feat(kv): define forward cursor interface

kv/store.go

@@ -94,19 +94,64 @@ type Bucket interface {
 	Put(key, value []byte) error
 	// Delete should error if the transaction it was called in is not writable.
 	Delete(key []byte) error
+	// ForwardCursor returns a forward cursor from the seek position provided.
+	// Other options can be supplied to provide direction and hints.
+	ForwardCursor(seek []byte, opts ...CursorOption) (ForwardCursor, error)
 }
 
 // Cursor is an abstraction for iterating/ranging through data. A concrete implementation
 // of a cursor can be found in cursor.go.
 type Cursor interface {
+	ForwardCursor
 	// Seek moves the cursor forward until reaching prefix in the key name.
 	Seek(prefix []byte) (k []byte, v []byte)
 	// First moves the cursor to the first key in the bucket.
 	First() (k []byte, v []byte)
 	// Last moves the cursor to the last key in the bucket.
 	Last() (k []byte, v []byte)
-	// Next moves the cursor to the next key in the bucket.
-	Next() (k []byte, v []byte)
 	// Prev moves the cursor to the prev key in the bucket.
 	Prev() (k []byte, v []byte)
 }
+
+// ForwardCursor is an abstraction for interating/ranging through data in one direction.
+type ForwardCursor interface {
+	// Next moves the cursor to the next key in the bucket.
+	Next() (k, v []byte)
+}
+
+// CursorDirection is an integer used to define the direction
+// a request cursor operates in.
+type CursorDirection int
+
+const (
+	// CursorAscending directs a cursor to range in ascending order
+	CursorAscending CursorDirection = iota
+	// CursorAscending directs a cursor to range in descending order
+	CursorDescending
+)
+
+// CursorConfig is a type used to configure a new forward cursor.
+// It includes a direction and a set of hints
+type CursorConfig struct {
+	Direction CursorDirection
+	Hints     CursorHints
+}
+
+// CursorOption is a functional option for configuring a forward cursor
+type CursorOption func(*CursorConfig)
+
+// WithCursorDirection sets the cursor direction on a provided cursor config
+func WithCursorDirection(direction CursorDirection) CursorOption {
+	return func(c *CursorConfig) {
+		c.Direction = direction
+	}
+}
+
+// WithCursorHints configs the provided hints on the cursor config
+func WithCursorHints(hints ...CursorHint) CursorOption {
+	return func(c *CursorConfig) {
+		for _, hint := range hints {
+			hint(&c.Hints)
+		}
+	}
+}