bouncer/internal/syncx/cached_resource.go

package syncx

import (
	"context"
	"sync"

	"forge.cadoles.com/cadoles/bouncer/internal/cache"
	"github.com/pkg/errors"
)

type RefreshFunc[K comparable, V any] func(ctx context.Context, key K) (V, error)

type CachedResource[K comparable, V any] struct {
	cache   cache.Cache[K, V]
	lock    sync.RWMutex
	refresh RefreshFunc[K, V]
}

func (r *CachedResource[K, V]) Clear() {
	r.cache.Clear()
}

func (r *CachedResource[K, V]) Get(ctx context.Context, key K) (V, bool, error) {
	value, exists := r.cache.Get(key)
	if exists {
		return value, false, nil
	}

	locked := r.lock.TryLock()
	if !locked {
		r.lock.RLock()

		value, exists := r.cache.Get(key)
		if exists {
			r.lock.RUnlock()
			return value, false, nil
		}

		r.lock.RUnlock()
	}

	if !locked {
		r.lock.Lock()
	}

	defer r.lock.Unlock()

	value, err := r.refresh(ctx, key)
	if err != nil {
		return *new(V), false, errors.WithStack(err)
	}

	r.cache.Set(key, value)

	return value, true, nil
}

func NewCachedResource[K comparable, V any](cache cache.Cache[K, V], refresh RefreshFunc[K, V]) *CachedResource[K, V] {
	return &CachedResource[K, V]{
		cache:   cache,
		refresh: refresh,
	}
}