package cache

import (
	"context"
	"errors"
	"time"
)

var (
	// DefaultCache is the default cache.
	DefaultCache Cache = NewCache()
	// DefaultExpiration is the default duration for items stored in
	// the cache to expire.
	DefaultExpiration time.Duration = 0

	// ErrItemExpired is returned in Cache.Get when the item found in the cache
	// has expired.
	ErrItemExpired error = errors.New("item has expired")
	// ErrKeyNotFound is returned in Cache.Get and Cache.Delete when the
	// provided key could not be found in cache.
	ErrKeyNotFound error = errors.New("key not found in cache")
)

// Cache is the interface that wraps the cache.
type Cache interface {
	// Get gets a cached value by key.
	Get(ctx context.Context, key string) (interface{}, time.Time, error)
	// Put stores a key-value pair into cache.
	Put(ctx context.Context, key string, val interface{}, d time.Duration) error
	// Delete removes a key from cache.
	Delete(ctx context.Context, key string) error
	// String returns the name of the implementation.
	String() string
}

// Item represents an item stored in the cache.
type Item struct {
	Value      interface{}
	Expiration int64
}

// Expired returns true if the item has expired.
func (i *Item) Expired() bool {
	if i.Expiration == 0 {
		return false
	}

	return time.Now().UnixNano() > i.Expiration
}

// NewCache returns a new cache.
func NewCache(opts ...Option) Cache {
	options := NewOptions(opts...)
	items := make(map[string]Item)

	if len(options.Items) > 0 {
		items = options.Items
	}

	return &memCache{
		opts:  options,
		items: items,
	}
}