use anyhow::Result;
use std::net::Ipv4Addr;
use tracing::info;

/// Configuration for creating a TUN device.
pub struct TunConfig {
    pub name: String,
    pub address: Ipv4Addr,
    pub netmask: Ipv4Addr,
    pub mtu: u16,
}

impl Default for TunConfig {
    fn default() -> Self {
        Self {
            name: "smartvpn0".to_string(),
            address: Ipv4Addr::new(10, 8, 0, 1),
            netmask: Ipv4Addr::new(255, 255, 255, 0),
            mtu: 1420,
        }
    }
}

/// Create and configure a TUN device.
/// Returns an async TUN device handle.
pub fn create_tun(config: &TunConfig) -> Result<tun::AsyncDevice> {
    let mut tun_config = tun::Configuration::default();
    tun_config
        .tun_name(&config.name)
        .address(config.address)
        .netmask(config.netmask)
        .mtu(config.mtu as u16)
        .up();

    #[cfg(target_os = "linux")]
    tun_config.platform_config(|p| {
        p.ensure_root_privileges(true);
    });

    let device = tun::create_as_async(&tun_config)?;
    info!(
        "TUN device {} created: addr={}, mtu={}",
        config.name, config.address, config.mtu
    );
    Ok(device)
}

/// Set up routing: add a route for the VPN subnet through the TUN device.
pub async fn add_route(subnet: &str, device_name: &str) -> Result<()> {
    let output = tokio::process::Command::new("ip")
        .args(["route", "add", subnet, "dev", device_name])
        .output()
        .await?;

    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr);
        // Ignore "File exists" errors (route already set)
        if !stderr.contains("File exists") {
            anyhow::bail!("Failed to add route: {}", stderr);
        }
    }

    info!("Added route {} via {}", subnet, device_name);
    Ok(())
}

/// Remove a route.
pub async fn remove_route(subnet: &str, device_name: &str) -> Result<()> {
    let output = tokio::process::Command::new("ip")
        .args(["route", "del", subnet, "dev", device_name])
        .output()
        .await?;

    if !output.status.success() {
        let stderr = String::from_utf8_lossy(&output.stderr);
        tracing::warn!("Failed to remove route (may not exist): {}", stderr);
    }
    Ok(())
}