1 files changed, 153 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 0000000..b11195d
--- /dev/null
+++ b/modules/markup/markdown/math/inline_parser.go
@@ -0,0 +1,153 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+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{'$'},
+	end:   []byte{'$'},
+}
+
+var defaultDualDollarParser = &inlineParser{
+	start: []byte{'$', '$'},
+	end:   []byte{'$', '$'},
+}
+
+// NewInlineDollarParser returns a new inline parser
+func NewInlineDollarParser() parser.InlineParser {
+	return defaultInlineDollarParser
+}
+
+func NewInlineDualDollarParser() parser.InlineParser {
+	return defaultDualDollarParser
+}
+
+var defaultInlineBracketParser = &inlineParser{
+	start: []byte{'\\', '('},
+	end:   []byte{'\\', ')'},
+}
+
+// NewInlineDollarParser returns a new inline parser
+func NewInlineBracketParser() parser.InlineParser {
+	return defaultInlineBracketParser
+}
+
+// Trigger triggers this parser on $ or \
+func (parser *inlineParser) Trigger() []byte {
+	return parser.start
+}
+
+func isPunctuation(b byte) bool {
+	return b == '.' || b == '!' || b == '?' || b == ',' || b == ';' || b == ':'
+}
+
+func isBracket(b byte) bool {
+	return b == ')'
+}
+
+func isAlphanumeric(b byte) bool {
+	return (b >= 'a' && b <= 'z') || (b >= 'A' && b <= 'Z') || (b >= '0' && b <= '9')
+}
+
+// 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()
+
+	if !bytes.HasPrefix(line, parser.start) {
+		// We'll catch this one on the next time round
+		return nil
+	}
+
+	precedingCharacter := block.PrecendingCharacter()
+	if precedingCharacter < 256 && (isAlphanumeric(byte(precedingCharacter)) || isPunctuation(byte(precedingCharacter))) {
+		// need to exclude things like `a$` from being considered a start
+		return nil
+	}
+
+	// move the opener marker point at the start of the text
+	opener := len(parser.start)
+
+	// Now look for an ending line
+	ender := opener
+	for {
+		pos := bytes.Index(line[ender:], parser.end)
+		if pos < 0 {
+			return nil
+		}
+
+		ender += pos
+
+		// Now we want to check the character at the end of our parser section
+		// that is ender + len(parser.end) and check if char before ender is '\'
+		pos = ender + len(parser.end)
+		if len(line) <= pos {
+			break
+		}
+		suceedingCharacter := line[pos]
+		// check valid ending character
+		if !isPunctuation(suceedingCharacter) &&
+			!(suceedingCharacter == ' ') &&
+			!(suceedingCharacter == '\n') &&
+			!isBracket(suceedingCharacter) {
+			return nil
+		}
+		if line[ender-1] != '\\' {
+			break
+		}
+
+		// move the pointer onwards
+		ender += len(parser.end)
+	}
+
+	block.Advance(opener)
+	_, pos := block.Position()
+	var node ast.Node
+	if parser == defaultDualDollarParser {
+		node = NewInlineBlock()
+	} else {
+		node = NewInline()
+	}
+	segment := pos.WithStop(pos.Start + ender - opener)
+	node.AppendChild(node, ast.NewRawTextSegment(segment))
+	block.Advance(ender - opener + len(parser.end))
+
+	if parser == defaultDualDollarParser {
+		trimBlock(&(node.(*InlineBlock)).Inline, block)
+	} else {
+		trimBlock(node.(*Inline), 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)
+}