Add initial Matrix->Discord HTML conversion

formatter.go

@@ -0,0 +1,63 @@
+package main
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+
+	"github.com/yuin/goldmark"
+
+	"maunium.net/go/mautrix/event"
+	"maunium.net/go/mautrix/format"
+	"maunium.net/go/mautrix/format/mdext"
+)
+
+var mdRenderer = goldmark.New(format.Extensions, format.HTMLOptions,
+	goldmark.WithExtensions(mdext.EscapeHTML, mdext.SimpleSpoiler, mdext.DiscordUnderline))
+var escapeFixer = regexp.MustCompile(`\\(__[^_]|\*\*[^*])`)
+
+func renderDiscordMarkdown(text string) event.MessageEventContent {
+	text = escapeFixer.ReplaceAllStringFunc(text, func(s string) string {
+		return s[:2] + `\` + s[2:]
+	})
+	return format.RenderMarkdownCustom(text, mdRenderer)
+}
+
+var matrixHTMLParser = &format.HTMLParser{
+	PillConverter:  nil,
+	TabsToSpaces:   4,
+	Newline:        "\n",
+	HorizontalLine: "\n---\n",
+	ItalicConverter: func(s string, context format.Context) string {
+		return fmt.Sprintf("*%s*", s)
+	},
+	UnderlineConverter: func(s string, context format.Context) string {
+		return fmt.Sprintf("__%s__", s)
+	},
+	TextConverter: func(s string, context format.Context) string {
+		return discordMarkdownEscaper.Replace(s)
+	},
+	SpoilerConverter: func(text, reason string, ctx format.Context) string {
+		if reason != "" {
+			return fmt.Sprintf("(%s) ||%s||", reason, text)
+		}
+		return fmt.Sprintf("||%s||", text)
+	},
+}
+
+var discordMarkdownEscaper = strings.NewReplacer(
+	`\`, `\\`,
+	`_`, `\_`,
+	`*`, `\*`,
+	`~`, `\~`,
+	"`", "\\`",
+	`|`, `\|`,
+)
+
+func parseMatrixHTML(content *event.MessageEventContent) string {
+	if content.Format == event.FormatHTML && len(content.FormattedBody) > 0 {
+		return matrixHTMLParser.Parse(content.FormattedBody, make(format.Context))
+	} else {
+		return discordMarkdownEscaper.Replace(content.Body)
+	}
+}