//! Transport-independent contract for the virtual **Steam Controller 2** (2026, Valve "Ibex" /
//! SDL "Triton", wired `28DE:1302`) — the as-is passthrough sibling of [`super::steam_proto`].
//!
//! Unlike the Deck/classic-SC backends, this device is NOT re-synthesized from typed wire state:
//! the client captures the physical controller (USB Puck / wired / BLE) and forwards its raw
//! input reports verbatim ([`RichInput::HidReport`](punktfunk_core::quic::RichInput)); the host
//! mirrors them out unchanged, and everything the host's hidraw consumer writes back (Steam's
//! lizard-off / IMU-enable feature reports, `0x80` rumble output reports) is forwarded raw to the
//! client for replay on the real controller ([`HidOutput::HidRaw`](punktfunk_core::quic::HidOutput)).
//! Mainline `hid-steam` does not bind this PID, so no kernel evdev exists — **Steam Input is the
//! consumer**, driving the hidraw node exactly as it drives the physical pad.
//!
//! Protocol ground truth: SDL's `SDL_hidapi_steam_triton.c` + `steam/controller_structs.h`
//! (Valve-maintained). Input report ids `0x42`/`0x45` (`TritonMTUNoQuat_t`, 46 bytes with id),
//! `0x47` (adds a trackpad timestamp), `0x43` battery, `0x46`/`0x79` wireless status. Feature
//! reports are 64 bytes on report id `1`; haptics are OUTPUT reports `0x80..=0x85`.
//!
//! A typed **fallback synthesizer** is kept for the degraded case (a client that declared the
//! kind but sends no raw feed): buttons/sticks/triggers from the ordinary gamepad plane are
//! serialized into a minimal `0x42` state report. The first raw report permanently switches the
//! pad to as-is mode.

use punktfunk_core::input::gamepad as gs;

/// Valve vendor id (same as [`super::steam_proto::STEAM_VENDOR`], repeated to keep this module
/// self-contained).
pub const TRITON_VENDOR: u32 = 0x28DE;
/// The wired Steam Controller 2 identity the virtual pad presents. The BLE (`0x1303`) and Puck
/// dongle (`0x1304`/`0x1305`) identities are client-side transports only — Steam treats the wired
/// PID as the canonical controller.
pub const TRITON_WIRED_PRODUCT: u32 = 0x1302;

/// Triton input-report ids (`ETritonReportIDTypes`, SDL `controller_structs.h`).
pub const ID_TRITON_CONTROLLER_STATE: u8 = 0x42;
pub const ID_TRITON_BATTERY_STATUS: u8 = 0x43;
pub const ID_TRITON_CONTROLLER_STATE_BLE: u8 = 0x45;
pub const ID_TRITON_CONTROLLER_STATE_TIMESTAMP: u8 = 0x47;

/// Haptic OUTPUT report ids (`ID_OUT_REPORT_*`). Only rumble is parsed host-side (for the
/// universal 0xCA plane); every output report is forwarded raw regardless.
pub const ID_OUT_REPORT_HAPTIC_RUMBLE: u8 = 0x80;

/// Physical `0x42` state report size: one report-id byte plus 53 payload bytes.
pub const TRITON_REPORT_LEN: usize = 64;
pub const TRITON_STATE_LEN: usize = 54;

/// The physical Triton HID report descriptor, captured byte-for-byte from both wired `28DE:1302`
/// and Puck `28DE:1304` controller interfaces. Its numbered reports are part of the protocol:
/// inputs `0x40`–`0x45`/`0x79`/`0x7B`, outputs `0x80`–`0x89`, and feature channels `1` and `2`.
/// In particular, Puck connection and bond queries use feature report 2; an unnumbered minimal
/// descriptor makes hidraw frame those queries incorrectly and Steam eventually closes the device.
#[rustfmt::skip]
pub const TRITON_RDESC: &[u8] = &[
    0x05, 0x01, 0x09, 0x02, 0xA1, 0x01, 0x85, 0x40, 0x09, 0x01, 0xA1, 0x00,
    0x05, 0x09, 0x19, 0x01, 0x29, 0x02, 0x15, 0x00, 0x25, 0x01, 0x75, 0x01,
    0x95, 0x02, 0x81, 0x02, 0x75, 0x06, 0x95, 0x01, 0x81, 0x01, 0x05, 0x01,
    0x09, 0x30, 0x09, 0x31, 0x15, 0x81, 0x25, 0x7F, 0x75, 0x08, 0x95, 0x02,
    0x81, 0x06, 0x95, 0x01, 0x09, 0x38, 0x81, 0x06, 0x05, 0x0C, 0x0A, 0x38,
    0x02, 0x95, 0x01, 0x81, 0x06, 0xC0, 0xC0, 0x05, 0x01, 0x09, 0x06, 0xA1,
    0x01, 0x85, 0x41, 0x05, 0x07, 0x19, 0xE0, 0x29, 0xE7, 0x15, 0x00, 0x25,
    0x01, 0x75, 0x01, 0x95, 0x08, 0x81, 0x02, 0x81, 0x01, 0x19, 0x00, 0x29,
    0x65, 0x15, 0x00, 0x25, 0x65, 0x75, 0x08, 0x95, 0x06, 0x81, 0x00, 0xC0,
    0x06, 0x00, 0xFF, 0x09, 0x01, 0xA1, 0x01, 0x85, 0x42, 0x15, 0x00, 0x26,
    0xFF, 0x00, 0x75, 0x08, 0x95, 0x35, 0x09, 0x42, 0x81, 0x02, 0x85, 0x44,
    0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x05, 0x09, 0x44, 0x81,
    0x02, 0x85, 0x79, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x01,
    0x09, 0x79, 0x81, 0x02, 0x85, 0x43, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75,
    0x08, 0x95, 0x0E, 0x09, 0x43, 0x81, 0x02, 0x85, 0x7B, 0x15, 0x00, 0x26,
    0xFF, 0x00, 0x75, 0x08, 0x95, 0x0C, 0x09, 0x7B, 0x81, 0x02, 0x85, 0x45,
    0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x2D, 0x09, 0x45, 0x81,
    0x02, 0x85, 0x80, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x09,
    0x09, 0x80, 0x91, 0x02, 0x85, 0x81, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75,
    0x08, 0x95, 0x07, 0x09, 0x81, 0x91, 0x02, 0x85, 0x82, 0x15, 0x00, 0x26,
    0xFF, 0x00, 0x75, 0x08, 0x95, 0x03, 0x09, 0x82, 0x91, 0x02, 0x85, 0x83,
    0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x09, 0x09, 0x83, 0x91,
    0x02, 0x85, 0x84, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x08,
    0x09, 0x84, 0x91, 0x02, 0x85, 0x85, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75,
    0x08, 0x95, 0x03, 0x09, 0x85, 0x91, 0x02, 0x85, 0x86, 0x15, 0x00, 0x26,
    0xFF, 0x00, 0x75, 0x08, 0x95, 0x03, 0x09, 0x86, 0x91, 0x02, 0x85, 0x87,
    0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x3F, 0x09, 0x87, 0x91,
    0x02, 0x85, 0x89, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75, 0x08, 0x95, 0x3F,
    0x09, 0x89, 0x91, 0x02, 0x85, 0x88, 0x15, 0x00, 0x26, 0xFF, 0x00, 0x75,
    0x08, 0x95, 0x3F, 0x09, 0x88, 0x91, 0x02, 0x85, 0x01, 0x95, 0x3F, 0x09,
    0x01, 0xB1, 0x02, 0x85, 0x02, 0x95, 0x3F, 0x09, 0x01, 0xB1, 0x02, 0xC0,
];

/// Triton button bits in the state report's `buttons` u32 — transcribed verbatim from SDL's
/// `TritonButtons`. Only the bits the typed fallback synthesizes are named; the raw path carries
/// whatever the physical pad set.
pub mod tbtn {
    pub const A: u32 = 0x0000_0001;
    pub const B: u32 = 0x0000_0002;
    pub const X: u32 = 0x0000_0004;
    pub const Y: u32 = 0x0000_0008;
    pub const QAM: u32 = 0x0000_0010;
    pub const R3: u32 = 0x0000_0020;
    pub const VIEW: u32 = 0x0000_0040;
    pub const R4: u32 = 0x0000_0080;
    pub const R5: u32 = 0x0000_0100;
    pub const RB: u32 = 0x0000_0200;
    pub const DPAD_DOWN: u32 = 0x0000_0400;
    pub const DPAD_RIGHT: u32 = 0x0000_0800;
    pub const DPAD_LEFT: u32 = 0x0000_1000;
    pub const DPAD_UP: u32 = 0x0000_2000;
    pub const MENU: u32 = 0x0000_4000;
    pub const L3: u32 = 0x0000_8000;
    pub const STEAM: u32 = 0x0001_0000;
    pub const L4: u32 = 0x0002_0000;
    pub const L5: u32 = 0x0004_0000;
    pub const LB: u32 = 0x0008_0000;
    pub const RPAD_TOUCH: u32 = 0x0020_0000;
    pub const RPAD_CLICK: u32 = 0x0040_0000;
    pub const RT_CLICK: u32 = 0x0080_0000;
    pub const LPAD_TOUCH: u32 = 0x0200_0000;
    pub const LPAD_CLICK: u32 = 0x0400_0000;
    pub const LT_CLICK: u32 = 0x0800_0000;
}

/// One virtual Triton pad's report state. In as-is mode (`raw_len > 0`) the raw report IS the
/// state; the typed fields only feed the fallback synthesizer until the first raw report lands.
#[derive(Clone, Copy)]
pub struct TritonState {
    /// The last raw report the client forwarded (report-id byte first); `raw_len == 0` until the
    /// first one arrives, after which the typed fields below stop mattering.
    pub raw: [u8; TRITON_REPORT_LEN],
    pub raw_len: u8,
    /// Typed fallback fields (Triton bit layout / raw axis units), from the ordinary wire plane.
    pub buttons: u32,
    pub lt: u16,
    pub rt: u16,
    pub lx: i16,
    pub ly: i16,
    pub rx: i16,
    pub ry: i16,
}

impl TritonState {
    pub fn neutral() -> TritonState {
        TritonState {
            raw: [0u8; TRITON_REPORT_LEN],
            raw_len: 0,
            buttons: 0,
            lt: 0,
            rt: 0,
            lx: 0,
            ly: 0,
            rx: 0,
            ry: 0,
        }
    }

    /// Typed fallback: fold one wire button/stick frame into Triton fields. Mapping follows the
    /// Deck backend's conventions (PADDLE1/2/3/4 = R4/L4/R5/L5, MISC1 = QAM, the DualSense
    /// touchpad-click wire bit = right-pad click); sticks are already the device convention
    /// (+y up), triggers scale 0..255 → 0..32767.
    pub fn from_gamepad(
        buttons: u32,
        lx: i16,
        ly: i16,
        rx: i16,
        ry: i16,
        lt: u8,
        rt: u8,
    ) -> TritonState {
        let on = |bit: u32| buttons & bit != 0;
        let trig = |v: u8| ((v as u32 * 32767) / 255) as u16;
        let mut b = 0u32;
        let set = |b: &mut u32, on: bool, m: u32| {
            if on {
                *b |= m;
            }
        };
        set(&mut b, on(gs::BTN_A), tbtn::A);
        set(&mut b, on(gs::BTN_B), tbtn::B);
        set(&mut b, on(gs::BTN_X), tbtn::X);
        set(&mut b, on(gs::BTN_Y), tbtn::Y);
        set(&mut b, on(gs::BTN_LB), tbtn::LB);
        set(&mut b, on(gs::BTN_RB), tbtn::RB);
        set(&mut b, on(gs::BTN_BACK), tbtn::VIEW);
        set(&mut b, on(gs::BTN_START), tbtn::MENU);
        set(&mut b, on(gs::BTN_GUIDE), tbtn::STEAM);
        set(&mut b, on(gs::BTN_LS_CLICK), tbtn::L3);
        set(&mut b, on(gs::BTN_RS_CLICK), tbtn::R3);
        set(&mut b, on(gs::BTN_DPAD_UP), tbtn::DPAD_UP);
        set(&mut b, on(gs::BTN_DPAD_DOWN), tbtn::DPAD_DOWN);
        set(&mut b, on(gs::BTN_DPAD_LEFT), tbtn::DPAD_LEFT);
        set(&mut b, on(gs::BTN_DPAD_RIGHT), tbtn::DPAD_RIGHT);
        set(&mut b, on(gs::BTN_TOUCHPAD), tbtn::RPAD_CLICK);
        set(&mut b, on(gs::BTN_PADDLE1), tbtn::R4);
        set(&mut b, on(gs::BTN_PADDLE2), tbtn::L4);
        set(&mut b, on(gs::BTN_PADDLE3), tbtn::R5);
        set(&mut b, on(gs::BTN_PADDLE4), tbtn::L5);
        set(&mut b, on(gs::BTN_MISC1), tbtn::QAM);
        // "Fully pressed" digital shadow of the analog triggers (the physical pad's own
        // threshold is a hard pull, not first-contact).
        set(&mut b, lt >= 240, tbtn::LT_CLICK);
        set(&mut b, rt >= 240, tbtn::RT_CLICK);
        TritonState {
            raw: [0u8; TRITON_REPORT_LEN],
            raw_len: 0,
            buttons: b,
            lt: trig(lt),
            rt: trig(rt),
            lx,
            ly,
            rx,
            ry,
        }
    }
}

/// Serialize the typed fallback state into a minimal `0x42` `TritonMTUNoQuat_t` report:
/// `[0x42][seq u8][buttons u32][trigL i16][trigR i16][sticks i16×4][lpad x/y + pressure]
/// [rpad x/y + pressure][imu ts u32 + accel i16×3 + gyro i16×3]` — pads and IMU stay zero
/// (no raw feed = no trackpad/motion source; Steam only sees IMU data after enabling
/// `SETTING_IMU_MODE` on a real feed anyway).
pub fn serialize_triton_state(buf: &mut [u8; TRITON_STATE_LEN], st: &TritonState, seq: u8) {
    buf.fill(0);
    buf[0] = ID_TRITON_CONTROLLER_STATE;
    buf[1] = seq;
    buf[2..6].copy_from_slice(&st.buttons.to_le_bytes());
    buf[6..8].copy_from_slice(&(st.lt as i16).to_le_bytes());
    buf[8..10].copy_from_slice(&(st.rt as i16).to_le_bytes());
    buf[10..12].copy_from_slice(&st.lx.to_le_bytes());
    buf[12..14].copy_from_slice(&st.ly.to_le_bytes());
    buf[14..16].copy_from_slice(&st.rx.to_le_bytes());
    buf[16..18].copy_from_slice(&st.ry.to_le_bytes());
    // [18..30] left/right pad + pressures stay zero; [30..46] IMU stays zero.
}

/// One service pass's extracted feedback: the raw reports to forward (kind-tagged for
/// [`HidOutput::HidRaw`](punktfunk_core::quic::HidOutput)) plus the rumble level parsed out of a
/// `0x80` report for the universal 0xCA plane (drives the phone-mirror path on clients whose
/// physical pad already gets the raw report).
#[derive(Default)]
pub struct TritonFeedback {
    /// `(low, high)` — `left.speed`/`right.speed` of the last rumble output report seen.
    pub rumble: Option<(u16, u16)>,
    /// Raw reports to forward: `(kind, bytes)` with kind = `HID_RAW_OUTPUT`/`HID_RAW_FEATURE`.
    pub raw: Vec<(u8, Vec<u8>)>,
}

/// Parse a Triton haptic-rumble OUTPUT report (`MsgHapticRumble`, 10 bytes with id):
/// `[0x80][type u8][intensity u16][left.speed u16][left.gain i8][right.speed u16][right.gain i8]`.
/// Returns `(left_speed, right_speed)` as `(low, high)`.
pub fn parse_triton_rumble(data: &[u8]) -> Option<(u16, u16)> {
    if data.len() < 10 || data[0] != ID_OUT_REPORT_HAPTIC_RUMBLE {
        return None;
    }
    let le = |o: usize| u16::from_le_bytes([data[o], data[o + 1]]);
    Some((le(4), le(7)))
}

/// Strip the hidraw unnumbered-report `0x00` prefix if present: Triton report/command ids are all
/// non-zero (`0x42+` input, `0x80+` output, `1` feature), so a leading zero can only be the
/// synthetic report-id byte hidraw prepends on this unnumbered virtual descriptor.
pub fn strip_report_prefix(data: &[u8]) -> &[u8] {
    match data {
        [0, rest @ ..] if !rest.is_empty() => rest,
        d => d,
    }
}

/// Per-instance unit id stamped into the fake `0x83` attributes (`'T','R','I'` + index).
pub fn triton_unit_id(index: u8) -> u32 {
    0x5452_4900 | index as u32
}

/// The virtual pad's serial, FVPF-prefixed: the physical-Steam-controller conflict gate
/// recognizes `FVPF…` (`HID_UNIQ`) as one of punktfunk's own virtual pads, so a concurrent
/// session never mistakes this device for real hardware. Shaped like the real `FXA…` serials
/// (13 chars). Shared by the UHID and usbip legs (identity + `0xAE` replies must agree).
pub fn triton_serial(index: u8) -> String {
    format!("FVPF1302{index:02}D03")
}

/// Build the reply to a feature GET_REPORT — the answer half of the Valve query dance. Steam's
/// `GetControllerInfo` SETs a query (`0x83` attributes / `0xAE` string) and then GETs the answer;
/// **the reply's command byte must echo the LAST SET's command** or Steam treats the pad as
/// broken and never adopts it (confirmed on-glass 2026-07-15: answering every GET with a serial
/// blob left the virtual pad unpicked). Mirrors the Deck's validated
/// [`feature_reply`](super::steam_proto::feature_reply), with two Triton deltas: the frame rides
/// feature report id **1** (`[0x01][cmd][len][payload…]`, matching SDL's send framing for this
/// device), and the `0x83` blob carries the Triton's product id. The attribute VALUES beyond the
/// product id mirror the Deck's hidraw capture (same firmware family conventions) — replace them
/// with a capture from a physical pad if Steam still balks.
///
/// `last_set` is the id-first SET payload (`[0x01, cmd, …]`); a stack that already stripped the
/// id byte (`[cmd, …]`, cmd ≥ 0x80) is handled too.
pub fn triton_feature_reply(last_set: &[u8], serial: &str, unit_id: u32) -> [u8; 64] {
    const ID_GET_ATTRIBUTES_VALUES: u8 = 0x83;
    const ID_GET_STRING_ATTRIBUTE: u8 = 0xAE;
    const ID_GET_FIRMWARE_INFO: u8 = 0xF2;
    const ATTRIB_STR_UNIT_SERIAL: u8 = 0x01;

    let body = match last_set {
        [0x01, rest @ ..] => rest,
        d => d,
    };
    let cmd = body.first().copied().unwrap_or(ID_GET_STRING_ATTRIBUTE);

    let mut r = [0u8; 64];
    r[0] = 0x01;
    match cmd {
        ID_GET_ATTRIBUTES_VALUES => {
            // Captured controller response: 25-byte payload containing five id/u32 attributes.
            r[1] = ID_GET_ATTRIBUTES_VALUES;
            r[2] = 0x19;
            let attrs = [
                (0x01, TRITON_WIRED_PRODUCT),
                (0x02, 0),
                (0x0A, unit_id),
                (0x04, unit_id ^ 0x0296_DAF9),
                (0x09, 0x49),
            ];
            let mut o = 3;
            for (id, val) in attrs {
                r[o] = id;
                r[o + 1..o + 5].copy_from_slice(&val.to_le_bytes());
                o += 5;
            }
        }
        ID_GET_STRING_ATTRIBUTE => {
            // Captured replies always declare 20 bytes: attribute id plus a 19-byte padded string.
            let attr = body.get(2).copied().unwrap_or(ATTRIB_STR_UNIT_SERIAL);
            let b = serial.as_bytes();
            let len = b.len().min(19);
            r[..4].copy_from_slice(&[0x01, ID_GET_STRING_ATTRIBUTE, 0x14, attr]);
            r[4..4 + len].copy_from_slice(&b[..len]);
        }
        ID_GET_FIRMWARE_INFO => {
            let index = body.get(2).copied().unwrap_or(0);
            r[1] = ID_GET_FIRMWARE_INFO;
            r[3] = index;
            match index {
                0 => {
                    r[2] = 0x29;
                    r[4..8].copy_from_slice(&(unit_id ^ 0x0296_DAF9).to_le_bytes());
                    r[8] = 0x49;
                    r[12..24].copy_from_slice(b"603f69218a85");
                    let b = serial.as_bytes();
                    let len = b.len().min(16);
                    r[28..28 + len].copy_from_slice(&b[..len]);
                }
                1 => {
                    r[2] = 0x22;
                    r[4..37].copy_from_slice(&[
                        0x00, 0x57, 0xD0, 0x18, 0x6A, 0x37, 0x30, 0x35, 0x34, 0x32, 0x35, 0x37,
                        0x64, 0x32, 0x64, 0x61, 0x37, 0x00, 0x00, 0x00, 0x00, 0x23, 0x00, 0x00,
                        0x00, 0x00, 0x00, 0x00, 0x00, 0x33, 0x6D, 0x02, 0x00,
                    ]);
                }
                _ => {
                    r[2] = 0x09;
                    r[4..12].copy_from_slice(&[0x7C, 0x4F, 0x01, 0x00, 0x01, 0, 0, 0]);
                }
            }
        }
        _ => {
            let n = body.len().min(63);
            r[1..1 + n].copy_from_slice(&body[..n]);
        }
    }
    r
}

#[cfg(test)]
mod tests {
    use super::*;

    /// The typed fallback lands the canonical wire mapping on the SDL-documented bit positions
    /// and byte offsets.
    #[test]
    fn fallback_state_serializes_sdl_layout() {
        let st = TritonState::from_gamepad(
            gs::BTN_A | gs::BTN_START | gs::BTN_PADDLE1 | gs::BTN_MISC1,
            1000,
            -2000,
            3000,
            -32768,
            255,
            0,
        );
        assert_eq!(
            st.buttons,
            tbtn::A | tbtn::MENU | tbtn::R4 | tbtn::QAM | tbtn::LT_CLICK
        );
        assert_eq!(st.lt, 32767); // exact full-scale, not the *128 approximation
        let mut r = [0u8; TRITON_STATE_LEN];
        serialize_triton_state(&mut r, &st, 7);
        assert_eq!(r[0], ID_TRITON_CONTROLLER_STATE);
        assert_eq!(r[1], 7);
        assert_eq!(u32::from_le_bytes([r[2], r[3], r[4], r[5]]), st.buttons);
        assert_eq!(i16::from_le_bytes([r[6], r[7]]), 32767); // sTriggerLeft
        assert_eq!(i16::from_le_bytes([r[10], r[11]]), 1000); // sLeftStickX
        assert_eq!(i16::from_le_bytes([r[16], r[17]]), -32768); // sRightStickY
        assert!(r[18..].iter().all(|&b| b == 0)); // pads + IMU zero
    }

    /// A rumble output report parses to `(left_speed, right_speed)`; other ids don't.
    #[test]
    fn rumble_output_report_parses() {
        // [0x80, type, intensity(2), left.speed(2), left.gain, right.speed(2), right.gain]
        let mut d = [0u8; 10];
        d[0] = ID_OUT_REPORT_HAPTIC_RUMBLE;
        d[4..6].copy_from_slice(&0x1234u16.to_le_bytes());
        d[7..9].copy_from_slice(&0x5678u16.to_le_bytes());
        assert_eq!(parse_triton_rumble(&d), Some((0x1234, 0x5678)));
        d[0] = 0x81; // haptic pulse — not rumble
        assert_eq!(parse_triton_rumble(&d), None);
        assert_eq!(parse_triton_rumble(&d[..8]), None); // short
    }

    /// The hidraw `0x00` unnumbered prefix strips; genuine command bytes survive.
    #[test]
    fn report_prefix_strips_only_leading_zero() {
        assert_eq!(strip_report_prefix(&[0x00, 0x80, 1, 2]), &[0x80, 1, 2]);
        assert_eq!(strip_report_prefix(&[0x80, 1, 2]), &[0x80, 1, 2]);
        assert_eq!(strip_report_prefix(&[0x01, 0x87]), &[0x01, 0x87]); // feature id 1 kept
        assert_eq!(strip_report_prefix(&[0x00]), &[0x00]); // lone zero: nothing to strip to
    }

    /// The GET reply echoes the LAST SET's command — the Valve query dance Steam's
    /// `GetControllerInfo` runs; a mismatched command type makes Steam drop the pad.
    #[test]
    fn feature_reply_echoes_the_queried_command() {
        let serial = triton_serial(0);
        let uid = triton_unit_id(0);
        // 0x83 attributes: id-first frame, 5 captured blocks, product id = 0x1302 in the first.
        let r = triton_feature_reply(&[0x01, 0x83, 0x00], &serial, uid);
        assert_eq!(&r[..3], &[0x01, 0x83, 0x19]);
        assert_eq!(r[3], 0x01); // ATTRIB product-id tag
        assert_eq!(
            u32::from_le_bytes([r[4], r[5], r[6], r[7]]),
            TRITON_WIRED_PRODUCT
        );
        // 0xAE serial: the captured fixed 20-byte payload — attribute id + padded string.
        let r = triton_feature_reply(&[0x01, 0xAE, 0x01, 0x01], &serial, uid);
        assert_eq!(&r[..3], &[0x01, 0xAE, 0x14]);
        assert_eq!(r[3], 0x01);
        assert_eq!(&r[4..4 + serial.len()], serial.as_bytes());
        // A stack that stripped the id byte still resolves the command.
        let r = triton_feature_reply(&[0x83u8, 0x00], &serial, uid);
        assert_eq!(&r[..3], &[0x01, 0x83, 0x19]);
        // Anything else (settings write) reads back as an echo.
        let r = triton_feature_reply(&[0x01, 0x87, 3, 9, 0, 0], &serial, uid);
        assert_eq!(&r[..6], &[0x01, 0x87, 3, 9, 0, 0]);
    }
}