Support formatting in rainbows

Fixes #119

1 files changed, 109 insertions, 0 deletions

diff --git a/ui/rainbow.go b/ui/rainbow.go
new file mode 100644
index 0000000..fca3cba
--- /dev/null
+++ b/ui/rainbow.go
@@ -0,0 +1,109 @@
+// gomuks - A terminal Matrix client written in Go.
+// Copyright (C) 2020 Tulir Asokan
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+package ui
+
+import (
+	"bytes"
+	"fmt"
+	"html"
+	"io"
+	"math/rand"
+	"unicode"
+
+	"github.com/rivo/uniseg"
+	"github.com/russross/blackfriday/v2"
+)
+
+type RainbowRenderer struct {
+	*blackfriday.HTMLRenderer
+	sr *blackfriday.SPRenderer
+
+	ColorID string
+}
+
+func Rand(n int) (str string) {
+	b := make([]byte, n)
+	rand.Read(b)
+	str = fmt.Sprintf("%x", b)
+	return
+}
+
+func NewRainbowRenderer(html *blackfriday.HTMLRenderer) *RainbowRenderer {
+	return &RainbowRenderer{
+		HTMLRenderer: html,
+		sr:           blackfriday.NewSmartypantsRenderer(html.Flags),
+		ColorID:      Rand(16),
+	}
+}
+
+func (r *RainbowRenderer) RenderNode(w io.Writer, node *blackfriday.Node, entering bool) blackfriday.WalkStatus {
+	if node.Type == blackfriday.Text {
+		var buf bytes.Buffer
+		if r.Flags&blackfriday.Smartypants != 0 {
+			var tmp bytes.Buffer
+			escapeHTML(&tmp, node.Literal)
+			r.sr.Process(&buf, tmp.Bytes())
+		} else {
+			if node.Parent.Type == blackfriday.Link {
+				escLink(&buf, node.Literal)
+			} else {
+				escapeHTML(&buf, node.Literal)
+			}
+		}
+		graphemes := uniseg.NewGraphemes(buf.String())
+		buf.Reset()
+		for graphemes.Next() {
+			runes := graphemes.Runes()
+			if len(runes) == 1 && unicode.IsSpace(runes[0]) {
+				buf.WriteRune(runes[0])
+			}
+			_, _ = fmt.Fprintf(&buf, "<font color=\"%s\">%s</font>", r.ColorID, graphemes.Str())
+		}
+		_, _ = w.Write(buf.Bytes())
+		return blackfriday.GoToNext
+	}
+	return r.HTMLRenderer.RenderNode(w, node, entering)
+}
+
+// This stuff is copied directly from blackfriday
+var htmlEscaper = [256][]byte{
+	'&': []byte("&amp;"),
+	'<': []byte("&lt;"),
+	'>': []byte("&gt;"),
+	'"': []byte("&quot;"),
+}
+
+func escapeHTML(w io.Writer, s []byte) {
+	var start, end int
+	for end < len(s) {
+		escSeq := htmlEscaper[s[end]]
+		if escSeq != nil {
+			w.Write(s[start:end])
+			w.Write(escSeq)
+			start = end + 1
+		}
+		end++
+	}
+	if start < len(s) && end <= len(s) {
+		w.Write(s[start:end])
+	}
+}
+
+func escLink(w io.Writer, text []byte) {
+	unesc := html.UnescapeString(string(text))
+	escapeHTML(w, []byte(unesc))
+}