share/apps/ios/GoBridge/share.go

// Package share is the gomobile bridge between the native iOS app and
// the Go swarm engine in this repository.
//
// gomobile cannot expose every Go type to Swift, so this package keeps the
// boundary deliberately narrow: Swift owns the screens and file pickers,
// while this package owns the one long-lived swarm.Client for the room on
// screen. Swift calls Start once, polls StatusJSON for progress, and calls
// Stop when the user leaves the room.
package share

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sync"

	"github.com/tzgyn/share/src/swarm"
	"github.com/tzgyn/share/src/utils"
)

// DefaultRelay is the public relay the CLI uses when the user does not
// pass --relay. The iOS app lets the user override it (for example with a
// relay running on their Mac's LAN address).
const DefaultRelay = "croc.schollz.com:9009"

// status is the JSON shape the Swift app decodes from StatusJSON. It
// mirrors swarm.RoomStatus but adds the session fields that live only on
// this bridge: whether the room is still running, which relay it used,
// and the last fatal error, if any. It stays unexported because Swift
// reads the JSON rather than this Go type directly.
type status struct {
	Code    string             `json:"code"`
	Relay   string             `json:"relay"`
	OutDir  string             `json:"outDir"`
	Running bool               `json:"running"`
	Peers   int                `json:"peers"`
	Files   []swarm.FileStatus `json:"files"`
	Error   string             `json:"error,omitempty"`
}

// Session is one room, owned by the iOS app. A Session is not safe to
// reuse for two rooms at once; Start refuses while another room is live.
// That is intentional: the phone UI has one Send/Receive sheet at a time,
// and one Client means one set of progress counters to display.
type Session struct {
	mu         sync.Mutex
	client     *swarm.Client
	code       string
	relay      string
	outDir     string
	running    bool
	lastErr    string
	generation uint64
	lastRoom   status // retained after the room ends, so the final 100% is visible
}

// NewSession creates an idle session. The Swift side holds exactly one of
// these for the lifetime of the app.
func NewSession() *Session {
	return &Session{}
}

// GenerateCode returns a new human-readable room code in the same
// "1234-word-word-word-word" shape the CLI prints. Both sides must type
// the same code to derive the same handshake secret.
func GenerateCode() string {
	return utils.GetRandomName()
}

// RelayDefault returns the relay address used when the app's relay field
// is empty. It is a function rather than a bare constant because gomobile
// only generates callable symbols for exported functions and methods.
func RelayDefault() string {
	return DefaultRelay
}

// Start joins one room. filesJSON is a JSON array of absolute paths inside
// the app sandbox; pass "[]" to be a pure receiver. outDir is created if
// needed and must also be absolute. oneTime stops the room as soon as every
// file currently known is complete, which is useful for a receiver that
// does not want to keep seeding in the background.
//
// Start returns as soon as the relay join succeeds; progress is read with
// StatusJSON. The room runs in a goroutine until Stop or oneTime
// completion.
func (s *Session) Start(relay, code, filesJSON, outDir string, oneTime bool) error {
	s.mu.Lock()
	if s.client != nil {
		s.mu.Unlock()
		return fmt.Errorf("a room is already active; stop it before starting another")
	}
	s.mu.Unlock()

	var files []string
	if filesJSON != "" {
		if err := json.Unmarshal([]byte(filesJSON), &files); err != nil {
			return fmt.Errorf("invalid file list: %w", err)
		}
	}

	if relay == "" {
		relay = DefaultRelay
	}
	if code == "" {
		code = GenerateCode()
	}
	if outDir == "" {
		return fmt.Errorf("output folder is required")
	}
	if !filepath.IsAbs(outDir) {
		return fmt.Errorf("output folder must be an absolute path: %s", outDir)
	}
	for _, file := range files {
		if !filepath.IsAbs(file) {
			return fmt.Errorf("file path must be absolute: %s", file)
		}
	}
	if err := os.MkdirAll(outDir, 0o755); err != nil {
		return fmt.Errorf("could not create output folder: %w", err)
	}

	cl, err := swarm.Start(swarm.Options{
		RelayAddress: relay,
		Code:         code,
		Files:        files,
		OutDir:       outDir,
		OneTime:      oneTime,
	})
	if err != nil {
		return err
	}

	s.mu.Lock()
	s.generation++
	generation := s.generation
	s.client = cl
	s.code = code
	s.relay = relay
	s.outDir = outDir
	s.running = true
	s.lastErr = ""
	s.lastRoom = status{
		Code:    code,
		Relay:   relay,
		OutDir:  outDir,
		Running: true,
		Files:   make([]swarm.FileStatus, 0),
	}
	s.mu.Unlock()

	// Wait is the only way to learn that the relay connection died. Do it
	// off the main thread and fold the final Client.Status into lastRoom
	// before releasing client, so a finished one-time transfer still shows
	// its completed files after the room stops. The generation check keeps
	// a stopped room's late Wait from clobbering a room the user started
	// immediately afterwards.
	go func() {
		waitErr := cl.Wait()
		final := cl.Status()
		s.mu.Lock()
		defer s.mu.Unlock()
		if s.generation != generation {
			return
		}
		s.running = false
		s.client = nil
		if waitErr != nil {
			s.lastErr = waitErr.Error()
		}
		s.lastRoom = status{
			Code:    s.code,
			Relay:   s.relay,
			OutDir:  s.outDir,
			Running: false,
			Peers:   final.Peers,
			Files:   final.Files,
			Error:   s.lastErr,
		}
	}()

	return nil
}

// StatusJSON serializes the room's current state for Swift. JSON at the
// boundary keeps the gomobile surface to strings, booleans, and []string
// instead of making every nested progress type a generated Swift class.
func (s *Session) StatusJSON() string {
	s.mu.Lock()
	cl := s.client
	room := s.lastRoom
	running := s.running
	lastErr := s.lastErr
	code, relay, outDir := s.code, s.relay, s.outDir
	s.mu.Unlock()

	if cl != nil {
		live := cl.Status()
		room = status{
			Code:    code,
			Relay:   relay,
			OutDir:  outDir,
			Running: running,
			Peers:   live.Peers,
			Files:   live.Files,
			Error:   lastErr,
		}
	} else {
		room.Running = false
		room.Error = lastErr
	}
	if room.Files == nil {
		room.Files = make([]swarm.FileStatus, 0)
	}

	b, err := json.Marshal(room)
	if err != nil {
		return `{"error":"could not encode status"}`
	}
	return string(b)
}

// Stop leaves the current room. It is safe to call when no room is
// running; the UI uses that on disappear and when the app returns to the
// foreground to avoid a stale relay connection.
func (s *Session) Stop() {
	s.mu.Lock()
	cl := s.client
	s.client = nil
	s.running = false
	s.mu.Unlock()

	if cl != nil {
		cl.Stop()
	}
}