ipswap/internal/switcher/switcher.go

// Package switcher is the one place a preset actually gets applied.
//
// It exists because there are now two front ends that can switch a preset —
// the tray, which confirms with a native MessageBox, and the web editor, which
// confirms in the browser — and the sequence between "user said yes" and "the
// adapter changed" must not be duplicated. Confirmation is the caller's job;
// everything after it is here.
package switcher

import (
	"errors"
	"fmt"
	"log"
	"sync"

	"gitea.apointless.space/bsncubed/ipswap/internal/netcfg"
	"gitea.apointless.space/bsncubed/ipswap/internal/preset"
)

// ErrNotFound is returned when the id does not name a preset.
var ErrNotFound = errors.New("no such preset")

// Switcher reads adapter state and applies presets.
type Switcher struct {
	store *preset.Store
	mgr   netcfg.Manager

	// applying serialises applies. Two concurrent netsh sequences against one
	// adapter would interleave their deletes and sets and leave the adapter in
	// a state matching neither preset, and the tray and the browser can now
	// both start one.
	applying sync.Mutex
}

// New builds a Switcher.
func New(store *preset.Store, mgr netcfg.Manager) *Switcher {
	return &Switcher{store: store, mgr: mgr}
}

// Preview returns a preset alongside the live configuration of its adapter,
// read at call time. This is what both confirmation prompts are built from, so
// it must never serve a cached view — a stale "CURRENT" block would undermine
// the only safety net before a destructive change.
func (s *Switcher) Preview(id string) (preset.Preset, netcfg.LiveConfig, error) {
	p, ok := s.store.Get(id)
	if !ok {
		return preset.Preset{}, netcfg.LiveConfig{}, ErrNotFound
	}

	live, err := s.mgr.Current(p.Adapter)
	if err != nil {
		return p, netcfg.LiveConfig{}, fmt.Errorf("reading the current configuration of adapter %q: %w", p.Adapter, err)
	}
	return p, live, nil
}

// Apply switches the adapter to the preset. The caller is responsible for
// having confirmed with the user first.
//
// The live configuration is read again here rather than taken from a preceding
// Preview: the plan's delete step is built from the addresses actually on the
// adapter, and between the prompt appearing and the user clicking Yes, a DHCP
// lease or another tool may have changed them.
func (s *Switcher) Apply(id string) error {
	s.applying.Lock()
	defer s.applying.Unlock()

	p, ok := s.store.Get(id)
	if !ok {
		return ErrNotFound
	}

	live, err := s.mgr.Current(p.Adapter)
	if err != nil {
		return fmt.Errorf("reading the current configuration of adapter %q: %w", p.Adapter, err)
	}

	log.Printf("applying preset %q to %q", p.Name, p.Adapter)
	if err := s.mgr.Apply(netcfg.Plan(p, live)); err != nil {
		log.Printf("apply of %q failed: %v", p.Name, err)
		return err
	}

	log.Printf("applied preset %q", p.Name)
	return nil
}

// State is a snapshot of which preset is live.
type State struct {
	// ActiveID is the preset exactly matching its adapter, empty if none does.
	ActiveID   string                       `json:"active_id"`
	ActiveName string                       `json:"active_name"`
	Adapters   map[string]netcfg.LiveConfig `json:"adapters"`
}

// Active works out which preset, if any, is currently applied.
//
// One read per distinct adapter rather than one per preset: fifty presets
// spread across three adapters is three reads, not fifty. This runs every 30
// seconds, so the difference matters.
func (s *Switcher) Active() State {
	presets := s.store.All()
	st := State{Adapters: make(map[string]netcfg.LiveConfig)}

	for _, p := range presets {
		if _, done := st.Adapters[p.Adapter]; done {
			continue
		}
		cfg, err := s.mgr.Current(p.Adapter)
		if err != nil {
			continue
		}
		st.Adapters[p.Adapter] = cfg
	}

	for _, p := range presets {
		if cfg, ok := st.Adapters[p.Adapter]; ok && netcfg.Matches(p, cfg) {
			st.ActiveID, st.ActiveName = p.ID, p.Name
			break
		}
	}
	return st
}

// ConfirmText renders the before/after text for a preset, for callers that
// want the prompt body without applying anything.
func (s *Switcher) ConfirmText(p preset.Preset, live netcfg.LiveConfig) string {
	return netcfg.ConfirmText(p, live)
}