// server/src/usb_gadget.rs
use std::{fs::{self, OpenOptions}, io::Write, 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(),
            ),
        }
    }

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

    /// Read the controller name currently written to `<gadget>/UDC`
    fn current_udc(&self) -> Result<String> {
        Ok(fs::read_to_string(self.udc_file)?.trim().to_owned())
    }

    /// Poll `/sys/class/udc/<name>/state` until it equals `wanted`.
    fn wait_state(name: &str, wanted: &str, limit_ms: u64) -> Result<()> {
        let p = format!("/sys/class/udc/{name}/state");
        let tries = limit_ms / 50;
        for attempt in 0..tries {
            let state = fs::read_to_string(&p).unwrap_or_default();
            if state.trim() == wanted {
                return Ok(());
            }
            trace!("⏳ wait_state polling UDC, retry #{attempt}");
            thread::sleep(Duration::from_millis(50));
        }
        Err(anyhow::anyhow!("🚧 UDC never reached '{wanted}' (last state = {:?})", 
                            fs::read_to_string(&p).unwrap_or_default()))
    }

    /// **Hard‑reset** the controller:  
    ///   1. detach gadget (`UDC=""`)  
    ///   2. un‑bind driver (`…/drivers/<udc>/unbind`)  
    ///   3. bind again  
    ///   4. re‑attach gadget  
    ///   5. wait until state == `configured`
    pub fn cycle(&self) -> Result<()> {
        let ctrl = Self::controller()?;

        /*----- 1. detach gadget from UDC  --------------------------------*/
        info!("🔌 detaching gadget from controller");
        OpenOptions::new().write(true).open(self.udc_file)?.write_all(b"")?;
        Self::wait_state(&ctrl, "not attached", 3_000)
            .context("waiting for controller to report not‑attached")?;

        /*----- 2./3. unbind / bind the UDC driver  -----------------------*/
        let drv_dir = "/sys/bus/platform/drivers/dwc2";              // rk35xx & raspi
        let unbind  = format!("{drv_dir}/unbind");
        let bind    = format!("{drv_dir}/bind");

        // Some kernels use dwc3 – try that if dwc2 is absent
        let (unbind, bind) = if std::path::Path::new(&unbind).exists() {
            (unbind, bind)
        } else {
            let d3 = "/sys/bus/platform/drivers/dwc3";
            (format!("{d3}/unbind"), format!("{d3}/bind"))
        };

        info!("🔧 unbinding UDC driver");
        OpenOptions::new().write(true).open(&unbind)?.write_all(ctrl.as_bytes())?;
        thread::sleep(Duration::from_millis(300));

        info!("🔧 binding   UDC driver");
        OpenOptions::new().write(true).open(&bind)?.write_all(ctrl.as_bytes())?;
        thread::sleep(Duration::from_millis(100));

        /*----- 4. re‑attach gadget to controller -------------------------*/
        info!("🔌 re‑attaching gadget to {ctrl}");
        OpenOptions::new().write(true).open(self.udc_file)?.write_all(ctrl.as_bytes())?;

        /*----- 5. wait until host finished enumeration -------------------*/
        Self::wait_state(&ctrl, "configured", 6_000)
            .context("waiting for host to enumerate gadget")?;

        info!("✅ USB gadget cycle complete; controller back to 'configured'");
        Ok(())
    }
}