object/typ: Implement object types

5 files changed, 100 insertions, 0 deletions

diff --git a/object/typ/doc.go b/object/typ/doc.go
new file mode 100644
index 00000000..155d60eb
--- /dev/null
+++ b/object/typ/doc.go
@@ -0,0 +1,5 @@
+// Package typ provides Git object type enums and names.
+//
+// I would prefer naming this package "type"
+// if it wasn't a keyword.
+package typ
diff --git a/object/typ/type.go b/object/typ/type.go
new file mode 100644
index 00000000..69a07de3
--- /dev/null
+++ b/object/typ/type.go
@@ -0,0 +1,38 @@
+package typ
+
+// Type represents a Git object type.
+//
+// The values currently mirror what's found in the Git packfile format.
+//
+// TODO: Revisit this.
+type Type uint8
+
+const (
+	// TypeInvalid represents an invalid Git object type.
+	TypeInvalid Type = 0
+
+	// TypeCommit represents a Git commit.
+	TypeCommit Type = 1
+
+	// TypeTree represents a Git tree.
+	TypeTree Type = 2
+
+	// TypeBlob represents a Git blob.
+	TypeBlob Type = 3
+
+	// TypeTag represents a Git tag.
+	TypeTag Type = 4
+
+	// TypeFuture is reserved for the future, just like in the packfile format.
+	TypeFuture Type = 5
+
+	// TypeOfsDelta is reserved for internal use in packfile handlers.
+	//
+	// TODO: Revisit this.
+	TypeOfsDelta Type = 6
+
+	// TypeRefDelta is reserved for internal use in packfile handlers.
+	//
+	// TODO: Revisit this.
+	TypeRefDelta Type = 7
+)
diff --git a/object/typ/type_details.go b/object/typ/type_details.go
new file mode 100644
index 00000000..48dcf829
--- /dev/null
+++ b/object/typ/type_details.go
@@ -0,0 +1,30 @@
+package typ
+
+type typeDetails struct {
+	name         string
+	isBaseObject bool
+}
+
+func (ty Type) details() typeDetails {
+	return typeTable[ty]
+}
+
+//nolint:gochecknoglobals
+var typeTable = [...]typeDetails{
+	TypeInvalid:  {name: "", isBaseObject: false},
+	TypeCommit:   {name: "commit", isBaseObject: true},
+	TypeTree:     {name: "tree", isBaseObject: true},
+	TypeBlob:     {name: "blob", isBaseObject: true},
+	TypeTag:      {name: "tag", isBaseObject: true},
+	TypeFuture:   {name: "", isBaseObject: false},
+	TypeOfsDelta: {name: "", isBaseObject: false},
+	TypeRefDelta: {name: "", isBaseObject: false},
+}
+
+//nolint:gochecknoglobals
+var typeByName = map[string]Type{
+	typeTable[TypeCommit].name: TypeCommit,
+	typeTable[TypeTree].name:   TypeTree,
+	typeTable[TypeBlob].name:   TypeBlob,
+	typeTable[TypeTag].name:    TypeTag,
+}
diff --git a/object/typ/type_ops.go b/object/typ/type_ops.go
new file mode 100644
index 00000000..82e68147
--- /dev/null
+++ b/object/typ/type_ops.go
@@ -0,0 +1,19 @@
+package typ
+
+// IsBaseObject reports whether ty is
+// one of the four ordinary Git object types.
+//
+// TODO: This should probably be removed.
+func (ty Type) IsBaseObject() bool {
+	return ty.details().isBaseObject
+}
+
+// Name returns the canonical Git object type name.
+func (ty Type) Name() (string, bool) {
+	details := ty.details()
+	if details.name == "" {
+		return "", false
+	}
+
+	return details.name, true
+}
diff --git a/object/typ/type_parse.go b/object/typ/type_parse.go
new file mode 100644
index 00000000..a39a1949
--- /dev/null
+++ b/object/typ/type_parse.go
@@ -0,0 +1,8 @@
+package typ
+
+// Parse parses a canonical Git object type name.
+func Parse(name string) (Type, bool) {
+	ty, ok := typeByName[name]
+
+	return ty, ok
+}