Add support for Wiki links and neuron's Folgezettel links

adapter/markdown/extensions/wikilink.go

@@ -0,0 +1,111 @@
+package extensions
+
+import (
+	"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"
+)
+
+// WikiLink is an extension parsing wiki links and neuron's Folgezettel.
+//
+// For example, [[wiki link]], [[[legacy downlink]]], #[[uplink]], [[downlink]]#.
+var WikiLink = &wikiLink{}
+
+type wikiLink struct{}
+
+func (w *wikiLink) Extend(m goldmark.Markdown) {
+	m.Parser().AddOptions(
+		parser.WithInlineParsers(
+			util.Prioritized(&wlParser{}, 199),
+		),
+	)
+}
+
+type wlParser struct{}
+
+func (p *wlParser) Trigger() []byte {
+	return []byte{'[', '#'}
+}
+
+func (p *wlParser) Parse(parent ast.Node, block text.Reader, pc parser.Context) ast.Node {
+	line, _ := block.PeekLine()
+
+	openerCharCount := 0
+	opened := false
+	closed := false
+	content := []byte{}
+	closerCharCount := 0
+	endPos := 0
+
+	// Folgezettel direction: -1 down, 0 unknown, 1 up
+	direction := 0
+
+	for i, char := range line {
+		endPos = i
+
+		if closed {
+			// Supports trailing hash syntax for neuron's Folgezettel, e.g. [[id]]#
+			if char == '#' {
+				direction = -1
+			}
+			break
+		}
+
+		if !opened {
+			switch char {
+			// Supports leading hash syntax for neuron's Folgezettel, e.g. #[[id]]
+			case '#':
+				direction = 1
+				continue
+			case '[':
+				openerCharCount += 1
+				continue
+			}
+
+			if openerCharCount < 2 || openerCharCount > 3 {
+				return nil
+			}
+		}
+		opened = true
+
+		if char == ']' {
+			closerCharCount += 1
+			if closerCharCount == openerCharCount {
+				closed = true
+				// neuron's legacy [[[Folgezettel]]].
+				if closerCharCount == 3 {
+					direction = -1
+				}
+			}
+		} else {
+			if closerCharCount > 0 {
+				content = append(content, strings.Repeat("]", closerCharCount)...)
+				closerCharCount = 0
+			}
+			content = append(content, char)
+		}
+	}
+
+	if !closed || len(content) == 0 {
+		return nil
+	}
+
+	block.Advance(endPos)
+
+	link := ast.NewLink()
+	link.Destination = content
+
+	// Title will be parsed as the link's rels.
+	switch direction {
+	case -1:
+		link.Title = []byte("down")
+	case 1:
+		link.Title = []byte("up")
+	}
+
+	return link
+}

adapter/markdown/markdown.go

@@ -5,6 +5,7 @@ import (
 	"regexp"
 	"strings"
 
+	"github.com/mickael-menu/zk/adapter/markdown/extensions"
 	"github.com/mickael-menu/zk/core/note"
 	"github.com/mickael-menu/zk/util/opt"
 	strutil "github.com/mickael-menu/zk/util/strings"
@@ -37,6 +38,7 @@ func NewParser() *Parser {
 						xurls.Strict,
 					),
 				),
+				extensions.WikiLink,
 			),
 		),
 	}

adapter/markdown/markdown_test.go

@@ -170,6 +170,14 @@ A link can have [one relation](one "rel-1") or [several relations](several "rel-
 
 An https://inline-link.com and http://another-inline-link.com.
 
+A [[Wiki link]] is surrounded by two brackets.
+
+A [[[Folgezettel link]]] is surrounded by three brackets.
+
+Neuron also supports a [[trailing hash]]# for Folgezettel links.
+
+A #[[leading hash]] is used for #uplinks.
+
 [External links](http://example.com) are marked [as such](ftp://domain).
 `, []note.Link{
 		{
@@ -225,6 +233,34 @@ A link can have [one relation](one "rel-1") or [several relations](several "rel-
 			Rels:     []string{},
 			Snippet:  "An https://inline-link.com and http://another-inline-link.com.",
 		},
+		{
+			Title:    "",
+			Href:     "Wiki link",
+			External: false,
+			Rels:     []string{},
+			Snippet:  "A [[Wiki link]] is surrounded by two brackets.",
+		},
+		{
+			Title:    "",
+			Href:     "Folgezettel link",
+			External: false,
+			Rels:     []string{"down"},
+			Snippet:  "A [[[Folgezettel link]]] is surrounded by three brackets.",
+		},
+		{
+			Title:    "",
+			Href:     "trailing hash",
+			External: false,
+			Rels:     []string{"down"},
+			Snippet:  "Neuron also supports a [[trailing hash]]# for Folgezettel links.",
+		},
+		{
+			Title:    "",
+			Href:     "leading hash",
+			External: false,
+			Rels:     []string{"up"},
+			Snippet:  "A #[[leading hash]] is used for #uplinks.",
+		},
 		{
 			Title:    "External links",
 			Href:     "http://example.com",