refstore/packed: Add packed refs backend

1 files changed, 100 insertions, 0 deletions

diff --git a/refstore/packed/parse.go b/refstore/packed/parse.go
new file mode 100644
index 00000000..6fe88061
--- /dev/null
+++ b/refstore/packed/parse.go
@@ -0,0 +1,100 @@
+package packed
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"strings"
+
+	"codeberg.org/lindenii/furgit/objectid"
+	"codeberg.org/lindenii/furgit/ref"
+)
+
+// parsePackedRefs parses packed-refs content into detached refs.
+func parsePackedRefs(r io.Reader, algo objectid.Algorithm) (map[string]ref.Detached, []ref.Detached, error) {
+	byName := make(map[string]ref.Detached)
+	ordered := make([]ref.Detached, 0, 32)
+
+	br := bufio.NewReader(r)
+	prev := -1
+	lineNum := 0
+
+	for {
+		line, err := br.ReadString('\n')
+		if err != nil && err != io.EOF {
+			return nil, nil, err
+		}
+		if line == "" && err == io.EOF {
+			break
+		}
+		lineNum++
+
+		line = strings.TrimSuffix(line, "\n")
+		line = strings.TrimSuffix(line, "\r")
+		line = strings.TrimSpace(line)
+		if line == "" {
+			if err == io.EOF {
+				break
+			}
+			continue
+		}
+		if strings.HasPrefix(line, "#") {
+			if err == io.EOF {
+				break
+			}
+			continue
+		}
+
+		if strings.HasPrefix(line, "^") {
+			if prev < 0 {
+				return nil, nil, fmt.Errorf("refstore/packed: line %d: peeled line without preceding ref", lineNum)
+			}
+			peeledHex := strings.TrimSpace(strings.TrimPrefix(line, "^"))
+			peeled, parseErr := objectid.ParseHex(algo, peeledHex)
+			if parseErr != nil {
+				return nil, nil, fmt.Errorf("refstore/packed: line %d: invalid peeled oid: %w", lineNum, parseErr)
+			}
+			peeledCopy := peeled
+			cur := ordered[prev]
+			cur.Peeled = &peeledCopy
+			ordered[prev] = cur
+			byName[cur.Name()] = cur
+			if err == io.EOF {
+				break
+			}
+			continue
+		}
+
+		fields := strings.Fields(line)
+		if len(fields) != 2 {
+			return nil, nil, fmt.Errorf("refstore/packed: line %d: malformed entry", lineNum)
+		}
+
+		id, parseErr := objectid.ParseHex(algo, fields[0])
+		if parseErr != nil {
+			return nil, nil, fmt.Errorf("refstore/packed: line %d: invalid oid: %w", lineNum, parseErr)
+		}
+
+		name := fields[1]
+		if name == "" {
+			return nil, nil, fmt.Errorf("refstore/packed: line %d: empty ref name", lineNum)
+		}
+		if _, exists := byName[name]; exists {
+			return nil, nil, fmt.Errorf("refstore/packed: line %d: duplicate ref %q", lineNum, name)
+		}
+
+		detached := ref.Detached{
+			RefName: name,
+			ID:      id,
+		}
+		ordered = append(ordered, detached)
+		prev = len(ordered) - 1
+		byName[name] = detached
+
+		if err == io.EOF {
+			break
+		}
+	}
+
+	return byName, ordered, nil
+}