// server/src/usb_gadget.rs
use std::{fs::{self, OpenOptions}, io::Write, path::Path, thread, time::Duration};
use anyhow::{Context, Result};
use tracing::{info, warn, trace};

#[derive(Clone)]
pub struct UsbGadget {
    udc_file: &'static str,
}

impl UsbGadget {
    pub fn new(name: &'static str) -> Self {
        Self {
            udc_file: Box::leak(
                format!("/sys/kernel/config/usb_gadget/{name}/UDC").into_boxed_str(),
            ),
        }
    }

    /*–––– helpers ––––*/

    /// Find the first controller in /sys/class/udc (e.g. `1000480000.usb`)
    fn find_controller() -> Result<String> {
        Ok(fs::read_dir("/sys/class/udc")?
            .next()
            .transpose()?
            .context("no UDC present")?
            .file_name()
            .to_string_lossy()
            .into_owned())
    }

    /// Busy‑loop (≤ `limit_ms`) until `state` matches `wanted`
    fn wait_state(ctrl: &str, wanted: &str, limit_ms: u64) -> Result<()> {
        let path = format!("/sys/class/udc/{ctrl}/state");
        for _ in 0..=limit_ms / 50 {
            let s = fs::read_to_string(&path).unwrap_or_default();
            trace!("⏳ state={s:?}, want={wanted}");
            if s.trim() == wanted {
                return Ok(());
            }
            thread::sleep(Duration::from_millis(50));
        }
        Err(anyhow::anyhow!("UDC never reached '{wanted}' (last = {:?})",
                            fs::read_to_string(&path).unwrap_or_default()))
    }

    /// Write `value` (plus “\n”) into a sysfs attribute
    fn write_attr<P: AsRef<Path>>(p: P, value: &str) -> Result<()> {
        OpenOptions::new()
            .write(true)
            .open(p)?
            .write_all(format!("{value}\n").as_bytes())?;
        Ok(())
    }

    /*–––– public API ––––*/

    /// Hard‑reset the gadget → identical to a physical cable re‑plug
    pub fn cycle(&self) -> Result<()> {
        /* 0 – ensure we *know* the controller even after a previous crash */
        let ctrl = match Self::find_controller() {
            Ok(c) => c,
            Err(_) => {
                // try to recover by reading the last name from the gadget’s UDC file
                let last = fs::read_to_string(self.udc_file)?.trim().to_owned();
                if last.is_empty() {
                    return Err(anyhow::anyhow!("no UDC present and UDC file is empty"));
                }
                warn!("⚠️  UDC missing, attempting to re‑bind {last}");
                Self::rebind_driver(&last)?;
                last
            }
        };

        /* 1 – detach gadget */
        info!("🔌 detaching gadget from {ctrl}");
        Self::write_attr(self.udc_file, "")?;
        Self::wait_state(&ctrl, "not attached", 3_000)?;

        /* 2 – unbind / bind platform driver (dwc2/dwc3) */
        Self::rebind_driver(&ctrl)?;

        /* 3 – re‑attach gadget */
        info!("🔌 re‑attaching gadget to {ctrl}");
        Self::write_attr(self.udc_file, &ctrl)?;

        /* 4 – toggle gadget */
        let sc = format!("/sys/class/udc/{ctrl}/soft_connect");
        // toggle 0 → 1 to force the controller to assert pull‑ups
        Self::write_attr(&sc, "0")?;                         // guarantee clean edge
        thread::sleep(Duration::from_millis(50));
        Self::write_attr(&sc, "1")?;

        /* 4 – wait for gadget */
        Self::wait_state(&ctrl, "configured", 6_000)
            .or_else(|e| {
                // If the host is physically absent (sleep / KVM paused)
                // we allow 'not attached' and continue – we can still
                // accept keyboard/mouse data and the host will enumerate
                // later without another reset.
                let last = fs::read_to_string(format!("/sys/class/udc/{ctrl}/state"))
                    .unwrap_or_default();
                if last.trim() == "not attached" {
                    warn!("⚠️ host did not enumerate within 6 s – continuing (state = {last:?})");
                    Ok(())
                } else {
                    Err(e)
                }
            })?;

        info!("✅ USB‑gadget cycle complete");
        Ok(())
    }

    /// helper: unbind + 300 ms reset + bind
    fn rebind_driver(ctrl: &str) -> Result<()> {
        let cand = ["dwc2", "dwc3"]; // cover RasPi, RK, AM62, …
        for drv in cand {
            let root = format!("/sys/bus/platform/drivers/{drv}");
            if !Path::new(&root).exists() {
                continue;
            }
            info!("🔧 unbinding UDC driver ({drv})");
            Self::write_attr(format!("{root}/unbind"), ctrl)?;
            thread::sleep(Duration::from_millis(300));

            info!("🔧 binding   UDC driver ({drv})");
            Self::write_attr(format!("{root}/bind"), ctrl)?;
            thread::sleep(Duration::from_millis(100));
            return Ok(());
        }
        Err(anyhow::anyhow!("no dwc2/dwc3 driver nodes found"))
    }
}