lncfg: move ParseHexColor to lncfg

lncfg/color.go

@@ -0,0 +1,34 @@
+package lncfg
+
+import (
+	"encoding/hex"
+	"errors"
+	"image/color"
+	"regexp"
+)
+
+var (
+	// validColorRegexp is a regexp that lets you check if a particular
+	// color string matches the standard hex color format #RRGGBB.
+	validColorRegexp = regexp.MustCompile("^#[A-Fa-f0-9]{6}$")
+)
+
+// ParseHexColor takes a hex string representation of a color in the
+// form "#RRGGBB", parses the hex color values, and returns a color.RGBA
+// struct of the same color.
+func ParseHexColor(colorStr string) (color.RGBA, error) {
+	// Check if the hex color string is a valid color representation.
+	if !validColorRegexp.MatchString(colorStr) {
+		return color.RGBA{}, errors.New("color must be specified " +
+			"using a hexadecimal value in the form #RRGGBB")
+	}
+
+	// Decode the hex color string to bytes.
+	// The resulting byte array is in the form [R, G, B].
+	colorBytes, err := hex.DecodeString(colorStr[1:])
+	if err != nil {
+		return color.RGBA{}, err
+	}
+
+	return color.RGBA{R: colorBytes[0], G: colorBytes[1], B: colorBytes[2]}, nil
+}