cursor

type Cursor interface {
	model.Iterator
	Id() uint64

	// Offset moves the cursor position to backward (negative offset) of forward(positive offset)
	// from the current cursor position
	Offset(ctx context.Context, offs int)
	ApplyState(state State) error
	State(context.Context) State
	WaitNewData(ctx context.Context) error
}

type ItFactory interface {
	// GetJournals returns map of journals by tags:partition.Journal or an error, if any. The returned journals
	// must be released after usage by Release() function
	GetJournals(ctx context.Context, tagsCond *lql.Source, maxLimit int) (map[tag.Line]journal.Journal, error)

	// GetJournal returns a journal by its source Id
	GetJournal(ctx context.Context, src string) (tag.Set, journal.Journal, error)

	// Iterator constructs new iterator for partition src. If the tmRange is provided the
	// iterator can utilize time-index for finding records
	Itearator(j journal.Journal, tmRange *model.TimeRange) journal.Iterator

	// Release releases the partition. Journal must not be used after the call
	Release(jn string)
}

type Provider interface {
	// GetOrCreate creates a new, or returns already exist cursor by its state (which contains cursor Id)
	GetOrCreate(ctx context.Context, state State, cache bool) (Cursor, error)

	// Release allows to release a cursor
	Release(ctx context.Context, curs Cursor) State
}

type State struct {
	// Id the cursor state Id
	Id uint64

	// The Query contains the initial query for the cursor.
	Query string

	// Src allows to overwrite From tags, by specifying the source of partition. If it is nil, the
	// sources from the Query will be taken
	Src string

	// Pos indicates the position of the record which must be read next. If it is not empty, it
	// will be applied to the Query
	Pos string
}