/*
Copyright © 2026 Mulga Defense Corporation

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program. If not, see <https://www.gnu.org/licenses/>.
*/

// Package systemd writes systemd unit files and drop-ins into an installed
// system root during the Spinifex ISO installation process.
package systemd

import (
	"fmt"
	"os"
	"path/filepath"
)

// WriteLANBridgeUnit installs a non-critical oneshot service that activates
// br-lan via networkctl *after* network-online.target. br-lan has
// ActivationPolicy=manual in its networkd .network file, so networkd creates
// the bridge at boot but does not bring it up automatically. This service
// triggers the activation once the WAN path is confirmed online, ensuring a
// missing LAN cable or DHCP timeout on the secondary bridge never stalls
// the management interface or firstboot.
func WriteLANBridgeUnit(root string) error {
	unit := `[Unit]
Description=Spinifex LAN bridge (non-critical)
After=network-online.target
Wants=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/bin/networkctl up br-lan
RemainAfterExit=yes
# Failure is non-critical — cable unplugged or switch not ready at boot.
SuccessExitStatus=0 1

[Install]
WantedBy=multi-user.target
`
	unitPath := filepath.Join(root, "etc/systemd/system/spinifex-lan-bridge.service")
	if err := os.WriteFile(unitPath, []byte(unit), 0o644); err != nil {
		return err
	}
	wantsDir := filepath.Join(root, "etc/systemd/system/multi-user.target.wants")
	if err := os.MkdirAll(wantsDir, 0o755); err != nil {
		return err
	}
	link := filepath.Join(wantsDir, "spinifex-lan-bridge.service")
	if err := os.Remove(link); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("remove stale symlink %s: %w", link, err)
	}
	return os.Symlink("/etc/systemd/system/spinifex-lan-bridge.service", link)
}

// WriteFirstbootUnit writes the spinifex-firstboot.service oneshot unit that
// runs the firstboot provisioning script on the first real boot after
// installation. The script writes /var/lib/spinifex/.firstboot-done on
// success; ConditionPathExists=! on that marker condition-skips the unit on
// every subsequent boot so it never re-runs (replacing the previous
// "disable on EXIT" trap which couldn't distinguish success from failure).
func WriteFirstbootUnit(root string) error {
	unit := `[Unit]
Description=Spinifex first-boot provisioning
After=network-online.target
Wants=network-online.target
ConditionPathExists=/usr/local/bin/spinifex-firstboot.sh
ConditionPathExists=!/var/lib/spinifex/.firstboot-done

[Service]
Type=oneshot
Environment=HOME=/root
ExecStart=/usr/local/bin/spinifex-firstboot.sh
RemainAfterExit=yes
# On non-zero exit, overwrite /etc/issue with a hint so the operator sees
# the failure on the console — the banner unit is never enabled in that
# case (firstboot didn't reach its enable --now line), so /etc/issue would
# otherwise stay at the Debian default with no signal that anything is wrong.
ExecStopPost=/bin/sh -c 'if [ "$EXIT_STATUS" != "0" ]; then printf "\n*** Spinifex firstboot FAILED ***\nLogin as spinifex, then run:\n  sudo journalctl -u spinifex-firstboot.service\n\n" > /etc/issue; fi'
# Cap total firstboot runtime so a hang in setup-ovn.sh / spx admin init /
# ovn-central startup cannot wedge multi-user.target and keep getty from
# ever reaching the login prompt.
TimeoutStartSec=300s
StandardOutput=journal
StandardError=journal

[Install]
WantedBy=multi-user.target
`
	path := filepath.Join(root, "etc/systemd/system/spinifex-firstboot.service")
	return os.WriteFile(path, []byte(unit), 0o644)
}

// WriteBannerUnit writes the spinifex-banner.service unit that runs
// `spx admin banner --boot-check` on every boot after spinifex.target is up.
// Running After=spinifex.target ensures the banner reflects a settled system
// state and that the IP check/restart happens once services are already running.
//
// The unit file is written by the installer but NOT enabled at install time.
// firstboot enables it (along with spinifex.target) at the end of its first
// run via `systemctl enable --now`. On every subsequent boot both units are
// driven by the multi-user.target.wants/ symlinks firstboot installed.
//
// Note: only After=spinifex.target — no Wants=. A Wants= would implicitly
// pull spinifex.target up at boot, which is exactly the race this whole
// change is fixing. After= alone is a no-op when the target isn't started,
// which is correct on first boot before firstboot has provisioned configs.
func WriteBannerUnit(root string) error {
	unit := `[Unit]
Description=Spinifex console banner and boot health check
After=network-online.target

[Service]
Type=oneshot
ExecStart=/usr/local/bin/spx admin banner --boot-check
RemainAfterExit=yes
# Banner is oneshot; cap it so a stuck boot-check (IP detection, try-restart)
# cannot block getty via the spinifex-wait.conf drop-in.
TimeoutStartSec=30s
StandardOutput=journal
StandardError=journal

[Install]
WantedBy=multi-user.target
`
	path := filepath.Join(root, "etc/systemd/system/spinifex-banner.service")
	return os.WriteFile(path, []byte(unit), 0o644)
}

// WriteGettyDropIn holds the primary consoles (tty1 and ttyS0) until
// spinifex-banner.service completes (when banner is enabled), so the MOTD
// banner is visible before the login prompt appears. Drop-ins are scoped to
// named instances (getty@tty1, serial-getty@ttyS0) so tty2, tty3, etc.
// remain available as rescue terminals.
//
// Only After=, not Wants=. A Wants= would implicitly start the (un-enabled)
// banner on the very first boot, partially undoing the "only firstboot is
// enabled on first boot" guarantee. On first boot, banner is not enabled,
// so After= is a no-op and login appears immediately with the default
// /etc/issue. Once firstboot completes and enables the banner, subsequent
// boots have banner enabled at multi-user.target and After= correctly
// orders getty after the banner has rendered /etc/issue.
func WriteGettyDropIn(root string) error {
	dropIn := `[Unit]
After=spinifex-firstboot.service
`
	for _, svc := range []string{"getty@tty1", "serial-getty@ttyS0"} {
		dropInDir := filepath.Join(root, "etc/systemd/system/"+svc+".service.d")
		if err := os.MkdirAll(dropInDir, 0o755); err != nil {
			return err
		}
		if err := os.WriteFile(filepath.Join(dropInDir, "spinifex-wait.conf"), []byte(dropIn), 0o644); err != nil {
			return err
		}
	}
	return nil
}

// EnableUnit creates the multi-user.target.wants symlink for serviceName,
// equivalent to `systemctl enable` for a unit that targets multi-user.target.
func EnableUnit(root, serviceName string) error {
	wantsDir := filepath.Join(root, "etc/systemd/system/multi-user.target.wants")
	if err := os.MkdirAll(wantsDir, 0o755); err != nil {
		return err
	}
	link := filepath.Join(wantsDir, serviceName)
	target := "/etc/systemd/system/" + serviceName
	if err := os.Remove(link); err != nil && !os.IsNotExist(err) {
		return fmt.Errorf("remove stale symlink %s: %w", link, err)
	}
	return os.Symlink(target, link)
}