object/tree: Add basic tree functions

1 files changed, 45 insertions, 0 deletions

diff --git a/object/tree/append.go b/object/tree/append.go
new file mode 100644
index 00000000..9985e668
--- /dev/null
+++ b/object/tree/append.go
@@ -0,0 +1,45 @@
+package tree
+
+import (
+	"slices"
+
+	"lindenii.org/go/furgit/object/header"
+	"lindenii.org/go/furgit/object/tree/mode"
+	"lindenii.org/go/furgit/object/typ"
+)
+
+// AppendWithoutHeader renders the raw tree body bytes.
+//
+// It trusts the package invariant that the entries are valid and ordered,
+// so it does not revalidate them.
+func (tree *Tree) AppendWithoutHeader(dst []byte) ([]byte, error) {
+	var bodyLen int
+	for _, entry := range tree.entries {
+		bodyLen += mode.MaxModeDigits + 1 + len(entry.Name) + 1 + entry.ID.ObjectFormat().Size()
+	}
+
+	dst = slices.Grow(dst, bodyLen)
+
+	for _, entry := range tree.entries {
+		dst = entry.Mode.Append(dst)
+		dst = append(dst, ' ')
+		dst = append(dst, entry.Name...)
+		dst = append(dst, 0)
+		dst = append(dst, entry.ID.RawBytes()...)
+	}
+
+	return dst, nil
+}
+
+// AppendWithHeader renders the raw object (header + body).
+func (tree *Tree) AppendWithHeader(dst []byte) ([]byte, error) {
+	// TODO: Try to not allocate?
+	body, err := tree.AppendWithoutHeader(nil)
+	if err != nil {
+		return dst, err
+	}
+
+	dst = header.Append(dst, typ.TypeTree, uint64(len(body)))
+
+	return append(dst, body...), nil
+}