feat: verify git repository before running git diff

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"
+}

util/util_test.go

@@ -2,6 +2,8 @@ package util
 
 import (
 	"os"
+	"os/exec"
+	"path/filepath"
 	"reflect"
 	"testing"
 )
@@ -82,3 +84,100 @@ func TestConvertToMap(t *testing.T) {
 		})
 	}
 }
+
+func TestIsGitRepo(t *testing.T) {
+	type fields struct {
+		setup func(t *testing.T)
+		want  bool
+	}
+
+	testCases := []struct {
+		name   string
+		fields fields
+	}{
+		{
+			name: "inside git repo root",
+			fields: fields{
+				want: true,
+				setup: func(t *testing.T) {
+					t.Helper()
+
+					tmpDir := t.TempDir()
+
+					cmd := exec.Command("git", "init")
+					cmd.Dir = tmpDir
+					if output, err := cmd.CombinedOutput(); err != nil {
+						t.Fatalf("failed to init git repo: %v, output: %s", err, string(output))
+					}
+
+					if err := os.Chdir(tmpDir); err != nil {
+						t.Fatalf("failed to chdir to repo root: %v", err)
+					}
+				},
+			},
+		},
+		{
+			name: "inside git repo subdir",
+			fields: fields{
+				want: true,
+				setup: func(t *testing.T) {
+					t.Helper()
+
+					tmpDir := t.TempDir()
+
+					cmd := exec.Command("git", "init")
+					cmd.Dir = tmpDir
+					if output, err := cmd.CombinedOutput(); err != nil {
+						t.Fatalf("failed to init git repo: %v, output: %s", err, string(output))
+					}
+
+					subDir := filepath.Join(tmpDir, "subdir", "nested")
+					if err := os.MkdirAll(subDir, 0o755); err != nil {
+						t.Fatalf("failed to create subdir: %v", err)
+					}
+
+					if err := os.Chdir(subDir); err != nil {
+						t.Fatalf("failed to chdir to subdir: %v", err)
+					}
+				},
+			},
+		},
+		{
+			name: "outside git repo",
+			fields: fields{
+				want: false,
+				setup: func(t *testing.T) {
+					t.Helper()
+
+					tmpDir := t.TempDir()
+
+					if err := os.Chdir(tmpDir); err != nil {
+						t.Fatalf("failed to chdir to temp dir: %v", err)
+					}
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			origWD, err := os.Getwd()
+			if err != nil {
+				t.Fatalf("failed to get current working directory: %v", err)
+			}
+			t.Cleanup(func() {
+				_ = os.Chdir(origWD)
+			})
+
+			if tc.fields.setup != nil {
+				tc.fields.setup(t)
+			}
+
+			got := IsGitRepo()
+			if got != tc.fields.want {
+				t.Errorf("IsGitRepo() = %v; want %v", got, tc.fields.want)
+			}
+		})
+	}
+}