feat(ansi): export XParseColor function

ansi/go.mod

@@ -2,4 +2,7 @@ module github.com/charmbracelet/x/ansi
 
 go 1.18
 
-require github.com/rivo/uniseg v0.4.7
+require (
+	github.com/lucasb-eyer/go-colorful v1.2.0
+	github.com/rivo/uniseg v0.4.7
+)

ansi/go.sum

@@ -1,2 +1,4 @@
+github.com/lucasb-eyer/go-colorful v1.2.0 h1:1nnpGOrhyZZuNyfu1QjKiUICQ74+3FNCN69Aj6K7nkY=
+github.com/lucasb-eyer/go-colorful v1.2.0/go.mod h1:R4dSotOR9KMtayYi1e77YzuveK+i7ruzyGqttikkLy0=
 github.com/rivo/uniseg v0.4.7 h1:WUdvkW8uEhrYfLC4ZzdpI2ztxP1I582+49Oc5Mq64VQ=
 github.com/rivo/uniseg v0.4.7/go.mod h1:FN3SvrM+Zdj16jyLfmOkMNblXMcoc8DfTHruCPUcx88=

ansi/style.go

@@ -487,10 +487,3 @@ func underlineColorString(c Color) string {
 	}
 	return defaultUnderlineColorAttr
 }
-
-func shift(v uint32) uint32 {
-	if v > 0xff {
-		return v >> 8
-	}
-	return v
-}

ansi/util.go

@@ -3,6 +3,10 @@ package ansi
 import (
 	"fmt"
 	"image/color"
+	"strconv"
+	"strings"
+
+	"github.com/lucasb-eyer/go-colorful"
 )
 
 // colorToHexString returns a hex string representation of a color.
@@ -27,3 +31,62 @@ func colorToHexString(c color.Color) string {
 func rgbToHex(r, g, b uint32) uint32 {
 	return r<<16 + g<<8 + b
 }
+
+type shiftable interface {
+	~uint | ~uint16 | ~uint32 | ~uint64
+}
+
+func shift[T shiftable](x T) T {
+	if x > 0xff {
+		x >>= 8
+	}
+	return x
+}
+
+// XParseColor is a helper function that parses a string into a color.Color. It
+// provides a similar interface to the XParseColor function in Xlib. It
+// supports the following formats:
+//
+//   - #RGB
+//   - #RRGGBB
+//   - rgb:RRRR/GGGG/BBBB
+//   - rgba:RRRR/GGGG/BBBB/AAAA
+//
+// If the string is not a valid color, nil is returned.
+//
+// See: https://linux.die.net/man/3/xparsecolor
+func XParseColor(s string) color.Color {
+	switch {
+	case strings.HasPrefix(s, "#"):
+		c, err := colorful.Hex(s)
+		if err != nil {
+			return nil
+		}
+
+		return c
+	case strings.HasPrefix(s, "rgb:"):
+		parts := strings.Split(s[4:], "/")
+		if len(parts) != 3 {
+			return nil
+		}
+
+		r, _ := strconv.ParseUint(parts[0], 16, 32)
+		g, _ := strconv.ParseUint(parts[1], 16, 32)
+		b, _ := strconv.ParseUint(parts[2], 16, 32)
+
+		return color.RGBA{uint8(shift(r)), uint8(shift(g)), uint8(shift(b)), 255} //nolint:gosec
+	case strings.HasPrefix(s, "rgba:"):
+		parts := strings.Split(s[5:], "/")
+		if len(parts) != 4 {
+			return nil
+		}
+
+		r, _ := strconv.ParseUint(parts[0], 16, 32)
+		g, _ := strconv.ParseUint(parts[1], 16, 32)
+		b, _ := strconv.ParseUint(parts[2], 16, 32)
+		a, _ := strconv.ParseUint(parts[3], 16, 32)
+
+		return color.RGBA{uint8(shift(r)), uint8(shift(g)), uint8(shift(b)), uint8(shift(a))} //nolint:gosec
+	}
+	return nil
+}