Add a less compatibility mode

Related to #53 and #55.

With this implementation we don't restore the screen on exit, but less
does. Figure out why and make -compat work even more like less.

m/pager.go

@@ -12,8 +12,6 @@ import (
 	"github.com/walles/moar/twin"
 )
 
-// FIXME: Profile the pager while searching through a large file
-
 type _PagerMode int
 
 const (

moar.go

@@ -134,6 +134,7 @@ func main() {
 		printUsage(os.Stdout, flagSet, false)
 	}
 	printVersion := flagSet.Bool("version", false, "Prints the moar version number")
+	compat := flagSet.Bool("compat", false, "Compatibility mode, no mouse support and no alternate screen")
 	debug := flagSet.Bool("debug", false, "Print debug logs after exiting")
 	trace := flagSet.Bool("trace", false, "Print trace logs after exiting")
 	styleOption := flagSet.String("style", "native",
@@ -235,7 +236,7 @@ func main() {
 	if stdinIsRedirected {
 		// Display input pipe contents
 		reader := m.NewReaderFromStream("", os.Stdin)
-		startPaging(reader)
+		startPaging(reader, *compat)
 		return
 	}
 
@@ -245,13 +246,19 @@ func main() {
 		fmt.Fprintf(os.Stderr, "ERROR: %v\n", err)
 		os.Exit(1)
 	}
-	startPaging(reader)
+	startPaging(reader, *compat)
 }
 
-func startPaging(reader *m.Reader) {
-	screen, e := twin.NewScreen()
-	if e != nil {
-		panic(e)
+func startPaging(reader *m.Reader, compat bool) {
+	var screen twin.Screen
+	var err error
+	if compat {
+		screen, err = twin.NewScreenCompat()
+	} else {
+		screen, err = twin.NewScreen()
+	}
+	if err != nil {
+		panic(err)
 	}
 
 	var loglines strings.Builder

twin/screen.go

@@ -59,6 +59,9 @@ type UnixScreen struct {
 
 	ttyOut        *os.File
 	oldTtyOutMode uint32 //lint:ignore U1000 Windows only
+
+	// See docs for NewScreenCompat()
+	compat bool
 }
 
 // Cell is a rune with a style to be written to a cell on screen
@@ -89,11 +92,27 @@ var MOUSE_EVENT_REGEX = regexp.MustCompile("^\x1b\\[<([0-9]+);([0-9]+);([0-9]+)M
 // NewScreen() requires Close() to be called after you are done with your new
 // screen, most likely somewhere in your shutdown code.
 func NewScreen() (Screen, error) {
+	return newScreenInternal(false)
+}
+
+// A compat screen works like less traditionally has, not using an alternate
+// screen and not having any mouse support.
+//
+// Upside is that marking with your mouse and copying works without holding any
+// modifiers, more info at https://github.com/walles/moar/issues/53.
+//
+// Kindly Close() the returned screen when done with it.
+func NewScreenCompat() (Screen, error) {
+	return newScreenInternal(true)
+}
+
+func newScreenInternal(compat bool) (Screen, error) {
 	if !term.IsTerminal(int(os.Stdout.Fd())) {
 		return nil, fmt.Errorf("stdout (fd=%d) must be a terminal for paging to work", os.Stdout.Fd())
 	}
 
 	screen := UnixScreen{}
+	screen.compat = compat
 
 	// The number "80" here is from manual testing on my MacBook:
 	//
@@ -111,8 +130,10 @@ func NewScreen() (Screen, error) {
 	if err != nil {
 		return nil, err
 	}
-	screen.setAlternateScreenMode(true)
-	screen.enableMouseTracking(true)
+	if !screen.compat {
+		screen.setAlternateScreenMode(true)
+		screen.enableMouseTracking(true)
+	}
 	screen.hideCursor(true)
 
 	go screen.mainLoop()
@@ -124,8 +145,10 @@ func NewScreen() (Screen, error) {
 // with the screen returned by NewScreen()
 func (screen *UnixScreen) Close() {
 	screen.hideCursor(false)
-	screen.enableMouseTracking(false)
-	screen.setAlternateScreenMode(false)
+	if !screen.compat {
+		screen.enableMouseTracking(false)
+		screen.setAlternateScreenMode(false)
+	}
 
 	err := screen.restoreTtyInTtyOut()
 	if err != nil {