Create printer pkg, fix color force enable/disable

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

internal/env/constants.go

@@ -0,0 +1,19 @@
+package env
+
+const (
+	// EnvFZFIgnore describes the environment variable to set to disable
+	// interactive context selection when fzf is installed.
+	EnvFZFIgnore = "KUBECTX_IGNORE_FZF"
+
+	// EnvForceColor describes the environment variable to disable color usage
+	// when printing current context in a list.
+	EnvNoColor = `NO_COLOR`
+
+	// EnvForceColor describes the "internal" environment variable to force
+	// color usage to show current context in a list.
+	EnvForceColor = `_KUBECTX_FORCE_COLOR`
+
+	// EnvDebug describes the internal environment variable for more verbose logging.
+	EnvDebug = `DEBUG`
+)
+

internal/printer/color.go

@@ -0,0 +1,20 @@
+package printer
+
+import (
+	"os"
+
+	"github.com/ahmetb/kubectx/internal/env"
+)
+
+// UseColors returns true if colors are force-enabled,
+// false if colors are disabled, or nil for default behavior
+// which is determined based on factors like if stdout is tty.
+func UseColors() *bool {
+	tr, fa := true, false
+	if os.Getenv(env.EnvForceColor) != "" {
+		return &tr
+	} else if os.Getenv(env.EnvNoColor) != "" {
+		return &fa
+	}
+	return nil
+}

internal/printer/color_test.go

@@ -0,0 +1,50 @@
+package printer
+
+import (
+	"os"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+)
+
+func withTestVar(key, value string) func() {
+	orig, ok := os.LookupEnv(key)
+	os.Setenv(key, value)
+	return func() {
+		if ok {
+			os.Setenv(key, orig)
+		} else {
+			os.Unsetenv(key)
+		}
+	}
+}
+
+var (
+	tr, fa = true, false
+)
+
+func Test_useColors_forceColors(t *testing.T) {
+	defer withTestVar("_KUBECTX_FORCE_COLOR", "1")()
+	defer withTestVar("NO_COLOR", "1")()
+
+	if v := UseColors(); !cmp.Equal(v, &tr) {
+		t.Fatalf("expected UseColors() = true; got = %v", v)
+	}
+}
+
+func Test_useColors_disableColors(t *testing.T) {
+	defer withTestVar("NO_COLOR", "1")()
+
+	if v := UseColors(); !cmp.Equal(v, &fa) {
+		t.Fatalf("expected UseColors() = false; got = %v", v)
+	}
+}
+
+func Test_useColors_default(t *testing.T) {
+	defer withTestVar("NO_COLOR", "")()
+	defer withTestVar("_KUBECTX_FORCE_COLOR", "")()
+
+	if v := UseColors(); v != nil {
+		t.Fatalf("expected UseColors() = nil; got=%v", *v)
+	}
+}

internal/printer/printer.go

@@ -0,0 +1,42 @@
+package printer
+
+import (
+	"fmt"
+	"io"
+
+	"github.com/fatih/color"
+)
+
+var (
+	errorColor   = color.New(color.FgRed, color.Bold)
+	warningColor = color.New(color.FgYellow, color.Bold)
+	successColor = color.New(color.FgGreen)
+)
+
+func init() {
+	colors := UseColors()
+	if colors == nil {
+		return
+	}
+	if *colors {
+		errorColor.EnableColor()
+		warningColor.EnableColor()
+		successColor.EnableColor()
+	} else {
+		errorColor.DisableColor()
+		warningColor.DisableColor()
+		successColor.DisableColor()
+	}
+}
+
+func Error(w io.Writer, format string, args ...interface{}) {
+	fmt.Fprintf(w, color.RedString("error: ")+format+"\n", args...)
+}
+
+func Warning(w io.Writer, format string, args ...interface{}) {
+	fmt.Fprintf(w, color.YellowString("warning: ")+format+"\n", args...)
+}
+
+func Success(w io.Writer, format string, args ...interface{}) {
+	fmt.Fprintf(w, color.GreenString(fmt.Sprintf(format+"\n", args...)))
+}