// server/src/usb_gadget.rs

use std::{fs::{self, OpenOptions}, io::Write, thread, time::Duration};
use anyhow::{Result, Context};
use tracing::{debug, error, info, warn};

fn wait_for_detach(udc_path: &str) {
    for _ in 0..20 {
        // as soon as the file is **empty**, the detach succeeded
        if fs::read_to_string(udc_path).map(|s| s.trim().is_empty()).unwrap_or(false) {
            debug!("🔌 UDC is now *detached*");
            return;
        }
        thread::sleep(Duration::from_millis(50));
    }
    warn!("⏳ UDC did not detach within the expected time-out");
}

/// Like `wait_for_detach`, but the opposite condition.
fn wait_for_attach(udc_path: &str) {
    for _ in 0..20 {
        if fs::read_to_string(udc_path).map(|s| !s.trim().is_empty()).unwrap_or(false) {
            debug!("🔌 UDC is *attached* again");
            return;
        }
        thread::sleep(Duration::from_millis(50));
    }
    warn!("⏳ UDC did not attach within the expected time-out");
}

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

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

    /// Force the host to re-enumerate our HID gadget.
    /// Retries on EBUSY so that a transient “resource busy” never kills the whole process.
    pub fn cycle(&self) -> Result<()> {
        info!("🔌 UDC-cycle: detaching gadget");
        OpenOptions::new()
            .write(true)
            .open(self.udc_file)?
            .write_all(b"")?;                // empty string → detach
        wait_for_detach(self.udc_file);

        // Let the controller settle
        thread::sleep(Duration::from_millis(200));

        let udc_name = std::fs::read_dir("/sys/class/udc")?
            .next()
            .transpose()?
            .context("no UDC present")?
            .file_name();

        // Retry loop for the notoriously fragile re-attach
        for attempt in 0..5 {
            info!("🔌 UDC-cycle: re-attaching to {} (try #{attempt})", udc_name.to_string_lossy());
            match OpenOptions::new()
                .write(true)
                .open(self.udc_file)?
                .write_all(udc_name.to_str().unwrap().as_bytes())
            {
                Ok(()) => {
                    wait_for_attach(self.udc_file);
                    info!("🟢 USB-gadget cycled successfully");
                    return Ok(());
                }
                Err(e) if e.raw_os_error() == Some(libc::EBUSY) => {
                    warn!("🚧 UDC busy on re-attach – retrying in 100 ms");
                    thread::sleep(Duration::from_millis(100));
                    continue;
                }
                Err(e) => {
                    error!("💥 unexpected error while re-attaching UDC: {e:?}");
                    return Err(e).context("re-attaching gadget to UDC");
                }
            }
        }

        Err(anyhow::anyhow!(
            "giving up after 5 attempts – UDC remained busy"
        ))
    }
}