internal/format/packfile: Add EntryType and associates

1 files changed, 67 insertions, 0 deletions

diff --git a/internal/format/packfile/entry_type.go b/internal/format/packfile/entry_type.go
new file mode 100644
index 00000000..784f9b69
--- /dev/null
+++ b/internal/format/packfile/entry_type.go
@@ -0,0 +1,67 @@
+package packfile
+
+import (
+	"errors"
+
+	"lindenii.org/go/furgit/object/typ"
+)
+
+var (
+	// ErrInternalEntryType reports that
+	// a supplied packfile [EntryType]
+	// cannot be converted into an ordinary [typ.Type]
+	// since it is a packfile implementation detail.
+	ErrInternalEntryType = errors.New("internal/format/packfile: packfile-internal entry type cannot be converted to an object type")
+
+	// ErrUnrepresentableObjectType reports that
+	// a supplied ordinary [typ.Type]
+	// is not currently representable
+	// as a packfile [EntryType].
+	ErrUnrepresentableObjectType = errors.New("internal/format/packfile: object type not representable in packfiles")
+)
+
+// EntryType represents the type of an entry in a git packfile.
+type EntryType uint8
+
+const (
+	EntryTypeInvalid  EntryType = 0
+	EntryTypeCommit   EntryType = 1
+	EntryTypeTree     EntryType = 2
+	EntryTypeBlob     EntryType = 3
+	EntryTypeTag      EntryType = 4
+	EntryTypeFuture   EntryType = 5
+	EntryTypeOfsDelta EntryType = 6
+	EntryTypeRefDelta EntryType = 7
+)
+
+// ObjectTypeToEntryType converts an ordinary [typ.Type] into a packfile [EntryType].
+func ObjectTypeToEntryType(ty typ.Type) (EntryType, error) {
+	switch ty {
+	case typ.Commit:
+		return EntryTypeCommit, nil
+	case typ.Tree:
+		return EntryTypeTree, nil
+	case typ.Blob:
+		return EntryTypeBlob, nil
+	case typ.Tag:
+		return EntryTypeTag, nil
+	}
+
+	return EntryTypeInvalid, ErrUnrepresentableObjectType
+}
+
+// ObjectTypeToEntryType converts a a packfile [EntryType] into an ordinary [typ.Type].
+func (entryType EntryType) EntryTypeToObjectType() (typ.Type, error) {
+	switch entryType {
+	case EntryTypeCommit:
+		return typ.Commit, nil
+	case EntryTypeTree:
+		return typ.Tree, nil
+	case EntryTypeBlob:
+		return typ.Blob, nil
+	case EntryTypeTag:
+		return typ.Tag, nil
+	}
+
+	return typ.Unknown, ErrInternalEntryType
+}