wal

type CommitOffsetProvider interface {
	CommitOffset() int64
}

type ReadOnlySegment interface {
	io.Closer

	BaseOffset() int64
	LastOffset() int64

	Read(offset int64) ([]byte, error)

	Delete() error

	OpenTimestamp() time.Time
}

type ReadOnlySegmentsGroup interface {
	io.Closer

	Get(offset int64) (common.RefCount[ReadOnlySegment], error)

	TrimSegments(offset int64) error

	AddedNewSegment(baseOffset int64)

	PollHighestSegment() (common.RefCount[ReadOnlySegment], error)
}

type ReadWriteSegment interface {
	ReadOnlySegment

	Append(offset int64, data []byte) error

	Truncate(lastSafeOffset int64) error

	HasSpace(len int) bool

	Flush() error
}

type Trimmer interface {
	io.Closer
}

type Wal interface {
	io.Closer
	// Append writes an entry to the end of the log.
	// The wal is synced when Append returns
	Append(entry *proto.LogEntry) error

	// AppendAsync an entry without syncing the WAL
	// Caller should use Sync to make the entry visible
	AppendAsync(entry *proto.LogEntry) error

	// Sync flushes all the entries in the wal to disk
	Sync(ctx context.Context) error

	// TruncateLog removes entries from the end of the log that have an ID greater than lastSafeEntry.
	TruncateLog(lastSafeEntry int64) (int64, error)

	// NewReader returns a new WalReader to traverse the log from the entry after `after` towards the log end
	NewReader(after int64) (WalReader, error)
	// NewReverseReader returns a new WalReader to traverse the log from the last entry towards the beginning
	NewReverseReader() (WalReader, error)

	// LastOffset Return the offset of the last entry committed to the WAL
	// Return InvalidOffset if the WAL is empty
	LastOffset() int64

	// FirstOffset Return the offset of the first valid entry that is present in the WAL
	// Return InvalidOffset if the WAL is empty
	FirstOffset() int64

	// Clear removes all the entries in the WAL
	Clear() error

	// Delete all the files and directories of the wal
	Delete() error
}

type WalFactory interface {
	io.Closer
	NewWal(namespace string, shard int64, provider CommitOffsetProvider) (Wal, error)
}

type WalFactoryOptions struct {
	BaseWalDir  string
	Retention   time.Duration
	SegmentSize int32
	SyncData    bool
}

type WalReader interface {
	io.Closer
	// ReadNext returns the next entry in the log according to the Reader's direction.
	// If a forward/reverse WalReader has passed the end/beginning of the log, it returns [ErrorEntryNotFound]. To avoid this error, use HasNext.
	ReadNext() (*proto.LogEntry, error)
	// HasNext returns true if there is an entry to read.
	HasNext() bool
}