// Package platform detects the host OS/distro/WSL status.
package platform

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"runtime"
	"strings"
)

// Distro is a narrow enum of distros we care about.
type Distro string

const (
	DistroArch    Distro = "arch"
	DistroUnknown Distro = "unknown"
)

// Platform holds detected host information.
type Platform struct {
	Distro Distro
	IsWSL  bool
	Arch   string // e.g. "amd64", "arm64"
}

// Detect reads the live system. Returns DistroUnknown rather than an error
// when /etc/os-release is missing or unrecognized; callers decide what to do.
func Detect() (Platform, error) {
	f, err := os.Open("/etc/os-release")
	distro := DistroUnknown
	if err == nil {
		distro = parseDistro(f)
		_ = f.Close()
	} else if !os.IsNotExist(err) {
		return Platform{}, fmt.Errorf("open /etc/os-release: %w", err)
	}

	wsl := false
	if data, err := os.ReadFile("/proc/sys/kernel/osrelease"); err == nil {
		lower := strings.ToLower(string(data))
		wsl = strings.Contains(lower, "microsoft") || strings.Contains(lower, "wsl")
	}

	return Platform{Distro: distro, IsWSL: wsl, Arch: runtime.GOARCH}, nil
}

func parseDistro(r io.Reader) Distro {
	sc := bufio.NewScanner(r)
	for sc.Scan() {
		line := sc.Text()
		if !strings.HasPrefix(line, "ID=") {
			continue
		}
		id := strings.Trim(strings.TrimPrefix(line, "ID="), `"`)
		if id == "arch" {
			return DistroArch
		}
		return DistroUnknown
	}
	return DistroUnknown
}