1 files changed, 99 insertions, 0 deletions
diff --git a/modules/markup/markdown/math/inline_parser.go b/modules/markup/markdown/math/inline_parser.go
new file mode 100644
index 0000000000..0339674b6c
--- /dev/null
+++ b/modules/markup/markdown/math/inline_parser.go
@@ -0,0 +1,99 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package math
+
+import (
+	"bytes"
+
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+)
+
+type inlineParser struct {
+	start []byte
+	end   []byte
+}
+
+var defaultInlineDollarParser = &inlineParser{
+	start: []byte{'$'},
+	end:   []byte{'$'},
+}
+
+// NewInlineDollarParser returns a new inline parser
+func NewInlineDollarParser() parser.InlineParser {
+	return defaultInlineDollarParser
+}
+
+var defaultInlineBracketParser = &inlineParser{
+	start: []byte{'\\', '('},
+	end:   []byte{'\\', ')'},
+}
+
+// NewInlineDollarParser returns a new inline parser
+func NewInlineBracketParser() parser.InlineParser {
+	return defaultInlineBracketParser
+}
+
+// Trigger triggers this parser on $
+func (parser *inlineParser) Trigger() []byte {
+	return parser.start[0:1]
+}
+
+func isAlphanumeric(b byte) bool {
+	// Github only cares about 0-9A-Za-z
+	return (b >= '0' && b <= '9') || (b >= 'A' && b <= 'Z') || (b >= 'a' && b <= 'z')
+}
+
+// Parse parses the current line and returns a result of parsing.
+func (parser *inlineParser) Parse(parent ast.Node, block text.Reader, pc parser.Context) ast.Node {
+	line, _ := block.PeekLine()
+	opener := bytes.Index(line, parser.start)
+	if opener < 0 {
+		return nil
+	}
+	if opener != 0 && isAlphanumeric(line[opener-1]) {
+		return nil
+	}
+
+	opener += len(parser.start)
+	ender := bytes.Index(line[opener:], parser.end)
+	if ender < 0 {
+		return nil
+	}
+	if len(line) > opener+ender+len(parser.end) && isAlphanumeric(line[opener+ender+len(parser.end)]) {
+		return nil
+	}
+
+	block.Advance(opener)
+	_, pos := block.Position()
+	node := NewInline()
+	segment := pos.WithStop(pos.Start + ender)
+	node.AppendChild(node, ast.NewRawTextSegment(segment))
+	block.Advance(ender + len(parser.end))
+
+	trimBlock(node, block)
+	return node
+}
+
+func trimBlock(node *Inline, block text.Reader) {
+	if node.IsBlank(block.Source()) {
+		return
+	}
+
+	// trim first space and last space
+	first := node.FirstChild().(*ast.Text)
+	if !(!first.Segment.IsEmpty() && block.Source()[first.Segment.Start] == ' ') {
+		return
+	}
+
+	last := node.LastChild().(*ast.Text)
+	if !(!last.Segment.IsEmpty() && block.Source()[last.Segment.Stop-1] == ' ') {
+		return
+	}
+
+	first.Segment = first.Segment.WithStart(first.Segment.Start + 1)
+	last.Segment = last.Segment.WithStop(last.Segment.Stop - 1)
+}