// Package system checks the host OS for pending package updates. It never
// installs or upgrades anything - read-only status only, using the
// existing apt package index (no "apt update" is run automatically, since
// that touches network/package state on every page load).
package system

import (
	"bufio"
	"context"
	"os"
	"os/exec"
	"strings"
	"time"
)

// UpdateStatus summarizes pending OS package updates on a Debian/Ubuntu host.
type UpdateStatus struct {
	Supported       bool     `json:"supported"` // false if apt isn't available (e.g. non-Debian host)
	UpgradableCount int      `json:"upgradable_count"`
	Packages        []string `json:"packages"`
	RebootRequired  bool     `json:"reboot_required"`
	CheckedAt       time.Time `json:"checked_at"`
	Error           string   `json:"error,omitempty"`
}

// CheckAptUpdates lists upgradable packages from the current apt index
// (`apt list --upgradable`) without refreshing it, and checks for the
// standard Debian/Ubuntu reboot-required marker file.
func CheckAptUpdates() UpdateStatus {
	status := UpdateStatus{CheckedAt: time.Now().UTC()}

	if _, err := exec.LookPath("apt"); err != nil {
		status.Supported = false
		return status
	}
	status.Supported = true

	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
	defer cancel()

	cmd := exec.CommandContext(ctx, "apt", "list", "--upgradable")
	out, err := cmd.Output()
	if err != nil {
		status.Error = "cannot list upgradable packages: " + err.Error()
		return status
	}

	scanner := bufio.NewScanner(strings.NewReader(string(out)))
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if line == "" || strings.HasPrefix(line, "Listing...") {
			continue
		}
		status.Packages = append(status.Packages, line)
	}
	status.UpgradableCount = len(status.Packages)

	if _, err := os.Stat("/var/run/reboot-required"); err == nil {
		status.RebootRequired = true
	}

	return status
}