/*
Copyright 2026 The Kubernetes Authors.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package blueprint

import (
	"sync"
	"time"

	log "github.com/sirupsen/logrus"
)

// ZoneCache is a generic cache for DNS zones with TTL-based expiration.
// It can store any type of zone data and provides thread-safe access.
type ZoneCache[T any] struct {
	mu       sync.RWMutex
	age      time.Time
	duration time.Duration
	data     T
}

// NewZoneCache creates a new ZoneCache with the specified TTL duration.
// A duration of 0 or less disables caching: Reset becomes a no-op and Expired always returns true.
func NewZoneCache[T any](duration time.Duration) *ZoneCache[T] {
	return &ZoneCache[T]{duration: duration}
}

// Get returns the cached data. Returns the zero value if the cache has never been populated.
// Data is not cleared on expiration; Get returns the last known value until Reset is called again.
func (c *ZoneCache[T]) Get() T {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.data
}

// Reset updates the cached data and refreshes the age timestamp.
// Only updates if caching is enabled (duration > 0).
func (c *ZoneCache[T]) Reset(data T) {
	if c.duration <= 0 {
		return
	}
	c.mu.Lock()
	defer c.mu.Unlock()
	c.data = data
	c.age = time.Now()
	log.WithField("duration", c.duration).Debug("zone cache reset")
}

// Expired returns true if the cache is empty (never populated) or the TTL has elapsed since
// the last Reset. When caching is disabled (duration <= 0), always returns true.
func (c *ZoneCache[T]) Expired() bool {
	c.mu.RLock()
	defer c.mu.RUnlock()
	return c.age.IsZero() || time.Since(c.age) > c.duration
}