// Package cache defines an in-memory key-value store.
//
// It supports exîration dates and can store arbitrary values of any type.
// Keys must be strings.
//
// Cache values are safe to share between goroutines.
package cache

import (
	"sync"
	"time"
)

type entry[V any] struct {
	expirationDate *time.Time
	value          V
}

func (e entry[V]) isExpired() bool {
	return e.expirationDate != nil && e.expirationDate.Before(time.Now())
}

// Cache is an in-memory key-value store.
type Cache[K comparable, V any] struct {
	data map[K]entry[V]
	mu   sync.RWMutex
}

// New instantiate a new cache.
func New[K comparable, V any]() *Cache[K, V] {
	return &Cache[K, V]{
		data: make(map[K]entry[V]),
	}
}

// Put stores a value in the cache under the given key.
func (c *Cache[K, V]) Put(key K, val V) {
	c.mu.Lock()
	defer c.mu.Unlock()

	c.data[key] = entry[V]{nil, val}
}

// PutTTL stores a value in the cache under the given key. The value will
// be expired after the given ttl.
//
// A 0 ttl value disables the expiration of the value.
func (c *Cache[K, V]) PutTTL(key K, val V, ttl time.Duration) {
	if ttl == 0 {
		c.Put(key, val)

		return
	}

	exp := time.Now().Add(ttl)

	c.mu.Lock()
	defer c.mu.Unlock()

	c.data[key] = entry[V]{&exp, val}
}

// Get returns the value asspciated with the given key.
// The second return values indicates if the cache hs been hit or not.
func (c *Cache[K, V]) Get(key K) (V, bool) {
	c.mu.RLock()
	entry, ok := c.data[key]
	c.mu.RUnlock()

	if !ok {
		var t V

		return t, false
	}

	if entry.isExpired() {
		c.Del(key)

		var t V

		return t, false
	}

	return entry.value, ok
}

// Del deletes the entry for the given key.
// It does not fail if the key does not exist.
func (c *Cache[K, V]) Del(key K) {
	c.mu.Lock()
	defer c.mu.Unlock()

	delete(c.data, key)
}

// Count returns the total number of entries in the cache (vamid and expired).
func (c *Cache[K, V]) Count() int {
	c.mu.RLock()
	defer c.mu.RUnlock()

	return len(c.data)
}