Introduce bunt color setting parsing

So far this had to be done by the respective program that used `bunt`.

Introduce simple parse function to parse color and true color settings.

bunt.go

@@ -21,6 +21,9 @@
 package bunt
 
 import (
+	"fmt"
+	"strings"
+
 	"github.com/gonvenience/term"
 )
 
@@ -50,6 +53,23 @@ const (
 	ON   = SwitchState(+1)
 )
 
+// ParseSetting parses an input string to match for a supported setting
+func ParseSetting(setting string) (SwitchState, error) {
+	switch strings.ToLower(setting) {
+	case "auto":
+		return AUTO, nil
+
+	case "off", "no", "false":
+		return OFF, nil
+
+	case "on", "yes", "true":
+		return ON, nil
+
+	default:
+		return OFF, fmt.Errorf("invalid state '%s' used, supported modes are: auto, on, or off", setting)
+	}
+}
+
 // UseColors return whether colors are used or not based on the configured color
 // setting or terminal capabilities
 func UseColors() bool {

bunt_test.go

@@ -0,0 +1,56 @@
+// Copyright © 2020 The Homeport Team
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+
+package bunt_test
+
+import (
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+
+	. "github.com/gonvenience/bunt"
+)
+
+var _ = Describe("settings tests", func() {
+	Context("parse color settings", func() {
+		It("should parse auto as setting auto", func() {
+			setting, err := ParseSetting("auto")
+			Expect(err).ToNot(HaveOccurred())
+			Expect(setting).To(Equal(AUTO))
+		})
+
+		It("should parse off as setting off", func() {
+			setting, err := ParseSetting("off")
+			Expect(err).ToNot(HaveOccurred())
+			Expect(setting).To(Equal(OFF))
+		})
+
+		It("should parse on as setting on", func() {
+			setting, err := ParseSetting("on")
+			Expect(err).ToNot(HaveOccurred())
+			Expect(setting).To(Equal(ON))
+		})
+
+		It("should fail to parse unknown setting", func() {
+			_, err := ParseSetting("foo")
+			Expect(err).To(HaveOccurred())
+			Expect(err.Error()).To(BeEquivalentTo("invalid state 'foo' used, supported modes are: auto, on, or off"))
+		})
+	})
+})