proxy/internal/app/app.go

package app

import (
	"errors"
	"fmt"

	"proxyctl/internal/profile"
)

type IntentKind int

const (
	CreateProfile IntentKind = iota + 1
	UpdateProfile
	DeleteProfile
	ActivateProfile
)

type Intent struct {
	Kind    IntentKind
	Name    string
	Profile profile.Profile
	Confirm bool
}

type Snapshot struct {
	Profiles      []profile.Profile
	ActiveProfile string
}

type Result struct {
	Snapshot Snapshot
	Notice   string
	Err      error
}

type Module interface {
	Snapshot() Snapshot
	Dispatch(Intent) Result
}

type Application struct {
	store profile.Store
	state profile.State
}

func New(store profile.Store) (*Application, error) {
	state, err := store.Load()
	if err != nil {
		return nil, err
	}
	return &Application{store: store, state: state}, nil
}

func (a *Application) Snapshot() Snapshot {
	profiles := append([]profile.Profile(nil), a.state.Profiles...)
	return Snapshot{Profiles: profiles, ActiveProfile: a.state.ActiveProfile}
}

func (a *Application) Dispatch(intent Intent) Result {
	var notice string
	next, err := a.store.Mutate(func(current profile.State) (profile.State, error) {
		var mutationErr error
		switch intent.Kind {
		case CreateProfile:
			current, notice, mutationErr = create(current, intent.Profile)
		case ActivateProfile:
			current, notice, mutationErr = activate(current, intent.Name)
		case UpdateProfile:
			current, notice, mutationErr = update(current, intent.Name, intent.Profile)
		case DeleteProfile:
			current, notice, mutationErr = deleteProfile(current, intent.Name, intent.Confirm)
		default:
			mutationErr = errors.New("unsupported Profile action")
		}
		return current, mutationErr
	})
	if err == nil {
		a.state = next
	} else {
		var committed *profile.CommitError
		if errors.As(err, &committed) {
			// Rename committed next before directory durability reporting failed.
			// Prefer that state even if the required verification reload also fails.
			a.state = next
			reloaded, loadErr := a.store.Load()
			if loadErr != nil {
				err = errors.Join(err, fmt.Errorf("reload committed Profile configuration: %w", loadErr))
			} else {
				a.state = reloaded
			}
		}
	}
	return Result{Snapshot: a.Snapshot(), Notice: notice, Err: err}
}

func create(state profile.State, input profile.Profile) (profile.State, string, error) {
	p, err := profile.ValidateAndNormalize(input)
	if err != nil {
		return state, "", err
	}
	if index(state, p.Name) >= 0 {
		return state, "", fmt.Errorf("a Profile named %q already exists", p.Name)
	}
	next := cloneState(state)
	next.Profiles = append(next.Profiles, p)
	return next, fmt.Sprintf("Created Profile %q", p.Name), nil
}

func activate(state profile.State, name string) (profile.State, string, error) {
	if index(state, name) < 0 {
		return state, "", fmt.Errorf("Profile %q does not exist", name)
	}
	next := cloneState(state)
	next.ActiveProfile = name
	return next, fmt.Sprintf("Activated Profile %q", name), nil
}

func update(state profile.State, originalName string, input profile.Profile) (profile.State, string, error) {
	profileIndex := index(state, originalName)
	if profileIndex < 0 {
		return state, "", fmt.Errorf("Profile %q does not exist", originalName)
	}
	p, err := profile.ValidateAndNormalize(input)
	if err != nil {
		return state, "", err
	}
	if other := index(state, p.Name); other >= 0 && other != profileIndex {
		return state, "", fmt.Errorf("a Profile named %q already exists", p.Name)
	}
	next := cloneState(state)
	next.Profiles[profileIndex] = p
	if next.ActiveProfile == originalName {
		next.ActiveProfile = p.Name
	}
	return next, fmt.Sprintf("Updated Profile %q", p.Name), nil
}

func deleteProfile(state profile.State, name string, confirm bool) (profile.State, string, error) {
	profileIndex := index(state, name)
	if profileIndex < 0 {
		return state, "", fmt.Errorf("Profile %q does not exist", name)
	}
	if len(state.Profiles) == 1 && !confirm {
		return state, "", errors.New("deleting the final Profile requires confirmation")
	}
	next := cloneState(state)
	next.Profiles = append(next.Profiles[:profileIndex], next.Profiles[profileIndex+1:]...)
	if next.ActiveProfile == name {
		next.ActiveProfile = ""
	}
	return next, fmt.Sprintf("Deleted Profile %q", name), nil
}

func index(state profile.State, name string) int {
	for i := range state.Profiles {
		if state.Profiles[i].Name == name {
			return i
		}
	}
	return -1
}

func cloneState(state profile.State) profile.State {
	state.Profiles = append([]profile.Profile(nil), state.Profiles...)
	return state
}