Initial commit: terminal file browser & markdown viewer

A beautiful TUI for browsing files and reading markdown/code:
- Two-pane layout with file tree and content viewer
- Markdown rendering via Glamour
- Syntax highlighting via Chroma
- Auto-detects light/dark terminal theme
- Arrow key navigation, Esc to go back
- Page Up/Down, Home/End for scrolling

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

filetree/model.go

@@ -0,0 +1,189 @@
+package filetree
+
+import (
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+)
+
+// Node represents a file or directory in the tree
+type Node struct {
+	Name     string
+	Path     string
+	IsDir    bool
+	IsOpen   bool
+	Level    int
+	Parent   *Node
+	Children []*Node
+}
+
+// Model represents the file tree state
+type Model struct {
+	Root     *Node
+	Nodes    []*Node // Flattened visible nodes for navigation
+	Cursor   int
+	RootPath string
+}
+
+// New creates a new file tree model
+func New(rootPath string) Model {
+	absPath, err := filepath.Abs(rootPath)
+	if err != nil {
+		absPath = rootPath
+	}
+
+	root := &Node{
+		Name:   filepath.Base(absPath),
+		Path:   absPath,
+		IsDir:  true,
+		IsOpen: true,
+		Level:  0,
+	}
+
+	m := Model{
+		Root:     root,
+		RootPath: absPath,
+		Cursor:   0,
+	}
+
+	m.loadChildren(root)
+	m.updateVisibleNodes()
+
+	return m
+}
+
+// loadChildren loads the children of a directory node
+func (m *Model) loadChildren(node *Node) {
+	if !node.IsDir {
+		return
+	}
+
+	entries, err := os.ReadDir(node.Path)
+	if err != nil {
+		return
+	}
+
+	// Sort: directories first, then alphabetically
+	sort.Slice(entries, func(i, j int) bool {
+		iDir := entries[i].IsDir()
+		jDir := entries[j].IsDir()
+		if iDir != jDir {
+			return iDir
+		}
+		return strings.ToLower(entries[i].Name()) < strings.ToLower(entries[j].Name())
+	})
+
+	node.Children = make([]*Node, 0, len(entries))
+	for _, entry := range entries {
+		// Skip hidden files
+		if strings.HasPrefix(entry.Name(), ".") {
+			continue
+		}
+
+		child := &Node{
+			Name:   entry.Name(),
+			Path:   filepath.Join(node.Path, entry.Name()),
+			IsDir:  entry.IsDir(),
+			Level:  node.Level + 1,
+			Parent: node,
+		}
+		node.Children = append(node.Children, child)
+	}
+}
+
+// updateVisibleNodes updates the flattened list of visible nodes
+func (m *Model) updateVisibleNodes() {
+	m.Nodes = make([]*Node, 0)
+	m.flattenNode(m.Root)
+}
+
+func (m *Model) flattenNode(node *Node) {
+	m.Nodes = append(m.Nodes, node)
+	if node.IsDir && node.IsOpen {
+		for _, child := range node.Children {
+			m.flattenNode(child)
+		}
+	}
+}
+
+// SelectedNode returns the currently selected node
+func (m *Model) SelectedNode() *Node {
+	if m.Cursor < 0 || m.Cursor >= len(m.Nodes) {
+		return nil
+	}
+	return m.Nodes[m.Cursor]
+}
+
+// Toggle expands or collapses the selected directory
+func (m *Model) Toggle() {
+	node := m.SelectedNode()
+	if node == nil || !node.IsDir {
+		return
+	}
+
+	node.IsOpen = !node.IsOpen
+	if node.IsOpen && len(node.Children) == 0 {
+		m.loadChildren(node)
+	}
+	m.updateVisibleNodes()
+}
+
+// MoveUp moves the cursor up
+func (m *Model) MoveUp() {
+	if m.Cursor > 0 {
+		m.Cursor--
+	}
+}
+
+// MoveDown moves the cursor down
+func (m *Model) MoveDown() {
+	if m.Cursor < len(m.Nodes)-1 {
+		m.Cursor++
+	}
+}
+
+// Collapse collapses the current directory or moves to parent
+func (m *Model) Collapse() {
+	node := m.SelectedNode()
+	if node == nil {
+		return
+	}
+
+	if node.IsDir && node.IsOpen {
+		node.IsOpen = false
+		m.updateVisibleNodes()
+	} else if node.Parent != nil {
+		// Find parent in visible nodes
+		for i, n := range m.Nodes {
+			if n == node.Parent {
+				m.Cursor = i
+				break
+			}
+		}
+	}
+}
+
+// Expand expands the current directory
+func (m *Model) Expand() {
+	node := m.SelectedNode()
+	if node == nil || !node.IsDir {
+		return
+	}
+
+	if !node.IsOpen {
+		node.IsOpen = true
+		if len(node.Children) == 0 {
+			m.loadChildren(node)
+		}
+		m.updateVisibleNodes()
+	}
+}
+
+// Ext returns the file extension of a node
+func (n *Node) Ext() string {
+	if n.IsDir {
+		return ""
+	}
+	return strings.ToLower(filepath.Ext(n.Name))
+}