storages

type Accessor interface {
	// Get item from storage. If not exists - os.ErrNotExist (implementation independent)
	Get(key []byte) ([]byte, error)
	// Put single item to storage. If already exists - override
	Put(key []byte, data []byte) error
	// Delete key and value
	Del(key []byte) error
}

type BatchedStorage interface {
	Storage
	BatchWriter() Writer
}

type Clearable interface {
	// Clear all data in storage
	Clear() error
}

type DReader func(key []byte, storages []Storage) ([]byte, error)

type DWriter func(key, data []byte, storages []Storage) error

type Dedup interface {
	// Is key already save?
	IsDuplicated(key []byte) (bool, error)
	// Save key for future checks
	Save(key []byte) error
}

type Iterator interface {
	// Is queue has next value
	Next() bool
	// Current id
	ID() int64
	// Current value
	Value() []byte
}

type KV interface {
	Writer
	// Get item from storage. If not exists - os.ErrNotExist (implementation independent)
	Get(key []byte) ([]byte, error)
	// Delete key and value
	Del(key []byte) error
}

type LegacyQueue interface {
	// put data to queue using new sequence id
	Put(data []byte) (id int64, err error)
	// peek latest data
	Peek() (id int64, data []byte, err error)
	// clean data in range: [first;end)
	Clean(end int64) error
	// size of queue (last-first)
	Size() int64
	// first (oldest) sequence id
	First() int64
	// last (latest) sequence id
	Last() int64
	// iterate over items from first (if from is 0) to last (next should be called first) or till first error.
	// Iterator keeps min and max sequence number so cleaning items during iteration may cause iteration stop
	Iterate(from int64) Iterator
}

type LimitedQueue interface {
	LegacyQueue
	// available space (limit - size)
	Available() int64
	// limit
	Limit() int64
}

type NamespacedStorage interface {
	Storage
	// Get or create nested storage. Optionally can be also NamespacedStorage but it is implementation defined
	Namespace(name []byte) (Storage, error)
	// Iterate over all namespaces in storage (not including nested)
	Namespaces(handler func(name []byte) error) error
	// Delete nested namespace by name. If namespace still in usage - result undefined
	DelNamespace(name []byte) error
}

type Queue interface {
	// Put data to the queue
	Put(data []byte) error
	// Get oldest record but not remove it. Returns os.ErrNotExists if queue is empty
	Peek() ([]byte, error)
	// Discard oldest record. Returns os.ErrNotExists if queue is empty
	Discard() error
	// Get oldest record and remove it.  Returns os.ErrNotExists if queue is empty. Basically - it's atomic version of Peek & Discard
	Get() ([]byte, error)
}

type Reader interface {
	// Get item from storage. If not exists - os.ErrNotExist (implementation independent)
	Get(key []byte) ([]byte, error)
}

type ShardPool interface {
	// Get storage based on key
	Get(key []byte) (Storage, error)
	// Iterate over shards
	Iterate(handler func(storage Storage) error) error
	io.Closer
}

type Storage interface {
	KV
	// Iterate over all keys. Modification during iteration may cause undefined behaviour (mostly - dead-lock)
	Keys(handler func(key []byte) error) error
}

type Writer interface {
	// Put single item to storage. If already exists - override
	Put(key []byte, data []byte) error
	// Close storage if needs
	io.Closer
}