fix!: output race condition

`ColorProfile` reads the terminal environment every time the function is
called. This is inefficient. We only need to read the `$TERM`
environment variable once when we initialize the output. So instead, we cache
the value we read.

Rename `ColorProfile` to `termColorProfile` and rely on
`EnvColorProfile` to detect the profile. Ideally, we would rely on the
terminal Terminfo to detect the profile and fallback to the environment.
But that's for another day :)

Make output profile accessible through `ColorProfile`.
Use `SetColorProfile` to change the output color profile.
Use a mutex to guard output writes.
Use pointer receiver since we have a lock in the struct

Fixes: charmbracelet/lipgloss#210
Fixes: #145

copy.go

@@ -7,7 +7,7 @@ import (
 )
 
 // Copy copies text to clipboard using OSC 52 escape sequence.
-func (o Output) Copy(str string) {
+func (o *Output) Copy(str string) {
 	s := osc52.New(str)
 	if strings.HasPrefix(o.environ.Getenv("TERM"), "screen") {
 		s = s.Screen()
@@ -17,7 +17,7 @@ func (o Output) Copy(str string) {
 
 // CopyPrimary copies text to primary clipboard (X11) using OSC 52 escape
 // sequence.
-func (o Output) CopyPrimary(str string) {
+func (o *Output) CopyPrimary(str string) {
 	s := osc52.New(str).Primary()
 	if strings.HasPrefix(o.environ.Getenv("TERM"), "screen") {
 		s = s.Screen()

output.go

@@ -22,7 +22,7 @@ type OutputOption = func(*Output)
 
 // Output is a terminal output.
 type Output struct {
-	Profile
+	profile Profile
 	tty     io.Writer
 	environ Environ
 
@@ -33,6 +33,8 @@ type Output struct {
 	fgColor   Color
 	bgSync    *sync.Once
 	bgColor   Color
+
+	mtx sync.RWMutex
 }
 
 // Environ is an interface for getting environment variables.
@@ -66,7 +68,7 @@ func NewOutput(tty io.Writer, opts ...OutputOption) *Output {
 	o := &Output{
 		tty:     tty,
 		environ: &osEnviron{},
-		Profile: -1,
+		profile: -1,
 		fgSync:  &sync.Once{},
 		fgColor: NoColor{},
 		bgSync:  &sync.Once{},
@@ -79,8 +81,8 @@ func NewOutput(tty io.Writer, opts ...OutputOption) *Output {
 	for _, opt := range opts {
 		opt(o)
 	}
-	if o.Profile < 0 {
-		o.Profile = o.EnvColorProfile()
+	if o.profile < 0 {
+		o.profile = o.EnvColorProfile()
 	}
 
 	return o
@@ -96,7 +98,7 @@ func WithEnvironment(environ Environ) OutputOption {
 // WithProfile returns a new OutputOption for the given profile.
 func WithProfile(profile Profile) OutputOption {
 	return func(o *Output) {
-		o.Profile = profile
+		o.profile = profile
 	}
 }
 
@@ -133,14 +135,31 @@ func WithUnsafe() OutputOption {
 	}
 }
 
+// ColorProfile returns the color profile.
+// Ascii, ANSI, ANSI256, or TrueColor.
+func (o *Output) ColorProfile() Profile {
+	o.mtx.RLock()
+	defer o.mtx.RUnlock()
+	return o.profile
+}
+
+// SetColorProfile sets the color profile.
+func (o *Output) SetColorProfile(profile Profile) {
+	o.mtx.Lock()
+	defer o.mtx.Unlock()
+	o.profile = profile
+}
+
 // ForegroundColor returns the terminal's default foreground color.
 func (o *Output) ForegroundColor() Color {
 	f := func() {
 		if !o.isTTY() {
 			return
 		}
 
+		o.mtx.Lock()
 		o.fgColor = o.foregroundColor()
+		o.mtx.Unlock()
 	}
 
 	if o.cache {
@@ -159,7 +178,9 @@ func (o *Output) BackgroundColor() Color {
 			return
 		}
 
+		o.mtx.Lock()
 		o.bgColor = o.backgroundColor()
+		o.mtx.Unlock()
 	}
 
 	if o.cache {
@@ -180,18 +201,18 @@ func (o *Output) HasDarkBackground() bool {
 
 // TTY returns the terminal's file descriptor. This may be nil if the output is
 // not a terminal.
-func (o Output) TTY() File {
+func (o *Output) TTY() File {
 	if f, ok := o.tty.(File); ok {
 		return f
 	}
 	return nil
 }
 
-func (o Output) Write(p []byte) (int, error) {
+func (o *Output) Write(p []byte) (int, error) {
 	return o.tty.Write(p)
 }
 
 // WriteString writes the given string to the output.
-func (o Output) WriteString(s string) (int, error) {
+func (o *Output) WriteString(s string) (int, error) {
 	return o.Write([]byte(s))
 }

output_test.go

@@ -0,0 +1,22 @@
+package termenv
+
+import (
+	"io"
+	"testing"
+)
+
+func TestOutputRace(t *testing.T) {
+	o := NewOutput(io.Discard)
+	for i := 0; i < 100; i++ {
+		t.Run("Test race", func(t *testing.T) {
+			t.Parallel()
+			o.Write([]byte("test"))
+			o.SetColorProfile(ANSI)
+			o.ColorProfile()
+			o.HasDarkBackground()
+			o.TTY()
+			o.ForegroundColor()
+			o.BackgroundColor()
+		})
+	}
+}