Initial commit

1 files changed, 94 insertions, 0 deletions

diff --git a/refs.go b/refs.go
new file mode 100644
index 00000000..df3a8303
--- /dev/null
+++ b/refs.go
@@ -0,0 +1,94 @@
+package furgit
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"os"
+	"strings"
+)
+
+// ResolveRef resolves a fully qualified ref name to its object ID.
+func (repo *Repository) ResolveRef(refname string) (Hash, error) {
+	id, err := repo.resolveLooseRef(refname)
+	if err == nil {
+		return id, nil
+	} else if !errors.Is(err, ErrNotFound) {
+		return Hash{}, err
+	}
+
+	return repo.resolvePackedRef(refname)
+}
+
+func (repo *Repository) resolveLooseRef(refname string) (Hash, error) {
+	data, err := os.ReadFile(repo.repoPath(refname))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return Hash{}, ErrNotFound
+		}
+		return Hash{}, err
+	}
+	line := strings.TrimSpace(string(data))
+	id, err := ParseHash(line)
+	if err != nil {
+		return Hash{}, err
+	}
+	return id, nil
+}
+
+func (repo *Repository) resolvePackedRef(refname string) (Hash, error) {
+	path := repo.repoPath("packed-refs")
+	f, err := os.Open(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return Hash{}, ErrInvalidObject
+		}
+		return Hash{}, err
+	}
+	defer func() { _ = f.Close() }()
+
+	want := []byte(refname)
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		line := scanner.Bytes()
+		if len(line) == 0 || line[0] == '#' || line[0] == '^' {
+			continue
+		}
+		sp := bytes.IndexByte(line, ' ')
+		if sp != HashSize*2 {
+			continue
+		}
+		name := line[sp+1:]
+		if bytes.Equal(name, want) {
+			hex := string(line[:sp])
+			id, err := ParseHash(hex)
+			if err != nil {
+				return Hash{}, err
+			}
+			return id, nil
+		}
+	}
+	scanErr := scanner.Err()
+	if scanErr != nil {
+		return Hash{}, scanErr
+	}
+	return Hash{}, ErrInvalidObject
+}
+
+// ResolveHEAD reads HEAD and returns the ref that HEAD points to.
+func (repo *Repository) ResolveHEAD() (string, error) {
+	data, err := os.ReadFile(repo.repoPath("HEAD"))
+	if err != nil {
+		return "", err
+	}
+	line := strings.TrimSpace(string(data))
+	const prefix = "ref: "
+	if strings.HasPrefix(line, prefix) {
+		ref := strings.TrimSpace(line[len(prefix):])
+		if ref == "" {
+			return "", ErrInvalidRef
+		}
+		return ref, nil
+	}
+	return "", ErrInvalidRef
+}