_VC_REQUEST_ERROR_CODE_CONTROL {
                Some(vec![0x00])
            } else {
                Some(vec![0x00])
            }
        }
        _ => None,
    }
}

fn sanitize_streaming_control(data: &[u8], state: &UvcState) -> [u8; STREAM_CTRL_SIZE] {
    let mut out = state.default;
    if data.len() >= STREAM_CTRL_SIZE {
        let format_index = data[2];
        let frame_index = data[3];
        let interval = read_le32(data, 4);
        let host_payload = read_le32(data, 22);

        if format_index == 1 {
            out[2] = 1;
        }
        if frame_index == 1 {
            out[3] = 1;
        }
        if interval == state.cfg.interval {
            write_le32(&mut out[4..8], interval);
        }
        if host_payload > 0 {
            let payload = host_payload.min(state.cfg.max_packet);
            write_le32(&mut out[22..26], payload);
        }
    }
    out
}

fn send_response(fd: i32, req: libc::c_ulong, payload: &[u8]) -> Result<()> {
    let mut resp = UvcRequestData {
        length: payload.len() as i32,
        data: [0u8; UVC_DATA_SIZE],
    };
    let n = payload.len().min(UVC_DATA_SIZE);
    resp.data[..n].copy_from_slice(&payload[..n]);

    let rc = unsafe { libc::ioctl(fd, req, &resp) };
    if rc < 0 {
        let err = std::io::Error::last_os_error();
        eprintln!("[lesavka-uvc] send_response failed: {err}");
        return Err(err).context("UVCIOC_SEND_RESPONSE");
    }
    Ok(())
}

fn send_stall(fd: i32, req: libc::c_ulong) -> Result<()> {
    let resp = UvcRequestData {
        length: -1,
        data: [0u8; UVC_DATA_SIZE],
    };
    let rc = unsafe { libc::ioctl(fd, req, &resp) };
    if rc < 0 {
        let err = std::io::Error::last_os_error();
        eprintln!("[lesavka-uvc] send_stall failed: {err}");
        return Err(err).context("UVCIOC_SEND_RESPONSE(stall)");
    }
    Ok(())
}

fn build_streaming_control(cfg: &UvcConfig) -> [u8; STREAM_CTRL_SIZE] {
    let mut buf = [0u8; STREAM_CTRL_SIZE];
    let frame_size = cfg.width * cfg.height * 2;

    write_le16(&mut buf[0..2], 1); // bmHint: dwFrameInterval
    buf[2] = 1; // bFormatIndex
    buf[3] = 1; // bFrameIndex
    write_le32(&mut buf[4..8], cfg.interval);
    write_le16(&mut buf[8..10], 0);
    write_le16(&mut buf[10..12], 0);
    write_le16(&mut buf[12..14], 0);
    write_le16(&mut buf[14..16], 0);
    write_le16(&mut buf[16..18], 0);
    write_le32(&mut buf[18..22], frame_size);
    write_le32(&mut buf[22..26], cfg.max_packet);
    write_le32(&mut buf[26..30], 48_000_000);
    buf[30] = 0;
    buf[31] = 0;
    buf[32] = 0;
    buf[33] = 0;

    buf
}

fn event_bytes(ev: &V4l2Event) -> [u8; 64] {
    unsafe { ev.u.data }
}

fn parse_ctrl_request(data: [u8; 64]) -> UsbCtrlRequest {
    UsbCtrlRequest {
        b_request_type: data[0],
        b_request: data[1],
        w_value: u16::from_le_bytes([data[2], data[3]]),
        w_index: u16::from_le_bytes([data[4], data[5]]),
        w_length: u16::from_le_bytes([data[6], data[7]]),
    }
}

fn parse_request_data(data: [u8; 64]) -> UvcRequestData {
    let length = i32::from_le_bytes([data[0], data[1], data[2], data[3]]);
    let mut out = [0u8; UVC_DATA_SIZE];
    out.copy_from_slice(&data[4..64]);
    UvcRequestData { length, data: out }
}

fn env_u32(name: &str, default: u32) -> u32 {
    env::var(name)
        .ok()
        .and_then(|v| v.parse::<u32>().ok())
        .unwrap_or(default)
}

fn write_le16(dst: &mut [u8], val: u16) {
    let bytes = val.to_le_bytes();
    dst[0] = bytes[0];
    dst[1] = bytes[1];
}

fn write_le32(dst: &mut [u8], val: u32) {
    let bytes = val.to_le_bytes();
    dst[0] = bytes[0];
    dst[1] = bytes[1];
    dst[2] = bytes[2];
    dst[3] = bytes[3];
}

fn read_le32(src: &[u8], offset: usize) -> u32 {
    u32::from_le_bytes([src[offset], src[offset + 1], src[offset + 2], src[offset + 3]])
}

const IOC_NRBITS: u8 = 8;
const IOC_TYPEBITS: u8 = 8;
const IOC_SIZEBITS: u8 = 14;
const IOC_DIRBITS: u8 = 2;

const IOC_NRSHIFT: u8 = 0;
const IOC_TYPESHIFT: u8 = IOC_NRSHIFT + IOC_NRBITS;
const IOC_SIZESHIFT: u8 = IOC_TYPESHIFT + IOC_TYPEBITS;
const IOC_DIRSHIFT: u8 = IOC_SIZESHIFT + IOC_SIZEBITS;

const IOC_READ: u8 = 2;
const IOC_WRITE: u8 = 1;

fn ioctl_read<T>(type_: u8, nr: u8) -> libc::c_ulong {
    ioc(IOC_READ, type_, nr, std::mem::size_of::<T>() as u16)
}

fn ioctl_write<T>(type_: u8, nr: u8) -> libc::c_ulong {
    ioc(IOC_WRITE, type_, nr, std::mem::size_of::<T>() as u16)
}

fn ioc(dir: u8, type_: u8, nr: u8, size: u16) -> libc::c_ulong {
    let dir = (dir as u32) << IOC_DIRSHIFT;
    let ty = (type_ as u32) << IOC_TYPESHIFT;
    let nr = (nr as u32) << IOC_NRSHIFT;
    let size = (size as u32) << IOC_SIZESHIFT;
    (dir | ty | nr | size) as libc::c_ulong
}