// Package osdetect provides OS detection from /etc/os-release (D-032).
// It's a separate package to avoid import cycles between internal/cli
// and internal/doctor (both need to detect the local OS).
package osdetect

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

// osReleasePaths are checked in order for the os-release file. The
// freedesktop.org spec says /etc/os-release is the canonical path,
// with /usr/lib/os-release as a fallback for minimal containers that
// may not symlink the former.
var osReleasePaths = []string{"/etc/os-release", "/usr/lib/os-release"}

// Detect reads /etc/os-release (then /usr/lib/os-release as a
// fallback) and returns the value of the ID= field. Returns "linux"
// (the generic fallback per D-032) if the file is missing, the ID
// field is absent, or the value is empty. Unknown ID values (e.g.
// "fedora", "arch") are returned verbatim — doctor os can warn on
// unknown values, but orca init must not fail.
func Detect() string {
	for _, p := range osReleasePaths {
		data, err := os.ReadFile(p)
		if err != nil {
			continue
		}
		if id := ParseID(data); id != "" {
			return id
		}
	}
	return "linux"
}

// ParseID extracts the ID= value from os-release content.
// The format is shell-compatible KEY=VALUE lines; values may be
// double-quoted. Returns "" if ID is absent or empty.
func ParseID(data []byte) string {
	scanner := bufio.NewScanner(strings.NewReader(string(data)))
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		key, value, ok := strings.Cut(line, "=")
		if !ok {
			continue
		}
		key = strings.TrimSpace(key)
		if key != "ID" {
			continue
		}
		value = strings.TrimSpace(value)
		// Strip surrounding double quotes (freedesktop spec allows quoted values).
		if len(value) >= 2 && value[0] == '"' && value[len(value)-1] == '"' {
			value = value[1 : len(value)-1]
		}
		return value
	}
	return ""
}