object: Add basic object code

1 files changed, 57 insertions, 0 deletions

diff --git a/object/tree_parse.go b/object/tree_parse.go
new file mode 100644
index 00000000..e1e560b6
--- /dev/null
+++ b/object/tree_parse.go
@@ -0,0 +1,57 @@
+package object
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+
+	"codeberg.org/lindenii/furgit/oid"
+)
+
+// ParseTree decodes a tree object body.
+func ParseTree(body []byte, algo oid.Algorithm) (*Tree, error) {
+	if algo.Size() == 0 {
+		return nil, ErrInvalidObject
+	}
+
+	var entries []TreeEntry
+	i := 0
+	for i < len(body) {
+		space := bytes.IndexByte(body[i:], ' ')
+		if space < 0 {
+			return nil, fmt.Errorf("object: tree: missing mode terminator")
+		}
+		modeBytes := body[i : i+space]
+		i += space + 1
+
+		nul := bytes.IndexByte(body[i:], 0)
+		if nul < 0 {
+			return nil, fmt.Errorf("object: tree: missing name terminator")
+		}
+		nameBytes := body[i : i+nul]
+		i += nul + 1
+
+		idEnd := i + algo.Size()
+		if idEnd > len(body) {
+			return nil, fmt.Errorf("object: tree: truncated child object id")
+		}
+		id, err := oid.FromBytes(algo, body[i:idEnd])
+		if err != nil {
+			return nil, err
+		}
+		i = idEnd
+
+		mode, err := strconv.ParseUint(string(modeBytes), 8, 32)
+		if err != nil {
+			return nil, fmt.Errorf("object: tree: parse mode: %w", err)
+		}
+
+		entries = append(entries, TreeEntry{
+			Mode: FileMode(mode),
+			Name: append([]byte(nil), nameBytes...),
+			ID:   id,
+		})
+	}
+
+	return &Tree{Entries: entries}, nil
+}