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package lease
import (
"context"
"sync"
"time"
"golang.org/x/sync/singleflight"
"github.com/johnandersen777/socialweb-computer-kcp/internal/kit/ttlcache"
)
type Fetch[T any] func(context.Context) (T, time.Time, error)
type Source[T any] struct {
fetch Fetch[T]
now func() time.Time
mu sync.Mutex
value T
valid bool
renewAt time.Time
expires time.Time
renewing bool
group singleflight.Group
}
const flightKey = "lease"
func New[T any](fetch Fetch[T]) *Source[T] {
return &Source[T]{fetch: fetch, now: time.Now}
}
func NewWithClock[T any](fetch Fetch[T], now func() time.Time) *Source[T] {
if now == nil {
now = time.Now
}
return &Source[T]{fetch: fetch, now: now}
}
func (s *Source[T]) Get(ctx context.Context) (T, error) {
s.mu.Lock()
now := s.now()
if s.valid && (s.expires.IsZero() || now.Before(s.expires)) {
value := s.value
if s.renewAt.IsZero() || now.Before(s.renewAt) || s.renewing {
s.mu.Unlock()
return value, nil
}
s.renewing = true
s.mu.Unlock()
fresh, err := s.load(ctx)
if err != nil {
return value, nil
}
return fresh, nil
}
s.mu.Unlock()
return s.load(ctx)
}
func (s *Source[T]) Peek() (T, time.Time, bool) {
s.mu.Lock()
defer s.mu.Unlock()
if !s.valid || (!s.expires.IsZero() && !s.now().Before(s.expires)) {
var zero T
return zero, time.Time{}, false
}
return s.value, s.expires, true
}
func (s *Source[T]) Invalidate() {
s.mu.Lock()
defer s.mu.Unlock()
var zero T
s.value = zero
s.valid = false
s.renewAt = time.Time{}
s.expires = time.Time{}
}
func (s *Source[T]) load(ctx context.Context) (T, error) {
ch := s.group.DoChan(flightKey, func() (any, error) {
start := s.now()
value, expires, err := s.fetch(ctx)
s.mu.Lock()
defer s.mu.Unlock()
s.renewing = false
if err != nil {
return value, err
}
s.value = value
s.valid = true
s.expires = expires
s.renewAt = time.Time{}
if !expires.IsZero() {
s.renewAt = start.Add(expires.Sub(start) * 2 / 3)
}
return value, nil
})
select {
case res := <-ch:
value, _ := res.Val.(T)
return value, res.Err
case <-ctx.Done():
var zero T
return zero, ctx.Err()
}
}
type Keyed[K comparable, T any] struct {
fetch func(context.Context, K) (T, time.Time, error)
sources *ttlcache.Cache[K, *Source[T]]
}
func NewKeyed[K comparable, T any](fetch func(context.Context, K) (T, time.Time, error)) *Keyed[K, T] {
return &Keyed[K, T]{fetch: fetch, sources: ttlcache.New[K, *Source[T]](ttlcache.Options{})}
}
func (k *Keyed[K, T]) Source(ctx context.Context, key K) (*Source[T], error) {
return k.sources.GetOrLoad(ctx, key, func(context.Context) (*Source[T], time.Duration, error) {
return New(func(ctx context.Context) (T, time.Time, error) { return k.fetch(ctx, key) }), 0, nil
})
}
func (k *Keyed[K, T]) Get(ctx context.Context, key K) (T, error) {
src, err := k.Source(ctx, key)
if err != nil {
var zero T
return zero, err
}
return src.Get(ctx)
}
func (k *Keyed[K, T]) Invalidate(key K) {
if src, ok := k.sources.Get(key); ok {
src.Invalidate()
}
}
func (k *Keyed[K, T]) Delete(key K) {
k.sources.Delete(key)
}
func (k *Keyed[K, T]) DeleteKeys(drop func(K) bool) int {
return k.sources.DeleteKeys(drop)
}
