1 files changed, 36 insertions, 0 deletions
diff --git a/lib/diskio/file_state.go b/lib/diskio/file_state.go
new file mode 100644
index 0000000..63ec53b
--- /dev/null
+++ b/lib/diskio/file_state.go
@@ -0,0 +1,36 @@
+// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
+//
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+package diskio
+
+type statefulFile[A ~int64] struct {
+	inner File[A]
+	pos   A
+}
+
+var _ File[assertAddr] = (*statefulFile[assertAddr])(nil)
+
+func NewStatefulFile[A ~int64](file File[A]) *statefulFile[A] {
+	return &statefulFile[A]{
+		inner: file,
+	}
+}
+
+func (sf *statefulFile[A]) Name() string                           { return sf.inner.Name() }
+func (sf *statefulFile[A]) Size() A                                { return sf.inner.Size() }
+func (sf *statefulFile[A]) Close() error                           { return sf.inner.Close() }
+func (sf *statefulFile[A]) ReadAt(dat []byte, off A) (int, error)  { return sf.inner.ReadAt(dat, off) }
+func (sf *statefulFile[A]) WriteAt(dat []byte, off A) (int, error) { return sf.inner.WriteAt(dat, off) }
+
+func (sf *statefulFile[A]) Read(dat []byte) (n int, err error) {
+	n, err = sf.ReadAt(dat, sf.pos)
+	sf.pos += A(n)
+	return n, err
+}
+
+func (sf *statefulFile[A]) ReadByte() (byte, error) {
+	var dat [1]byte
+	_, err := sf.Read(dat[:])
+	return dat[0], err
+}