add switch branch (#102)

cmd/switch.go

@@ -5,6 +5,7 @@ package cmd
 
 import (
 	"errors"
+	"fmt"
 
 	"github.com/spf13/cobra"
 )
@@ -35,6 +36,13 @@ var switchCmd = &cobra.Command{
 			return errors.New("invalid create option format")
 		}
 
+		// switch branch == update HEAD
+		if len(args) == 1 {
+			if err := client.Head.Update(client.Refs, client.RootGoitPath, args[0]); err != nil {
+				return fmt.Errorf("fail to update HEAD: %w", err)
+			}
+		}
+
 		return nil
 	},
 }

internal/store/head.go

@@ -85,7 +85,13 @@ func newHead() *Head {
 	return &Head{}
 }
 
-func (h *Head) Update(rootGoitPath, newRef string) error {
+func (h *Head) Update(refs *Refs, rootGoitPath, newRef string) error {
+	// check if branch exists
+	n := refs.getBranchPos(newRef)
+	if n == NewBranchFlag {
+		return fmt.Errorf("branch %s does not exist", newRef)
+	}
+
 	headPath := filepath.Join(rootGoitPath, "HEAD")
 	if _, err := os.Stat(headPath); os.IsNotExist(err) {
 		return errors.New("fail to find HEAD, cannot update")

internal/store/refs.go

@@ -134,7 +134,7 @@ func (r *Refs) RenameBranch(head *Head, rootGoitPath, newBranchName string) erro
 	}
 
 	// update HEAD
-	if err := head.Update(rootGoitPath, newBranchName); err != nil {
+	if err := head.Update(r, rootGoitPath, newBranchName); err != nil {
 		return fmt.Errorf("fail to update HEAD: %w", err)
 	}