use anyhow::{Context, Result};
use ssh2::Session;
use std::io::Read;
use std::net::TcpStream;
use std::path::Path;
use tracing::debug;

/// An active SSH connection to an OpenWrt router.
pub struct Router {
    pub host: String,
    pub port: u16,
    session: Session,
}

impl Router {
    /// Connect to an OpenWrt router via SSH using a private key.
    pub fn connect(host: &str, port: u16, user: &str, key_path: &Path) -> Result<Self> {
        let addr = format!("{}:{}", host, port);
        let tcp = TcpStream::connect(&addr)
            .with_context(|| format!("TCP connect to {}", addr))?;

        let mut session = Session::new().context("create SSH session")?;
        session.set_tcp_stream(tcp);
        session.handshake().context("SSH handshake")?;
        session
            .userauth_pubkey_file(user, None, key_path, None)
            .with_context(|| format!("SSH auth as {} with key {:?}", user, key_path))?;

        Ok(Self {
            host: host.to_string(),
            port,
            session,
        })
    }

    /// Connect using a password (fallback for routers not yet provisioned with a key).
    pub fn connect_password(host: &str, port: u16, user: &str, password: &str) -> Result<Self> {
        let addr = format!("{}:{}", host, port);
        let tcp = TcpStream::connect(&addr)
            .with_context(|| format!("TCP connect to {}", addr))?;

        let mut session = Session::new().context("create SSH session")?;
        session.set_tcp_stream(tcp);
        session.handshake().context("SSH handshake")?;
        session
            .userauth_password(user, password)
            .with_context(|| format!("SSH password auth as {}", user))?;

        Ok(Self {
            host: host.to_string(),
            port,
            session,
        })
    }

    /// Run a command and return (stdout, exit_code).
    pub fn run(&self, cmd: &str) -> Result<(String, i32)> {
        debug!("ssh [{}] $ {}", self.host, cmd);

        let mut channel = self.session.channel_session().context("open channel")?;
        channel.exec(cmd).with_context(|| format!("exec: {}", cmd))?;

        let mut stdout = String::new();
        channel.read_to_string(&mut stdout).context("read stdout")?;
        channel.wait_close().context("wait close")?;
        let exit = channel.exit_status().context("exit status")?;

        Ok((stdout, exit))
    }

    /// Run a command, fail if exit code is non-zero.
    pub fn run_ok(&self, cmd: &str) -> Result<String> {
        let (out, code) = self.run(cmd)?;
        if code != 0 {
            anyhow::bail!("command `{}` exited with code {}: {}", cmd, code, out.trim());
        }
        Ok(out)
    }

    /// Verify the remote device is actually running OpenWrt.
    pub fn verify_openwrt(&self) -> Result<String> {
        let release = self
            .run_ok("cat /etc/openwrt_release")
            .context("read /etc/openwrt_release — is this an OpenWrt device?")?;
        Ok(release)
    }
}