format/pack/ingest: Init

1 files changed, 97 insertions, 0 deletions

diff --git a/format/pack/ingest/rev_write.go b/format/pack/ingest/rev_write.go
new file mode 100644
index 00000000..cf95c782
--- /dev/null
+++ b/format/pack/ingest/rev_write.go
@@ -0,0 +1,97 @@
+package ingest
+
+import (
+	"encoding/binary"
+	"slices"
+
+	"codeberg.org/lindenii/furgit/objectid"
+)
+
+const (
+	revMagic   = 0x52494458
+	revVersion = 1
+)
+
+// writeRev writes rev index for resolved records.
+func writeRev(state *ingestState) error {
+	if !state.writeRev {
+		return nil
+	}
+
+	idxOrder := buildIdxOrder(state)
+	recordToIdxPos := make([]int, len(state.records))
+	for pos, recordIdx := range idxOrder {
+		recordToIdxPos[recordIdx] = pos
+	}
+	packOrder := buildPackOrder(state)
+
+	hashImpl, err := state.algo.New()
+	if err != nil {
+		return err
+	}
+
+	var scratch [8]byte
+	binary.BigEndian.PutUint32(scratch[:4], revMagic)
+	if err := writeAndHash(state.revFile, hashImpl, scratch[:4]); err != nil {
+		return err
+	}
+	binary.BigEndian.PutUint32(scratch[:4], revVersion)
+	if err := writeAndHash(state.revFile, hashImpl, scratch[:4]); err != nil {
+		return err
+	}
+	binary.BigEndian.PutUint32(scratch[:4], hashID(state.algo))
+	if err := writeAndHash(state.revFile, hashImpl, scratch[:4]); err != nil {
+		return err
+	}
+
+	for _, recordIdx := range packOrder {
+		binary.BigEndian.PutUint32(scratch[:4], uint32(recordToIdxPos[recordIdx]))
+		if err := writeAndHash(state.revFile, hashImpl, scratch[:4]); err != nil {
+			return err
+		}
+	}
+
+	if err := writeAndHash(state.revFile, hashImpl, state.packHash.Bytes()); err != nil {
+		return err
+	}
+	revHash := hashImpl.Sum(nil)
+	if _, err := state.revFile.Write(revHash); err != nil {
+		return err
+	}
+
+	return state.revFile.Sync()
+}
+
+// buildPackOrder returns record indexes sorted by pack offset.
+func buildPackOrder(state *ingestState) []int {
+	out := make([]int, 0, len(state.records))
+	for idx := range state.records {
+		out = append(out, idx)
+	}
+	slices.SortFunc(out, func(a, b int) int {
+		offA := state.records[a].offset
+		offB := state.records[b].offset
+		switch {
+		case offA < offB:
+			return -1
+		case offA > offB:
+			return 1
+		default:
+			return 0
+		}
+	})
+
+	return out
+}
+
+// hashID converts object algorithm to pack hash-id encoding.
+func hashID(algo objectid.Algorithm) uint32 {
+	switch algo {
+	case objectid.AlgorithmSHA1:
+		return 1
+	case objectid.AlgorithmSHA256:
+		return 2
+	default:
+		return 0
+	}
+}