package main

import (
	"bufio"
	"os"
	"strings"
)

// OSInfo holds the detected distribution identity and init system.
type OSInfo struct {
	ID      string
	Version string
	Init    string // "systemd" or "openrc"
}

// detectOS parses /etc/os-release and maps the distro to its init system.
func detectOS() *OSInfo {
	f, err := os.Open("/etc/os-release")
	if err != nil {
		die("Cannot detect OS: /etc/os-release not found")
	}
	defer f.Close()

	vals := map[string]string{}
	scanner := bufio.NewScanner(f)
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		if i := strings.Index(line, "="); i >= 0 {
			key := strings.TrimSpace(line[:i])
			vals[key] = unquoteShell(line[i+1:])
		}
	}

	osInfo := &OSInfo{
		ID:      valueOr(vals["ID"], "unknown"),
		Version: valueOr(vals["VERSION_ID"], "unknown"),
	}

	switch osInfo.ID {
	case "ubuntu", "debian", "linuxmint":
		osInfo.Init = "systemd"
	case "alpine":
		osInfo.Init = "openrc"
	default:
		die("Unsupported OS: %s (supported: ubuntu, debian, linuxmint, alpine)", osInfo.ID)
	}

	// A systemd-based distro may still be running here without systemd as
	// PID 1 — the container case (e.g. the Linux Mint image used for the
	// alternative container build). systemd creates /run/systemd/system only
	// when it is actually active as the init system, so its absence is the
	// standard way to detect this. Fall back to driving awg-quick directly,
	// same as the Alpine/OpenRC path.
	if osInfo.Init == "systemd" && !systemdRunning() {
		osInfo.Init = "openrc"
	}

	info("Detected OS: %s %s (init: %s)", osInfo.ID, osInfo.Version, osInfo.Init)
	return osInfo
}

// systemdRunning reports whether systemd is active as PID 1.
func systemdRunning() bool {
	_, err := os.Stat("/run/systemd/system")
	return err == nil
}

func valueOr(v, def string) string {
	if v == "" {
		return def
	}
	return v
}