feat: verify git repository before running git diff

Author: VarusHsu

cmd/hepler.go

@@ -17,6 +17,11 @@ func check() error {
 		return errors.New("git command not found in your system's PATH. Please install Git and try again")
 	}
 
+	// Check if current working directory is inside a Git repository.
+	if !util.IsGitRepo() {
+		return errors.New("not a git repository")
+	}
+
 	// Apply configuration values from CLI flags to Viper
 	if diffUnified != 3 {
 		viper.Set("git.diff_unified", diffUnified)

util/util.go

@@ -1,6 +1,7 @@
 package util
 
 import (
+	"bytes"
 	"os/exec"
 	"strings"
 )
@@ -35,3 +36,16 @@ func ConvertToMap(args []string) Data {
 	}
 	return m
 }
+
+// IsGitRepo returns true if the current working directory is inside a Git work tree.
+func IsGitRepo() bool {
+	cmd := exec.Command("git", "rev-parse", "--is-inside-work-tree")
+
+	var out bytes.Buffer
+	cmd.Stdout = &out
+	if err := cmd.Run(); err != nil {
+		return false
+	}
+
+	return strings.TrimSpace(out.String()) == "true"
+}