queue

type Item struct {
	// ID uniquely identifies the item in a single queue
	ID ItemID

	// Priority orders items in the queue so that due items with a higher
	// priority come before other due items, even if they were due sooner.
	Priority int // default 0, limit +/- math.MaxInt16

	// Message is any user-supplied string of bytes
	Message string

	// Attempt records how many times the given item has been unsuccessfully
	// processed and put back in the queue
	Attempt int

	// Created is the time the item was first added to the queue
	// (use `time.Now().UTC()`)
	Created time.Time // UTC

	// RetryAfter is the earliest time the queue will attempt to process the
	// item
	RetryAfter time.Time // UTC
}

type ItemID int64

type NewItem struct {
	Message    string
	Priority   int
	Created    time.Time
	RetryAfter time.Time
}

type Queue interface {
	// CreateItem places a new Item in the queue
	CreateItem(item NewItem) error

	// PeekItems returns up to `n` items with a priority >= `minPriority`,
	// and with a due time >= `due`. Returned items are ordered by (highest
	// priority, earliest due, earliest created, lowest ID). Items with IDs
	// in `excluding` (which may be nil or empty) are not included.
	PeekItems(n int, minPriority int, due time.Time, excluding []ItemID) ([]Item, error)

	// RetryItem reorders an item in the queue at a later `due` time and a
	// given priority. Also updates its attempt number (e.g. on the case of
	// temporary failure, this will be set to the item's Attempt field plus
	// one. In other cases, such as rescheduling to a better time, it might
	// be kept at the current Attempt value)
	RetryItem(item ItemID, priority int, due time.Time, attempt int) error

	// DeleteItem removes an item from the queue.
	DeleteItem(ItemID) error

	// Close any resources such as database handles.
	Close() error

	// Delete removes a queue database from disk. If you've opened an in-memory
	// database then don't try deleting it!
	Delete() error
}

type QueueService interface {
	// OpenQueue opens (or creates) a new queue with a given name, backed
	// by a file at the given path (the SQLite backend also supports
	// ":memory:" as a target path)
	OpenQueue(name string, path string) (Queue, error)

	// Close any resources such as database handles. You should individually
	// close any open queues first.
	Close() error
}

type UUIDService interface {
	Generate() ([]byte, error)
}