3 files changed, 178 insertions, 0 deletions
diff --git a/pkg/doc.go b/pkg/doc.go
new file mode 100644
index 0000000..9f85b3a
--- /dev/null
+++ b/pkg/doc.go
@@ -0,0 +1,154 @@
+package pkg
+
+import (
+	"bytes"
+	"io/fs"
+	"net/url"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/yuin/goldmark"
+	"github.com/yuin/goldmark/ast"
+	"github.com/yuin/goldmark/extension"
+	"github.com/yuin/goldmark/parser"
+	"github.com/yuin/goldmark/text"
+)
+
+var md = goldmark.New(
+	goldmark.WithExtensions(extension.TaskList),
+)
+
+type Doc struct {
+	path      string
+	content   []byte
+	links     Set[string]
+	Backlinks Set[string]
+}
+
+func (doc *Doc) UpdateLinks(source, target string) {
+	dirname := filepath.Dir(doc.path)
+	relpath, err := filepath.Rel(dirname, target)
+	if err != nil {
+		return
+	}
+
+	for link := range doc.links {
+		if filepath.Join(dirname, link) != source {
+			continue
+		}
+
+		doc.content = bytes.Replace(doc.content, []byte(link), []byte(relpath), -1)
+		// TODO: Update doc.links
+	}
+
+	doc.Overwrite()
+}
+
+func (doc *Doc) Overwrite() {
+	os.WriteFile(doc.path, doc.content, 0644)
+}
+
+func NewDoc(filename string) *Doc {
+	// NOTE: so far, only markdown is supported
+	if !strings.HasSuffix(filename, ".md") {
+		return nil
+	}
+
+	content, err := os.ReadFile(filename)
+	if err != nil {
+		return nil
+	}
+
+	root := md.Parser().Parse(
+		text.NewReader(content),
+		parser.WithContext(parser.NewContext()),
+	)
+
+	links := Set[string]{}
+	err = ast.Walk(root, func(n ast.Node, entering bool) (ast.WalkStatus, error) {
+		if entering {
+			switch link := n.(type) {
+			case *ast.Link:
+				href, err := url.PathUnescape(string(link.Destination))
+				if err != nil {
+					return ast.WalkStop, err
+				}
+
+				links.Insert(href)
+			}
+		}
+		return ast.WalkContinue, nil
+	})
+
+	if err != nil {
+		return nil
+	}
+
+	return &Doc{
+		path:      filename,
+		content:   content,
+		links:     links,
+		Backlinks: Set[string]{},
+	}
+}
+
+type Docs Map[string, *Doc]
+
+func (docs Docs) GetOrNew(filename string) *Doc {
+	if doc, ok := docs[filename]; ok {
+		return doc
+	}
+
+	doc := NewDoc(filename)
+	docs[filename] = doc
+	return doc
+}
+
+func NewDocs(dirname string) Docs {
+	docs := Docs{}
+
+	dirname, err := filepath.Abs(dirname)
+	if err != nil {
+		return nil
+	}
+
+	if err := filepath.Walk(dirname, func(path string, info fs.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// TODO: Add skip dir config
+		if info.IsDir() && (info.Name() == ".git" || info.Name() == "vendor") {
+			return filepath.SkipDir
+		}
+
+		if doc := NewDoc(path); doc != nil {
+			docs[path] = doc
+		}
+
+		return nil
+	}); err != nil {
+		return nil
+	}
+
+	for filename, doc := range docs {
+		for link := range doc.links {
+			abslink := filepath.Join(filepath.Dir(filename), link)
+			if _, ok := docs[abslink]; !ok {
+				continue
+			}
+
+			docs[abslink].Backlinks.Insert(filename)
+		}
+	}
+
+	return docs
+}
+
+func (docs Docs) Contain(filename string) bool {
+	_, ok := docs[filename]
+	return ok
+}
+
+var DocCollection Docs
diff --git a/pkg/map.go b/pkg/map.go
new file mode 100644
index 0000000..a9f8ccb
--- /dev/null
+++ b/pkg/map.go
@@ -0,0 +1,8 @@
+package pkg
+
+type Map[K comparable, V interface{}] map[K]V
+
+func (m Map[K, V]) Contain(key K) bool {
+	_, ok := m[key]
+	return ok
+}
diff --git a/pkg/set.go b/pkg/set.go
new file mode 100644
index 0000000..634bb59
--- /dev/null
+++ b/pkg/set.go
@@ -0,0 +1,16 @@
+package pkg
+
+type Set[T comparable] map[T]bool
+
+func (s Set[T]) Contain(val T) bool {
+	_, ok := s[val]
+	return ok
+}
+
+func (s Set[T]) Insert(val T) {
+	s[val] = true
+}
+
+func (s Set[T]) Erase(val T) {
+	delete(s, val)
+}