Improve TTY detection

Prior to this commit there was no TTY detection in the manager or tput
package. The result was that during non-interactive executions escape
sequences would also be written to the output stream. Additionally each
frame would also be written.

For example, running the following would result in a messy log file:

```
go run examples/advanced/main.go |& tee log.log
```

This introduces changes that do the following:

* If a TTY is not detected, do not render any spinner frames
* If a TTY is not detected, do not write escape sequences

It is also possible to override the above by setting the environment
variable `YSMRR_FORCE_TTY` to `true`. This will make ysmrr ignore tty
detection and render frames and write escape sequences.

An example of the above override can be seen in the `tput_test.go` file.

go.mod

@@ -5,12 +5,12 @@ go 1.18
 require (
 	github.com/fatih/color v1.13.0
 	github.com/mattn/go-colorable v0.1.12
+	github.com/mattn/go-isatty v0.0.14
 	github.com/stretchr/testify v1.8.0
 )
 
 require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
-	github.com/mattn/go-isatty v0.0.14 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	golang.org/x/sys v0.0.0-20210927094055-39ccf1dd6fa6 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect

manager.go

@@ -13,6 +13,7 @@ import (
 	"github.com/chelnak/ysmrr/pkg/colors"
 	"github.com/chelnak/ysmrr/pkg/tput"
 	"github.com/mattn/go-colorable"
+	"github.com/mattn/go-isatty"
 )
 
 // SpinnerManager manages spinners
@@ -42,6 +43,7 @@ type spinnerManager struct {
 	done          chan bool
 	ticks         *time.Ticker
 	frame         int
+	tty           bool
 }
 
 // AddSpinner adds a new spinner to the manager.
@@ -156,7 +158,10 @@ func (sm *spinnerManager) render() {
 		case <-sm.done:
 			return
 		case <-sm.ticks.C:
-			sm.renderFrame()
+			// Only render the frame if we are in a terminal.
+			if sm.tty {
+				sm.renderFrame()
+			}
 		}
 
 		tput.Rc(sm.writer)
@@ -208,6 +213,7 @@ func NewSpinnerManager(options ...managerOption) SpinnerManager {
 		messageColor:  colors.NoColor,
 		writer:        getWriter(),
 		done:          make(chan bool),
+		tty:           tty(),
 	}
 
 	for _, option := range options {
@@ -217,6 +223,10 @@ func NewSpinnerManager(options ...managerOption) SpinnerManager {
 	return sm
 }
 
+func tty() bool {
+	return isatty.IsTerminal(os.Stdout.Fd()) || os.Getenv("YSMRR_FORCE_TTY") == "true"
+}
+
 func getWriter() io.Writer {
 	// Windows support conveniently provided by github.com/mattn/go-colorable <3.
 	if runtime.GOOS == "windows" {

pkg/tput/tput.go

@@ -5,36 +5,55 @@ package tput
 import (
 	"fmt"
 	"io"
+	"os"
 	"strings"
+
+	"github.com/mattn/go-isatty"
 )
 
 // Sc saves the current position of the cursor.
 func Sc(w io.Writer) {
-	fmt.Fprint(w, "\u001b7")
+	write(w, "\u001b7")
 }
 
 // Rc restores the cursor to the saved position.
 func Rc(w io.Writer) {
-	fmt.Fprint(w, "\u001b8")
+	write(w, "\u001b8")
 }
 
 // Civis hides the cursor.
 func Civis(w io.Writer) {
-	fmt.Fprint(w, "\u001b[?25l")
+	write(w, "\u001b[?25l")
 }
 
 // Cnorm shows the cursor.
 func Cnorm(w io.Writer) {
-	fmt.Fprintf(w, "\u001b[?25h")
+	writef(w, "\u001b[?25h")
 }
 
 // Cuu moves the cursor up by n lines.
 func Cuu(w io.Writer, n int) {
-	fmt.Fprintf(w, "\u001b[%dA", n)
+	writef(w, "\u001b[%dA", n)
 }
 
 // BufScreen ensures that there are enough lines available
 // by sending n * newlines to the writer.
 func BufScreen(w io.Writer, n int) {
-	fmt.Fprintf(w, "%s", strings.Repeat("\n", n))
+	writef(w, "%s", strings.Repeat("\n", n))
+}
+
+func tty() bool {
+	return isatty.IsTerminal(os.Stdout.Fd()) || os.Getenv("YSMRR_FORCE_TTY") == "true"
+}
+
+func write(w io.Writer, s string) {
+	if tty() {
+		fmt.Fprint(w, s)
+	}
+}
+
+func writef(w io.Writer, format string, a ...interface{}) {
+	if tty() {
+		fmt.Fprintf(w, format, a...)
+	}
 }

pkg/tput/tput_test.go

@@ -3,14 +3,26 @@ package tput_test
 import (
 	"bytes"
 	"io"
+	"os"
 	"strings"
 	"testing"
 
 	"github.com/chelnak/ysmrr/pkg/tput"
 	"github.com/stretchr/testify/assert"
 )
 
+func setup() {
+	_ = os.Setenv("YSMRR_FORCE_TTY", "true")
+}
+
+func cleanup() {
+	_ = os.Unsetenv("YSMRR_FORCE_TTY")
+}
+
 func TestTput(t *testing.T) {
+	setup()
+	defer cleanup()
+
 	tests := []struct {
 		name string
 		fn   func(w io.Writer)
@@ -48,6 +60,9 @@ func TestTput(t *testing.T) {
 }
 
 func TestTputCommandsWithInputs(t *testing.T) {
+	setup()
+	defer cleanup()
+
 	tests := []struct {
 		name  string
 		input int