add parser for blog articles

Signed-off-by: Tobias Erbshäußer <tobias@tesoft.dev>

backend/md/properties.go

@@ -0,0 +1,109 @@
+package md
+
+import (
+	"errors"
+	"strings"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+	"github.com/yuin/goldmark/util"
+)
+
+var propertiesContextKey = parser.NewContextKey()
+
+type propertiesData struct {
+	properties map[string]string
+	Error      error
+}
+
+type propertiesExtension struct {
+}
+
+func (e *propertiesExtension) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(
+		parser.WithBlockParsers(
+			util.Prioritized(&propertiesParser{}, 0),
+		),
+	)
+}
+
+type propertiesParser struct {
+}
+
+func (p *propertiesParser) Trigger() []byte {
+	return []byte{'-'}
+}
+
+func (p *propertiesParser) Open(parent ast.Node, reader text.Reader, pc parser.Context) (ast.Node, parser.State) {
+	lineNumber, _ := reader.Position()
+	if lineNumber != 0 {
+		return nil, parser.NoChildren
+	}
+
+	line, _ := reader.PeekLine()
+	if isSeparator(line) {
+		return ast.NewTextBlock(), parser.NoChildren
+	}
+
+	return nil, parser.NoChildren
+}
+
+func (p *propertiesParser) Continue(node ast.Node, reader text.Reader, pc parser.Context) parser.State {
+	line, segment := reader.PeekLine()
+	if isSeparator(line) && !util.IsBlank(line) {
+		reader.Advance(segment.Len())
+		return parser.Close
+	}
+
+	node.Lines().Append(segment)
+	return parser.Continue | parser.NoChildren
+}
+
+func (p *propertiesParser) Close(node ast.Node, reader text.Reader, pc parser.Context) {
+	lines := node.Lines()
+
+	data := &propertiesData{
+		make(map[string]string),
+		nil,
+	}
+	pc.Set(propertiesContextKey, data)
+
+	for i := 0; i < lines.Len(); i++ {
+		segment := lines.At(i)
+		line := string(segment.Value(reader.Source()))
+
+		index := strings.IndexRune(line, ':')
+		if index == -1 {
+			data.Error = errors.New("invalid property line")
+			break
+		}
+
+		key := strings.TrimSpace(line[:index])
+		value := strings.TrimSpace(line[index+1:])
+		data.properties[key] = value
+	}
+
+	node.Parent().RemoveChild(node.Parent(), node)
+}
+
+func (p *propertiesParser) CanInterruptParagraph() bool {
+	return false
+}
+
+func (p *propertiesParser) CanAcceptIndentedLine() bool {
+	return false
+}
+
+func isSeparator(line []byte) bool {
+	line = util.TrimRightSpace(util.TrimLeftSpace(line))
+
+	for i := 0; i < len(line); i++ {
+		if line[i] != '-' {
+			return false
+		}
+	}
+
+	return true
+}