/
state.go
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/
state.go
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package app
import (
"encoding/json"
"reflect"
"sync"
"time"
"github.com/google/uuid"
"github.com/maxence-charriere/go-app/v9/pkg/errors"
)
// Observer is an observer that observes changes for a given state.
type Observer interface {
// Defines a condition that reports whether the observer keeps observing the
// associated state. Multiple conditions can be defined by successively
// calling While().
While(condition func() bool) Observer
// Executes the given function on the UI goroutine when the observed value
// changes. Multiple functions can be executed by successively calling
// OnChange().
OnChange(fn func()) Observer
// Stores the value associated with the observed state into the given
// receiver. Panics when the receiver is not a pointer or nil.
//
// The receiver is updated each time the associated state changes. It is
// unchanged when its pointed value has a different type than the associated
// state value.
Value(recv any)
}
// A state represents an observable value available across the app.
type State struct {
// Reports whether the state is persisted in local storage.
IsPersistent bool
// Reports whether the state is encrypted before being persisted in local
// storage.
IsEncrypted bool
// The time when the state expires. The state never expires when zero value.
ExpiresAt time.Time
// Reports whether a state is broadcasted to other browser tabs and windows.
IsBroadcasted bool
value any
observers map[*observer]struct{}
}
func (s *State) isExpired(now time.Time) bool {
return s.ExpiresAt != time.Time{} && now.After(s.ExpiresAt)
}
// StateOption represents an option applied when a state is set.
type StateOption func(*State)
// Persist is a state option that persists a state in local storage.
//
// Be mindful to not use this option as a cache since local storage is limited
// to 5MB in a lot of web browsers.
func Persist(s *State) {
s.IsPersistent = true
}
// Encrypt is a state option that encrypts a state before persisting it in local
// storage. Encryption is performed only when the Persist option is also set.
func Encrypt(s *State) {
s.IsEncrypted = true
}
// ExpiresIn returns a state option that sets a state value to its zero value
// after the given duration.
//
// Values persisted to local storage with the Persist option are removed from
// it.
func ExpiresIn(d time.Duration) StateOption {
return ExpiresAt(time.Now().Add(d))
}
// ExpiresAt returns a state option that sets a state value to its zero value at
// the given time.
//
// Values persisted to local storage with the Persist option are removed from
// it.
func ExpiresAt(t time.Time) StateOption {
return func(s *State) {
s.ExpiresAt = t
}
}
// Broadcast is a state option that broadcasts a state to other browser tabs and
// windows from the same origin.
func Broadcast(s *State) {
s.IsBroadcasted = true
}
type observer struct {
element UI
subscribe func(*observer)
conditions []func() bool
onChanges []func()
receiver any
}
func newObserver(elem UI, subscribe func(*observer)) *observer {
return &observer{
element: elem,
subscribe: subscribe,
}
}
func (o *observer) While(fn func() bool) Observer {
o.conditions = append(o.conditions, fn)
return o
}
func (o *observer) OnChange(fn func()) Observer {
o.onChanges = append(o.onChanges, fn)
return o
}
func (o *observer) Value(recv any) {
if reflect.ValueOf(recv).Kind() != reflect.Ptr {
panic(errors.New("observer value receiver is not a pointer"))
}
o.receiver = recv
o.subscribe(o)
}
func (o *observer) isObserving() bool {
if !o.element.Mounted() {
return false
}
for _, c := range o.conditions {
if !c() {
return false
}
}
return true
}
type store struct {
mutex sync.Mutex
id string
states map[string]State
disp Dispatcher
broadcastChannel Value
onBroadcastClose func()
}
func newStore(d Dispatcher) *store {
s := &store{
id: uuid.NewString(),
states: make(map[string]State),
disp: d,
}
s.initBroadcast()
return s
}
func (s *store) Set(key string, v any, opts ...StateOption) {
s.mutex.Lock()
defer s.mutex.Unlock()
state := s.states[key]
state.value = v
for _, o := range opts {
o(&state)
}
s.states[key] = state
if state.IsPersistent {
if err := s.setPersistent(key, state.IsEncrypted, state.ExpiresAt, v); err != nil {
Log(errors.New("persisting state failed").
WithTag("state", key).
Wrap(err))
return
}
}
if state.isExpired(time.Now()) {
state = s.expire(key, state)
s.states[key] = state
return
}
if state.IsBroadcasted {
if err := s.broadcast(key, v); err != nil {
Log(errors.New("broadcasting state failed").
WithTag("state", key).
Wrap(err))
return
}
}
for obs := range state.observers {
o := obs
if !o.element.Mounted() {
delete(state.observers, o)
continue
}
s.disp.Dispatch(Dispatch{
Mode: Update,
Source: o.element,
Function: func(ctx Context) {
if !o.isObserving() {
s.mutex.Lock()
delete(state.observers, o)
s.mutex.Unlock()
return
}
if err := storeValue(o.receiver, v); err != nil {
Log(errors.New("notifying observer failed").
WithTag("state", key).
WithTag("element", reflect.TypeOf(o.element)).
Wrap(err))
return
}
for _, fn := range o.onChanges {
fn()
}
},
})
}
}
func (s *store) Get(key string, recv any) {
s.mutex.Lock()
defer s.mutex.Unlock()
var err error
state := s.states[key]
if state.isExpired(time.Now()) {
state = s.expire(key, state)
s.states[key] = state
}
if state.value != nil {
err = storeValue(recv, state.value)
} else {
err = s.getPersistent(key, recv)
}
if err != nil {
Log(errors.New("getting state value failed").
WithTag("state", key).
Wrap(err))
}
}
func (s *store) Del(key string) {
s.mutex.Lock()
defer s.mutex.Unlock()
delete(s.states, key)
s.disp.getLocalStorage().Del(key)
}
func (s *store) Observe(key string, elem UI) Observer {
return newObserver(elem, func(o *observer) {
s.mutex.Lock()
defer s.mutex.Unlock()
if err := s.subscribe(key, o); err != nil {
Log(errors.New("notifying observer failed").
WithTag("state", key).
WithTag("element", reflect.TypeOf(elem)).
Wrap(err))
}
})
}
func (s *store) Cleanup() {
s.mutex.Lock()
defer s.mutex.Unlock()
s.removeUnusedObservers()
s.expireExpiredValues()
s.expireExpriredPersistentValues()
}
func (s *store) Close() {
if s.broadcastChannel != nil {
s.broadcastChannel.Call("close")
s.broadcastChannel = nil
}
s.onBroadcastClose()
}
func (s *store) subscribe(key string, o *observer) error {
state := s.states[key]
if state.observers == nil {
state.observers = make(map[*observer]struct{})
}
state.observers[o] = struct{}{}
if state.isExpired(time.Now()) {
state = s.expire(key, state)
}
s.states[key] = state
if state.value != nil {
return storeValue(o.receiver, state.value)
}
return s.getPersistent(key, o.receiver)
}
func (s *store) removeUnusedObservers() {
for _, state := range s.states {
for o := range state.observers {
if !o.isObserving() {
delete(state.observers, o)
}
}
}
}
func (s *store) getPersistent(key string, recv any) error {
var state persistentState
s.disp.getLocalStorage().Get(key, &state)
if state.EncryptedValue == nil && state.Value == nil && state.ExpiresAt == (time.Time{}) {
return nil
}
if state.isExpired(time.Now()) {
s.disp.getLocalStorage().Del(key)
return nil
}
if len(state.EncryptedValue) == 0 {
return json.Unmarshal(state.Value, recv)
}
return s.disp.Context().Decrypt(state.EncryptedValue, recv)
}
func (s *store) setPersistent(key string, encrypt bool, expiresAt time.Time, v any) error {
var err error
state := persistentState{
ExpiresAt: expiresAt,
}
if encrypt {
state.EncryptedValue, err = s.disp.Context().Encrypt(v)
} else {
state.Value, err = json.Marshal(v)
}
if err != nil {
return err
}
return s.disp.getLocalStorage().Set(key, state)
}
func (s *store) expireExpiredValues() {
now := time.Now()
for k, state := range s.states {
if state.isExpired(now) {
state = s.expire(k, state)
s.states[k] = state
}
}
}
func (s *store) expireExpriredPersistentValues() {
object := Window().Get("Object")
if !object.Truthy() {
return
}
keys := object.Call("keys", Window().Get("localStorage"))
for i, l := 0, keys.Get("length").Int(); i < l; i++ {
key := keys.Index(i).String()
var state persistentState
s.disp.getLocalStorage().Get(key, &state)
if state.EncryptedValue == nil && state.Value == nil && state.ExpiresAt == (time.Time{}) {
continue
}
if state.isExpired(time.Now()) {
s.disp.getLocalStorage().Del(key)
}
}
}
func (s *store) expire(key string, state State) State {
s.disp.getLocalStorage().Del(key)
state.value = nil
return state
}
func (s *store) initBroadcast() {
broadcastChannel := Window().Get("BroadcastChannel")
if !broadcastChannel.Truthy() {
s.onBroadcastClose = func() {}
return
}
broadcastChannel = broadcastChannel.New("go-app-broadcast-states")
s.broadcastChannel = broadcastChannel
onBroadcast := FuncOf(func(this Value, args []Value) any {
s.onBroadcast(args[0].Get("data"))
return nil
})
s.onBroadcastClose = onBroadcast.Release
broadcastChannel.Set("onmessage", onBroadcast)
}
func (s *store) broadcast(key string, v any) error {
b, err := json.Marshal(v)
if err != nil {
return err
}
if s.broadcastChannel != nil {
s.broadcastChannel.Call("postMessage", map[string]any{
"StoreID": s.id,
"State": key,
"Value": string(b),
})
}
return nil
}
func (s *store) onBroadcast(event Value) {
if storeID := event.Get("StoreID").String(); storeID == "" || storeID == s.id {
return
}
s.mutex.Lock()
defer s.mutex.Unlock()
key := event.Get("State").String()
v := []byte(event.Get("Value").String())
state := s.states[key]
for obs := range state.observers {
o := obs
if !o.element.Mounted() {
delete(state.observers, o)
continue
}
s.disp.Dispatch(Dispatch{
Mode: Update,
Source: o.element,
Function: func(ctx Context) {
if !o.isObserving() {
s.mutex.Lock()
delete(state.observers, o)
s.mutex.Unlock()
return
}
if err := json.Unmarshal(v, o.receiver); err != nil {
Log(errors.New("notifying observer failed").
WithTag("state", key).
WithTag("element", reflect.TypeOf(o.element)).
Wrap(err))
return
}
for _, fn := range o.onChanges {
fn()
}
},
})
}
}
func storeValue(recv, v any) error {
dst := reflect.ValueOf(recv)
if dst.Kind() != reflect.Ptr {
return errors.New("receiver is not a pointer")
}
dst = dst.Elem()
src := reflect.ValueOf(v)
switch {
case src == reflect.Value{}:
dst.Set(reflect.Zero(dst.Type()))
return nil
case src.Kind() == reflect.Ptr:
src = src.Elem()
}
if src.Type() != dst.Type() {
return errors.New("value and receiver are not of the same type").
WithTag("value", src.Type()).
WithTag("receiver", dst.Type())
}
dst.Set(src)
return nil
}
type persistentState struct {
Value json.RawMessage `json:",omitempty"`
EncryptedValue []byte `json:",omitempty"`
ExpiresAt time.Time `json:",omitempty"`
}
func (s *persistentState) isExpired(now time.Time) bool {
return s.ExpiresAt != time.Time{} && now.After(s.ExpiresAt)
}