feat(cellbuf): add common sequence decoding utilities

This abstracts the decoding of Select Graphic Rendition (SGR) escape
sequences and hyperlink escape sequences from the cellbuf package. This
will allow other packages to use these utilities without having to
duplicate the code.

cellbuf/sequence.go

@@ -0,0 +1,126 @@
+package cellbuf
+
+import (
+	"bytes"
+
+	"github.com/charmbracelet/x/ansi"
+)
+
+// DecodeStyle decodes a Select Graphic Rendition (SGR) escape sequences from a
+// list of parameters.
+func DecodeStyle(params []ansi.Parameter, pen *Style) {
+	if len(params) == 0 {
+		pen.Reset()
+		return
+	}
+
+	for i := 0; i < len(params); i++ {
+		r := params[i]
+		param, hasMore := r.Param(0), r.HasMore() // Are there more subparameters i.e. separated by ":"?
+		switch param {
+		case 0: // Reset
+			pen.Reset()
+		case 1: // Bold
+			pen.Bold(true)
+		case 2: // Dim/Faint
+			pen.Faint(true)
+		case 3: // Italic
+			pen.Italic(true)
+		case 4: // Underline
+			if hasMore { // Only accept subparameters i.e. separated by ":"
+				nextParam := params[i+1].Param(0)
+				switch nextParam {
+				case 0, 1, 2, 3, 4, 5:
+					i++
+					switch nextParam {
+					case 0: // No Underline
+						pen.UnderlineStyle(NoUnderline)
+					case 1: // Single Underline
+						pen.UnderlineStyle(SingleUnderline)
+					case 2: // Double Underline
+						pen.UnderlineStyle(DoubleUnderline)
+					case 3: // Curly Underline
+						pen.UnderlineStyle(CurlyUnderline)
+					case 4: // Dotted Underline
+						pen.UnderlineStyle(DottedUnderline)
+					case 5: // Dashed Underline
+						pen.UnderlineStyle(DashedUnderline)
+					}
+				}
+			} else {
+				// Single Underline
+				pen.Underline(true)
+			}
+		case 5: // Slow Blink
+			pen.SlowBlink(true)
+		case 6: // Rapid Blink
+			pen.RapidBlink(true)
+		case 7: // Reverse
+			pen.Reverse(true)
+		case 8: // Conceal
+			pen.Conceal(true)
+		case 9: // Crossed-out/Strikethrough
+			pen.Strikethrough(true)
+		case 22: // Normal Intensity (not bold or faint)
+			pen.Bold(false).Faint(false)
+		case 23: // Not italic, not Fraktur
+			pen.Italic(false)
+		case 24: // Not underlined
+			pen.Underline(false)
+		case 25: // Blink off
+			pen.SlowBlink(false).RapidBlink(false)
+		case 27: // Positive (not reverse)
+			pen.Reverse(false)
+		case 28: // Reveal
+			pen.Conceal(false)
+		case 29: // Not crossed out
+			pen.Strikethrough(false)
+		case 30, 31, 32, 33, 34, 35, 36, 37: // Set foreground
+			pen.Foreground(ansi.Black + ansi.BasicColor(param-30)) //nolint:gosec
+		case 38: // Set foreground 256 or truecolor
+			n, c := ansi.DecodeColor(params[i:])
+			if n > 0 {
+				pen.Foreground(c)
+				i += n - 1
+			}
+		case 39: // Default foreground
+			pen.Foreground(nil)
+		case 40, 41, 42, 43, 44, 45, 46, 47: // Set background
+			pen.Background(ansi.Black + ansi.BasicColor(param-40)) //nolint:gosec
+		case 48: // Set background 256 or truecolor
+			n, c := ansi.DecodeColor(params[i:])
+			if n > 0 {
+				pen.Background(c)
+				i += n - 1
+			}
+		case 49: // Default Background
+			pen.Background(nil)
+		case 58: // Set underline color
+			n, c := ansi.DecodeColor(params[i:])
+			if n > 0 {
+				pen.UnderlineColor(c)
+				i += n - 1
+			}
+		case 59: // Default underline color
+			pen.UnderlineColor(nil)
+		case 90, 91, 92, 93, 94, 95, 96, 97: // Set bright foreground
+			pen.Foreground(ansi.BrightBlack + ansi.BasicColor(param-90)) //nolint:gosec
+		case 100, 101, 102, 103, 104, 105, 106, 107: // Set bright background
+			pen.Background(ansi.BrightBlack + ansi.BasicColor(param-100)) //nolint:gosec
+		}
+	}
+}
+
+// DecodeLine decodes a hyperlink escape sequence from a data buffer.
+func DecodeLink(p []byte, link *Link) {
+	params := bytes.Split(p, []byte{';'})
+	if len(params) != 3 {
+		return
+	}
+	for _, param := range bytes.Split(params[1], []byte{':'}) {
+		if bytes.HasPrefix(param, []byte("id=")) {
+			link.URLID = string(param)
+		}
+	}
+	link.URL = string(params[2])
+}