Build a Tree View

TreeViewModel is the tree counterpart to ListViewModel. It flattens expanded TreeItem nodes into visible items and renders them with the same line number and viewport primitives used by lists.

from rich.text import Text

from lazy_cuh import LineNumberMode, LineNumberSpec, TreeGuideStyle, TreeItem, TreeViewModel, TreeViewSpec

tree = (
    TreeItem(
        id="guild",
        label=Text("Guild"),
        children=(TreeItem(id="general", label=Text("general")),),
    ),
)

view = TreeViewModel(
    roots=tree,
    cursor_index=1,
    spec=TreeViewSpec(
        width=60,
        line_numbers=LineNumberSpec(LineNumberMode.RELATIVE),
        guide_style=TreeGuideStyle.unicode_guides(),
    ),
)

for line in view.rendered_lines():
    print(line.plain)

view = view.toggle_current()
view = view.expand_current()
view = view.collapse_current()

The model is intentionally pure. Textual tree widgets should adapt this output instead of owning tree state directly.

TreeGuideStyle controls guide glyphs, markers, and guide colors. It keeps tree structure styling separate from item labels so guide color does not bleed into row content.

Tree updates are immutable. toggle_current(), expand_current(), and collapse_current() return a new TreeViewModel with updated roots. Lower-level helpers such as set_tree_item_expanded() and toggle_tree_item_expanded() are available when an app needs to update tree state outside a view model.