Push: Initial push

internal/ui/navigation/navigator.go

@@ -0,0 +1,127 @@
+// Package navigation implements the menu navigation stack for Nebara OS TUI.
+package navigation
+
+import "github.com/nebara/nebara-os/internal/model"
+
+// Level represents one level in the navigation stack.
+type Level struct {
+	Items       []model.MenuItem
+	SelectedIdx int
+}
+
+// Navigator maintains a stack of menu levels and tracks the current position.
+type Navigator struct {
+	stack []Level
+}
+
+// NewNavigator creates a Navigator rooted at the main menu.
+func NewNavigator(items []model.MenuItem, initialIdx int) *Navigator {
+	if initialIdx < 0 || initialIdx >= len(items) {
+		initialIdx = 0
+	}
+	return &Navigator{
+		stack: []Level{
+			{Items: items, SelectedIdx: initialIdx},
+		},
+	}
+}
+
+// Current returns the active menu level.
+func (n *Navigator) Current() *Level {
+	if len(n.stack) == 0 {
+		return nil
+	}
+	return &n.stack[len(n.stack)-1]
+}
+
+// Depth returns the current nesting depth (0 = main menu).
+func (n *Navigator) Depth() int {
+	return len(n.stack) - 1
+}
+
+// IsAtRoot reports whether the navigator is at the main menu level.
+func (n *Navigator) IsAtRoot() bool {
+	return len(n.stack) == 1
+}
+
+// SelectedItem returns the currently highlighted menu item.
+func (n *Navigator) SelectedItem() *model.MenuItem {
+	cur := n.Current()
+	if cur == nil {
+		return nil
+	}
+	return &cur.Items[cur.SelectedIdx]
+}
+
+// MoveUp moves the selection one row up, clamping at the first item.
+func (n *Navigator) MoveUp() {
+	cur := n.Current()
+	if cur == nil {
+		return
+	}
+	if cur.SelectedIdx > 0 {
+		cur.SelectedIdx--
+	}
+}
+
+// MoveDown moves the selection one row down, clamping at the last item.
+func (n *Navigator) MoveDown() {
+	cur := n.Current()
+	if cur == nil {
+		return
+	}
+	if cur.SelectedIdx < len(cur.Items)-1 {
+		cur.SelectedIdx++
+	}
+}
+
+// MoveFirst jumps to the first item.
+func (n *Navigator) MoveFirst() {
+	cur := n.Current()
+	if cur != nil {
+		cur.SelectedIdx = 0
+	}
+}
+
+// MoveLast jumps to the last item.
+func (n *Navigator) MoveLast() {
+	cur := n.Current()
+	if cur != nil {
+		cur.SelectedIdx = len(cur.Items) - 1
+	}
+}
+
+// Enter descends into the submenu of the currently selected item.
+// Returns false when the item has no children (leaf node).
+func (n *Navigator) Enter() bool {
+	item := n.SelectedItem()
+	if item == nil || len(item.Children) == 0 {
+		return false
+	}
+	n.stack = append(n.stack, Level{
+		Items:       item.Children,
+		SelectedIdx: 0,
+	})
+	return true
+}
+
+// Back pops the current level from the stack, returning to the parent.
+// Returns false when already at the root.
+func (n *Navigator) Back() bool {
+	if len(n.stack) <= 1 {
+		return false
+	}
+	n.stack = n.stack[:len(n.stack)-1]
+	return true
+}
+
+// BreadcrumbTitle builds a display title for the current navigation depth.
+// It returns empty string when at the root.
+func (n *Navigator) BreadcrumbTitle() string {
+	if len(n.stack) <= 1 {
+		return ""
+	}
+	// Return the label of the parent item whose children we are browsing.
+	parent := n.stack[len(n.stack)-2]
+	return parent.Items[parent.SelectedIdx].Label
+}