wal

type Config struct {
	// DataSegmentSize defines the maximum size of a given Data Segment. This
	// values does not affect segments already present in the disk, if any.
	DataSegmentSize int64

	// IndexSegmentSize indicates the maximum size of the system index before
	// it is split into a next file. Each index record takes 41 bytes
	// choosing a multiple of that value will prevent index segments from
	// consuming more than it may require.
	IndexSegmentSize int64

	// WorkDir represents the absolute path to the directory where the WAL will
	// retain information. It is advised to use a directory in which only the
	// WAL instance will have access, as all files within that directory will
	// be automatically managed by the instance itself.
	WorkDir string

	// Logger allows a given stdlog.Logger instance to be set as the system
	// logger. If unset, no logs will be generated.
	Logger stdlog.Logger
}

type Cursor interface {
	Next() bool
	Read() (io.Reader, error)
	Offset() int64
}

type WAL interface {
	// WriteObject writes a given object to the WAL. Returns an error in case
	// the write operation fails.
	WriteObject(data []byte) error

	// ReadObject attempts to read a previously stored object under a given
	// id. Either returns an io.Reader for the object's data, or an error. In
	// case the object has been marked for removal, a NotFoundError is returned.
	ReadObject(id int64) (io.Reader, error)

	// ReadObjects returns a new Cursor pointing to either the object under the
	// specified id, or its right sibling, depending on the value of the
	// inclusive flag.
	ReadObjects(id int64, inclusive bool) Cursor

	// Close flushes all data to disk, and safely closes underlying facilities
	// of the WAL.
	Close() error

	// VacuumRecords marks and removes all records from the storage medium.
	// Whether the provided id is also included in the vacuuming is defined by
	// the inclusive flag.
	VacuumRecords(id int64, inclusive bool) error

	// CountObjects returns the amount of objects after a given id. In case the
	// inclusive flag is set, the object itself is also accounted in the
	// returned total.
	CountObjects(id int64, inclusive bool) int64

	// CurrentRecordID returns the id of the latest written object
	CurrentRecordID() int64

	// IsEmpty returns whether the WAL contains any items. Returns true in case
	// no item is currently stored, otherwise returns false.
	IsEmpty() bool

	// MinimumRecordID returns the minimum record available in the WAL. Returns
	// -1 in case no record is available.
	MinimumRecordID() int64
}