From e15054a4f93fc54806e84aa7036e60168e78e823 Mon Sep 17 00:00:00 2001
From: Runxi Yu
Date: Fri, 6 Mar 2026 08:05:51 +0800
Subject: format/commitgraph: Add initial commit-graph support

---
 format/commitgraph/hash.go | 79 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 79 insertions(+)
 create mode 100644 format/commitgraph/hash.go

(limited to 'format/commitgraph/hash.go')

diff --git a/format/commitgraph/hash.go b/format/commitgraph/hash.go
new file mode 100644
index 00000000..55bc0195
--- /dev/null
+++ b/format/commitgraph/hash.go
@@ -0,0 +1,79 @@
+package commitgraph
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+
+	"codeberg.org/lindenii/furgit/objectid"
+)
+
+// HashVersion returns the commit-graph hash version.
+func (reader *Reader) HashVersion() uint8 {
+	return reader.hashVersion
+}
+
+func validateChainBaseHashes(algo objectid.Algorithm, chain []string, idx int, graph *layer) error {
+	if idx == 0 {
+		if len(graph.chunkBaseGraphs) != 0 {
+			return &ErrMalformed{Path: graph.path, Reason: "unexpected BASE chunk in first graph"}
+		}
+
+		return nil
+	}
+
+	hashSize := algo.Size()
+
+	expectedLen := idx * hashSize
+	if len(graph.chunkBaseGraphs) != expectedLen {
+		return &ErrMalformed{
+			Path:   graph.path,
+			Reason: fmt.Sprintf("BASE chunk length %d does not match expected %d", len(graph.chunkBaseGraphs), expectedLen),
+		}
+	}
+
+	for i := range idx {
+		start := i * hashSize
+		end := start + hashSize
+
+		baseHash, err := objectid.FromBytes(algo, graph.chunkBaseGraphs[start:end])
+		if err != nil {
+			return err
+		}
+
+		if baseHash.String() != chain[i] {
+			return &ErrMalformed{
+				Path:   graph.path,
+				Reason: fmt.Sprintf("BASE chunk mismatch at index %d", i),
+			}
+		}
+	}
+
+	return nil
+}
+
+func verifyTrailerHash(data []byte, algo objectid.Algorithm, path string) error {
+	hashSize := algo.Size()
+	if len(data) < hashSize {
+		return &ErrMalformed{Path: path, Reason: "file too short for trailer"}
+	}
+
+	hashImpl, err := algo.New()
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(hashImpl, bytes.NewReader(data[:len(data)-hashSize]))
+	if err != nil {
+		return err
+	}
+
+	got := hashImpl.Sum(nil)
+
+	want := data[len(data)-hashSize:]
+	if !bytes.Equal(got, want) {
+		return &ErrMalformed{Path: path, Reason: "trailer hash mismatch"}
+	}
+
+	return nil
+}
-- 
cgit v1.3.1-10-gc9f91