1 files changed, 138 insertions, 0 deletions
diff --git a/format/packfile/ingest/rev_write.go b/format/packfile/ingest/rev_write.go
new file mode 100644
index 00000000..f8c30c1b
--- /dev/null
+++ b/format/packfile/ingest/rev_write.go
@@ -0,0 +1,138 @@
+package ingest
+
+import (
+	"encoding/binary"
+	"slices"
+
+	"codeberg.org/lindenii/furgit/internal/intconv"
+	"codeberg.org/lindenii/furgit/internal/progress"
+)
+
+const (
+	revMagic   = 0x52494458
+	revVersion = 1
+)
+
+// writeRev writes rev index for resolved records.
+func writeRev(state *ingestState) error {
+	if !state.opts.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
+
+	writeProgressf(state, "writing reverse index header...\r")
+	binary.BigEndian.PutUint32(scratch[:4], revMagic)
+
+	err = writeAndHash(state.revFile, hashImpl, scratch[:4])
+	if err != nil {
+		return err
+	}
+
+	binary.BigEndian.PutUint32(scratch[:4], revVersion)
+
+	err = writeAndHash(state.revFile, hashImpl, scratch[:4])
+	if err != nil {
+		return err
+	}
+
+	binary.BigEndian.PutUint32(scratch[:4], state.algo.PackHashID())
+
+	err = writeAndHash(state.revFile, hashImpl, scratch[:4])
+	if err != nil {
+		return err
+	}
+
+	writeProgressf(state, "writing reverse index header: done.\n")
+
+	entriesMeter := progress.New(progress.Options{
+		Writer: state.opts.Progress,
+		Flush:  state.opts.ProgressFlush,
+		Title:  "writing reverse index entries",
+		Total:  uint64(len(packOrder)),
+	})
+
+	var entriesDone uint64
+
+	for _, recordIdx := range packOrder {
+		recordPos, err := intconv.IntToUint32(recordToIdxPos[recordIdx])
+		if err != nil {
+			return err
+		}
+
+		binary.BigEndian.PutUint32(scratch[:4], recordPos)
+
+		err = writeAndHash(state.revFile, hashImpl, scratch[:4])
+		if err != nil {
+			return err
+		}
+
+		entriesDone++
+		entriesMeter.Set(entriesDone, 0)
+	}
+
+	if entriesDone > 0 {
+		entriesMeter.Stop("done")
+	}
+
+	writeProgressf(state, "writing reverse index trailer...\r")
+
+	err = writeAndHash(state.revFile, hashImpl, state.packHash.Bytes())
+	if err != nil {
+		return err
+	}
+
+	revHash := hashImpl.Sum(nil)
+
+	_, err = state.revFile.Write(revHash)
+	if err != nil {
+		return err
+	}
+
+	err = state.revFile.Sync()
+	if err != nil {
+		return err
+	}
+
+	writeProgressf(state, "writing reverse index trailer: done.\n")
+
+	return nil
+}
+
+// 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
+}