use std::{fs, process::Command};

use crate::config::Config;

pub fn ensure_swap(cfg: &Config) -> anyhow::Result<()> {
    if !cfg.swap.enabled {
        return Ok(());
    }

    let path = &cfg.swap.path;
    let expected_size = cfg.swap.size_mb * 1024 * 1024;
    if std::path::Path::new(path).exists() {
        let actual_size = fs::metadata(path)?.len();
        if actual_size != expected_size {
            anyhow::bail!(
                "existing swapfile has wrong size: {} bytes, expected {} bytes; manual intervention required",
                actual_size,
                expected_size
            );
        }
    } else {
        run(
            "fallocate",
            &["-l", &format!("{}M", cfg.swap.size_mb), path],
        )?;
        run("chmod", &["600", path])?;
        run("mkswap", &[path])?;
    }

    let swapon = Command::new("swapon").args(["--show"]).output()?;
    let active = String::from_utf8_lossy(&swapon.stdout);
    if !active.contains(path) {
        run("swapon", &["-p", &cfg.swap.priority.to_string(), path])?;
    }

    ensure_fstab(path, cfg.swap.priority)?;
    run(
        "sysctl",
        &["-w", &format!("vm.swappiness={}", cfg.swap.swappiness)],
    )?;
    ensure_swappiness_persist(cfg.swap.swappiness)?;
    Ok(())
}

fn ensure_fstab(path: &str, priority: i32) -> anyhow::Result<()> {
    let file = "/etc/fstab";
    let content = fs::read_to_string(file).unwrap_or_default();
    if content
        .lines()
        .any(|l| l.contains(path) && l.contains("swap"))
    {
        return Ok(());
    }
    let line = format!("{path} none swap sw,pri={priority} 0 0\n");
    fs::write(file, format!("{}{}", content, line))?;
    Ok(())
}

fn run(program: &str, args: &[&str]) -> anyhow::Result<()> {
    let out = Command::new(program).args(args).output()?;
    if !out.status.success() {
        anyhow::bail!(
            "{} {:?} failed: {}",
            program,
            args,
            String::from_utf8_lossy(&out.stderr)
        );
    }
    Ok(())
}

fn ensure_swappiness_persist(swappiness: u8) -> anyhow::Result<()> {
    let conf_path = "/etc/sysctl.d/99-awg2-harness.conf";
    let expected = format!("vm.swappiness = {}\n", swappiness);
    let current = fs::read_to_string(conf_path).unwrap_or_default();
    if current != expected {
        fs::write(conf_path, expected)?;
    }
    Ok(())
}